Auto merge of #2944 - oli-obk:rustup, r=oli-obk

Rustup

.github/ISSUE_TEMPLATE/config.yml

@@ -6,3 +6,6 @@ contact_links:
   - name: Feature Request
     url: https://internals.rust-lang.org/
     about: Please discuss language feature requests on the internals forum.
+  - name: Clippy Bug
+    url: https://github.com/rust-lang/rust-clippy/issues/new/choose
+    about: Please report Clippy bugs such as false positives in the Clippy repo.

.github/workflows/ci.yml

@@ -30,10 +30,11 @@ permissions:
 defaults:
   run:
     shell: bash
+concurrency:
+  group: "${{ github.workflow }}-${{ github.event.pull_request.number || github.ref }}"
+  cancel-in-progress: true
 jobs:
   pr:
-    permissions:
-      actions: write
     name: "PR - ${{ matrix.name }}"
     env:
       CI_JOB_NAME: "${{ matrix.name }}"
@@ -84,11 +85,6 @@ jobs:
       - name: ensure the channel matches the target branch
         run: src/ci/scripts/verify-channel.sh
         if: success() && !env.SKIP_JOB
-      - name: configure GitHub Actions to kill the build when outdated
-        uses: rust-lang/simpleinfra/github-actions/cancel-outdated-builds@master
-        with:
-          github_token: "${{ secrets.github_token }}"
-        if: "success() && !env.SKIP_JOB && github.ref != 'refs/heads/try' && github.ref != 'refs/heads/try-perf'"
       - name: collect CPU statistics
         run: src/ci/scripts/collect-cpu-stats.sh
         if: success() && !env.SKIP_JOB
@@ -162,8 +158,6 @@ jobs:
           AWS_SECRET_ACCESS_KEY: "${{ secrets[format('AWS_SECRET_ACCESS_KEY_{0}', env.ARTIFACTS_AWS_ACCESS_KEY_ID)] }}"
         if: "success() && !env.SKIP_JOB && (github.event_name == 'push' || env.DEPLOY == '1' || env.DEPLOY_ALT == '1')"
   auto:
-    permissions:
-      actions: write
     name: "auto - ${{ matrix.name }}"
     env:
       CI_JOB_NAME: "${{ matrix.name }}"
@@ -496,11 +490,6 @@ jobs:
       - name: ensure the channel matches the target branch
         run: src/ci/scripts/verify-channel.sh
         if: success() && !env.SKIP_JOB
-      - name: configure GitHub Actions to kill the build when outdated
-        uses: rust-lang/simpleinfra/github-actions/cancel-outdated-builds@master
-        with:
-          github_token: "${{ secrets.github_token }}"
-        if: "success() && !env.SKIP_JOB && github.ref != 'refs/heads/try' && github.ref != 'refs/heads/try-perf'"
       - name: collect CPU statistics
         run: src/ci/scripts/collect-cpu-stats.sh
         if: success() && !env.SKIP_JOB
@@ -574,8 +563,6 @@ jobs:
           AWS_SECRET_ACCESS_KEY: "${{ secrets[format('AWS_SECRET_ACCESS_KEY_{0}', env.ARTIFACTS_AWS_ACCESS_KEY_ID)] }}"
         if: "success() && !env.SKIP_JOB && (github.event_name == 'push' || env.DEPLOY == '1' || env.DEPLOY_ALT == '1')"
   try:
-    permissions:
-      actions: write
     name: "try - ${{ matrix.name }}"
     env:
       DIST_TRY_BUILD: 1
@@ -623,11 +610,6 @@ jobs:
       - name: ensure the channel matches the target branch
         run: src/ci/scripts/verify-channel.sh
         if: success() && !env.SKIP_JOB
-      - name: configure GitHub Actions to kill the build when outdated
-        uses: rust-lang/simpleinfra/github-actions/cancel-outdated-builds@master
-        with:
-          github_token: "${{ secrets.github_token }}"
-        if: "success() && !env.SKIP_JOB && github.ref != 'refs/heads/try' && github.ref != 'refs/heads/try-perf'"
       - name: collect CPU statistics
         run: src/ci/scripts/collect-cpu-stats.sh
         if: success() && !env.SKIP_JOB

.github/workflows/dependencies.yml

@@ -25,6 +25,7 @@ env:
 
 jobs:
   not-waiting-on-bors:
+    if: github.repository_owner == 'rust-lang'
     name: skip if S-waiting-on-bors
     runs-on: ubuntu-latest
     steps:
@@ -43,6 +44,7 @@ jobs:
           fi
 
   update:
+    if: github.repository_owner == 'rust-lang'
     name: update dependencies
     needs: not-waiting-on-bors
     runs-on: ubuntu-latest
@@ -76,6 +78,7 @@ jobs:
           retention-days: 1
 
   pr:
+    if: github.repository_owner == 'rust-lang'
     name: amend PR
     needs: update
     runs-on: ubuntu-latest

Cargo.lock

@@ -480,23 +480,6 @@ dependencies = [
  "winapi",
 ]
 
-[[package]]
-name = "clap"
-version = "3.2.20"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "23b71c3ce99b7611011217b366d923f1d0a7e07a92bb2dbf1e84508c673ca3bd"
-dependencies = [
- "atty",
- "bitflags",
- "clap_derive 3.2.18",
- "clap_lex 0.2.2",
- "indexmap",
- "once_cell",
- "strsim",
- "termcolor",
- "textwrap",
-]
-
 [[package]]
 name = "clap"
 version = "4.2.1"
@@ -504,7 +487,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "046ae530c528f252094e4a77886ee1374437744b2bff1497aa898bbddbbb29b3"
 dependencies = [
  "clap_builder",
- "clap_derive 4.2.0",
+ "clap_derive",
  "once_cell",
 ]
 
@@ -517,7 +500,7 @@ dependencies = [
  "anstream",
  "anstyle",
  "bitflags",
- "clap_lex 0.4.1",
+ "clap_lex",
  "once_cell",
  "strsim",
  "terminal_size",
@@ -529,20 +512,7 @@ version = "4.0.7"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "10861370d2ba66b0f5989f83ebf35db6421713fd92351790e7fdd6c36774c56b"
 dependencies = [
- "clap 4.2.1",
+ "clap",
-]
-
-[[package]]
-name = "clap_derive"
-version = "3.2.18"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ea0c8bce528c4be4da13ea6fead8965e95b6073585a2f05204bd8f4119f82a65"
-dependencies = [
- "heck",
- "proc-macro-error",
- "proc-macro2",
- "quote",
- "syn 1.0.102",
 ]
 
 [[package]]
@@ -557,15 +527,6 @@ dependencies = [
  "syn 2.0.8",
 ]
 
-[[package]]
-name = "clap_lex"
-version = "0.2.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "5538cd660450ebeb4234cfecf8f2284b844ffc4c50531e66d584ad5b91293613"
-dependencies = [
- "os_str_bytes",
-]
-
 [[package]]
 name = "clap_lex"
 version = "0.4.1"
@@ -576,7 +537,7 @@ checksum = "8a2dd5a6fe8c6e3502f568a6353e5273bbb15193ad9a89e457b9970798efbea1"
 name = "clippy"
 version = "0.1.72"
 dependencies = [
- "clap 4.2.1",
+ "clap",
  "clippy_lints",
  "clippy_utils",
  "compiletest_rs",
@@ -605,7 +566,7 @@ name = "clippy_dev"
 version = "0.0.1"
 dependencies = [
  "aho-corasick",
- "clap 4.2.1",
+ "clap",
  "indoc",
  "itertools",
  "opener",
@@ -1749,7 +1710,7 @@ name = "installer"
 version = "0.0.0"
 dependencies = [
  "anyhow",
- "clap 3.2.20",
+ "clap",
  "flate2",
  "num_cpus",
  "rayon",
@@ -1869,7 +1830,7 @@ name = "jsondoclint"
 version = "0.1.0"
 dependencies = [
  "anyhow",
- "clap 4.2.1",
+ "clap",
  "fs-err",
  "rustc-hash",
  "rustdoc-json-types",
@@ -2086,7 +2047,7 @@ dependencies = [
  "ammonia",
  "anyhow",
  "chrono",
- "clap 4.2.1",
+ "clap",
  "clap_complete",
  "elasticlunr-rs",
  "env_logger 0.10.0",
@@ -2370,12 +2331,6 @@ dependencies = [
  "vcpkg",
 ]
 
-[[package]]
-name = "os_str_bytes"
-version = "6.0.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "8e22443d1643a904602595ba1cd8f7d896afe56d26712531c5ff73a15b2fbf64"
-
 [[package]]
 name = "owo-colors"
 version = "3.5.0"
@@ -2617,30 +2572,6 @@ version = "0.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "925383efa346730478fb4838dbe9137d2a47675ad789c546d150a6e1dd4ab31c"
 
-[[package]]
-name = "proc-macro-error"
-version = "1.0.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "da25490ff9892aab3fcf7c36f08cfb902dd3e71ca0f9f9517bea02a73a5ce38c"
-dependencies = [
- "proc-macro-error-attr",
- "proc-macro2",
- "quote",
- "syn 1.0.102",
- "version_check",
-]
-
-[[package]]
-name = "proc-macro-error-attr"
-version = "1.0.4"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "a1be40180e52ecc98ad80b184934baf3d0d29f979574e439af5a55274b35f869"
-dependencies = [
- "proc-macro2",
- "quote",
- "version_check",
-]
-
 [[package]]
 name = "proc-macro-hack"
 version = "0.5.19"
@@ -2897,7 +2828,7 @@ dependencies = [
 name = "rustbook"
 version = "0.1.0"
 dependencies = [
- "clap 4.2.1",
+ "clap",
  "env_logger 0.10.0",
  "mdbook",
 ]
@@ -4346,7 +4277,7 @@ dependencies = [
  "anyhow",
  "bytecount",
  "cargo_metadata",
- "clap 4.2.1",
+ "clap",
  "diff",
  "dirs",
  "env_logger 0.10.0",
@@ -4874,12 +4805,6 @@ dependencies = [
  "term",
 ]
 
-[[package]]
-name = "textwrap"
-version = "0.15.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "b1141d4d61095b28419e22cb0bbf02755f5e54e0526f97f1e3d1d160e60885fb"
-
 [[package]]
 name = "thin-vec"
 version = "0.2.12"

README.md

@@ -33,24 +33,13 @@ format:
 ```
 
 This is how the documentation and examples assume you are running `x.py`.
-Some alternative ways are:
+See the [rustc dev guide][rustcguidebuild] if this does not work on your platform.
-
-```sh
-# On a Unix shell if you don't have the necessary `python3` command
-./x <subcommand> [flags]
-
-# On the Windows Command Prompt (if .py files are configured to run Python)
-x.py <subcommand> [flags]
-
-# You can also run Python yourself, e.g.:
-python x.py <subcommand> [flags]
-```
 
 More information about `x.py` can be found by running it with the `--help` flag
 or reading the [rustc dev guide][rustcguidebuild].
 
 [gettingstarted]: https://rustc-dev-guide.rust-lang.org/getting-started.html
-[rustcguidebuild]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html
+[rustcguidebuild]: https://rustc-dev-guide.rust-lang.org/building/how-to-build-and-run.html#what-is-xpy
 
 ### Dependencies
 

compiler/rustc_ast_lowering/src/expr.rs

@@ -277,9 +277,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 ExprKind::Yeet(sub_expr) => self.lower_expr_yeet(e.span, sub_expr.as_deref()),
                 ExprKind::Become(sub_expr) => {
                     let sub_expr = self.lower_expr(sub_expr);
-
+                    hir::ExprKind::Become(sub_expr)
-                    // FIXME(explicit_tail_calls): Use `hir::ExprKind::Become` once we implemented it
-                    hir::ExprKind::Ret(Some(sub_expr))
                 }
                 ExprKind::InlineAsm(asm) => {
                     hir::ExprKind::InlineAsm(self.lower_inline_asm(e.span, asm))

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -623,13 +623,12 @@ impl<'a> AstValidator<'a> {
     fn maybe_lint_missing_abi(&mut self, span: Span, id: NodeId) {
         // FIXME(davidtwco): This is a hack to detect macros which produce spans of the
         // call site which do not have a macro backtrace. See #61963.
-        let is_macro_callsite = self
+        if self
             .session
             .source_map()
             .span_to_snippet(span)
-            .map(|snippet| snippet.starts_with("#["))
+            .is_ok_and(|snippet| !snippet.starts_with("#["))
-            .unwrap_or(true);
+        {
-        if !is_macro_callsite {
             self.lint_buffer.buffer_lint_with_diagnostic(
                 MISSING_ABI,
                 id,

compiler/rustc_ast_passes/src/errors.rs

@@ -77,13 +77,6 @@ pub struct ForbiddenLifetimeBound {
     pub spans: Vec<Span>,
 }
 
-#[derive(Diagnostic)]
-#[diag(ast_passes_forbidden_non_lifetime_param)]
-pub struct ForbiddenNonLifetimeParam {
-    #[primary_span]
-    pub spans: Vec<Span>,
-}
-
 #[derive(Diagnostic)]
 #[diag(ast_passes_fn_param_too_many)]
 pub struct FnParamTooMany {

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -678,8 +678,8 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
         let tcx = self.infcx.tcx;
 
         // Find out if the predicates show that the type is a Fn or FnMut
-        let find_fn_kind_from_did = |(pred, _): (ty::Predicate<'tcx>, _)| {
+        let find_fn_kind_from_did = |(pred, _): (ty::Clause<'tcx>, _)| {
-            if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) = pred.kind().skip_binder()
+            if let ty::ClauseKind::Trait(pred) = pred.kind().skip_binder()
                 && pred.self_ty() == ty
             {
                 if Some(pred.def_id()) == tcx.lang_items().fn_trait() {
@@ -705,7 +705,7 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. }) => tcx
                 .explicit_item_bounds(def_id)
                 .subst_iter_copied(tcx, substs)
-                .find_map(|(clause, span)| find_fn_kind_from_did((clause.as_predicate(), span))),
+                .find_map(|(clause, span)| find_fn_kind_from_did((clause, span))),
             ty::Closure(_, substs) => match substs.as_closure().kind() {
                 ty::ClosureKind::Fn => Some(hir::Mutability::Not),
                 ty::ClosureKind::FnMut => Some(hir::Mutability::Mut),

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -123,13 +123,7 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
                     item_msg = access_place_desc;
                     debug_assert!(self.body.local_decls[ty::CAPTURE_STRUCT_LOCAL].ty.is_ref());
                     debug_assert!(is_closure_or_generator(
-                        Place::ty_from(
+                        the_place_err.ty(self.body, self.infcx.tcx).ty
-                            the_place_err.local,
-                            the_place_err.projection,
-                            self.body,
-                            self.infcx.tcx
-                        )
-                        .ty
                     ));
 
                     reason = if self.is_upvar_field_projection(access_place.as_ref()).is_some() {

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -928,7 +928,7 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
 
     fn any_param_predicate_mentions(
         &self,
-        predicates: &[ty::Predicate<'tcx>],
+        clauses: &[ty::Clause<'tcx>],
         ty: Ty<'tcx>,
         region: ty::EarlyBoundRegion,
     ) -> bool {
@@ -937,10 +937,10 @@ impl<'tcx> MirBorrowckCtxt<'_, 'tcx> {
             if let ty::GenericArgKind::Type(ty) = arg.unpack()
                 && let ty::Param(_) = ty.kind()
             {
-                predicates.iter().any(|pred| {
+                clauses.iter().any(|pred| {
                     match pred.kind().skip_binder() {
-                        ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) if data.self_ty() == ty => {}
+                        ty::ClauseKind::Trait(data) if data.self_ty() == ty => {}
-                        ty::PredicateKind::Clause(ty::ClauseKind::Projection(data)) if data.projection_ty.self_ty() == ty => {}
+                        ty::ClauseKind::Projection(data) if data.projection_ty.self_ty() == ty => {}
                         _ => return false,
                     }
                     tcx.any_free_region_meets(pred, |r| {

compiler/rustc_borrowck/src/place_ext.rs

@@ -46,11 +46,9 @@ impl<'tcx> PlaceExt<'tcx> for Place<'tcx> {
             }
         }
 
-        for (i, elem) in self.projection.iter().enumerate() {
+        for (i, (proj_base, elem)) in self.iter_projections().enumerate() {
-            let proj_base = &self.projection[..i];
-
             if elem == ProjectionElem::Deref {
-                let ty = Place::ty_from(self.local, proj_base, body, tcx).ty;
+                let ty = proj_base.ty(body, tcx).ty;
                 match ty.kind() {
                     ty::Ref(_, _, hir::Mutability::Not) if i == 0 => {
                         // For references to thread-local statics, we do need

compiler/rustc_borrowck/src/places_conflict.rs

@@ -137,13 +137,11 @@ fn place_components_conflict<'tcx>(
     }
 
     // loop invariant: borrow_c is always either equal to access_c or disjoint from it.
-    for (i, (borrow_c, &access_c)) in
+    for ((borrow_place, borrow_c), &access_c) in
-        iter::zip(borrow_place.projection, access_place.projection).enumerate()
+        iter::zip(borrow_place.iter_projections(), access_place.projection)
     {
         debug!(?borrow_c, ?access_c);
 
-        let borrow_proj_base = &borrow_place.projection[..i];
-
         // Borrow and access path both have more components.
         //
         // Examples:
@@ -156,15 +154,7 @@ fn place_components_conflict<'tcx>(
         // check whether the components being borrowed vs
         // accessed are disjoint (as in the second example,
         // but not the first).
-        match place_projection_conflict(
+        match place_projection_conflict(tcx, body, borrow_place, borrow_c, access_c, bias) {
-            tcx,
-            body,
-            borrow_local,
-            borrow_proj_base,
-            borrow_c,
-            access_c,
-            bias,
-        ) {
             Overlap::Arbitrary => {
                 // We have encountered different fields of potentially
                 // the same union - the borrow now partially overlaps.
@@ -195,8 +185,7 @@ fn place_components_conflict<'tcx>(
     }
 
     if borrow_place.projection.len() > access_place.projection.len() {
-        for (i, elem) in borrow_place.projection[access_place.projection.len()..].iter().enumerate()
+        for (base, elem) in borrow_place.iter_projections().skip(access_place.projection.len()) {
-        {
             // Borrow path is longer than the access path. Examples:
             //
             // - borrow of `a.b.c`, access to `a.b`
@@ -205,8 +194,7 @@ fn place_components_conflict<'tcx>(
             // our place. This is a conflict if that is a part our
             // access cares about.
 
-            let proj_base = &borrow_place.projection[..access_place.projection.len() + i];
+            let base_ty = base.ty(body, tcx).ty;
-            let base_ty = Place::ty_from(borrow_local, proj_base, body, tcx).ty;
 
             match (elem, &base_ty.kind(), access) {
                 (_, _, Shallow(Some(ArtificialField::ArrayLength)))
@@ -310,8 +298,7 @@ fn place_base_conflict(l1: Local, l2: Local) -> Overlap {
 fn place_projection_conflict<'tcx>(
     tcx: TyCtxt<'tcx>,
     body: &Body<'tcx>,
-    pi1_local: Local,
+    pi1: PlaceRef<'tcx>,
-    pi1_proj_base: &[PlaceElem<'tcx>],
     pi1_elem: PlaceElem<'tcx>,
     pi2_elem: PlaceElem<'tcx>,
     bias: PlaceConflictBias,
@@ -333,7 +320,7 @@ fn place_projection_conflict<'tcx>(
                 debug!("place_element_conflict: DISJOINT-OR-EQ-FIELD");
                 Overlap::EqualOrDisjoint
             } else {
-                let ty = Place::ty_from(pi1_local, pi1_proj_base, body, tcx).ty;
+                let ty = pi1.ty(body, tcx).ty;
                 if ty.is_union() {
                     // Different fields of a union, we are basically stuck.
                     debug!("place_element_conflict: STUCK-UNION");

compiler/rustc_borrowck/src/type_check/mod.rs

@@ -50,7 +50,6 @@ use rustc_mir_dataflow::impls::MaybeInitializedPlaces;
 use rustc_mir_dataflow::move_paths::MoveData;
 use rustc_mir_dataflow::ResultsCursor;
 
-use crate::renumber::RegionCtxt;
 use crate::session_diagnostics::MoveUnsized;
 use crate::{
     borrow_set::BorrowSet,
@@ -1040,9 +1039,9 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             .collect();
 
         let renumbered_opaques = self.infcx.tcx.fold_regions(opaques, |_, _| {
-            self.infcx.next_nll_region_var(
+            self.infcx.next_nll_region_var_in_universe(
                 NllRegionVariableOrigin::Existential { from_forall: false },
-                || RegionCtxt::Unknown,
+                ty::UniverseIndex::ROOT,
             )
         });
 
@@ -2503,7 +2502,6 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             location, borrow_region, borrowed_place
         );
 
-        let mut cursor = borrowed_place.projection.as_ref();
         let tcx = self.infcx.tcx;
         let field = path_utils::is_upvar_field_projection(
             tcx,
@@ -2517,14 +2515,12 @@ impl<'a, 'tcx> TypeChecker<'a, 'tcx> {
             ConstraintCategory::Boring
         };
 
-        while let [proj_base @ .., elem] = cursor {
+        for (base, elem) in borrowed_place.as_ref().iter_projections().rev() {
-            cursor = proj_base;
-
             debug!("add_reborrow_constraint - iteration {:?}", elem);
 
             match elem {
                 ProjectionElem::Deref => {
-                    let base_ty = Place::ty_from(borrowed_place.local, proj_base, body, tcx).ty;
+                    let base_ty = base.ty(body, tcx).ty;
 
                     debug!("add_reborrow_constraint - base_ty = {:?}", base_ty);
                     match base_ty.kind() {

compiler/rustc_builtin_macros/src/derive.rs

@@ -8,7 +8,7 @@ use rustc_feature::AttributeTemplate;
 use rustc_parse::validate_attr;
 use rustc_session::Session;
 use rustc_span::symbol::{sym, Ident};
-use rustc_span::Span;
+use rustc_span::{ErrorGuaranteed, Span};
 
 pub(crate) struct Expander(pub bool);
 
@@ -22,7 +22,7 @@ impl MultiItemModifier for Expander {
         _: bool,
     ) -> ExpandResult<Vec<Annotatable>, Annotatable> {
         let sess = ecx.sess;
-        if report_bad_target(sess, &item, span) {
+        if report_bad_target(sess, &item, span).is_err() {
             // We don't want to pass inappropriate targets to derive macros to avoid
             // follow up errors, all other errors below are recoverable.
             return ExpandResult::Ready(vec![item]);
@@ -103,7 +103,11 @@ fn dummy_annotatable() -> Annotatable {
     })
 }
 
-fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
+fn report_bad_target(
+    sess: &Session,
+    item: &Annotatable,
+    span: Span,
+) -> Result<(), ErrorGuaranteed> {
     let item_kind = match item {
         Annotatable::Item(item) => Some(&item.kind),
         Annotatable::Stmt(stmt) => match &stmt.kind {
@@ -116,9 +120,9 @@ fn report_bad_target(sess: &Session, item: &Annotatable, span: Span) -> bool {
     let bad_target =
         !matches!(item_kind, Some(ItemKind::Struct(..) | ItemKind::Enum(..) | ItemKind::Union(..)));
     if bad_target {
-        sess.emit_err(errors::BadDeriveTarget { span, item: item.span() });
+        return Err(sess.emit_err(errors::BadDeriveTarget { span, item: item.span() }));
     }
-    bad_target
+    Ok(())
 }
 
 fn report_unexpected_meta_item_lit(sess: &Session, lit: &ast::MetaItemLit) {

compiler/rustc_builtin_macros/src/test.rs

@@ -8,7 +8,7 @@ use rustc_ast_pretty::pprust;
 use rustc_errors::Applicability;
 use rustc_expand::base::*;
 use rustc_span::symbol::{sym, Ident, Symbol};
-use rustc_span::{FileNameDisplayPreference, Span};
+use rustc_span::{ErrorGuaranteed, FileNameDisplayPreference, Span};
 use std::iter;
 use thin_vec::{thin_vec, ThinVec};
 
@@ -128,12 +128,15 @@ pub fn expand_test_or_bench(
         };
     };
 
-    // has_*_signature will report any errors in the type so compilation
+    // check_*_signature will report any errors in the type so compilation
     // will fail. We shouldn't try to expand in this case because the errors
     // would be spurious.
-    if (!is_bench && !has_test_signature(cx, &item))
+    let check_result = if is_bench {
-        || (is_bench && !has_bench_signature(cx, &item))
+        check_bench_signature(cx, &item, &fn_)
-    {
+    } else {
+        check_test_signature(cx, &item, &fn_)
+    };
+    if check_result.is_err() {
         return if is_stmt {
             vec![Annotatable::Stmt(P(cx.stmt_item(item.span, item)))]
         } else {
@@ -523,72 +526,62 @@ fn test_type(cx: &ExtCtxt<'_>) -> TestType {
     }
 }
 
-fn has_test_signature(cx: &ExtCtxt<'_>, i: &ast::Item) -> bool {
+fn check_test_signature(
+    cx: &ExtCtxt<'_>,
+    i: &ast::Item,
+    f: &ast::Fn,
+) -> Result<(), ErrorGuaranteed> {
     let has_should_panic_attr = attr::contains_name(&i.attrs, sym::should_panic);
     let sd = &cx.sess.parse_sess.span_diagnostic;
-    match &i.kind {
-        ast::ItemKind::Fn(box ast::Fn { sig, generics, .. }) => {
-            if let ast::Unsafe::Yes(span) = sig.header.unsafety {
-                sd.emit_err(errors::TestBadFn { span: i.span, cause: span, kind: "unsafe" });
-                return false;
-            }
-            if let ast::Async::Yes { span, .. } = sig.header.asyncness {
-                sd.emit_err(errors::TestBadFn { span: i.span, cause: span, kind: "async" });
-                return false;
-            }
 
-            // If the termination trait is active, the compiler will check that the output
+    if let ast::Unsafe::Yes(span) = f.sig.header.unsafety {
-            // type implements the `Termination` trait as `libtest` enforces that.
+        return Err(sd.emit_err(errors::TestBadFn { span: i.span, cause: span, kind: "unsafe" }));
-            let has_output = match &sig.decl.output {
-                ast::FnRetTy::Default(..) => false,
-                ast::FnRetTy::Ty(t) if t.kind.is_unit() => false,
-                _ => true,
-            };
-
-            if !sig.decl.inputs.is_empty() {
-                sd.span_err(i.span, "functions used as tests can not have any arguments");
-                return false;
-            }
-
-            if has_should_panic_attr && has_output {
-                sd.span_err(i.span, "functions using `#[should_panic]` must return `()`");
-                return false;
-            }
-
-            if generics.params.iter().any(|param| !matches!(param.kind, GenericParamKind::Lifetime))
-            {
-                sd.span_err(
-                    i.span,
-                    "functions used as tests can not have any non-lifetime generic parameters",
-                );
-                return false;
-            }
-
-            true
-        }
-        _ => {
-            // should be unreachable because `is_test_fn_item` should catch all non-fn items
-            debug_assert!(false);
-            false
-        }
     }
-}
 
-fn has_bench_signature(cx: &ExtCtxt<'_>, i: &ast::Item) -> bool {
+    if let ast::Async::Yes { span, .. } = f.sig.header.asyncness {
-    let has_sig = match &i.kind {
+        return Err(sd.emit_err(errors::TestBadFn { span: i.span, cause: span, kind: "async" }));
-        // N.B., inadequate check, but we're running
+    }
-        // well before resolve, can't get too deep.
+
-        ast::ItemKind::Fn(box ast::Fn { sig, .. }) => sig.decl.inputs.len() == 1,
+    // If the termination trait is active, the compiler will check that the output
-        _ => false,
+    // type implements the `Termination` trait as `libtest` enforces that.
+    let has_output = match &f.sig.decl.output {
+        ast::FnRetTy::Default(..) => false,
+        ast::FnRetTy::Ty(t) if t.kind.is_unit() => false,
+        _ => true,
     };
 
-    if !has_sig {
+    if !f.sig.decl.inputs.is_empty() {
-        cx.sess.parse_sess.span_diagnostic.span_err(
+        return Err(sd.span_err(i.span, "functions used as tests can not have any arguments"));
+    }
+
+    if has_should_panic_attr && has_output {
+        return Err(sd.span_err(i.span, "functions using `#[should_panic]` must return `()`"));
+    }
+
+    if f.generics.params.iter().any(|param| !matches!(param.kind, GenericParamKind::Lifetime)) {
+        return Err(sd.span_err(
+            i.span,
+            "functions used as tests can not have any non-lifetime generic parameters",
+        ));
+    }
+
+    Ok(())
+}
+
+fn check_bench_signature(
+    cx: &ExtCtxt<'_>,
+    i: &ast::Item,
+    f: &ast::Fn,
+) -> Result<(), ErrorGuaranteed> {
+    // N.B., inadequate check, but we're running
+    // well before resolve, can't get too deep.
+    if f.sig.decl.inputs.len() != 1 {
+        return Err(cx.sess.parse_sess.span_diagnostic.span_err(
             i.span,
             "functions used as benches must have \
             signature `fn(&mut Bencher) -> impl Termination`",
-        );
+        ));
     }
 
-    has_sig
+    Ok(())
 }

compiler/rustc_codegen_cranelift/src/pretty_clif.rs

@@ -225,10 +225,10 @@ pub(crate) fn write_ir_file(
     let res = std::fs::File::create(clif_file_name).and_then(|mut file| write(&mut file));
     if let Err(err) = res {
         // Using early_warn as no Session is available here
-        rustc_session::early_warn(
+        let handler = rustc_session::EarlyErrorHandler::new(
             rustc_session::config::ErrorOutputType::default(),
-            format!("error writing ir file: {}", err),
         );
+        handler.early_warn(format!("error writing ir file: {}", err));
     }
 }
 

compiler/rustc_codegen_llvm/src/builder.rs

@@ -572,8 +572,6 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
     ) {
         let zero = self.const_usize(0);
         let count = self.const_usize(count);
-        let start = dest.project_index(self, zero).llval;
-        let end = dest.project_index(self, count).llval;
 
         let header_bb = self.append_sibling_block("repeat_loop_header");
         let body_bb = self.append_sibling_block("repeat_loop_body");
@@ -582,24 +580,18 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
         self.br(header_bb);
 
         let mut header_bx = Self::build(self.cx, header_bb);
-        let current = header_bx.phi(self.val_ty(start), &[start], &[self.llbb()]);
+        let i = header_bx.phi(self.val_ty(zero), &[zero], &[self.llbb()]);
 
-        let keep_going = header_bx.icmp(IntPredicate::IntNE, current, end);
+        let keep_going = header_bx.icmp(IntPredicate::IntULT, i, count);
         header_bx.cond_br(keep_going, body_bb, next_bb);
 
         let mut body_bx = Self::build(self.cx, body_bb);
-        let align = dest.align.restrict_for_offset(dest.layout.field(self.cx(), 0).size);
+        let dest_elem = dest.project_index(&mut body_bx, i);
-        cg_elem
+        cg_elem.val.store(&mut body_bx, dest_elem);
-            .val
-            .store(&mut body_bx, PlaceRef::new_sized_aligned(current, cg_elem.layout, align));
 
-        let next = body_bx.inbounds_gep(
+        let next = body_bx.unchecked_uadd(i, self.const_usize(1));
-            self.backend_type(cg_elem.layout),
-            current,
-            &[self.const_usize(1)],
-        );
         body_bx.br(header_bb);
-        header_bx.add_incoming_to_phi(current, next, body_bb);
+        header_bx.add_incoming_to_phi(i, next, body_bb);
 
         *self = Self::build(self.cx, next_bb);
     }

compiler/rustc_codegen_ssa/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(if_let_guard)]
 #![feature(int_roundings)]
 #![feature(let_chains)]
+#![feature(negative_impls)]
 #![feature(never_type)]
 #![feature(strict_provenance)]
 #![feature(try_blocks)]

compiler/rustc_codegen_ssa/src/mir/block.rs

@@ -1729,7 +1729,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
             IndirectOperand(tmp, index) => {
                 let op = bx.load_operand(tmp);
                 tmp.storage_dead(bx);
-                self.locals[index] = LocalRef::Operand(op);
+                self.overwrite_local(index, LocalRef::Operand(op));
                 self.debug_introduce_local(bx, index);
             }
             DirectOperand(index) => {
@@ -1744,7 +1744,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                 } else {
                     OperandRef::from_immediate_or_packed_pair(bx, llval, ret_abi.layout)
                 };
-                self.locals[index] = LocalRef::Operand(op);
+                self.overwrite_local(index, LocalRef::Operand(op));
                 self.debug_introduce_local(bx, index);
             }
         }

compiler/rustc_codegen_ssa/src/mir/debuginfo.rs

@@ -248,7 +248,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
     }
 
     fn spill_operand_to_stack(
-        operand: &OperandRef<'tcx, Bx::Value>,
+        operand: OperandRef<'tcx, Bx::Value>,
         name: Option<String>,
         bx: &mut Bx,
     ) -> PlaceRef<'tcx, Bx::Value> {
@@ -375,7 +375,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                     return;
                 }
 
-                Self::spill_operand_to_stack(operand, name, bx)
+                Self::spill_operand_to_stack(*operand, name, bx)
             }
 
             LocalRef::Place(place) => *place,
@@ -550,7 +550,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         if let Ok(operand) = self.eval_mir_constant_to_operand(bx, &c) {
                             self.set_debug_loc(bx, var.source_info);
                             let base = Self::spill_operand_to_stack(
-                                &operand,
+                                operand,
                                 Some(var.name.to_string()),
                                 bx,
                             );

compiler/rustc_codegen_ssa/src/mir/locals.rs

@@ -0,0 +1,75 @@
+//! Locals are in a private module as updating `LocalRef::Operand` has to
+//! be careful wrt to subtyping. To deal with this we only allow updates by using
+//! `FunctionCx::overwrite_local` which handles it automatically.
+use crate::mir::{FunctionCx, LocalRef};
+use crate::traits::BuilderMethods;
+use rustc_index::IndexVec;
+use rustc_middle::mir;
+use rustc_middle::ty::print::with_no_trimmed_paths;
+use std::ops::{Index, IndexMut};
+
+pub(super) struct Locals<'tcx, V> {
+    values: IndexVec<mir::Local, LocalRef<'tcx, V>>,
+}
+
+impl<'tcx, V> Index<mir::Local> for Locals<'tcx, V> {
+    type Output = LocalRef<'tcx, V>;
+    #[inline]
+    fn index(&self, index: mir::Local) -> &LocalRef<'tcx, V> {
+        &self.values[index]
+    }
+}
+
+/// To mutate locals, use `FunctionCx::overwrite_local` instead.
+impl<'tcx, V, Idx: ?Sized> !IndexMut<Idx> for Locals<'tcx, V> {}
+
+impl<'tcx, V> Locals<'tcx, V> {
+    pub(super) fn empty() -> Locals<'tcx, V> {
+        Locals { values: IndexVec::default() }
+    }
+
+    pub(super) fn indices(&self) -> impl DoubleEndedIterator<Item = mir::Local> + Clone + 'tcx {
+        self.values.indices()
+    }
+}
+
+impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
+    pub(super) fn initialize_locals(&mut self, values: Vec<LocalRef<'tcx, Bx::Value>>) {
+        assert!(self.locals.values.is_empty());
+
+        for (local, value) in values.into_iter().enumerate() {
+            match value {
+                LocalRef::Place(_) | LocalRef::UnsizedPlace(_) | LocalRef::PendingOperand => (),
+                LocalRef::Operand(op) => {
+                    let local = mir::Local::from_usize(local);
+                    let expected_ty = self.monomorphize(self.mir.local_decls[local].ty);
+                    assert_eq!(expected_ty, op.layout.ty, "unexpected initial operand type");
+                }
+            }
+
+            self.locals.values.push(value);
+        }
+    }
+
+    pub(super) fn overwrite_local(
+        &mut self,
+        local: mir::Local,
+        mut value: LocalRef<'tcx, Bx::Value>,
+    ) {
+        match value {
+            LocalRef::Place(_) | LocalRef::UnsizedPlace(_) | LocalRef::PendingOperand => (),
+            LocalRef::Operand(ref mut op) => {
+                let local_ty = self.monomorphize(self.mir.local_decls[local].ty);
+                if local_ty != op.layout.ty {
+                    // FIXME(#112651): This can be changed to an ICE afterwards.
+                    debug!("updating type of operand due to subtyping");
+                    with_no_trimmed_paths!(debug!(?op.layout.ty));
+                    with_no_trimmed_paths!(debug!(?local_ty));
+                    op.layout.ty = local_ty;
+                }
+            }
+        };
+
+        self.locals.values[local] = value;
+    }
+}

compiler/rustc_codegen_ssa/src/mir/mod.rs

@@ -1,21 +1,31 @@
 use crate::base;
 use crate::traits::*;
+use rustc_index::bit_set::BitSet;
+use rustc_index::IndexVec;
 use rustc_middle::mir;
 use rustc_middle::mir::interpret::ErrorHandled;
+use rustc_middle::mir::traversal;
 use rustc_middle::ty::layout::{FnAbiOf, HasTyCtxt, TyAndLayout};
 use rustc_middle::ty::{self, Instance, Ty, TyCtxt, TypeFoldable, TypeVisitableExt};
 use rustc_target::abi::call::{FnAbi, PassMode};
 
 use std::iter;
 
-use rustc_index::bit_set::BitSet;
+mod analyze;
-use rustc_index::IndexVec;
+mod block;
+pub mod constant;
+pub mod coverageinfo;
+pub mod debuginfo;
+mod intrinsic;
+mod locals;
+pub mod operand;
+pub mod place;
+mod rvalue;
+mod statement;
 
 use self::debuginfo::{FunctionDebugContext, PerLocalVarDebugInfo};
-use self::place::PlaceRef;
-use rustc_middle::mir::traversal;
-
 use self::operand::{OperandRef, OperandValue};
+use self::place::PlaceRef;
 
 // Used for tracking the state of generated basic blocks.
 enum CachedLlbb<T> {
@@ -91,7 +101,7 @@ pub struct FunctionCx<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> {
     ///
     /// Avoiding allocs can also be important for certain intrinsics,
     /// notably `expect`.
-    locals: IndexVec<mir::Local, LocalRef<'tcx, Bx::Value>>,
+    locals: locals::Locals<'tcx, Bx::Value>,
 
     /// All `VarDebugInfo` from the MIR body, partitioned by `Local`.
     /// This is `None` if no var`#[non_exhaustive]`iable debuginfo/names are needed.
@@ -192,7 +202,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         cleanup_kinds,
         landing_pads: IndexVec::from_elem(None, &mir.basic_blocks),
         funclets: IndexVec::from_fn_n(|_| None, mir.basic_blocks.len()),
-        locals: IndexVec::new(),
+        locals: locals::Locals::empty(),
         debug_context,
         per_local_var_debug_info: None,
         caller_location: None,
@@ -223,7 +233,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
     let memory_locals = analyze::non_ssa_locals(&fx);
 
     // Allocate variable and temp allocas
-    fx.locals = {
+    let local_values = {
         let args = arg_local_refs(&mut start_bx, &mut fx, &memory_locals);
 
         let mut allocate_local = |local| {
@@ -256,6 +266,7 @@ pub fn codegen_mir<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
             .chain(mir.vars_and_temps_iter().map(allocate_local))
             .collect()
     };
+    fx.initialize_locals(local_values);
 
     // Apply debuginfo to the newly allocated locals.
     fx.debug_introduce_locals(&mut start_bx);
@@ -289,14 +300,13 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
         .enumerate()
         .map(|(arg_index, local)| {
             let arg_decl = &mir.local_decls[local];
+            let arg_ty = fx.monomorphize(arg_decl.ty);
 
             if Some(local) == mir.spread_arg {
                 // This argument (e.g., the last argument in the "rust-call" ABI)
                 // is a tuple that was spread at the ABI level and now we have
                 // to reconstruct it into a tuple local variable, from multiple
                 // individual LLVM function arguments.
-
-                let arg_ty = fx.monomorphize(arg_decl.ty);
                 let ty::Tuple(tupled_arg_tys) = arg_ty.kind() else {
                     bug!("spread argument isn't a tuple?!");
                 };
@@ -331,8 +341,6 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
             }
 
             if fx.fn_abi.c_variadic && arg_index == fx.fn_abi.args.len() {
-                let arg_ty = fx.monomorphize(arg_decl.ty);
-
                 let va_list = PlaceRef::alloca(bx, bx.layout_of(arg_ty));
                 bx.va_start(va_list.llval);
 
@@ -429,14 +437,3 @@ fn arg_local_refs<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>>(
 
     args
 }
-
-mod analyze;
-mod block;
-pub mod constant;
-pub mod coverageinfo;
-pub mod debuginfo;
-mod intrinsic;
-pub mod operand;
-pub mod place;
-mod rvalue;
-mod statement;

compiler/rustc_codegen_ssa/src/mir/statement.rs

@@ -20,7 +20,7 @@ impl<'a, 'tcx, Bx: BuilderMethods<'a, 'tcx>> FunctionCx<'a, 'tcx, Bx> {
                         }
                         LocalRef::PendingOperand => {
                             let operand = self.codegen_rvalue_operand(bx, rvalue);
-                            self.locals[index] = LocalRef::Operand(operand);
+                            self.overwrite_local(index, LocalRef::Operand(operand));
                             self.debug_introduce_local(bx, index);
                         }
                         LocalRef::Operand(op) => {

compiler/rustc_codegen_ssa/src/target_features.rs

@@ -44,6 +44,7 @@ const ARM_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     // #[target_feature].
     ("thumb-mode", Some(sym::arm_target_feature)),
     ("thumb2", Some(sym::arm_target_feature)),
+    ("trustzone", Some(sym::arm_target_feature)),
     ("v5te", Some(sym::arm_target_feature)),
     ("v6", Some(sym::arm_target_feature)),
     ("v6k", Some(sym::arm_target_feature)),
@@ -53,6 +54,7 @@ const ARM_ALLOWED_FEATURES: &[(&str, Option<Symbol>)] = &[
     ("vfp2", Some(sym::arm_target_feature)),
     ("vfp3", Some(sym::arm_target_feature)),
     ("vfp4", Some(sym::arm_target_feature)),
+    ("virtualization", Some(sym::arm_target_feature)),
     // tidy-alphabetical-end
 ];
 

compiler/rustc_const_eval/src/const_eval/eval_queries.rs

@@ -14,7 +14,7 @@ use rustc_middle::ty::{self, TyCtxt};
 use rustc_span::source_map::Span;
 use rustc_target::abi::{self, Abi};
 
-use super::{CompileTimeEvalContext, CompileTimeInterpreter};
+use super::{CanAccessStatics, CompileTimeEvalContext, CompileTimeInterpreter};
 use crate::errors;
 use crate::interpret::eval_nullary_intrinsic;
 use crate::interpret::{
@@ -93,7 +93,7 @@ pub(super) fn mk_eval_cx<'mir, 'tcx>(
     tcx: TyCtxt<'tcx>,
     root_span: Span,
     param_env: ty::ParamEnv<'tcx>,
-    can_access_statics: bool,
+    can_access_statics: CanAccessStatics,
 ) -> CompileTimeEvalContext<'mir, 'tcx> {
     debug!("mk_eval_cx: {:?}", param_env);
     InterpCx::new(
@@ -207,7 +207,7 @@ pub(crate) fn turn_into_const_value<'tcx>(
         tcx,
         tcx.def_span(key.value.instance.def_id()),
         key.param_env,
-        /*can_access_statics:*/ is_static,
+        CanAccessStatics::from(is_static),
     );
 
     let mplace = ecx.raw_const_to_mplace(constant).expect(
@@ -309,7 +309,7 @@ pub fn eval_to_allocation_raw_provider<'tcx>(
         // Statics (and promoteds inside statics) may access other statics, because unlike consts
         // they do not have to behave "as if" they were evaluated at runtime.
         CompileTimeInterpreter::new(
-            /*can_access_statics:*/ is_static,
+            CanAccessStatics::from(is_static),
             if tcx.sess.opts.unstable_opts.extra_const_ub_checks {
                 CheckAlignment::Error
             } else {

compiler/rustc_const_eval/src/const_eval/machine.rs

@@ -57,7 +57,7 @@ pub struct CompileTimeInterpreter<'mir, 'tcx> {
     /// * Interning makes everything outside of statics immutable.
     /// * Pointers to allocations inside of statics can never leak outside, to a non-static global.
     /// This boolean here controls the second part.
-    pub(super) can_access_statics: bool,
+    pub(super) can_access_statics: CanAccessStatics,
 
     /// Whether to check alignment during evaluation.
     pub(super) check_alignment: CheckAlignment,
@@ -83,8 +83,23 @@ impl CheckAlignment {
     }
 }
 
+#[derive(Copy, Clone, PartialEq)]
+pub(crate) enum CanAccessStatics {
+    No,
+    Yes,
+}
+
+impl From<bool> for CanAccessStatics {
+    fn from(value: bool) -> Self {
+        if value { Self::Yes } else { Self::No }
+    }
+}
+
 impl<'mir, 'tcx> CompileTimeInterpreter<'mir, 'tcx> {
-    pub(crate) fn new(can_access_statics: bool, check_alignment: CheckAlignment) -> Self {
+    pub(crate) fn new(
+        can_access_statics: CanAccessStatics,
+        check_alignment: CheckAlignment,
+    ) -> Self {
         CompileTimeInterpreter {
             num_evaluated_steps: 0,
             stack: Vec::new(),
@@ -699,7 +714,7 @@ impl<'mir, 'tcx> interpret::Machine<'mir, 'tcx> for CompileTimeInterpreter<'mir,
             }
         } else {
             // Read access. These are usually allowed, with some exceptions.
-            if machine.can_access_statics {
+            if machine.can_access_statics == CanAccessStatics::Yes {
                 // Machine configuration allows us read from anything (e.g., `static` initializer).
                 Ok(())
             } else if static_def_id.is_some() {

compiler/rustc_const_eval/src/const_eval/mod.rs

@@ -26,7 +26,7 @@ pub(crate) fn const_caller_location(
     (file, line, col): (Symbol, u32, u32),
 ) -> ConstValue<'_> {
     trace!("const_caller_location: {}:{}:{}", file, line, col);
-    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, ty::ParamEnv::reveal_all(), false);
+    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, ty::ParamEnv::reveal_all(), CanAccessStatics::No);
 
     let loc_place = ecx.alloc_caller_location(file, line, col);
     if intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &loc_place).is_err() {
@@ -55,10 +55,12 @@ pub(crate) fn eval_to_valtree<'tcx>(
 
     // FIXME Need to provide a span to `eval_to_valtree`
     let ecx = mk_eval_cx(
-        tcx, DUMMY_SP, param_env,
+        tcx,
+        DUMMY_SP,
+        param_env,
         // It is absolutely crucial for soundness that
         // we do not read from static items or other mutable memory.
-        false,
+        CanAccessStatics::No,
     );
     let place = ecx.raw_const_to_mplace(const_alloc).unwrap();
     debug!(?place);
@@ -91,7 +93,7 @@ pub(crate) fn try_destructure_mir_constant<'tcx>(
     val: mir::ConstantKind<'tcx>,
 ) -> InterpResult<'tcx, mir::DestructuredConstant<'tcx>> {
     trace!("destructure_mir_constant: {:?}", val);
-    let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
+    let ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, CanAccessStatics::No);
     let op = ecx.eval_mir_constant(&val, None, None)?;
 
     // We go to `usize` as we cannot allocate anything bigger anyway.

compiler/rustc_const_eval/src/const_eval/valtrees.rs

@@ -1,6 +1,7 @@
 use super::eval_queries::{mk_eval_cx, op_to_const};
 use super::machine::CompileTimeEvalContext;
 use super::{ValTreeCreationError, ValTreeCreationResult, VALTREE_MAX_NODES};
+use crate::const_eval::CanAccessStatics;
 use crate::interpret::{
     intern_const_alloc_recursive, ConstValue, ImmTy, Immediate, InternKind, MemPlaceMeta,
     MemoryKind, PlaceTy, Scalar,
@@ -263,7 +264,11 @@ pub fn valtree_to_const_value<'tcx>(
     // FIXME Does this need an example?
 
     let (param_env, ty) = param_env_ty.into_parts();
-    let mut ecx = mk_eval_cx(tcx, DUMMY_SP, param_env, false);
+    let mut ecx: crate::interpret::InterpCx<
+        '_,
+        '_,
+        crate::const_eval::CompileTimeInterpreter<'_, '_>,
+    > = mk_eval_cx(tcx, DUMMY_SP, param_env, CanAccessStatics::No);
 
     match ty.kind() {
         ty::FnDef(..) => {

compiler/rustc_const_eval/src/transform/check_consts/check.rs

@@ -612,30 +612,28 @@ impl<'tcx> Visitor<'tcx> for Checker<'_, 'tcx> {
     }
     fn visit_projection_elem(
         &mut self,
-        place_local: Local,
+        place_ref: PlaceRef<'tcx>,
-        proj_base: &[PlaceElem<'tcx>],
         elem: PlaceElem<'tcx>,
         context: PlaceContext,
         location: Location,
     ) {
         trace!(
-            "visit_projection_elem: place_local={:?} proj_base={:?} elem={:?} \
+            "visit_projection_elem: place_ref={:?} elem={:?} \
             context={:?} location={:?}",
-            place_local,
+            place_ref,
-            proj_base,
             elem,
             context,
             location,
         );
 
-        self.super_projection_elem(place_local, proj_base, elem, context, location);
+        self.super_projection_elem(place_ref, elem, context, location);
 
         match elem {
             ProjectionElem::Deref => {
-                let base_ty = Place::ty_from(place_local, proj_base, self.body, self.tcx).ty;
+                let base_ty = place_ref.ty(self.body, self.tcx).ty;
                 if base_ty.is_unsafe_ptr() {
-                    if proj_base.is_empty() {
+                    if place_ref.projection.is_empty() {
-                        let decl = &self.body.local_decls[place_local];
+                        let decl = &self.body.local_decls[place_ref.local];
                         if let LocalInfo::StaticRef { def_id, .. } = *decl.local_info() {
                             let span = decl.source_info.span;
                             self.check_static(def_id, span);

compiler/rustc_const_eval/src/transform/validate.rs

@@ -318,8 +318,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
 
     fn visit_projection_elem(
         &mut self,
-        local: Local,
+        place_ref: PlaceRef<'tcx>,
-        proj_base: &[PlaceElem<'tcx>],
         elem: PlaceElem<'tcx>,
         context: PlaceContext,
         location: Location,
@@ -334,7 +333,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
             ProjectionElem::Deref
                 if self.mir_phase >= MirPhase::Runtime(RuntimePhase::PostCleanup) =>
             {
-                let base_ty = Place::ty_from(local, proj_base, &self.body.local_decls, self.tcx).ty;
+                let base_ty = place_ref.ty(&self.body.local_decls, self.tcx).ty;
 
                 if base_ty.is_box() {
                     self.fail(
@@ -344,8 +343,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                 }
             }
             ProjectionElem::Field(f, ty) => {
-                let parent = Place { local, projection: self.tcx.mk_place_elems(proj_base) };
+                let parent_ty = place_ref.ty(&self.body.local_decls, self.tcx);
-                let parent_ty = parent.ty(&self.body.local_decls, self.tcx);
                 let fail_out_of_bounds = |this: &Self, location| {
                     this.fail(location, format!("Out of bounds field {:?} for {:?}", f, parent_ty));
                 };
@@ -355,7 +353,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
                             location,
                             format!(
                                 "Field projection `{:?}.{:?}` specified type `{:?}`, but actual type is `{:?}`",
-                                parent, f, ty, f_ty
+                                place_ref, f, ty, f_ty
                             )
                         )
                     }
@@ -434,7 +432,7 @@ impl<'a, 'tcx> Visitor<'tcx> for TypeChecker<'a, 'tcx> {
             }
             _ => {}
         }
-        self.super_projection_elem(local, proj_base, elem, context, location);
+        self.super_projection_elem(place_ref, elem, context, location);
     }
 
     fn visit_var_debug_info(&mut self, debuginfo: &VarDebugInfo<'tcx>) {

compiler/rustc_const_eval/src/util/check_validity_requirement.rs

@@ -2,7 +2,7 @@ use rustc_middle::ty::layout::{LayoutCx, LayoutError, LayoutOf, TyAndLayout, Val
 use rustc_middle::ty::{ParamEnv, ParamEnvAnd, Ty, TyCtxt};
 use rustc_target::abi::{Abi, FieldsShape, Scalar, Variants};
 
-use crate::const_eval::{CheckAlignment, CompileTimeInterpreter};
+use crate::const_eval::{CanAccessStatics, CheckAlignment, CompileTimeInterpreter};
 use crate::interpret::{InterpCx, MemoryKind, OpTy};
 
 /// Determines if this type permits "raw" initialization by just transmuting some memory into an
@@ -44,8 +44,7 @@ fn might_permit_raw_init_strict<'tcx>(
     tcx: TyCtxt<'tcx>,
     kind: ValidityRequirement,
 ) -> Result<bool, LayoutError<'tcx>> {
-    let machine =
+    let machine = CompileTimeInterpreter::new(CanAccessStatics::No, CheckAlignment::Error);
-        CompileTimeInterpreter::new(/*can_access_statics:*/ false, CheckAlignment::Error);
 
     let mut cx = InterpCx::new(tcx, rustc_span::DUMMY_SP, ParamEnv::reveal_all(), machine);
 

compiler/rustc_driver_impl/src/args.rs

@@ -3,6 +3,8 @@ use std::fmt;
 use std::fs;
 use std::io;
 
+use rustc_session::EarlyErrorHandler;
+
 fn arg_expand(arg: String) -> Result<Vec<String>, Error> {
     if let Some(path) = arg.strip_prefix('@') {
         let file = match fs::read_to_string(path) {
@@ -21,15 +23,12 @@ fn arg_expand(arg: String) -> Result<Vec<String>, Error> {
 /// **Note:** This function doesn't interpret argument 0 in any special way.
 /// If this function is intended to be used with command line arguments,
 /// `argv[0]` must be removed prior to calling it manually.
-pub fn arg_expand_all(at_args: &[String]) -> Vec<String> {
+pub fn arg_expand_all(handler: &EarlyErrorHandler, at_args: &[String]) -> Vec<String> {
     let mut args = Vec::new();
     for arg in at_args {
         match arg_expand(arg.clone()) {
             Ok(arg) => args.extend(arg),
-            Err(err) => rustc_session::early_error(
+            Err(err) => handler.early_error(format!("Failed to load argument file: {err}")),
-                rustc_session::config::ErrorOutputType::default(),
-                format!("Failed to load argument file: {err}"),
-            ),
         }
     }
     args

compiler/rustc_driver_impl/src/lib.rs

@@ -40,8 +40,7 @@ use rustc_session::config::{
 use rustc_session::cstore::MetadataLoader;
 use rustc_session::getopts::{self, Matches};
 use rustc_session::lint::{Lint, LintId};
-use rustc_session::{config, Session};
+use rustc_session::{config, EarlyErrorHandler, Session};
-use rustc_session::{early_error, early_error_no_abort, early_warn};
 use rustc_span::source_map::{FileLoader, FileName};
 use rustc_span::symbol::sym;
 use rustc_target::json::ToJson;
@@ -174,6 +173,7 @@ pub trait Callbacks {
     /// continue the compilation afterwards (defaults to `Compilation::Continue`)
     fn after_analysis<'tcx>(
         &mut self,
+        _handler: &EarlyErrorHandler,
         _compiler: &interface::Compiler,
         _queries: &'tcx Queries<'tcx>,
     ) -> Compilation {
@@ -260,6 +260,8 @@ fn run_compiler(
         Box<dyn FnOnce(&config::Options) -> Box<dyn CodegenBackend> + Send>,
     >,
 ) -> interface::Result<()> {
+    let mut early_error_handler = EarlyErrorHandler::new(ErrorOutputType::default());
+
     // Throw away the first argument, the name of the binary.
     // In case of at_args being empty, as might be the case by
     // passing empty argument array to execve under some platforms,
@@ -270,22 +272,22 @@ fn run_compiler(
     // the compiler with @empty_file as argv[0] and no more arguments.
     let at_args = at_args.get(1..).unwrap_or_default();
 
-    let args = args::arg_expand_all(at_args);
+    let args = args::arg_expand_all(&early_error_handler, at_args);
 
-    let Some(matches) = handle_options(&args) else { return Ok(()) };
+    let Some(matches) = handle_options(&early_error_handler, &args) else { return Ok(()) };
 
-    let sopts = config::build_session_options(&matches);
+    let sopts = config::build_session_options(&mut early_error_handler, &matches);
 
     // Set parallel mode before thread pool creation, which will create `Lock`s.
     interface::set_thread_safe_mode(&sopts.unstable_opts);
 
     if let Some(ref code) = matches.opt_str("explain") {
-        handle_explain(diagnostics_registry(), code, sopts.error_format);
+        handle_explain(&early_error_handler, diagnostics_registry(), code);
         return Ok(());
     }
 
-    let cfg = interface::parse_cfgspecs(matches.opt_strs("cfg"));
+    let cfg = interface::parse_cfgspecs(&early_error_handler, matches.opt_strs("cfg"));
-    let check_cfg = interface::parse_check_cfg(matches.opt_strs("check-cfg"));
+    let check_cfg = interface::parse_check_cfg(&early_error_handler, matches.opt_strs("check-cfg"));
     let (odir, ofile) = make_output(&matches);
     let mut config = interface::Config {
         opts: sopts,
@@ -304,7 +306,7 @@ fn run_compiler(
         registry: diagnostics_registry(),
     };
 
-    match make_input(config.opts.error_format, &matches.free) {
+    match make_input(&early_error_handler, &matches.free) {
         Err(reported) => return Err(reported),
         Ok(Some(input)) => {
             config.input = input;
@@ -314,8 +316,13 @@ fn run_compiler(
         Ok(None) => match matches.free.len() {
             0 => {
                 callbacks.config(&mut config);
+
+                early_error_handler.abort_if_errors();
+
                 interface::run_compiler(config, |compiler| {
                     let sopts = &compiler.session().opts;
+                    let handler = EarlyErrorHandler::new(sopts.error_format);
+
                     if sopts.describe_lints {
                         let mut lint_store =
                             rustc_lint::new_lint_store(compiler.session().enable_internal_lints());
@@ -329,31 +336,38 @@ fn run_compiler(
                         describe_lints(compiler.session(), &lint_store, registered_lints);
                         return;
                     }
-                    let should_stop =
+                    let should_stop = print_crate_info(
-                        print_crate_info(&**compiler.codegen_backend(), compiler.session(), false);
+                        &handler,
+                        &**compiler.codegen_backend(),
+                        compiler.session(),
+                        false,
+                    );
 
                     if should_stop == Compilation::Stop {
                         return;
                     }
-                    early_error(sopts.error_format, "no input filename given")
+                    handler.early_error("no input filename given")
                 });
                 return Ok(());
             }
             1 => panic!("make_input should have provided valid inputs"),
-            _ => early_error(
+            _ => early_error_handler.early_error(format!(
-                config.opts.error_format,
+                "multiple input filenames provided (first two filenames are `{}` and `{}`)",
-                format!(
+                matches.free[0], matches.free[1],
-                    "multiple input filenames provided (first two filenames are `{}` and `{}`)",
+            )),
-                    matches.free[0], matches.free[1],
-                ),
-            ),
         },
     };
 
+    early_error_handler.abort_if_errors();
+
     interface::run_compiler(config, |compiler| {
         let sess = compiler.session();
-        let should_stop = print_crate_info(&**compiler.codegen_backend(), sess, true)
+        let handler = EarlyErrorHandler::new(sess.opts.error_format);
-            .and_then(|| list_metadata(sess, &*compiler.codegen_backend().metadata_loader()))
+
+        let should_stop = print_crate_info(&handler, &**compiler.codegen_backend(), sess, true)
+            .and_then(|| {
+                list_metadata(&handler, sess, &*compiler.codegen_backend().metadata_loader())
+            })
             .and_then(|| try_process_rlink(sess, compiler));
 
         if should_stop == Compilation::Stop {
@@ -421,7 +435,7 @@ fn run_compiler(
 
             queries.global_ctxt()?.enter(|tcx| tcx.analysis(()))?;
 
-            if callbacks.after_analysis(compiler, queries) == Compilation::Stop {
+            if callbacks.after_analysis(&handler, compiler, queries) == Compilation::Stop {
                 return early_exit();
             }
 
@@ -475,7 +489,7 @@ fn make_output(matches: &getopts::Matches) -> (Option<PathBuf>, Option<OutFileNa
 
 // Extract input (string or file and optional path) from matches.
 fn make_input(
-    error_format: ErrorOutputType,
+    handler: &EarlyErrorHandler,
     free_matches: &[String],
 ) -> Result<Option<Input>, ErrorGuaranteed> {
     if free_matches.len() == 1 {
@@ -485,8 +499,7 @@ fn make_input(
             if io::stdin().read_to_string(&mut src).is_err() {
                 // Immediately stop compilation if there was an issue reading
                 // the input (for example if the input stream is not UTF-8).
-                let reported = early_error_no_abort(
+                let reported = handler.early_error_no_abort(
-                    error_format,
                     "couldn't read from stdin, as it did not contain valid UTF-8",
                 );
                 return Err(reported);
@@ -527,7 +540,7 @@ impl Compilation {
     }
 }
 
-fn handle_explain(registry: Registry, code: &str, output: ErrorOutputType) {
+fn handle_explain(handler: &EarlyErrorHandler, registry: Registry, code: &str) {
     let upper_cased_code = code.to_ascii_uppercase();
     let normalised =
         if upper_cased_code.starts_with('E') { upper_cased_code } else { format!("E{code:0>4}") };
@@ -557,7 +570,7 @@ fn handle_explain(registry: Registry, code: &str, output: ErrorOutputType) {
             }
         }
         Err(InvalidErrorCode) => {
-            early_error(output, format!("{code} is not a valid error code"));
+            handler.early_error(format!("{code} is not a valid error code"));
         }
     }
 }
@@ -636,7 +649,11 @@ pub fn try_process_rlink(sess: &Session, compiler: &interface::Compiler) -> Comp
     }
 }
 
-pub fn list_metadata(sess: &Session, metadata_loader: &dyn MetadataLoader) -> Compilation {
+pub fn list_metadata(
+    handler: &EarlyErrorHandler,
+    sess: &Session,
+    metadata_loader: &dyn MetadataLoader,
+) -> Compilation {
     if sess.opts.unstable_opts.ls {
         match sess.io.input {
             Input::File(ref ifile) => {
@@ -646,7 +663,7 @@ pub fn list_metadata(sess: &Session, metadata_loader: &dyn MetadataLoader) -> Co
                 safe_println!("{}", String::from_utf8(v).unwrap());
             }
             Input::Str { .. } => {
-                early_error(ErrorOutputType::default(), "cannot list metadata for stdin");
+                handler.early_error("cannot list metadata for stdin");
             }
         }
         return Compilation::Stop;
@@ -656,6 +673,7 @@ pub fn list_metadata(sess: &Session, metadata_loader: &dyn MetadataLoader) -> Co
 }
 
 fn print_crate_info(
+    handler: &EarlyErrorHandler,
     codegen_backend: &dyn CodegenBackend,
     sess: &Session,
     parse_attrs: bool,
@@ -787,10 +805,8 @@ fn print_crate_info(
                             .expect("unknown Apple target OS")
                     )
                 } else {
-                    early_error(
+                    handler
-                        ErrorOutputType::default(),
+                        .early_error("only Apple targets currently support deployment version info")
-                        "only Apple targets currently support deployment version info",
-                    )
                 }
             }
         }
@@ -801,11 +817,12 @@ fn print_crate_info(
 /// Prints version information
 ///
 /// NOTE: this is a macro to support drivers built at a different time than the main `rustc_driver` crate.
-pub macro version($binary: literal, $matches: expr) {
+pub macro version($handler: expr, $binary: literal, $matches: expr) {
     fn unw(x: Option<&str>) -> &str {
         x.unwrap_or("unknown")
     }
     $crate::version_at_macro_invocation(
+        $handler,
         $binary,
         $matches,
         unw(option_env!("CFG_VERSION")),
@@ -817,6 +834,7 @@ pub macro version($binary: literal, $matches: expr) {
 
 #[doc(hidden)] // use the macro instead
 pub fn version_at_macro_invocation(
+    handler: &EarlyErrorHandler,
     binary: &str,
     matches: &getopts::Matches,
     version: &str,
@@ -837,7 +855,7 @@ pub fn version_at_macro_invocation(
 
         let debug_flags = matches.opt_strs("Z");
         let backend_name = debug_flags.iter().find_map(|x| x.strip_prefix("codegen-backend="));
-        get_codegen_backend(&None, backend_name).print_version();
+        get_codegen_backend(handler, &None, backend_name).print_version();
     }
 }
 
@@ -1014,7 +1032,7 @@ Available lint options:
 /// Show help for flag categories shared between rustdoc and rustc.
 ///
 /// Returns whether a help option was printed.
-pub fn describe_flag_categories(matches: &Matches) -> bool {
+pub fn describe_flag_categories(handler: &EarlyErrorHandler, matches: &Matches) -> bool {
     // Handle the special case of -Wall.
     let wall = matches.opt_strs("W");
     if wall.iter().any(|x| *x == "all") {
@@ -1036,15 +1054,12 @@ pub fn describe_flag_categories(matches: &Matches) -> bool {
     }
 
     if cg_flags.iter().any(|x| *x == "no-stack-check") {
-        early_warn(
+        handler.early_warn("the --no-stack-check flag is deprecated and does nothing");
-            ErrorOutputType::default(),
-            "the --no-stack-check flag is deprecated and does nothing",
-        );
     }
 
     if cg_flags.iter().any(|x| *x == "passes=list") {
         let backend_name = debug_flags.iter().find_map(|x| x.strip_prefix("codegen-backend="));
-        get_codegen_backend(&None, backend_name).print_passes();
+        get_codegen_backend(handler, &None, backend_name).print_passes();
         return true;
     }
 
@@ -1101,7 +1116,7 @@ fn print_flag_list<T>(
 ///
 /// So with all that in mind, the comments below have some more detail about the
 /// contortions done here to get things to work out correctly.
-pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
+pub fn handle_options(handler: &EarlyErrorHandler, args: &[String]) -> Option<getopts::Matches> {
     if args.is_empty() {
         // user did not write `-v` nor `-Z unstable-options`, so do not
         // include that extra information.
@@ -1127,7 +1142,7 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
                 .map(|(flag, _)| format!("{e}. Did you mean `-{flag} {opt}`?")),
             _ => None,
         };
-        early_error(ErrorOutputType::default(), msg.unwrap_or_else(|| e.to_string()));
+        handler.early_error(msg.unwrap_or_else(|| e.to_string()));
     });
 
     // For all options we just parsed, we check a few aspects:
@@ -1141,7 +1156,7 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
     //   we're good to go.
     // * Otherwise, if we're an unstable option then we generate an error
     //   (unstable option being used on stable)
-    nightly_options::check_nightly_options(&matches, &config::rustc_optgroups());
+    nightly_options::check_nightly_options(handler, &matches, &config::rustc_optgroups());
 
     if matches.opt_present("h") || matches.opt_present("help") {
         // Only show unstable options in --help if we accept unstable options.
@@ -1151,12 +1166,12 @@ pub fn handle_options(args: &[String]) -> Option<getopts::Matches> {
         return None;
     }
 
-    if describe_flag_categories(&matches) {
+    if describe_flag_categories(handler, &matches) {
         return None;
     }
 
     if matches.opt_present("version") {
-        version!("rustc", &matches);
+        version!(handler, "rustc", &matches);
         return None;
     }
 
@@ -1276,7 +1291,8 @@ pub fn install_ice_hook(bug_report_url: &'static str, extra_info: fn(&Handler))
         if let Some(msg) = info.payload().downcast_ref::<String>() {
             if msg.starts_with("failed printing to stdout: ") && msg.ends_with("(os error 232)") {
                 // the error code is already going to be reported when the panic unwinds up the stack
-                let _ = early_error_no_abort(ErrorOutputType::default(), msg.clone());
+                let handler = EarlyErrorHandler::new(ErrorOutputType::default());
+                let _ = handler.early_error_no_abort(msg.clone());
                 return;
             }
         };
@@ -1359,16 +1375,16 @@ pub fn report_ice(info: &panic::PanicInfo<'_>, bug_report_url: &str, extra_info:
 
 /// This allows tools to enable rust logging without having to magically match rustc's
 /// tracing crate version.
-pub fn init_rustc_env_logger() {
+pub fn init_rustc_env_logger(handler: &EarlyErrorHandler) {
-    init_env_logger("RUSTC_LOG");
+    init_env_logger(handler, "RUSTC_LOG");
 }
 
 /// This allows tools to enable rust logging without having to magically match rustc's
 /// tracing crate version. In contrast to `init_rustc_env_logger` it allows you to choose an env var
 /// other than `RUSTC_LOG`.
-pub fn init_env_logger(env: &str) {
+pub fn init_env_logger(handler: &EarlyErrorHandler, env: &str) {
     if let Err(error) = rustc_log::init_env_logger(env) {
-        early_error(ErrorOutputType::default(), error.to_string());
+        handler.early_error(error.to_string());
     }
 }
 
@@ -1424,7 +1440,10 @@ mod signal_handler {
 pub fn main() -> ! {
     let start_time = Instant::now();
     let start_rss = get_resident_set_size();
-    init_rustc_env_logger();
+
+    let handler = EarlyErrorHandler::new(ErrorOutputType::default());
+
+    init_rustc_env_logger(&handler);
     signal_handler::install();
     let mut callbacks = TimePassesCallbacks::default();
     install_ice_hook(DEFAULT_BUG_REPORT_URL, |_| ());
@@ -1433,10 +1452,7 @@ pub fn main() -> ! {
             .enumerate()
             .map(|(i, arg)| {
                 arg.into_string().unwrap_or_else(|arg| {
-                    early_error(
+                    handler.early_error(format!("argument {i} is not valid Unicode: {arg:?}"))
-                        ErrorOutputType::default(),
-                        format!("argument {i} is not valid Unicode: {arg:?}"),
-                    )
                 })
             })
             .collect::<Vec<_>>();

compiler/rustc_expand/src/config.rs

@@ -445,7 +445,7 @@ impl<'a> StripUnconfigured<'a> {
     /// If attributes are not allowed on expressions, emit an error for `attr`
     #[instrument(level = "trace", skip(self))]
     pub(crate) fn maybe_emit_expr_attr_err(&self, attr: &Attribute) {
-        if !self.features.map_or(true, |features| features.stmt_expr_attributes) {
+        if self.features.is_some_and(|features| !features.stmt_expr_attributes) {
             let mut err = feature_err(
                 &self.sess.parse_sess,
                 sym::stmt_expr_attributes,

compiler/rustc_fluent_macro/src/fluent.rs

@@ -179,7 +179,8 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
     let mut previous_defns = HashMap::new();
     let mut message_refs = Vec::new();
     for entry in resource.entries() {
-        if let Entry::Message(Message { id: Identifier { name }, attributes, value, .. }) = entry {
+        if let Entry::Message(msg) = entry {
+            let Message { id: Identifier { name }, attributes, value, .. } = msg;
             let _ = previous_defns.entry(name.to_string()).or_insert(resource_span);
             if name.contains('-') {
                 Diagnostic::spanned(
@@ -229,9 +230,10 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
                 continue;
             }
 
-            let msg = format!("Constant referring to Fluent message `{name}` from `{crate_name}`");
+            let docstr =
+                format!("Constant referring to Fluent message `{name}` from `{crate_name}`");
             constants.extend(quote! {
-                #[doc = #msg]
+                #[doc = #docstr]
                 pub const #snake_name: crate::DiagnosticMessage =
                     crate::DiagnosticMessage::FluentIdentifier(
                         std::borrow::Cow::Borrowed(#name),
@@ -269,6 +271,15 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
                         );
                 });
             }
+
+            // Record variables referenced by these messages so we can produce
+            // tests in the derive diagnostics to validate them.
+            let ident = quote::format_ident!("{snake_name}_refs");
+            let vrefs = variable_references(msg);
+            constants.extend(quote! {
+                #[cfg(test)]
+                pub const #ident: &[&str] = &[#(#vrefs),*];
+            })
         }
     }
 
@@ -334,3 +345,28 @@ pub(crate) fn fluent_messages(input: proc_macro::TokenStream) -> proc_macro::Tok
     }
     .into()
 }
+
+fn variable_references<'a>(msg: &Message<&'a str>) -> Vec<&'a str> {
+    let mut refs = vec![];
+    if let Some(Pattern { elements }) = &msg.value {
+        for elt in elements {
+            if let PatternElement::Placeable {
+                expression: Expression::Inline(InlineExpression::VariableReference { id }),
+            } = elt
+            {
+                refs.push(id.name);
+            }
+        }
+    }
+    for attr in &msg.attributes {
+        for elt in &attr.value.elements {
+            if let PatternElement::Placeable {
+                expression: Expression::Inline(InlineExpression::VariableReference { id }),
+            } = elt
+            {
+                refs.push(id.name);
+            }
+        }
+    }
+    refs
+}

compiler/rustc_hir/src/hir.rs

@@ -1719,6 +1719,7 @@ impl Expr<'_> {
             ExprKind::Break(..) => ExprPrecedence::Break,
             ExprKind::Continue(..) => ExprPrecedence::Continue,
             ExprKind::Ret(..) => ExprPrecedence::Ret,
+            ExprKind::Become(..) => ExprPrecedence::Become,
             ExprKind::InlineAsm(..) => ExprPrecedence::InlineAsm,
             ExprKind::OffsetOf(..) => ExprPrecedence::OffsetOf,
             ExprKind::Struct(..) => ExprPrecedence::Struct,
@@ -1776,6 +1777,7 @@ impl Expr<'_> {
             | ExprKind::Break(..)
             | ExprKind::Continue(..)
             | ExprKind::Ret(..)
+            | ExprKind::Become(..)
             | ExprKind::Let(..)
             | ExprKind::Loop(..)
             | ExprKind::Assign(..)
@@ -1866,6 +1868,7 @@ impl Expr<'_> {
             | ExprKind::Break(..)
             | ExprKind::Continue(..)
             | ExprKind::Ret(..)
+            | ExprKind::Become(..)
             | ExprKind::Let(..)
             | ExprKind::Loop(..)
             | ExprKind::Assign(..)
@@ -2025,6 +2028,8 @@ pub enum ExprKind<'hir> {
     Continue(Destination),
     /// A `return`, with an optional value to be returned.
     Ret(Option<&'hir Expr<'hir>>),
+    /// A `become`, with the value to be returned.
+    Become(&'hir Expr<'hir>),
 
     /// Inline assembly (from `asm!`), with its outputs and inputs.
     InlineAsm(&'hir InlineAsm<'hir>),

compiler/rustc_hir/src/intravisit.rs

@@ -791,6 +791,7 @@ pub fn walk_expr<'v, V: Visitor<'v>>(visitor: &mut V, expression: &'v Expr<'v>)
         ExprKind::Ret(ref optional_expression) => {
             walk_list!(visitor, visit_expr, optional_expression);
         }
+        ExprKind::Become(ref expr) => visitor.visit_expr(expr),
         ExprKind::InlineAsm(ref asm) => {
             visitor.visit_inline_asm(asm, expression.hir_id);
         }

compiler/rustc_hir_analysis/messages.ftl

@@ -137,7 +137,7 @@ hir_analysis_missing_trait_item_suggestion = implement the missing item: `{$snip
 
 hir_analysis_missing_trait_item_unstable = not all trait items implemented, missing: `{$missing_item_name}`
     .note = default implementation of `{$missing_item_name}` is unstable
-    .some_note = use of unstable library feature '{$feature}': {$r}
+    .some_note = use of unstable library feature '{$feature}': {$reason}
     .none_note = use of unstable library feature '{$feature}'
 
 hir_analysis_missing_type_params =

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -945,40 +945,30 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
 
         let mut trait_bounds = vec![];
         let mut projection_bounds = vec![];
-        for (clause, span) in bounds.clauses() {
+        for (pred, span) in bounds.clauses() {
-            let pred: ty::Predicate<'tcx> = clause.as_predicate();
             let bound_pred = pred.kind();
             match bound_pred.skip_binder() {
-                ty::PredicateKind::Clause(clause) => match clause {
+                ty::ClauseKind::Trait(trait_pred) => {
-                    ty::ClauseKind::Trait(trait_pred) => {
+                    assert_eq!(trait_pred.polarity, ty::ImplPolarity::Positive);
-                        assert_eq!(trait_pred.polarity, ty::ImplPolarity::Positive);
+                    trait_bounds.push((
-                        trait_bounds.push((
+                        bound_pred.rebind(trait_pred.trait_ref),
-                            bound_pred.rebind(trait_pred.trait_ref),
+                        span,
-                            span,
+                        trait_pred.constness,
-                            trait_pred.constness,
+                    ));
-                        ));
+                }
-                    }
+                ty::ClauseKind::Projection(proj) => {
-                    ty::ClauseKind::Projection(proj) => {
+                    projection_bounds.push((bound_pred.rebind(proj), span));
-                        projection_bounds.push((bound_pred.rebind(proj), span));
+                }
-                    }
+                ty::ClauseKind::TypeOutlives(_) => {
-                    ty::ClauseKind::TypeOutlives(_) => {
+                    // Do nothing, we deal with regions separately
-                        // Do nothing, we deal with regions separately
+                }
-                    }
+                ty::ClauseKind::RegionOutlives(_)
-                    ty::ClauseKind::RegionOutlives(_)
+                | ty::ClauseKind::ConstArgHasType(..)
-                    | ty::ClauseKind::ConstArgHasType(..)
+                | ty::ClauseKind::WellFormed(_)
-                    | ty::ClauseKind::WellFormed(_)
+                | ty::ClauseKind::ConstEvaluatable(_)
-                    | ty::ClauseKind::ConstEvaluatable(_) => {
+                | ty::ClauseKind::TypeWellFormedFromEnv(_) => {
-                        bug!()
+                    bug!()
-                    }
+                }
-                },
-                ty::PredicateKind::AliasRelate(..)
-                | ty::PredicateKind::ObjectSafe(_)
-                | ty::PredicateKind::ClosureKind(_, _, _)
-                | ty::PredicateKind::Subtype(_)
-                | ty::PredicateKind::Coerce(_)
-                | ty::PredicateKind::ConstEquate(_, _)
-                | ty::PredicateKind::TypeWellFormedFromEnv(_)
-                | ty::PredicateKind::Ambiguous => bug!(),
             }
         }
 
@@ -1425,9 +1415,9 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             || {
                 traits::transitive_bounds_that_define_assoc_item(
                     tcx,
-                    predicates.iter().filter_map(|(p, _)| {
+                    predicates
-                        Some(p.to_opt_poly_trait_pred()?.map_bound(|t| t.trait_ref))
+                        .iter()
-                    }),
+                        .filter_map(|(p, _)| Some(p.as_trait_clause()?.map_bound(|t| t.trait_ref))),
                     assoc_name,
                 )
             },

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -220,7 +220,7 @@ fn compare_method_predicate_entailment<'tcx>(
     // the new hybrid bounds we computed.
     let normalize_cause = traits::ObligationCause::misc(impl_m_span, impl_m_def_id);
     let param_env = ty::ParamEnv::new(
-        tcx.mk_predicates(&hybrid_preds.predicates),
+        tcx.mk_clauses(&hybrid_preds.predicates),
         Reveal::UserFacing,
         hir::Constness::NotConst,
     );
@@ -1835,7 +1835,7 @@ fn compare_type_predicate_entailment<'tcx>(
     let impl_ty_span = tcx.def_span(impl_ty_def_id);
     let normalize_cause = traits::ObligationCause::misc(impl_ty_span, impl_ty_def_id);
     let param_env = ty::ParamEnv::new(
-        tcx.mk_predicates(&hybrid_preds.predicates),
+        tcx.mk_clauses(&hybrid_preds.predicates),
         Reveal::UserFacing,
         hir::Constness::NotConst,
     );
@@ -2011,7 +2011,7 @@ pub(super) fn check_type_bounds<'tcx>(
                 .to_predicate(tcx),
             ),
         };
-        ty::ParamEnv::new(tcx.mk_predicates(&predicates), Reveal::UserFacing, param_env.constness())
+        ty::ParamEnv::new(tcx.mk_clauses(&predicates), Reveal::UserFacing, param_env.constness())
     };
     debug!(?normalize_param_env);
 

compiler/rustc_hir_analysis/src/check/mod.rs

@@ -296,7 +296,7 @@ fn default_body_is_unstable(
 /// Re-sugar `ty::GenericPredicates` in a way suitable to be used in structured suggestions.
 fn bounds_from_generic_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    predicates: impl IntoIterator<Item = (ty::Predicate<'tcx>, Span)>,
+    predicates: impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>,
 ) -> (String, String) {
     let mut types: FxHashMap<Ty<'tcx>, Vec<DefId>> = FxHashMap::default();
     let mut projections = vec![];
@@ -304,7 +304,7 @@ fn bounds_from_generic_predicates<'tcx>(
         debug!("predicate {:?}", predicate);
         let bound_predicate = predicate.kind();
         match bound_predicate.skip_binder() {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_predicate)) => {
+            ty::ClauseKind::Trait(trait_predicate) => {
                 let entry = types.entry(trait_predicate.self_ty()).or_default();
                 let def_id = trait_predicate.def_id();
                 if Some(def_id) != tcx.lang_items().sized_trait() {
@@ -313,7 +313,7 @@ fn bounds_from_generic_predicates<'tcx>(
                     entry.push(trait_predicate.def_id());
                 }
             }
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(projection_pred)) => {
+            ty::ClauseKind::Projection(projection_pred) => {
                 projections.push(bound_predicate.rebind(projection_pred));
             }
             _ => {}
@@ -362,7 +362,7 @@ fn fn_sig_suggestion<'tcx>(
     tcx: TyCtxt<'tcx>,
     sig: ty::FnSig<'tcx>,
     ident: Ident,
-    predicates: impl IntoIterator<Item = (ty::Predicate<'tcx>, Span)>,
+    predicates: impl IntoIterator<Item = (ty::Clause<'tcx>, Span)>,
     assoc: ty::AssocItem,
 ) -> String {
     let args = sig

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -15,7 +15,7 @@ use rustc_middle::mir::ConstraintCategory;
 use rustc_middle::query::Providers;
 use rustc_middle::ty::trait_def::TraitSpecializationKind;
 use rustc_middle::ty::{
-    self, AdtKind, GenericParamDefKind, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
+    self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable, TypeSuperVisitable,
     TypeVisitable, TypeVisitableExt, TypeVisitor,
 };
 use rustc_middle::ty::{GenericArgKind, InternalSubsts};
@@ -322,7 +322,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
             // Gather the bounds with which all other items inside of this trait constrain the GAT.
             // This is calculated by taking the intersection of the bounds that each item
             // constrains the GAT with individually.
-            let mut new_required_bounds: Option<FxHashSet<ty::Predicate<'_>>> = None;
+            let mut new_required_bounds: Option<FxHashSet<ty::Clause<'_>>> = None;
             for item in associated_items {
                 let item_def_id = item.id.owner_id;
                 // Skip our own GAT, since it does not constrain itself at all.
@@ -419,9 +419,17 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
         let mut unsatisfied_bounds: Vec<_> = required_bounds
             .into_iter()
             .filter(|clause| match clause.kind().skip_binder() {
-                ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
+                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(a, b)) => {
-                    ty::OutlivesPredicate(a, b),
+                    !region_known_to_outlive(
-                )) => !region_known_to_outlive(
+                        tcx,
+                        gat_def_id.def_id,
+                        param_env,
+                        &FxIndexSet::default(),
+                        a,
+                        b,
+                    )
+                }
+                ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(a, b)) => !ty_known_to_outlive(
                     tcx,
                     gat_def_id.def_id,
                     param_env,
@@ -429,18 +437,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
                     a,
                     b,
                 ),
-                ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(
+                _ => bug!("Unexpected ClauseKind"),
-                    a,
-                    b,
-                ))) => !ty_known_to_outlive(
-                    tcx,
-                    gat_def_id.def_id,
-                    param_env,
-                    &FxIndexSet::default(),
-                    a,
-                    b,
-                ),
-                _ => bug!("Unexpected PredicateKind"),
             })
             .map(|clause| clause.to_string())
             .collect();
@@ -488,7 +485,7 @@ fn check_gat_where_clauses(tcx: TyCtxt<'_>, associated_items: &[hir::TraitItemRe
 fn augment_param_env<'tcx>(
     tcx: TyCtxt<'tcx>,
     param_env: ty::ParamEnv<'tcx>,
-    new_predicates: Option<&FxHashSet<ty::Predicate<'tcx>>>,
+    new_predicates: Option<&FxHashSet<ty::Clause<'tcx>>>,
 ) -> ty::ParamEnv<'tcx> {
     let Some(new_predicates) = new_predicates else {
         return param_env;
@@ -498,7 +495,7 @@ fn augment_param_env<'tcx>(
         return param_env;
     }
 
-    let bounds = tcx.mk_predicates_from_iter(
+    let bounds = tcx.mk_clauses_from_iter(
         param_env.caller_bounds().iter().chain(new_predicates.iter().cloned()),
     );
     // FIXME(compiler-errors): Perhaps there is a case where we need to normalize this
@@ -524,7 +521,7 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
     wf_tys: &FxIndexSet<Ty<'tcx>>,
     gat_def_id: LocalDefId,
     gat_generics: &'tcx ty::Generics,
-) -> Option<FxHashSet<ty::Predicate<'tcx>>> {
+) -> Option<FxHashSet<ty::Clause<'tcx>>> {
     // The bounds we that we would require from `to_check`
     let mut bounds = FxHashSet::default();
 
@@ -573,11 +570,10 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
                 );
                 // The predicate we expect to see. (In our example,
                 // `Self: 'me`.)
-                let clause = ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(
+                bounds.insert(
-                    ty::OutlivesPredicate(ty_param, region_param),
+                    ty::ClauseKind::TypeOutlives(ty::OutlivesPredicate(ty_param, region_param))
-                ));
+                        .to_predicate(tcx),
-                let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
+                );
-                bounds.insert(clause);
             }
         }
 
@@ -622,11 +618,13 @@ fn gather_gat_bounds<'tcx, T: TypeFoldable<TyCtxt<'tcx>>>(
                     },
                 );
                 // The predicate we expect to see.
-                let clause = ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
+                bounds.insert(
-                    ty::OutlivesPredicate(region_a_param, region_b_param),
+                    ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
-                ));
+                        region_a_param,
-                let clause = tcx.mk_predicate(ty::Binder::dummy(clause));
+                        region_b_param,
-                bounds.insert(clause);
+                    ))
+                    .to_predicate(tcx),
+                );
             }
         }
     }
@@ -1406,7 +1404,7 @@ fn check_where_clauses<'tcx>(wfcx: &WfCheckingCtxt<'_, 'tcx>, span: Span, def_id
             infcx,
             wfcx.param_env.without_const(),
             wfcx.body_def_id,
-            p,
+            p.as_predicate(),
             sp,
         )
     });
@@ -1549,7 +1547,7 @@ impl<'tcx> TypeVisitor<TyCtxt<'tcx>> for ImplTraitInTraitFinder<'_, 'tcx> {
         {
             let opaque_ty = tcx.fold_regions(unshifted_opaque_ty, |re, _depth| {
                 match re.kind() {
-                    ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReError(_) => re,
+                    ty::ReEarlyBound(_) | ty::ReFree(_) | ty::ReError(_) | ty::ReStatic => re,
                     r => bug!("unexpected region: {r:?}"),
                 }
             });
@@ -1875,9 +1873,7 @@ impl<'tcx> WfCheckingCtxt<'_, 'tcx> {
             // We lower empty bounds like `Vec<dyn Copy>:` as
             // `WellFormed(Vec<dyn Copy>)`, which will later get checked by
             // regular WF checking
-            if let ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(..)) =
+            if let ty::ClauseKind::WellFormed(..) = pred.kind().skip_binder() {
-                pred.kind().skip_binder()
-            {
                 continue;
             }
             // Match the existing behavior.

compiler/rustc_hir_analysis/src/coherence/inherent_impls_overlap.rs

@@ -140,7 +140,7 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
         impl1_def_id: DefId,
         impl2_def_id: DefId,
     ) {
-        traits::overlapping_impls(
+        let maybe_overlap = traits::overlapping_impls(
             self.tcx,
             impl1_def_id,
             impl2_def_id,
@@ -148,11 +148,11 @@ impl<'tcx> InherentOverlapChecker<'tcx> {
             // inherent impls without warning.
             SkipLeakCheck::Yes,
             overlap_mode,
-        )
+        );
-        .map_or(true, |overlap| {
+
+        if let Some(overlap) = maybe_overlap {
             self.check_for_common_items_in_impls(impl1_def_id, impl2_def_id, overlap);
-            false
+        }
-        });
     }
 
     fn check_item(&mut self, id: hir::ItemId) {

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -38,16 +38,12 @@ fn associated_type_bounds<'tcx>(
         .iter()
         .copied()
         .filter(|(pred, _)| match pred.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(tr)) => tr.self_ty() == item_ty,
+            ty::ClauseKind::Trait(tr) => tr.self_ty() == item_ty,
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)) => {
+            ty::ClauseKind::Projection(proj) => proj.projection_ty.self_ty() == item_ty,
-                proj.projection_ty.self_ty() == item_ty
+            ty::ClauseKind::TypeOutlives(outlives) => outlives.0 == item_ty,
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(outlives)) => {
-                outlives.0 == item_ty
-            }
             _ => false,
         })
-        .map(|(pred, span)| (pred.expect_clause(), span));
+        .map(|(clause, span)| (clause, span));
 
     let all_bounds = tcx.arena.alloc_from_iter(bounds.clauses().chain(bounds_from_parent));
     debug!(

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -75,7 +75,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
 
     // We use an `IndexSet` to preserve order of insertion.
     // Preserving the order of insertion is important here so as not to break UI tests.
-    let mut predicates: FxIndexSet<(ty::Predicate<'_>, Span)> = FxIndexSet::default();
+    let mut predicates: FxIndexSet<(ty::Clause<'_>, Span)> = FxIndexSet::default();
 
     let ast_generics = match node {
         Node::TraitItem(item) => item.generics,
@@ -126,8 +126,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
         predicates.extend(
             icx.astconv()
                 .compute_bounds(tcx.types.self_param, self_bounds, OnlySelfBounds(false))
-                .clauses()
+                .clauses(),
-                .map(|(clause, span)| (clause.as_predicate(), span)),
         );
     }
 
@@ -176,8 +175,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     param.span,
                 );
                 trace!(?bounds);
-                predicates
+                predicates.extend(bounds.clauses());
-                    .extend(bounds.clauses().map(|(clause, span)| (clause.as_predicate(), span)));
                 trace!(?predicates);
             }
             GenericParamKind::Const { .. } => {
@@ -188,11 +186,10 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
 
                 let ct = tcx.mk_const(param_const, ct_ty);
 
-                let predicate = ty::Binder::dummy(ty::PredicateKind::Clause(
+                predicates.insert((
-                    ty::ClauseKind::ConstArgHasType(ct, ct_ty),
+                    ty::ClauseKind::ConstArgHasType(ct, ct_ty).to_predicate(tcx),
-                ))
+                    param.span,
-                .to_predicate(tcx);
+                ));
-                predicates.insert((predicate, param.span));
 
                 index += 1;
             }
@@ -221,7 +218,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     } else {
                         let span = bound_pred.bounded_ty.span;
                         let predicate = ty::Binder::bind_with_vars(
-                            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(ty.into())),
+                            ty::ClauseKind::WellFormed(ty.into()),
                             bound_vars,
                         );
                         predicates.insert((predicate.to_predicate(tcx), span));
@@ -236,8 +233,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                     bound_vars,
                     OnlySelfBounds(false),
                 );
-                predicates
+                predicates.extend(bounds.clauses());
-                    .extend(bounds.clauses().map(|(clause, span)| (clause.as_predicate(), span)));
             }
 
             hir::WherePredicate::RegionPredicate(region_pred) => {
@@ -249,11 +245,8 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                         }
                         _ => bug!(),
                     };
-                    let pred = ty::Binder::dummy(ty::PredicateKind::Clause(
+                    let pred = ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r1, r2))
-                        ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r1, r2)),
+                        .to_predicate(icx.tcx);
-                    ))
-                    .to_predicate(icx.tcx);
-
                     (pred, span)
                 }))
             }
@@ -318,17 +311,13 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
                 },
             );
             predicates.push((
-                ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
+                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(orig_region, dup_region))
-                    ty::OutlivesPredicate(orig_region, dup_region),
+                    .to_predicate(icx.tcx),
-                )))
-                .to_predicate(icx.tcx),
                 duplicate.span,
             ));
             predicates.push((
-                ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
+                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(dup_region, orig_region))
-                    ty::OutlivesPredicate(dup_region, orig_region),
+                    .to_predicate(icx.tcx),
-                )))
-                .to_predicate(icx.tcx),
                 duplicate.span,
             ));
         }
@@ -344,10 +333,10 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
 fn const_evaluatable_predicates_of(
     tcx: TyCtxt<'_>,
     def_id: LocalDefId,
-) -> FxIndexSet<(ty::Predicate<'_>, Span)> {
+) -> FxIndexSet<(ty::Clause<'_>, Span)> {
     struct ConstCollector<'tcx> {
         tcx: TyCtxt<'tcx>,
-        preds: FxIndexSet<(ty::Predicate<'tcx>, Span)>,
+        preds: FxIndexSet<(ty::Clause<'tcx>, Span)>,
     }
 
     impl<'tcx> intravisit::Visitor<'tcx> for ConstCollector<'tcx> {
@@ -355,13 +344,8 @@ fn const_evaluatable_predicates_of(
             let ct = ty::Const::from_anon_const(self.tcx, c.def_id);
             if let ty::ConstKind::Unevaluated(_) = ct.kind() {
                 let span = self.tcx.def_span(c.def_id);
-                self.preds.insert((
+                self.preds
-                    ty::Binder::dummy(ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(
+                    .insert((ty::ClauseKind::ConstEvaluatable(ct).to_predicate(self.tcx), span));
-                        ct,
-                    )))
-                    .to_predicate(self.tcx),
-                    span,
-                ));
             }
         }
 
@@ -449,15 +433,9 @@ pub(super) fn explicit_predicates_of<'tcx>(
             .iter()
             .copied()
             .filter(|(pred, _)| match pred.kind().skip_binder() {
-                ty::PredicateKind::Clause(ty::ClauseKind::Trait(tr)) => {
+                ty::ClauseKind::Trait(tr) => !is_assoc_item_ty(tr.self_ty()),
-                    !is_assoc_item_ty(tr.self_ty())
+                ty::ClauseKind::Projection(proj) => !is_assoc_item_ty(proj.projection_ty.self_ty()),
-                }
+                ty::ClauseKind::TypeOutlives(outlives) => !is_assoc_item_ty(outlives.0),
-                ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)) => {
-                    !is_assoc_item_ty(proj.projection_ty.self_ty())
-                }
-                ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(outlives)) => {
-                    !is_assoc_item_ty(outlives.0)
-                }
                 _ => true,
             })
             .collect();
@@ -498,9 +476,7 @@ pub(super) fn explicit_predicates_of<'tcx>(
                     .predicates
                     .into_iter()
                     .filter(|(pred, _)| {
-                        if let ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, _)) =
+                        if let ty::ClauseKind::ConstArgHasType(ct, _) = pred.kind().skip_binder() {
-                            pred.kind().skip_binder()
-                        {
                             match ct.kind() {
                                 ty::ConstKind::Param(param_const) => {
                                     let defaulted_param_idx = tcx
@@ -665,12 +641,8 @@ pub(super) fn implied_predicates_with_filter(
     };
 
     // Combine the two lists to form the complete set of superbounds:
-    let implied_bounds = &*tcx.arena.alloc_from_iter(
+    let implied_bounds =
-        superbounds
+        &*tcx.arena.alloc_from_iter(superbounds.clauses().chain(where_bounds_that_match));
-            .clauses()
-            .map(|(clause, span)| (clause.as_predicate(), span))
-            .chain(where_bounds_that_match),
-    );
     debug!(?implied_bounds);
 
     // Now require that immediate supertraits are converted, which will, in
@@ -679,7 +651,7 @@ pub(super) fn implied_predicates_with_filter(
     if matches!(filter, PredicateFilter::SelfOnly) {
         for &(pred, span) in implied_bounds {
             debug!("superbound: {:?}", pred);
-            if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(bound)) = pred.kind().skip_binder()
+            if let ty::ClauseKind::Trait(bound) = pred.kind().skip_binder()
                 && bound.polarity == ty::ImplPolarity::Positive
             {
                 tcx.at(span).super_predicates_of(bound.def_id());
@@ -776,9 +748,7 @@ pub(super) fn type_param_predicates(
         )
         .into_iter()
         .filter(|(predicate, _)| match predicate.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => {
+            ty::ClauseKind::Trait(data) => data.self_ty().is_param(index),
-                data.self_ty().is_param(index)
-            }
             _ => false,
         }),
     );
@@ -800,7 +770,7 @@ impl<'tcx> ItemCtxt<'tcx> {
         ty: Ty<'tcx>,
         only_self_bounds: OnlySelfBounds,
         assoc_name: Option<Ident>,
-    ) -> Vec<(ty::Predicate<'tcx>, Span)> {
+    ) -> Vec<(ty::Clause<'tcx>, Span)> {
         let mut bounds = Bounds::default();
 
         for predicate in ast_generics.predicates {
@@ -829,7 +799,7 @@ impl<'tcx> ItemCtxt<'tcx> {
             );
         }
 
-        bounds.clauses().map(|(clause, span)| (clause.as_predicate(), span)).collect()
+        bounds.clauses().collect()
     }
 
     #[instrument(level = "trace", skip(self))]

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -1761,7 +1761,7 @@ impl<'a, 'tcx> BoundVarContext<'a, 'tcx> {
             let obligations = predicates.predicates.iter().filter_map(|&(pred, _)| {
                 let bound_predicate = pred.kind();
                 match bound_predicate.skip_binder() {
-                    ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) => {
+                    ty::ClauseKind::Trait(data) => {
                         // The order here needs to match what we would get from `subst_supertrait`
                         let pred_bound_vars = bound_predicate.bound_vars();
                         let mut all_bound_vars = bound_vars.clone();

compiler/rustc_hir_analysis/src/constrained_generic_params.rs

@@ -151,7 +151,7 @@ pub fn identify_constrained_generic_params<'tcx>(
 /// think of any.
 pub fn setup_constraining_predicates<'tcx>(
     tcx: TyCtxt<'tcx>,
-    predicates: &mut [(ty::Predicate<'tcx>, Span)],
+    predicates: &mut [(ty::Clause<'tcx>, Span)],
     impl_trait_ref: Option<ty::TraitRef<'tcx>>,
     input_parameters: &mut FxHashSet<Parameter>,
 ) {
@@ -187,9 +187,7 @@ pub fn setup_constraining_predicates<'tcx>(
         for j in i..predicates.len() {
             // Note that we don't have to care about binders here,
             // as the impl trait ref never contains any late-bound regions.
-            if let ty::PredicateKind::Clause(ty::ClauseKind::Projection(projection)) =
+            if let ty::ClauseKind::Projection(projection) = predicates[j].0.kind().skip_binder() {
-                predicates[j].0.kind().skip_binder()
-            {
                 // Special case: watch out for some kind of sneaky attempt
                 // to project out an associated type defined by this very
                 // trait.

compiler/rustc_hir_analysis/src/impl_wf_check/min_specialization.rs

@@ -235,10 +235,8 @@ fn unconstrained_parent_impl_substs<'tcx>(
     // what we want here. We want only a list of constrained parameters while
     // the functions in `cgp` add the constrained parameters to a list of
     // unconstrained parameters.
-    for (predicate, _) in impl_generic_predicates.predicates.iter() {
+    for (clause, _) in impl_generic_predicates.predicates.iter() {
-        if let ty::PredicateKind::Clause(ty::ClauseKind::Projection(proj)) =
+        if let ty::ClauseKind::Projection(proj) = clause.kind().skip_binder() {
-            predicate.kind().skip_binder()
-        {
             let projection_ty = proj.projection_ty;
             let projected_ty = proj.term;
 
@@ -340,8 +338,11 @@ fn check_predicates<'tcx>(
     impl2_substs: SubstsRef<'tcx>,
     span: Span,
 ) {
-    let instantiated = tcx.predicates_of(impl1_def_id).instantiate(tcx, impl1_substs);
+    let impl1_predicates: Vec<_> = traits::elaborate(
-    let impl1_predicates: Vec<_> = traits::elaborate(tcx, instantiated.into_iter()).collect();
+        tcx,
+        tcx.predicates_of(impl1_def_id).instantiate(tcx, impl1_substs).into_iter(),
+    )
+    .collect();
 
     let mut impl2_predicates = if impl2_node.is_from_trait() {
         // Always applicable traits have to be always applicable without any
@@ -352,8 +353,8 @@ fn check_predicates<'tcx>(
             tcx,
             tcx.predicates_of(impl2_node.def_id())
                 .instantiate(tcx, impl2_substs)
-                .predicates
+                .into_iter()
-                .into_iter(),
+                .map(|(c, _s)| c.as_predicate()),
         )
         .collect()
     };
@@ -377,13 +378,13 @@ fn check_predicates<'tcx>(
     let always_applicable_traits = impl1_predicates
         .iter()
         .copied()
-        .filter(|&(predicate, _)| {
+        .filter(|(clause, _span)| {
             matches!(
-                trait_predicate_kind(tcx, predicate),
+                trait_predicate_kind(tcx, clause.as_predicate()),
                 Some(TraitSpecializationKind::AlwaysApplicable)
             )
         })
-        .map(|(pred, _span)| pred);
+        .map(|(c, _span)| c.as_predicate());
 
     // Include the well-formed predicates of the type parameters of the impl.
     for arg in tcx.impl_trait_ref(impl1_def_id).unwrap().subst_identity().substs {
@@ -398,9 +399,12 @@ fn check_predicates<'tcx>(
     }
     impl2_predicates.extend(traits::elaborate(tcx, always_applicable_traits));
 
-    for (predicate, span) in impl1_predicates {
+    for (clause, span) in impl1_predicates {
-        if !impl2_predicates.iter().any(|pred2| trait_predicates_eq(tcx, predicate, *pred2, span)) {
+        if !impl2_predicates
-            check_specialization_on(tcx, predicate, span)
+            .iter()
+            .any(|pred2| trait_predicates_eq(tcx, clause.as_predicate(), *pred2, span))
+        {
+            check_specialization_on(tcx, clause.as_predicate(), span)
         }
     }
 }
@@ -550,6 +554,6 @@ fn trait_predicate_kind<'tcx>(
         | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
         | ty::PredicateKind::ConstEquate(..)
         | ty::PredicateKind::Ambiguous
-        | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
+        | ty::PredicateKind::Clause(ty::ClauseKind::TypeWellFormedFromEnv(..)) => None,
     }
 }

compiler/rustc_hir_analysis/src/outlives/explicit.rs

@@ -30,40 +30,31 @@ impl<'tcx> ExplicitPredicatesMap<'tcx> {
             // process predicates and convert to `RequiredPredicates` entry, see below
             for &(predicate, span) in predicates.predicates {
                 match predicate.kind().skip_binder() {
-                    ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(OutlivesPredicate(
+                    ty::ClauseKind::TypeOutlives(OutlivesPredicate(ty, reg)) => {
-                        ty,
+                        insert_outlives_predicate(
-                        reg,
+                            tcx,
-                    ))) => insert_outlives_predicate(
+                            ty.into(),
-                        tcx,
+                            reg,
-                        ty.into(),
+                            span,
-                        reg,
+                            &mut required_predicates,
-                        span,
+                        )
-                        &mut required_predicates,
+                    }
-                    ),
 
-                    ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(
+                    ty::ClauseKind::RegionOutlives(OutlivesPredicate(reg1, reg2)) => {
-                        OutlivesPredicate(reg1, reg2),
+                        insert_outlives_predicate(
-                    )) => insert_outlives_predicate(
+                            tcx,
-                        tcx,
+                            reg1.into(),
-                        reg1.into(),
+                            reg2,
-                        reg2,
+                            span,
-                        span,
+                            &mut required_predicates,
-                        &mut required_predicates,
+                        )
-                    ),
+                    }
-
+                    ty::ClauseKind::Trait(_)
-                    ty::PredicateKind::Clause(ty::ClauseKind::Trait(..))
+                    | ty::ClauseKind::Projection(_)
-                    | ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
+                    | ty::ClauseKind::ConstArgHasType(_, _)
-                    | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
+                    | ty::ClauseKind::WellFormed(_)
-                    | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(..))
+                    | ty::ClauseKind::ConstEvaluatable(_)
-                    | ty::PredicateKind::AliasRelate(..)
+                    | ty::ClauseKind::TypeWellFormedFromEnv(_) => {}
-                    | ty::PredicateKind::ObjectSafe(..)
-                    | ty::PredicateKind::ClosureKind(..)
-                    | ty::PredicateKind::Subtype(..)
-                    | ty::PredicateKind::Coerce(..)
-                    | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
-                    | ty::PredicateKind::ConstEquate(..)
-                    | ty::PredicateKind::Ambiguous
-                    | ty::PredicateKind::TypeWellFormedFromEnv(..) => (),
                 }
             }
 

compiler/rustc_hir_pretty/src/lib.rs

@@ -1554,6 +1554,11 @@ impl<'a> State<'a> {
                     self.print_expr_maybe_paren(expr, parser::PREC_JUMP);
                 }
             }
+            hir::ExprKind::Become(result) => {
+                self.word("become");
+                self.word(" ");
+                self.print_expr_maybe_paren(result, parser::PREC_JUMP);
+            }
             hir::ExprKind::InlineAsm(asm) => {
                 self.word("asm!");
                 self.print_inline_asm(asm);

compiler/rustc_hir_typeck/messages.ftl

@@ -78,8 +78,8 @@ hir_typeck_note_edition_guide = for more on editions, read https://doc.rust-lang
 hir_typeck_op_trait_generic_params = `{$method_name}` must not have any generic parameters
 
 hir_typeck_return_stmt_outside_of_fn_body =
-    return statement outside of function body
+    {$statement_kind} statement outside of function body
-    .encl_body_label = the return is part of this body...
+    .encl_body_label = the {$statement_kind} is part of this body...
     .encl_fn_label = ...not the enclosing function body
 
 hir_typeck_struct_expr_non_exhaustive =

compiler/rustc_hir_typeck/src/demand.rs

@@ -83,6 +83,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         self.annotate_expected_due_to_let_ty(err, expr, error);
+
+        if self.is_destruct_assignment_desugaring(expr) {
+            return;
+        }
         self.emit_type_mismatch_suggestions(err, expr, expr_ty, expected, expected_ty_expr, error);
         self.note_type_is_not_clone(err, expected, expr_ty, expr);
         self.note_internal_mutation_in_method(err, expr, Some(expected), expr_ty);
@@ -1253,6 +1257,26 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         false
     }
 
+    // Returns whether the given expression is a destruct assignment desugaring.
+    // For example, `(a, b) = (1, &2);`
+    // Here we try to find the pattern binding of the expression,
+    // `default_binding_modes` is false only for destruct assignment desugaring.
+    pub(crate) fn is_destruct_assignment_desugaring(&self, expr: &hir::Expr<'_>) -> bool {
+        if let hir::ExprKind::Path(hir::QPath::Resolved(
+            _,
+            hir::Path { res: hir::def::Res::Local(bind_hir_id), .. },
+        )) = expr.kind
+        {
+            let bind = self.tcx.hir().find(*bind_hir_id);
+            let parent = self.tcx.hir().find(self.tcx.hir().parent_id(*bind_hir_id));
+            if let Some(hir::Node::Pat(hir::Pat { kind: hir::PatKind::Binding(_, _hir_id, _, _), .. })) = bind &&
+                let Some(hir::Node::Pat(hir::Pat { default_binding_modes: false, .. })) = parent {
+                    return true;
+                }
+        }
+        return false;
+    }
+
     /// This function is used to determine potential "simple" improvements or users' errors and
     /// provide them useful help. For example:
     ///
@@ -1443,6 +1467,20 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 _,
                 &ty::Ref(_, checked, _),
             ) if self.can_sub(self.param_env, checked, expected) => {
+                let make_sugg = |start: Span, end: BytePos| {
+                    // skip `(` for tuples such as `(c) = (&123)`.
+                    // make sure we won't suggest like `(c) = 123)` which is incorrect.
+                    let sp = sm.span_extend_while(start.shrink_to_lo(), |c| c == '(' || c.is_whitespace())
+                                .map_or(start, |s| s.shrink_to_hi());
+                    Some((
+                        vec![(sp.with_hi(end), String::new())],
+                        "consider removing the borrow".to_string(),
+                        Applicability::MachineApplicable,
+                        true,
+                        true,
+                    ))
+                };
+
                 // We have `&T`, check if what was expected was `T`. If so,
                 // we may want to suggest removing a `&`.
                 if sm.is_imported(expr.span) {
@@ -1456,24 +1494,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             .find(|&s| sp.contains(s))
                         && sm.is_span_accessible(call_span)
                     {
-                        return Some((
+                        return make_sugg(sp, call_span.lo())
-                            vec![(sp.with_hi(call_span.lo()), String::new())],
-                            "consider removing the borrow".to_string(),
-                            Applicability::MachineApplicable,
-                            true,
-                            true,
-                        ));
                     }
                     return None;
                 }
                 if sp.contains(expr.span) && sm.is_span_accessible(expr.span) {
-                    return Some((
+                    return make_sugg(sp, expr.span.lo())
-                        vec![(sp.with_hi(expr.span.lo()), String::new())],
-                        "consider removing the borrow".to_string(),
-                        Applicability::MachineApplicable,
-                        true,
-                        true,
-                    ));
                 }
             }
             (

compiler/rustc_hir_typeck/src/errors.rs

@@ -2,7 +2,10 @@
 use std::borrow::Cow;
 
 use crate::fluent_generated as fluent;
-use rustc_errors::{AddToDiagnostic, Applicability, Diagnostic, MultiSpan, SubdiagnosticMessage};
+use rustc_errors::{
+    AddToDiagnostic, Applicability, Diagnostic, DiagnosticArgValue, IntoDiagnosticArg, MultiSpan,
+    SubdiagnosticMessage,
+};
 use rustc_macros::{Diagnostic, Subdiagnostic};
 use rustc_middle::ty::Ty;
 use rustc_span::{
@@ -31,6 +34,24 @@ pub struct ReturnStmtOutsideOfFnBody {
     pub encl_body_span: Option<Span>,
     #[label(hir_typeck_encl_fn_label)]
     pub encl_fn_span: Option<Span>,
+    pub statement_kind: ReturnLikeStatementKind,
+}
+
+pub enum ReturnLikeStatementKind {
+    Return,
+    Become,
+}
+
+impl IntoDiagnosticArg for ReturnLikeStatementKind {
+    fn into_diagnostic_arg(self) -> DiagnosticArgValue<'static> {
+        let kind = match self {
+            Self::Return => "return",
+            Self::Become => "become",
+        }
+        .into();
+
+        DiagnosticArgValue::Str(kind)
+    }
 }
 
 #[derive(Diagnostic)]

compiler/rustc_hir_typeck/src/expr.rs

@@ -5,6 +5,7 @@
 use crate::cast;
 use crate::coercion::CoerceMany;
 use crate::coercion::DynamicCoerceMany;
+use crate::errors::ReturnLikeStatementKind;
 use crate::errors::TypeMismatchFruTypo;
 use crate::errors::{AddressOfTemporaryTaken, ReturnStmtOutsideOfFnBody, StructExprNonExhaustive};
 use crate::errors::{
@@ -324,6 +325,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 }
             }
             ExprKind::Ret(ref expr_opt) => self.check_expr_return(expr_opt.as_deref(), expr),
+            ExprKind::Become(call) => self.check_expr_become(call, expr),
             ExprKind::Let(let_expr) => self.check_expr_let(let_expr),
             ExprKind::Loop(body, _, source, _) => {
                 self.check_expr_loop(body, source, expected, expr)
@@ -735,47 +737,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expr: &'tcx hir::Expr<'tcx>,
     ) -> Ty<'tcx> {
         if self.ret_coercion.is_none() {
-            let mut err = ReturnStmtOutsideOfFnBody {
+            self.emit_return_outside_of_fn_body(expr, ReturnLikeStatementKind::Return);
-                span: expr.span,
-                encl_body_span: None,
-                encl_fn_span: None,
-            };
-
-            let encl_item_id = self.tcx.hir().get_parent_item(expr.hir_id);
-
-            if let Some(hir::Node::Item(hir::Item {
-                kind: hir::ItemKind::Fn(..),
-                span: encl_fn_span,
-                ..
-            }))
-            | Some(hir::Node::TraitItem(hir::TraitItem {
-                kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
-                span: encl_fn_span,
-                ..
-            }))
-            | Some(hir::Node::ImplItem(hir::ImplItem {
-                kind: hir::ImplItemKind::Fn(..),
-                span: encl_fn_span,
-                ..
-            })) = self.tcx.hir().find_by_def_id(encl_item_id.def_id)
-            {
-                // We are inside a function body, so reporting "return statement
-                // outside of function body" needs an explanation.
-
-                let encl_body_owner_id = self.tcx.hir().enclosing_body_owner(expr.hir_id);
-
-                // If this didn't hold, we would not have to report an error in
-                // the first place.
-                assert_ne!(encl_item_id.def_id, encl_body_owner_id);
-
-                let encl_body_id = self.tcx.hir().body_owned_by(encl_body_owner_id);
-                let encl_body = self.tcx.hir().body(encl_body_id);
-
-                err.encl_body_span = Some(encl_body.value.span);
-                err.encl_fn_span = Some(*encl_fn_span);
-            }
-
-            self.tcx.sess.emit_err(err);
 
             if let Some(e) = expr_opt {
                 // We still have to type-check `e` (issue #86188), but calling
@@ -815,6 +777,38 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         self.tcx.types.never
     }
 
+    fn check_expr_become(
+        &self,
+        call: &'tcx hir::Expr<'tcx>,
+        expr: &'tcx hir::Expr<'tcx>,
+    ) -> Ty<'tcx> {
+        match &self.ret_coercion {
+            Some(ret_coercion) => {
+                let ret_ty = ret_coercion.borrow().expected_ty();
+                let call_expr_ty = self.check_expr_with_hint(call, ret_ty);
+
+                // N.B. don't coerce here, as tail calls can't support most/all coercions
+                // FIXME(explicit_tail_calls): add a diagnostic note that `become` doesn't allow coercions
+                self.demand_suptype(expr.span, ret_ty, call_expr_ty);
+            }
+            None => {
+                self.emit_return_outside_of_fn_body(expr, ReturnLikeStatementKind::Become);
+
+                // Fallback to simply type checking `call` without hint/demanding the right types.
+                // Best effort to highlight more errors.
+                self.check_expr(call);
+            }
+        }
+
+        self.tcx.types.never
+    }
+
+    /// Check an expression that _is being returned_.
+    /// For example, this is called with `return_expr: $expr` when `return $expr`
+    /// is encountered.
+    ///
+    /// Note that this function must only be called in function bodies.
+    ///
     /// `explicit_return` is `true` if we're checking an explicit `return expr`,
     /// and `false` if we're checking a trailing expression.
     pub(super) fn check_return_expr(
@@ -831,10 +825,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         let mut span = return_expr.span;
         // Use the span of the trailing expression for our cause,
         // not the span of the entire function
-        if !explicit_return {
+        if !explicit_return
-            if let ExprKind::Block(body, _) = return_expr.kind && let Some(last_expr) = body.expr {
+            && let ExprKind::Block(body, _) = return_expr.kind
+            && let Some(last_expr) = body.expr
+        {
                 span = last_expr.span;
-            }
         }
         ret_coercion.borrow_mut().coerce(
             self,
@@ -854,6 +849,55 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
     }
 
+    /// Emit an error because `return` or `become` is used outside of a function body.
+    ///
+    /// `expr` is the `return` (`become`) "statement", `kind` is the kind of the statement
+    /// either `Return` or `Become`.
+    fn emit_return_outside_of_fn_body(&self, expr: &hir::Expr<'_>, kind: ReturnLikeStatementKind) {
+        let mut err = ReturnStmtOutsideOfFnBody {
+            span: expr.span,
+            encl_body_span: None,
+            encl_fn_span: None,
+            statement_kind: kind,
+        };
+
+        let encl_item_id = self.tcx.hir().get_parent_item(expr.hir_id);
+
+        if let Some(hir::Node::Item(hir::Item {
+            kind: hir::ItemKind::Fn(..),
+            span: encl_fn_span,
+            ..
+        }))
+        | Some(hir::Node::TraitItem(hir::TraitItem {
+            kind: hir::TraitItemKind::Fn(_, hir::TraitFn::Provided(_)),
+            span: encl_fn_span,
+            ..
+        }))
+        | Some(hir::Node::ImplItem(hir::ImplItem {
+            kind: hir::ImplItemKind::Fn(..),
+            span: encl_fn_span,
+            ..
+        })) = self.tcx.hir().find_by_def_id(encl_item_id.def_id)
+        {
+            // We are inside a function body, so reporting "return statement
+            // outside of function body" needs an explanation.
+
+            let encl_body_owner_id = self.tcx.hir().enclosing_body_owner(expr.hir_id);
+
+            // If this didn't hold, we would not have to report an error in
+            // the first place.
+            assert_ne!(encl_item_id.def_id, encl_body_owner_id);
+
+            let encl_body_id = self.tcx.hir().body_owned_by(encl_body_owner_id);
+            let encl_body = self.tcx.hir().body(encl_body_id);
+
+            err.encl_body_span = Some(encl_body.value.span);
+            err.encl_fn_span = Some(*encl_fn_span);
+        }
+
+        self.tcx.sess.emit_err(err);
+    }
+
     fn point_at_return_for_opaque_ty_error(
         &self,
         errors: &mut Vec<traits::FulfillmentError<'tcx>>,

compiler/rustc_hir_typeck/src/expr_use_visitor.rs

@@ -326,6 +326,10 @@ impl<'a, 'tcx> ExprUseVisitor<'a, 'tcx> {
                 }
             }
 
+            hir::ExprKind::Become(call) => {
+                self.consume_expr(call);
+            }
+
             hir::ExprKind::Assign(lhs, rhs, _) => {
                 self.mutate_expr(lhs);
                 self.consume_expr(rhs);

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -683,7 +683,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 // inference variable.
                 | ty::PredicateKind::ClosureKind(..)
                 | ty::PredicateKind::Ambiguous
-                | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
+                | ty::PredicateKind::Clause(ty::ClauseKind::TypeWellFormedFromEnv(..)) => None,
             },
         )
     }

compiler/rustc_hir_typeck/src/fn_ctxt/adjust_fulfillment_errors.rs

@@ -25,16 +25,12 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         let generics = self.tcx.generics_of(def_id);
         let predicate_substs = match unsubstituted_pred.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) => {
+            ty::ClauseKind::Trait(pred) => pred.trait_ref.substs.to_vec(),
-                pred.trait_ref.substs.to_vec()
+            ty::ClauseKind::Projection(pred) => pred.projection_ty.substs.to_vec(),
-            }
+            ty::ClauseKind::ConstArgHasType(arg, ty) => {
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(pred)) => {
-                pred.projection_ty.substs.to_vec()
-            }
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(arg, ty)) => {
                 vec![ty.into(), arg.into()]
             }
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(e)) => vec![e.into()],
+            ty::ClauseKind::ConstEvaluatable(e) => vec![e.into()],
             _ => return false,
         };
 
@@ -512,11 +508,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // This shouldn't happen, but since this is only a diagnostic improvement, avoid breaking things.
             return Err(expr);
         }
-        let relevant_broken_predicate: ty::PredicateKind<'tcx> =
-            impl_predicates.predicates[impl_predicate_index].0.kind().skip_binder();
 
-        match relevant_broken_predicate {
+        match impl_predicates.predicates[impl_predicate_index].0.kind().skip_binder() {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(broken_trait)) => {
+            ty::ClauseKind::Trait(broken_trait) => {
                 // ...
                 self.blame_specific_part_of_expr_corresponding_to_generic_param(
                     broken_trait.trait_ref.self_ty().into(),

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -955,9 +955,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         //   - f(0, 1,)
                         //   + f()
                         if only_extras_so_far
-                            && errors
+                            && !errors
                                 .peek()
-                                .map_or(true, |next_error| !matches!(next_error, Error::Extra(_)))
+                                .is_some_and(|next_error| matches!(next_error, Error::Extra(_)))
                         {
                             let next = provided_arg_tys
                                 .get(arg_idx + 1)
@@ -1948,7 +1948,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                         // do that, so it's OK.
                         for (predicate, span) in instantiated
                         {
-                            if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(pred)) = predicate.kind().skip_binder()
+                            if let ty::ClauseKind::Trait(pred) = predicate.kind().skip_binder()
                                 && pred.self_ty().peel_refs() == callee_ty
                                 && self.tcx.is_fn_trait(pred.def_id())
                             {

compiler/rustc_hir_typeck/src/fn_ctxt/mod.rs

@@ -226,9 +226,7 @@ impl<'a, 'tcx> AstConv<'tcx> for FnCtxt<'a, 'tcx> {
             predicates: tcx.arena.alloc_from_iter(
                 self.param_env.caller_bounds().iter().filter_map(|predicate| {
                     match predicate.kind().skip_binder() {
-                        ty::PredicateKind::Clause(ty::ClauseKind::Trait(data))
+                        ty::ClauseKind::Trait(data) if data.self_ty().is_param(index) => {
-                            if data.self_ty().is_param(index) =>
-                        {
                             // HACK(eddyb) should get the original `Span`.
                             let span = tcx.def_span(def_id);
                             Some((predicate, span))

compiler/rustc_hir_typeck/src/generator_interior/drop_ranges/cfg_build.rs

@@ -214,6 +214,7 @@ impl<'a, 'tcx> DropRangeVisitor<'a, 'tcx> {
             | ExprKind::Break(..)
             | ExprKind::Continue(..)
             | ExprKind::Ret(..)
+            | ExprKind::Become(..)
             | ExprKind::InlineAsm(..)
             | ExprKind::OffsetOf(..)
             | ExprKind::Struct(..)
@@ -451,6 +452,8 @@ impl<'a, 'tcx> Visitor<'tcx> for DropRangeVisitor<'a, 'tcx> {
                 }
             }
 
+            ExprKind::Become(_call) => bug!("encountered a tail-call inside a generator"),
+
             ExprKind::Call(f, args) => {
                 self.visit_expr(f);
                 for arg in args {

compiler/rustc_hir_typeck/src/mem_categorization.rs

@@ -361,6 +361,7 @@ impl<'a, 'tcx> MemCategorizationContext<'a, 'tcx> {
             | hir::ExprKind::AssignOp(..)
             | hir::ExprKind::Closure { .. }
             | hir::ExprKind::Ret(..)
+            | hir::ExprKind::Become(..)
             | hir::ExprKind::Unary(..)
             | hir::ExprKind::Yield(..)
             | hir::ExprKind::MethodCall(..)

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -606,9 +606,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
         traits::elaborate(self.tcx, predicates.predicates.iter().copied())
             // We don't care about regions here.
             .filter_map(|pred| match pred.kind().skip_binder() {
-                ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_pred))
+                ty::ClauseKind::Trait(trait_pred) if trait_pred.def_id() == sized_def_id => {
-                    if trait_pred.def_id() == sized_def_id =>
-                {
                     let span = predicates
                         .iter()
                         .find_map(|(p, span)| if p == pred { Some(span) } else { None })

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -834,7 +834,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
         let bounds = self.param_env.caller_bounds().iter().filter_map(|predicate| {
             let bound_predicate = predicate.kind();
             match bound_predicate.skip_binder() {
-                ty::PredicateKind::Clause(ty::ClauseKind::Trait(trait_predicate)) => {
+                ty::ClauseKind::Trait(trait_predicate) => {
                     match *trait_predicate.trait_ref.self_ty().kind() {
                         ty::Param(p) if p == param_ty => {
                             Some(bound_predicate.rebind(trait_predicate.trait_ref))
@@ -842,20 +842,13 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                         _ => None,
                     }
                 }
-                ty::PredicateKind::Subtype(..)
+                ty::ClauseKind::RegionOutlives(_)
-                | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
+                | ty::ClauseKind::TypeOutlives(_)
-                | ty::PredicateKind::Coerce(..)
+                | ty::ClauseKind::Projection(_)
-                | ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
+                | ty::ClauseKind::ConstArgHasType(_, _)
-                | ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(..))
+                | ty::ClauseKind::WellFormed(_)
-                | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(..))
+                | ty::ClauseKind::ConstEvaluatable(_)
-                | ty::PredicateKind::ObjectSafe(..)
+                | ty::ClauseKind::TypeWellFormedFromEnv(_) => None,
-                | ty::PredicateKind::ClosureKind(..)
-                | ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(..))
-                | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
-                | ty::PredicateKind::ConstEquate(..)
-                | ty::PredicateKind::Ambiguous
-                | ty::PredicateKind::AliasRelate(..)
-                | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
             }
         });
 

compiler/rustc_hir_typeck/src/pat.rs

@@ -393,8 +393,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // They can denote both statically and dynamically-sized byte arrays.
         let mut pat_ty = ty;
         if let hir::ExprKind::Lit(Spanned { node: ast::LitKind::ByteStr(..), .. }) = lt.kind {
-            if let ty::Ref(_, inner_ty, _) = *self.structurally_resolved_type(span, expected).kind()
+            let expected = self.structurally_resolved_type(span, expected);
-                && self.structurally_resolved_type(span, inner_ty).is_slice()
+            if let ty::Ref(_, inner_ty, _) = expected.kind()
+                && matches!(inner_ty.kind(), ty::Slice(_))
             {
                 let tcx = self.tcx;
                 trace!(?lt.hir_id.local_id, "polymorphic byte string lit");

compiler/rustc_infer/src/infer/canonical/query_response.rs

@@ -739,10 +739,8 @@ impl<'tcx> TypeRelatingDelegate<'tcx> for QueryTypeRelatingDelegate<'_, 'tcx> {
         self.obligations.push(Obligation {
             cause: self.cause.clone(),
             param_env: self.param_env,
-            predicate: ty::Binder::dummy(ty::PredicateKind::Clause(
+            predicate: ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(sup, sub))
-                ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(sup, sub)),
+                .to_predicate(self.infcx.tcx),
-            ))
-            .to_predicate(self.infcx.tcx),
             recursion_depth: 0,
         });
     }

compiler/rustc_infer/src/infer/error_reporting/note_and_explain.rs

@@ -139,7 +139,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                     tcx,
                                     generics,
                                     diag,
-                                    &format!("{}", proj.self_ty()),
+                                    &proj.self_ty().to_string(),
                                     &path,
                                     None,
                                     matching_span,
@@ -153,7 +153,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                                     tcx,
                                     generics,
                                     diag,
-                                    &format!("{}", proj.self_ty()),
+                                    &proj.self_ty().to_string(),
                                     &path,
                                     None,
                                     matching_span,

compiler/rustc_infer/src/infer/mod.rs

@@ -1474,6 +1474,7 @@ impl<'tcx> InferCtxt<'tcx> {
     /// universes. Updates `self.universe` to that new universe.
     pub fn create_next_universe(&self) -> ty::UniverseIndex {
         let u = self.universe.get().next_universe();
+        debug!("create_next_universe {u:?}");
         self.universe.set(u);
         u
     }

compiler/rustc_infer/src/infer/outlives/mod.rs

@@ -20,27 +20,19 @@ pub fn explicit_outlives_bounds<'tcx>(
     param_env
         .caller_bounds()
         .into_iter()
-        .map(ty::Predicate::kind)
+        .map(ty::Clause::kind)
         .filter_map(ty::Binder::no_bound_vars)
         .filter_map(move |kind| match kind {
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(..))
+            ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(r_a, r_b)) => {
-            | ty::PredicateKind::Clause(ty::ClauseKind::Trait(..))
+                Some(OutlivesBound::RegionSubRegion(r_b, r_a))
-            | ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(..))
+            }
-            | ty::PredicateKind::AliasRelate(..)
+            ty::ClauseKind::Trait(_)
-            | ty::PredicateKind::Coerce(..)
+            | ty::ClauseKind::TypeOutlives(_)
-            | ty::PredicateKind::Subtype(..)
+            | ty::ClauseKind::Projection(_)
-            | ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(..))
+            | ty::ClauseKind::ConstArgHasType(_, _)
-            | ty::PredicateKind::ObjectSafe(..)
+            | ty::ClauseKind::WellFormed(_)
-            | ty::PredicateKind::ClosureKind(..)
+            | ty::ClauseKind::ConstEvaluatable(_)
-            | ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(..))
+            | ty::ClauseKind::TypeWellFormedFromEnv(_) => None,
-            | ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(..))
-            | ty::PredicateKind::ConstEquate(..)
-            | ty::PredicateKind::Ambiguous
-            | ty::PredicateKind::TypeWellFormedFromEnv(..) => None,
-            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(ty::OutlivesPredicate(
-                r_a,
-                r_b,
-            ))) => Some(OutlivesBound::RegionSubRegion(r_b, r_a)),
         })
 }
 

compiler/rustc_infer/src/infer/outlives/verify.rs

@@ -223,7 +223,7 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
         // parameter environments are already elaborated, so we don't
         // have to worry about that.
         let c_b = self.param_env.caller_bounds();
-        let param_bounds = self.collect_outlives_from_predicate_list(erased_ty, c_b.into_iter());
+        let param_bounds = self.collect_outlives_from_clause_list(erased_ty, c_b.into_iter());
 
         // Next, collect regions we scraped from the well-formedness
         // constraints in the fn signature. To do that, we walk the list
@@ -307,15 +307,15 @@ impl<'cx, 'tcx> VerifyBoundCx<'cx, 'tcx> {
     /// when comparing `ty` for equality, so `ty` must be something
     /// that does not involve inference variables and where you
     /// otherwise want a precise match.
-    fn collect_outlives_from_predicate_list(
+    fn collect_outlives_from_clause_list(
         &self,
         erased_ty: Ty<'tcx>,
-        predicates: impl Iterator<Item = ty::Predicate<'tcx>>,
+        clauses: impl Iterator<Item = ty::Clause<'tcx>>,
     ) -> impl Iterator<Item = ty::Binder<'tcx, ty::OutlivesPredicate<Ty<'tcx>, ty::Region<'tcx>>>>
     {
         let tcx = self.tcx;
         let param_env = self.param_env;
-        predicates.filter_map(|p| p.to_opt_type_outlives()).filter(move |outlives_predicate| {
+        clauses.filter_map(|p| p.as_type_outlives_clause()).filter(move |outlives_predicate| {
             super::test_type_match::can_match_erased_ty(
                 tcx,
                 param_env,

compiler/rustc_infer/src/traits/util.rs

@@ -258,7 +258,8 @@ impl<'tcx, O: Elaboratable<'tcx>> Elaborator<'tcx, O> {
                             pred = pred.without_const(tcx);
                         }
                         elaboratable.child_with_derived_cause(
-                            pred.subst_supertrait(tcx, &bound_predicate.rebind(data.trait_ref)),
+                            pred.subst_supertrait(tcx, &bound_predicate.rebind(data.trait_ref))
+                                .as_predicate(),
                             span,
                             bound_predicate.rebind(data),
                             index,
@@ -367,7 +368,7 @@ impl<'tcx, O: Elaboratable<'tcx>> Elaborator<'tcx, O> {
                         .map(|predicate| elaboratable.child(predicate)),
                 );
             }
-            ty::PredicateKind::TypeWellFormedFromEnv(..) => {
+            ty::PredicateKind::Clause(ty::ClauseKind::TypeWellFormedFromEnv(..)) => {
                 // Nothing to elaborate
             }
             ty::PredicateKind::Ambiguous => {}
@@ -440,7 +441,7 @@ pub fn transitive_bounds_that_define_assoc_item<'tcx>(
                     tcx.super_predicates_that_define_assoc_item((trait_ref.def_id(), assoc_name));
                 for (super_predicate, _) in super_predicates.predicates {
                     let subst_predicate = super_predicate.subst_supertrait(tcx, &trait_ref);
-                    if let Some(binder) = subst_predicate.to_opt_poly_trait_pred() {
+                    if let Some(binder) = subst_predicate.as_trait_clause() {
                         stack.push(binder.map_bound(|t| t.trait_ref));
                     }
                 }

compiler/rustc_interface/src/interface.rs

@@ -14,12 +14,11 @@ use rustc_middle::{bug, ty};
 use rustc_parse::maybe_new_parser_from_source_str;
 use rustc_query_impl::QueryCtxt;
 use rustc_query_system::query::print_query_stack;
-use rustc_session::config::{self, ErrorOutputType, Input, OutFileName, OutputFilenames};
+use rustc_session::config::{self, CheckCfg, ExpectedValues, Input, OutFileName, OutputFilenames};
-use rustc_session::config::{CheckCfg, ExpectedValues};
-use rustc_session::lint;
 use rustc_session::parse::{CrateConfig, ParseSess};
+use rustc_session::CompilerIO;
 use rustc_session::Session;
-use rustc_session::{early_error, CompilerIO};
+use rustc_session::{lint, EarlyErrorHandler};
 use rustc_span::source_map::{FileLoader, FileName};
 use rustc_span::symbol::sym;
 use std::path::PathBuf;
@@ -66,7 +65,10 @@ pub fn set_thread_safe_mode(sopts: &config::UnstableOptions) {
 }
 
 /// Converts strings provided as `--cfg [cfgspec]` into a `crate_cfg`.
-pub fn parse_cfgspecs(cfgspecs: Vec<String>) -> FxHashSet<(String, Option<String>)> {
+pub fn parse_cfgspecs(
+    handler: &EarlyErrorHandler,
+    cfgspecs: Vec<String>,
+) -> FxHashSet<(String, Option<String>)> {
     rustc_span::create_default_session_if_not_set_then(move |_| {
         let cfg = cfgspecs
             .into_iter()
@@ -78,10 +80,10 @@ pub fn parse_cfgspecs(cfgspecs: Vec<String>) -> FxHashSet<(String, Option<String
 
                 macro_rules! error {
                     ($reason: expr) => {
-                        early_error(
+                        handler.early_error(format!(
-                            ErrorOutputType::default(),
+                            concat!("invalid `--cfg` argument: `{}` (", $reason, ")"),
-                            format!(concat!("invalid `--cfg` argument: `{}` (", $reason, ")"), s),
+                            s
-                        );
+                        ));
                     };
                 }
 
@@ -125,7 +127,7 @@ pub fn parse_cfgspecs(cfgspecs: Vec<String>) -> FxHashSet<(String, Option<String
 }
 
 /// Converts strings provided as `--check-cfg [specs]` into a `CheckCfg`.
-pub fn parse_check_cfg(specs: Vec<String>) -> CheckCfg {
+pub fn parse_check_cfg(handler: &EarlyErrorHandler, specs: Vec<String>) -> CheckCfg {
     rustc_span::create_default_session_if_not_set_then(move |_| {
         let mut check_cfg = CheckCfg::default();
 
@@ -137,10 +139,10 @@ pub fn parse_check_cfg(specs: Vec<String>) -> CheckCfg {
 
             macro_rules! error {
                 ($reason: expr) => {
-                    early_error(
+                    handler.early_error(format!(
-                        ErrorOutputType::default(),
+                        concat!("invalid `--check-cfg` argument: `{}` (", $reason, ")"),
-                        format!(concat!("invalid `--check-cfg` argument: `{}` (", $reason, ")"), s),
+                        s
-                    )
+                    ))
                 };
             }
 
@@ -294,8 +296,11 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
 
             let registry = &config.registry;
 
+            let handler = EarlyErrorHandler::new(config.opts.error_format);
+
             let temps_dir = config.opts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
             let (mut sess, codegen_backend) = util::create_session(
+                &handler,
                 config.opts,
                 config.crate_cfg,
                 config.crate_check_cfg,

compiler/rustc_interface/src/tests.rs

@@ -21,8 +21,8 @@ use rustc_session::config::{InstrumentCoverage, Passes};
 use rustc_session::lint::Level;
 use rustc_session::search_paths::SearchPath;
 use rustc_session::utils::{CanonicalizedPath, NativeLib, NativeLibKind};
-use rustc_session::CompilerIO;
 use rustc_session::{build_session, getopts, Session};
+use rustc_session::{CompilerIO, EarlyErrorHandler};
 use rustc_span::edition::{Edition, DEFAULT_EDITION};
 use rustc_span::symbol::sym;
 use rustc_span::FileName;
@@ -36,15 +36,18 @@ use std::path::{Path, PathBuf};
 
 type CfgSpecs = FxHashSet<(String, Option<String>)>;
 
-fn build_session_options_and_crate_config(matches: getopts::Matches) -> (Options, CfgSpecs) {
+fn build_session_options_and_crate_config(
-    let sessopts = build_session_options(&matches);
+    handler: &mut EarlyErrorHandler,
-    let cfg = parse_cfgspecs(matches.opt_strs("cfg"));
+    matches: getopts::Matches,
+) -> (Options, CfgSpecs) {
+    let sessopts = build_session_options(handler, &matches);
+    let cfg = parse_cfgspecs(handler, matches.opt_strs("cfg"));
     (sessopts, cfg)
 }
 
-fn mk_session(matches: getopts::Matches) -> (Session, CfgSpecs) {
+fn mk_session(handler: &mut EarlyErrorHandler, matches: getopts::Matches) -> (Session, CfgSpecs) {
     let registry = registry::Registry::new(&[]);
-    let (sessopts, cfg) = build_session_options_and_crate_config(matches);
+    let (sessopts, cfg) = build_session_options_and_crate_config(handler, matches);
     let temps_dir = sessopts.unstable_opts.temps_dir.as_deref().map(PathBuf::from);
     let io = CompilerIO {
         input: Input::Str { name: FileName::Custom(String::new()), input: String::new() },
@@ -52,8 +55,18 @@ fn mk_session(matches: getopts::Matches) -> (Session, CfgSpecs) {
         output_file: None,
         temps_dir,
     };
-    let sess =
+    let sess = build_session(
-        build_session(sessopts, io, None, registry, vec![], Default::default(), None, None, "");
+        handler,
+        sessopts,
+        io,
+        None,
+        registry,
+        vec![],
+        Default::default(),
+        None,
+        None,
+        "",
+    );
     (sess, cfg)
 }
 
@@ -120,7 +133,8 @@ fn assert_non_crate_hash_different(x: &Options, y: &Options) {
 fn test_switch_implies_cfg_test() {
     rustc_span::create_default_session_globals_then(|| {
         let matches = optgroups().parse(&["--test".to_string()]).unwrap();
-        let (sess, cfg) = mk_session(matches);
+        let mut handler = EarlyErrorHandler::new(ErrorOutputType::default());
+        let (sess, cfg) = mk_session(&mut handler, matches);
         let cfg = build_configuration(&sess, to_crate_config(cfg));
         assert!(cfg.contains(&(sym::test, None)));
     });
@@ -131,7 +145,8 @@ fn test_switch_implies_cfg_test() {
 fn test_switch_implies_cfg_test_unless_cfg_test() {
     rustc_span::create_default_session_globals_then(|| {
         let matches = optgroups().parse(&["--test".to_string(), "--cfg=test".to_string()]).unwrap();
-        let (sess, cfg) = mk_session(matches);
+        let mut handler = EarlyErrorHandler::new(ErrorOutputType::default());
+        let (sess, cfg) = mk_session(&mut handler, matches);
         let cfg = build_configuration(&sess, to_crate_config(cfg));
         let mut test_items = cfg.iter().filter(|&&(name, _)| name == sym::test);
         assert!(test_items.next().is_some());
@@ -143,20 +158,23 @@ fn test_switch_implies_cfg_test_unless_cfg_test() {
 fn test_can_print_warnings() {
     rustc_span::create_default_session_globals_then(|| {
         let matches = optgroups().parse(&["-Awarnings".to_string()]).unwrap();
-        let (sess, _) = mk_session(matches);
+        let mut handler = EarlyErrorHandler::new(ErrorOutputType::default());
+        let (sess, _) = mk_session(&mut handler, matches);
         assert!(!sess.diagnostic().can_emit_warnings());
     });
 
     rustc_span::create_default_session_globals_then(|| {
         let matches =
             optgroups().parse(&["-Awarnings".to_string(), "-Dwarnings".to_string()]).unwrap();
-        let (sess, _) = mk_session(matches);
+        let mut handler = EarlyErrorHandler::new(ErrorOutputType::default());
+        let (sess, _) = mk_session(&mut handler, matches);
         assert!(sess.diagnostic().can_emit_warnings());
     });
 
     rustc_span::create_default_session_globals_then(|| {
         let matches = optgroups().parse(&["-Adead_code".to_string()]).unwrap();
-        let (sess, _) = mk_session(matches);
+        let mut handler = EarlyErrorHandler::new(ErrorOutputType::default());
+        let (sess, _) = mk_session(&mut handler, matches);
         assert!(sess.diagnostic().can_emit_warnings());
     });
 }
@@ -302,35 +320,36 @@ fn test_search_paths_tracking_hash_different_order() {
     let mut v3 = Options::default();
     let mut v4 = Options::default();
 
+    let handler = EarlyErrorHandler::new(JSON);
     const JSON: ErrorOutputType = ErrorOutputType::Json {
         pretty: false,
         json_rendered: HumanReadableErrorType::Default(ColorConfig::Never),
     };
 
     // Reference
-    v1.search_paths.push(SearchPath::from_cli_opt("native=abc", JSON));
+    v1.search_paths.push(SearchPath::from_cli_opt(&handler, "native=abc"));
-    v1.search_paths.push(SearchPath::from_cli_opt("crate=def", JSON));
+    v1.search_paths.push(SearchPath::from_cli_opt(&handler, "crate=def"));
-    v1.search_paths.push(SearchPath::from_cli_opt("dependency=ghi", JSON));
+    v1.search_paths.push(SearchPath::from_cli_opt(&handler, "dependency=ghi"));
-    v1.search_paths.push(SearchPath::from_cli_opt("framework=jkl", JSON));
+    v1.search_paths.push(SearchPath::from_cli_opt(&handler, "framework=jkl"));
-    v1.search_paths.push(SearchPath::from_cli_opt("all=mno", JSON));
+    v1.search_paths.push(SearchPath::from_cli_opt(&handler, "all=mno"));
 
-    v2.search_paths.push(SearchPath::from_cli_opt("native=abc", JSON));
+    v2.search_paths.push(SearchPath::from_cli_opt(&handler, "native=abc"));
-    v2.search_paths.push(SearchPath::from_cli_opt("dependency=ghi", JSON));
+    v2.search_paths.push(SearchPath::from_cli_opt(&handler, "dependency=ghi"));
-    v2.search_paths.push(SearchPath::from_cli_opt("crate=def", JSON));
+    v2.search_paths.push(SearchPath::from_cli_opt(&handler, "crate=def"));
-    v2.search_paths.push(SearchPath::from_cli_opt("framework=jkl", JSON));
+    v2.search_paths.push(SearchPath::from_cli_opt(&handler, "framework=jkl"));
-    v2.search_paths.push(SearchPath::from_cli_opt("all=mno", JSON));
+    v2.search_paths.push(SearchPath::from_cli_opt(&handler, "all=mno"));
 
-    v3.search_paths.push(SearchPath::from_cli_opt("crate=def", JSON));
+    v3.search_paths.push(SearchPath::from_cli_opt(&handler, "crate=def"));
-    v3.search_paths.push(SearchPath::from_cli_opt("framework=jkl", JSON));
+    v3.search_paths.push(SearchPath::from_cli_opt(&handler, "framework=jkl"));
-    v3.search_paths.push(SearchPath::from_cli_opt("native=abc", JSON));
+    v3.search_paths.push(SearchPath::from_cli_opt(&handler, "native=abc"));
-    v3.search_paths.push(SearchPath::from_cli_opt("dependency=ghi", JSON));
+    v3.search_paths.push(SearchPath::from_cli_opt(&handler, "dependency=ghi"));
-    v3.search_paths.push(SearchPath::from_cli_opt("all=mno", JSON));
+    v3.search_paths.push(SearchPath::from_cli_opt(&handler, "all=mno"));
 
-    v4.search_paths.push(SearchPath::from_cli_opt("all=mno", JSON));
+    v4.search_paths.push(SearchPath::from_cli_opt(&handler, "all=mno"));
-    v4.search_paths.push(SearchPath::from_cli_opt("native=abc", JSON));
+    v4.search_paths.push(SearchPath::from_cli_opt(&handler, "native=abc"));
-    v4.search_paths.push(SearchPath::from_cli_opt("crate=def", JSON));
+    v4.search_paths.push(SearchPath::from_cli_opt(&handler, "crate=def"));
-    v4.search_paths.push(SearchPath::from_cli_opt("dependency=ghi", JSON));
+    v4.search_paths.push(SearchPath::from_cli_opt(&handler, "dependency=ghi"));
-    v4.search_paths.push(SearchPath::from_cli_opt("framework=jkl", JSON));
+    v4.search_paths.push(SearchPath::from_cli_opt(&handler, "framework=jkl"));
 
     assert_same_hash(&v1, &v2);
     assert_same_hash(&v1, &v3);
@@ -851,7 +870,9 @@ fn test_edition_parsing() {
     let options = Options::default();
     assert!(options.edition == DEFAULT_EDITION);
 
+    let mut handler = EarlyErrorHandler::new(ErrorOutputType::default());
+
     let matches = optgroups().parse(&["--edition=2018".to_string()]).unwrap();
-    let (sessopts, _) = build_session_options_and_crate_config(matches);
+    let (sessopts, _) = build_session_options_and_crate_config(&mut handler, matches);
     assert!(sessopts.edition == Edition::Edition2018)
 }

compiler/rustc_interface/src/util.rs

@@ -11,16 +11,16 @@ use rustc_parse::validate_attr;
 use rustc_session as session;
 use rustc_session::config::CheckCfg;
 use rustc_session::config::{self, CrateType};
-use rustc_session::config::{ErrorOutputType, OutFileName, OutputFilenames, OutputTypes};
+use rustc_session::config::{OutFileName, OutputFilenames, OutputTypes};
 use rustc_session::filesearch::sysroot_candidates;
 use rustc_session::lint::{self, BuiltinLintDiagnostics, LintBuffer};
 use rustc_session::parse::CrateConfig;
-use rustc_session::{early_error, filesearch, output, Session};
+use rustc_session::{filesearch, output, Session};
 use rustc_span::edit_distance::find_best_match_for_name;
 use rustc_span::edition::Edition;
 use rustc_span::source_map::FileLoader;
 use rustc_span::symbol::{sym, Symbol};
-use session::CompilerIO;
+use session::{CompilerIO, EarlyErrorHandler};
 use std::env;
 use std::env::consts::{DLL_PREFIX, DLL_SUFFIX};
 use std::mem;
@@ -58,6 +58,7 @@ pub fn add_configuration(
 }
 
 pub fn create_session(
+    handler: &EarlyErrorHandler,
     sopts: config::Options,
     cfg: FxHashSet<(String, Option<String>)>,
     check_cfg: CheckCfg,
@@ -73,7 +74,11 @@ pub fn create_session(
     let codegen_backend = if let Some(make_codegen_backend) = make_codegen_backend {
         make_codegen_backend(&sopts)
     } else {
-        get_codegen_backend(&sopts.maybe_sysroot, sopts.unstable_opts.codegen_backend.as_deref())
+        get_codegen_backend(
+            handler,
+            &sopts.maybe_sysroot,
+            sopts.unstable_opts.codegen_backend.as_deref(),
+        )
     };
 
     // target_override is documented to be called before init(), so this is okay
@@ -88,7 +93,7 @@ pub fn create_session(
     ) {
         Ok(bundle) => bundle,
         Err(e) => {
-            early_error(sopts.error_format, format!("failed to load fluent bundle: {e}"));
+            handler.early_error(format!("failed to load fluent bundle: {e}"));
         }
     };
 
@@ -96,6 +101,7 @@ pub fn create_session(
     locale_resources.push(codegen_backend.locale_resource());
 
     let mut sess = session::build_session(
+        handler,
         sopts,
         io,
         bundle,
@@ -218,16 +224,16 @@ pub(crate) fn run_in_thread_pool_with_globals<F: FnOnce() -> R + Send, R: Send>(
     })
 }
 
-fn load_backend_from_dylib(path: &Path) -> MakeBackendFn {
+fn load_backend_from_dylib(handler: &EarlyErrorHandler, path: &Path) -> MakeBackendFn {
     let lib = unsafe { Library::new(path) }.unwrap_or_else(|err| {
         let err = format!("couldn't load codegen backend {path:?}: {err}");
-        early_error(ErrorOutputType::default(), err);
+        handler.early_error(err);
     });
 
     let backend_sym = unsafe { lib.get::<MakeBackendFn>(b"__rustc_codegen_backend") }
         .unwrap_or_else(|e| {
             let err = format!("couldn't load codegen backend: {e}");
-            early_error(ErrorOutputType::default(), err);
+            handler.early_error(err);
         });
 
     // Intentionally leak the dynamic library. We can't ever unload it
@@ -242,6 +248,7 @@ fn load_backend_from_dylib(path: &Path) -> MakeBackendFn {
 ///
 /// A name of `None` indicates that the default backend should be used.
 pub fn get_codegen_backend(
+    handler: &EarlyErrorHandler,
     maybe_sysroot: &Option<PathBuf>,
     backend_name: Option<&str>,
 ) -> Box<dyn CodegenBackend> {
@@ -251,10 +258,12 @@ pub fn get_codegen_backend(
         let default_codegen_backend = option_env!("CFG_DEFAULT_CODEGEN_BACKEND").unwrap_or("llvm");
 
         match backend_name.unwrap_or(default_codegen_backend) {
-            filename if filename.contains('.') => load_backend_from_dylib(filename.as_ref()),
+            filename if filename.contains('.') => {
+                load_backend_from_dylib(handler, filename.as_ref())
+            }
             #[cfg(feature = "llvm")]
             "llvm" => rustc_codegen_llvm::LlvmCodegenBackend::new,
-            backend_name => get_codegen_sysroot(maybe_sysroot, backend_name),
+            backend_name => get_codegen_sysroot(handler, maybe_sysroot, backend_name),
         }
     });
 
@@ -286,7 +295,11 @@ fn get_rustc_path_inner(bin_path: &str) -> Option<PathBuf> {
     })
 }
 
-fn get_codegen_sysroot(maybe_sysroot: &Option<PathBuf>, backend_name: &str) -> MakeBackendFn {
+fn get_codegen_sysroot(
+    handler: &EarlyErrorHandler,
+    maybe_sysroot: &Option<PathBuf>,
+    backend_name: &str,
+) -> MakeBackendFn {
     // For now we only allow this function to be called once as it'll dlopen a
     // few things, which seems to work best if we only do that once. In
     // general this assertion never trips due to the once guard in `get_codegen_backend`,
@@ -321,7 +334,7 @@ fn get_codegen_sysroot(maybe_sysroot: &Option<PathBuf>, backend_name: &str) -> M
             "failed to find a `codegen-backends` folder \
                            in the sysroot candidates:\n* {candidates}"
         );
-        early_error(ErrorOutputType::default(), err);
+        handler.early_error(err);
     });
     info!("probing {} for a codegen backend", sysroot.display());
 
@@ -332,7 +345,7 @@ fn get_codegen_sysroot(maybe_sysroot: &Option<PathBuf>, backend_name: &str) -> M
             sysroot.display(),
             e
         );
-        early_error(ErrorOutputType::default(), err);
+        handler.early_error(err);
     });
 
     let mut file: Option<PathBuf> = None;
@@ -360,16 +373,16 @@ fn get_codegen_sysroot(maybe_sysroot: &Option<PathBuf>, backend_name: &str) -> M
                 prev.display(),
                 path.display()
             );
-            early_error(ErrorOutputType::default(), err);
+            handler.early_error(err);
         }
         file = Some(path.clone());
     }
 
     match file {
-        Some(ref s) => load_backend_from_dylib(s),
+        Some(ref s) => load_backend_from_dylib(handler, s),
         None => {
             let err = format!("unsupported builtin codegen backend `{backend_name}`");
-            early_error(ErrorOutputType::default(), err);
+            handler.early_error(err);
         }
     }
 }

compiler/rustc_lint/src/builtin.rs

@@ -1593,33 +1593,25 @@ declare_lint_pass!(
 impl<'tcx> LateLintPass<'tcx> for TrivialConstraints {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
         use rustc_middle::ty::ClauseKind;
-        use rustc_middle::ty::PredicateKind::*;
 
         if cx.tcx.features().trivial_bounds {
             let predicates = cx.tcx.predicates_of(item.owner_id);
             for &(predicate, span) in predicates.predicates {
                 let predicate_kind_name = match predicate.kind().skip_binder() {
-                    Clause(ClauseKind::Trait(..)) => "trait",
+                    ClauseKind::Trait(..) => "trait",
-                    Clause(ClauseKind::TypeOutlives(..)) |
+                    ClauseKind::TypeOutlives(..) |
-                    Clause(ClauseKind::RegionOutlives(..)) => "lifetime",
+                    ClauseKind::RegionOutlives(..) => "lifetime",
 
                     // `ConstArgHasType` is never global as `ct` is always a param
-                    Clause(ClauseKind::ConstArgHasType(..)) |
+                    ClauseKind::ConstArgHasType(..)
                     // Ignore projections, as they can only be global
                     // if the trait bound is global
-                    Clause(ClauseKind::Projection(..)) |
+                    | ClauseKind::Projection(..)
                     // Ignore bounds that a user can't type
-                    Clause(ClauseKind::WellFormed(..)) |
+                    | ClauseKind::WellFormed(..)
                     // FIXME(generic_const_exprs): `ConstEvaluatable` can be written
-                    Clause(ClauseKind::ConstEvaluatable(..)) |
+                    | ClauseKind::ConstEvaluatable(..)
-                    AliasRelate(..) |
+                    | ClauseKind::TypeWellFormedFromEnv(_)  => continue,
-                    ObjectSafe(..) |
-                    ClosureKind(..) |
-                    Subtype(..) |
-                    Coerce(..) |
-                    ConstEquate(..) |
-                    Ambiguous |
-                    TypeWellFormedFromEnv(..) => continue,
                 };
                 if predicate.is_global() {
                     cx.emit_spanned_lint(

compiler/rustc_lint/src/lints.rs

@@ -10,7 +10,7 @@ use rustc_errors::{
 use rustc_hir::def_id::DefId;
 use rustc_macros::{LintDiagnostic, Subdiagnostic};
 use rustc_middle::ty::{
-    inhabitedness::InhabitedPredicate, PolyExistentialTraitRef, Predicate, Ty, TyCtxt,
+    inhabitedness::InhabitedPredicate, Clause, PolyExistentialTraitRef, Ty, TyCtxt,
 };
 use rustc_session::parse::ParseSess;
 use rustc_span::{edition::Edition, sym, symbol::Ident, Span, Symbol};
@@ -352,7 +352,7 @@ impl AddToDiagnostic for BuiltinTypeAliasGenericBoundsSuggestion {
 #[diag(lint_builtin_trivial_bounds)]
 pub struct BuiltinTrivialBounds<'a> {
     pub predicate_kind_name: &'a str,
-    pub predicate: Predicate<'a>,
+    pub predicate: Clause<'a>,
 }
 
 #[derive(LintDiagnostic)]
@@ -1262,7 +1262,7 @@ pub struct RedundantSemicolonsDiag {
 
 // traits.rs
 pub struct DropTraitConstraintsDiag<'a> {
-    pub predicate: Predicate<'a>,
+    pub predicate: Clause<'a>,
     pub tcx: TyCtxt<'a>,
     pub def_id: DefId,
 }

compiler/rustc_lint/src/multiple_supertrait_upcastable.rs

@@ -45,7 +45,7 @@ impl<'tcx> LateLintPass<'tcx> for MultipleSupertraitUpcastable {
                     .super_predicates_of(def_id)
                     .predicates
                     .into_iter()
-                    .filter_map(|(pred, _)| pred.to_opt_poly_trait_pred());
+                    .filter_map(|(pred, _)| pred.as_trait_clause());
             if direct_super_traits_iter.count() > 1 {
                 cx.emit_spanned_lint(
                     MULTIPLE_SUPERTRAIT_UPCASTABLE,

compiler/rustc_lint/src/traits.rs

@@ -88,11 +88,10 @@ declare_lint_pass!(
 impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx hir::Item<'tcx>) {
         use rustc_middle::ty::ClauseKind;
-        use rustc_middle::ty::PredicateKind::*;
 
         let predicates = cx.tcx.explicit_predicates_of(item.owner_id);
         for &(predicate, span) in predicates.predicates {
-            let Clause(ClauseKind::Trait(trait_predicate)) = predicate.kind().skip_binder() else {
+            let ClauseKind::Trait(trait_predicate) = predicate.kind().skip_binder() else {
                 continue
             };
             let def_id = trait_predicate.trait_ref.def_id;

compiler/rustc_macros/src/diagnostics/diagnostic.rs

@@ -1,5 +1,7 @@
 #![deny(unused_must_use)]
 
+use std::cell::RefCell;
+
 use crate::diagnostics::diagnostic_builder::{DiagnosticDeriveBuilder, DiagnosticDeriveKind};
 use crate::diagnostics::error::{span_err, DiagnosticDeriveError};
 use crate::diagnostics::utils::SetOnce;
@@ -28,6 +30,7 @@ impl<'a> DiagnosticDerive<'a> {
     pub(crate) fn into_tokens(self) -> TokenStream {
         let DiagnosticDerive { mut structure, mut builder } = self;
 
+        let slugs = RefCell::new(Vec::new());
         let implementation = builder.each_variant(&mut structure, |mut builder, variant| {
             let preamble = builder.preamble(variant);
             let body = builder.body(variant);
@@ -56,6 +59,7 @@ impl<'a> DiagnosticDerive<'a> {
                     return DiagnosticDeriveError::ErrorHandled.to_compile_error();
                 }
                 Some(slug) => {
+                    slugs.borrow_mut().push(slug.clone());
                     quote! {
                         let mut #diag = #handler.struct_diagnostic(crate::fluent_generated::#slug);
                     }
@@ -73,7 +77,8 @@ impl<'a> DiagnosticDerive<'a> {
         });
 
         let DiagnosticDeriveKind::Diagnostic { handler } = &builder.kind else { unreachable!() };
-        structure.gen_impl(quote! {
+
+        let mut imp = structure.gen_impl(quote! {
             gen impl<'__diagnostic_handler_sess, G>
                     rustc_errors::IntoDiagnostic<'__diagnostic_handler_sess, G>
                     for @Self
@@ -89,7 +94,11 @@ impl<'a> DiagnosticDerive<'a> {
                     #implementation
                 }
             }
-        })
+        });
+        for test in slugs.borrow().iter().map(|s| generate_test(s, &structure)) {
+            imp.extend(test);
+        }
+        imp
     }
 }
 
@@ -124,6 +133,7 @@ impl<'a> LintDiagnosticDerive<'a> {
             }
         });
 
+        let slugs = RefCell::new(Vec::new());
         let msg = builder.each_variant(&mut structure, |mut builder, variant| {
             // Collect the slug by generating the preamble.
             let _ = builder.preamble(variant);
@@ -148,6 +158,7 @@ impl<'a> LintDiagnosticDerive<'a> {
                     DiagnosticDeriveError::ErrorHandled.to_compile_error()
                 }
                 Some(slug) => {
+                    slugs.borrow_mut().push(slug.clone());
                     quote! {
                         crate::fluent_generated::#slug.into()
                     }
@@ -156,7 +167,7 @@ impl<'a> LintDiagnosticDerive<'a> {
         });
 
         let diag = &builder.diag;
-        structure.gen_impl(quote! {
+        let mut imp = structure.gen_impl(quote! {
             gen impl<'__a> rustc_errors::DecorateLint<'__a, ()> for @Self {
                 #[track_caller]
                 fn decorate_lint<'__b>(
@@ -171,7 +182,12 @@ impl<'a> LintDiagnosticDerive<'a> {
                     #msg
                 }
             }
-        })
+        });
+        for test in slugs.borrow().iter().map(|s| generate_test(s, &structure)) {
+            imp.extend(test);
+        }
+
+        imp
     }
 }
 
@@ -198,3 +214,40 @@ impl Mismatch {
         }
     }
 }
+
+/// Generates a `#[test]` that verifies that all referenced variables
+/// exist on this structure.
+fn generate_test(slug: &syn::Path, structure: &Structure<'_>) -> TokenStream {
+    // FIXME: We can't identify variables in a subdiagnostic
+    for field in structure.variants().iter().flat_map(|v| v.ast().fields.iter()) {
+        for attr_name in field.attrs.iter().filter_map(|at| at.path().get_ident()) {
+            if attr_name == "subdiagnostic" {
+                return quote!();
+            }
+        }
+    }
+    use std::sync::atomic::{AtomicUsize, Ordering};
+    // We need to make sure that the same diagnostic slug can be used multiple times without causing an
+    // error, so just have a global counter here.
+    static COUNTER: AtomicUsize = AtomicUsize::new(0);
+    let slug = slug.get_ident().unwrap();
+    let ident = quote::format_ident!("verify_{slug}_{}", COUNTER.fetch_add(1, Ordering::Relaxed));
+    let ref_slug = quote::format_ident!("{slug}_refs");
+    let struct_name = &structure.ast().ident;
+    let variables: Vec<_> = structure
+        .variants()
+        .iter()
+        .flat_map(|v| v.ast().fields.iter().filter_map(|f| f.ident.as_ref().map(|i| i.to_string())))
+        .collect();
+    // tidy errors on `#[test]` outside of test files, so we use `#[test ]` to work around this
+    quote! {
+        #[cfg(test)]
+        #[test ]
+        fn #ident() {
+            let variables = [#(#variables),*];
+            for vref in crate::fluent_generated::#ref_slug {
+                assert!(variables.contains(vref), "{}: variable `{vref}` not found ({})", stringify!(#struct_name), stringify!(#slug));
+            }
+        }
+    }
+}

compiler/rustc_metadata/src/rmeta/decoder.rs

@@ -636,12 +636,6 @@ impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for Symbol {
     }
 }
 
-impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for &'tcx [(ty::Predicate<'tcx>, Span)] {
-    fn decode(d: &mut DecodeContext<'a, 'tcx>) -> Self {
-        ty::codec::RefDecodable::decode(d)
-    }
-}
-
 impl<'a, 'tcx> Decodable<DecodeContext<'a, 'tcx>> for &'tcx [(ty::Clause<'tcx>, Span)] {
     fn decode(d: &mut DecodeContext<'a, 'tcx>) -> Self {
         ty::codec::RefDecodable::decode(d)

compiler/rustc_middle/src/arena.rs

@@ -83,9 +83,9 @@ macro_rules! arena_types {
                 rustc_middle::infer::canonical::Canonical<'tcx,
                     rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::FnSig<'tcx>>
                 >,
-            [] type_op_normalize_predicate:
+            [] type_op_normalize_clause:
                 rustc_middle::infer::canonical::Canonical<'tcx,
-                    rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::Predicate<'tcx>>
+                    rustc_middle::infer::canonical::QueryResponse<'tcx, rustc_middle::ty::Clause<'tcx>>
                 >,
             [] type_op_normalize_ty:
                 rustc_middle::infer::canonical::Canonical<'tcx,

compiler/rustc_middle/src/lint.rs

@@ -388,10 +388,11 @@ pub fn struct_lint_level(
             // it'll become a hard error, so we have to emit *something*. Also,
             // if this lint occurs in the expansion of a macro from an external crate,
             // allow individual lints to opt-out from being reported.
-            let not_future_incompatible =
+            let incompatible = future_incompatible.is_some_and(|f| f.reason.edition().is_none());
-                future_incompatible.map(|f| f.reason.edition().is_some()).unwrap_or(true);
+
-            if not_future_incompatible && !lint.report_in_external_macro {
+            if !incompatible && !lint.report_in_external_macro {
                 err.cancel();
+
                 // Don't continue further, since we don't want to have
                 // `diag_span_note_once` called for a diagnostic that isn't emitted.
                 return;

compiler/rustc_middle/src/mir/terminator.rs

@@ -272,7 +272,8 @@ impl<'tcx> Debug for TerminatorKind<'tcx> {
 
         let unwind = match self.unwind() {
             // Not needed or included in successors
-            None | Some(UnwindAction::Continue) | Some(UnwindAction::Cleanup(_)) => None,
+            None | Some(UnwindAction::Cleanup(_)) => None,
+            Some(UnwindAction::Continue) => Some("unwind continue"),
             Some(UnwindAction::Unreachable) => Some("unwind unreachable"),
             Some(UnwindAction::Terminate) => Some("unwind terminate"),
         };

compiler/rustc_middle/src/mir/visit.rs

@@ -1133,13 +1133,12 @@ macro_rules! visit_place_fns {
 
         fn visit_projection_elem(
             &mut self,
-            local: Local,
+            place_ref: PlaceRef<'tcx>,
-            proj_base: &[PlaceElem<'tcx>],
             elem: PlaceElem<'tcx>,
             context: PlaceContext,
             location: Location,
         ) {
-            self.super_projection_elem(local, proj_base, elem, context, location);
+            self.super_projection_elem(place_ref, elem, context, location);
         }
 
         fn super_place(&mut self, place: &Place<'tcx>, context: PlaceContext, location: Location) {
@@ -1168,15 +1167,13 @@ macro_rules! visit_place_fns {
             location: Location,
         ) {
             for (base, elem) in place_ref.iter_projections().rev() {
-                let base_proj = base.projection;
+                self.visit_projection_elem(base, elem, context, location);
-                self.visit_projection_elem(place_ref.local, base_proj, elem, context, location);
             }
         }
 
         fn super_projection_elem(
             &mut self,
-            _local: Local,
+            _place_ref: PlaceRef<'tcx>,
-            _proj_base: &[PlaceElem<'tcx>],
             elem: PlaceElem<'tcx>,
             _context: PlaceContext,
             location: Location,

compiler/rustc_middle/src/query/keys.rs

@@ -420,7 +420,7 @@ impl<'tcx> Key for (Ty<'tcx>, Ty<'tcx>) {
     }
 }
 
-impl<'tcx> Key for &'tcx ty::List<ty::Predicate<'tcx>> {
+impl<'tcx> Key for &'tcx ty::List<ty::Clause<'tcx>> {
     type CacheSelector = DefaultCacheSelector<Self>;
 
     fn default_span(&self, _: TyCtxt<'_>) -> Span {

compiler/rustc_middle/src/query/mod.rs

@@ -2031,10 +2031,10 @@ rustc_queries! {
     }
 
     /// Do not call this query directly: part of the `Normalize` type-op
-    query type_op_normalize_predicate(
+    query type_op_normalize_clause(
-        goal: CanonicalTypeOpNormalizeGoal<'tcx, ty::Predicate<'tcx>>
+        goal: CanonicalTypeOpNormalizeGoal<'tcx, ty::Clause<'tcx>>
     ) -> Result<
-        &'tcx Canonical<'tcx, canonical::QueryResponse<'tcx, ty::Predicate<'tcx>>>,
+        &'tcx Canonical<'tcx, canonical::QueryResponse<'tcx, ty::Clause<'tcx>>>,
         NoSolution,
     > {
         desc { "normalizing `{:?}`", goal.value.value.value }
@@ -2125,7 +2125,7 @@ rustc_queries! {
         desc { "resolving instance `{}`", ty::Instance::new(key.value.0, key.value.1) }
     }
 
-    query reveal_opaque_types_in_bounds(key: &'tcx ty::List<ty::Predicate<'tcx>>) -> &'tcx ty::List<ty::Predicate<'tcx>> {
+    query reveal_opaque_types_in_bounds(key: &'tcx ty::List<ty::Clause<'tcx>>) -> &'tcx ty::List<ty::Clause<'tcx>> {
         desc { "revealing opaque types in `{:?}`", key }
     }
 

compiler/rustc_middle/src/query/on_disk_cache.rs

@@ -791,13 +791,6 @@ impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>>
     }
 }
 
-impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [(ty::Predicate<'tcx>, Span)] {
-    #[inline]
-    fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {
-        RefDecodable::decode(d)
-    }
-}
-
 impl<'a, 'tcx> Decodable<CacheDecoder<'a, 'tcx>> for &'tcx [(ty::Clause<'tcx>, Span)] {
     #[inline]
     fn decode(d: &mut CacheDecoder<'a, 'tcx>) -> Self {

compiler/rustc_middle/src/thir.rs

@@ -410,6 +410,10 @@ pub enum ExprKind<'tcx> {
     Return {
         value: Option<ExprId>,
     },
+    /// A `become` expression.
+    Become {
+        value: ExprId,
+    },
     /// An inline `const` block, e.g. `const {}`.
     ConstBlock {
         did: DefId,

compiler/rustc_middle/src/thir/visit.rs

@@ -100,6 +100,7 @@ pub fn walk_expr<'a, 'tcx: 'a, V: Visitor<'a, 'tcx>>(visitor: &mut V, expr: &Exp
                 visitor.visit_expr(&visitor.thir()[value])
             }
         }
+        Become { value } => visitor.visit_expr(&visitor.thir()[value]),
         ConstBlock { did: _, substs: _ } => {}
         Repeat { value, count: _ } => {
             visitor.visit_expr(&visitor.thir()[value]);

compiler/rustc_middle/src/traits/chalk.rs

@@ -385,7 +385,7 @@ impl<'tcx> chalk_ir::interner::HasInterner for RustInterner<'tcx> {
 /// A chalk environment and goal.
 #[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, HashStable, TypeFoldable, TypeVisitable)]
 pub struct ChalkEnvironmentAndGoal<'tcx> {
-    pub environment: &'tcx ty::List<ty::Predicate<'tcx>>,
+    pub environment: &'tcx ty::List<ty::Clause<'tcx>>,
     pub goal: ty::Predicate<'tcx>,
 }
 

compiler/rustc_middle/src/traits/util.rs

@@ -25,9 +25,7 @@ impl<'tcx> Elaborator<'tcx> {
             .super_predicates_of(trait_ref.def_id())
             .predicates
             .into_iter()
-            .flat_map(|(pred, _)| {
+            .flat_map(|(pred, _)| pred.subst_supertrait(self.tcx, &trait_ref).as_trait_clause())
-                pred.subst_supertrait(self.tcx, &trait_ref).to_opt_poly_trait_pred()
-            })
             .map(|t| t.map_bound(|pred| pred.trait_ref))
             .filter(|supertrait_ref| self.visited.insert(*supertrait_ref));
 

compiler/rustc_middle/src/ty/codec.rs

@@ -368,16 +368,6 @@ impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> Decodable<D> for AdtDef<'tcx> {
     }
 }
 
-impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D>
-    for [(ty::Predicate<'tcx>, Span)]
-{
-    fn decode(decoder: &mut D) -> &'tcx Self {
-        decoder.interner().arena.alloc_from_iter(
-            (0..decoder.read_usize()).map(|_| Decodable::decode(decoder)).collect::<Vec<_>>(),
-        )
-    }
-}
-
 impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for [(ty::Clause<'tcx>, Span)] {
     fn decode(decoder: &mut D) -> &'tcx Self {
         decoder.interner().arena.alloc_from_iter(
@@ -406,11 +396,11 @@ impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for ty::List<ty
     }
 }
 
-impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for ty::List<ty::Predicate<'tcx>> {
+impl<'tcx, D: TyDecoder<I = TyCtxt<'tcx>>> RefDecodable<'tcx, D> for ty::List<ty::Clause<'tcx>> {
     fn decode(decoder: &mut D) -> &'tcx Self {
         let len = decoder.read_usize();
-        decoder.interner().mk_predicates_from_iter(
+        decoder.interner().mk_clauses_from_iter(
-            (0..len).map::<ty::Predicate<'tcx>, _>(|_| Decodable::decode(decoder)),
+            (0..len).map::<ty::Clause<'tcx>, _>(|_| Decodable::decode(decoder)),
         )
     }
 }
@@ -434,7 +424,7 @@ impl_decodable_via_ref! {
     &'tcx mir::BorrowCheckResult<'tcx>,
     &'tcx mir::coverage::CodeRegion,
     &'tcx ty::List<ty::BoundVariableKind>,
-    &'tcx ty::List<ty::Predicate<'tcx>>,
+    &'tcx ty::List<ty::Clause<'tcx>>,
     &'tcx ty::List<FieldIdx>,
 }
 

compiler/rustc_middle/src/ty/context.rs

@@ -141,8 +141,6 @@ pub struct CtxtInterners<'tcx> {
     region: InternedSet<'tcx, RegionKind<'tcx>>,
     poly_existential_predicates: InternedSet<'tcx, List<PolyExistentialPredicate<'tcx>>>,
     predicate: InternedSet<'tcx, WithCachedTypeInfo<ty::Binder<'tcx, PredicateKind<'tcx>>>>,
-    // FIXME(clause): remove this when all usages are moved to predicate
-    predicates: InternedSet<'tcx, List<Predicate<'tcx>>>,
     clauses: InternedSet<'tcx, List<Clause<'tcx>>>,
     projs: InternedSet<'tcx, List<ProjectionKind>>,
     place_elems: InternedSet<'tcx, List<PlaceElem<'tcx>>>,
@@ -168,7 +166,6 @@ impl<'tcx> CtxtInterners<'tcx> {
             poly_existential_predicates: Default::default(),
             canonical_var_infos: Default::default(),
             predicate: Default::default(),
-            predicates: Default::default(),
             clauses: Default::default(),
             projs: Default::default(),
             place_elems: Default::default(),
@@ -1260,10 +1257,11 @@ nop_lift! {region; Region<'a> => Region<'tcx>}
 nop_lift! {const_; Const<'a> => Const<'tcx>}
 nop_lift! {const_allocation; ConstAllocation<'a> => ConstAllocation<'tcx>}
 nop_lift! {predicate; Predicate<'a> => Predicate<'tcx>}
+nop_lift! {predicate; Clause<'a> => Clause<'tcx>}
 
 nop_list_lift! {type_lists; Ty<'a> => Ty<'tcx>}
 nop_list_lift! {poly_existential_predicates; PolyExistentialPredicate<'a> => PolyExistentialPredicate<'tcx>}
-nop_list_lift! {predicates; Predicate<'a> => Predicate<'tcx>}
+nop_list_lift! {clauses; Clause<'a> => Clause<'tcx>}
 nop_list_lift! {canonical_var_infos; CanonicalVarInfo<'a> => CanonicalVarInfo<'tcx>}
 nop_list_lift! {projs; ProjectionKind => ProjectionKind}
 nop_list_lift! {bound_variable_kinds; ty::BoundVariableKind => ty::BoundVariableKind}
@@ -1541,7 +1539,6 @@ slice_interners!(
     type_lists: pub mk_type_list(Ty<'tcx>),
     canonical_var_infos: pub mk_canonical_var_infos(CanonicalVarInfo<'tcx>),
     poly_existential_predicates: intern_poly_existential_predicates(PolyExistentialPredicate<'tcx>),
-    predicates: intern_predicates(Predicate<'tcx>),
     clauses: intern_clauses(Clause<'tcx>),
     projs: pub mk_projs(ProjectionKind),
     place_elems: pub mk_place_elems(PlaceElem<'tcx>),
@@ -1597,9 +1594,7 @@ impl<'tcx> TyCtxt<'tcx> {
             let generic_predicates = self.super_predicates_of(trait_did);
 
             for (predicate, _) in generic_predicates.predicates {
-                if let ty::PredicateKind::Clause(ty::ClauseKind::Trait(data)) =
+                if let ty::ClauseKind::Trait(data) = predicate.kind().skip_binder() {
-                    predicate.kind().skip_binder()
-                {
                     if set.insert(data.def_id()) {
                         stack.push(data.def_id());
                     }
@@ -2087,18 +2082,11 @@ impl<'tcx> TyCtxt<'tcx> {
         self.intern_poly_existential_predicates(eps)
     }
 
-    pub fn mk_predicates(self, preds: &[Predicate<'tcx>]) -> &'tcx List<Predicate<'tcx>> {
+    pub fn mk_clauses(self, clauses: &[Clause<'tcx>]) -> &'tcx List<Clause<'tcx>> {
         // FIXME consider asking the input slice to be sorted to avoid
         // re-interning permutations, in which case that would be asserted
         // here.
-        self.intern_predicates(preds)
+        self.intern_clauses(clauses)
-    }
-
-    pub fn mk_clauses(self, preds: &[Clause<'tcx>]) -> &'tcx List<Clause<'tcx>> {
-        // FIXME consider asking the input slice to be sorted to avoid
-        // re-interning permutations, in which case that would be asserted
-        // here.
-        self.intern_clauses(preds)
     }
 
     pub fn mk_const_list_from_iter<I, T>(self, iter: I) -> T::Output
@@ -2144,14 +2132,6 @@ impl<'tcx> TyCtxt<'tcx> {
         T::collect_and_apply(iter, |xs| self.mk_poly_existential_predicates(xs))
     }
 
-    pub fn mk_predicates_from_iter<I, T>(self, iter: I) -> T::Output
-    where
-        I: Iterator<Item = T>,
-        T: CollectAndApply<Predicate<'tcx>, &'tcx List<Predicate<'tcx>>>,
-    {
-        T::collect_and_apply(iter, |xs| self.mk_predicates(xs))
-    }
-
     pub fn mk_clauses_from_iter<I, T>(self, iter: I) -> T::Output
     where
         I: Iterator<Item = T>,

compiler/rustc_middle/src/ty/flags.rs

@@ -287,7 +287,7 @@ impl FlagComputation {
                 self.add_const(expected);
                 self.add_const(found);
             }
-            ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
+            ty::PredicateKind::Clause(ty::ClauseKind::TypeWellFormedFromEnv(ty)) => {
                 self.add_ty(ty);
             }
             ty::PredicateKind::Ambiguous => {}

compiler/rustc_middle/src/ty/generics.rs

@@ -6,7 +6,7 @@ use rustc_hir::def_id::DefId;
 use rustc_span::symbol::{kw, Symbol};
 use rustc_span::Span;
 
-use super::{EarlyBoundRegion, InstantiatedPredicates, ParamConst, ParamTy, Predicate, TyCtxt};
+use super::{Clause, EarlyBoundRegion, InstantiatedPredicates, ParamConst, ParamTy, TyCtxt};
 
 #[derive(Clone, Debug, TyEncodable, TyDecodable, HashStable)]
 pub enum GenericParamDefKind {
@@ -323,7 +323,7 @@ impl<'tcx> Generics {
 #[derive(Copy, Clone, Default, Debug, TyEncodable, TyDecodable, HashStable)]
 pub struct GenericPredicates<'tcx> {
     pub parent: Option<DefId>,
-    pub predicates: &'tcx [(Predicate<'tcx>, Span)],
+    pub predicates: &'tcx [(Clause<'tcx>, Span)],
 }
 
 impl<'tcx> GenericPredicates<'tcx> {
@@ -341,8 +341,7 @@ impl<'tcx> GenericPredicates<'tcx> {
         &self,
         tcx: TyCtxt<'tcx>,
         substs: SubstsRef<'tcx>,
-    ) -> impl Iterator<Item = (Predicate<'tcx>, Span)> + DoubleEndedIterator + ExactSizeIterator
+    ) -> impl Iterator<Item = (Clause<'tcx>, Span)> + DoubleEndedIterator + ExactSizeIterator {
-    {
         EarlyBinder::bind(self.predicates).subst_iter_copied(tcx, substs)
     }
 

compiler/rustc_middle/src/ty/inhabitedness/inhabited_predicate.rs

@@ -62,7 +62,18 @@ impl<'tcx> InhabitedPredicate<'tcx> {
                 Some(1..) => Ok(false),
             },
             Self::NotInModule(id) => in_module(id).map(|in_mod| !in_mod),
-            Self::GenericType(_) => Ok(true),
+            // `t` may be a projection, for which `inhabited_predicate` returns a `GenericType`. As
+            // we have a param_env available, we can do better.
+            Self::GenericType(t) => {
+                let normalized_pred = tcx
+                    .try_normalize_erasing_regions(param_env, t)
+                    .map_or(self, |t| t.inhabited_predicate(tcx));
+                match normalized_pred {
+                    // We don't have more information than we started with, so consider inhabited.
+                    Self::GenericType(_) => Ok(true),
+                    pred => pred.apply_inner(tcx, param_env, in_module),
+                }
+            }
             Self::And([a, b]) => try_and(a, b, |x| x.apply_inner(tcx, param_env, in_module)),
             Self::Or([a, b]) => try_or(a, b, |x| x.apply_inner(tcx, param_env, in_module)),
         }

compiler/rustc_middle/src/ty/mod.rs

@@ -555,7 +555,7 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(_))
             | PredicateKind::ConstEquate(_, _)
             | PredicateKind::Ambiguous
-            | PredicateKind::TypeWellFormedFromEnv(_) => true,
+            | PredicateKind::Clause(ClauseKind::TypeWellFormedFromEnv(_)) => true,
         }
     }
 }
@@ -566,6 +566,12 @@ impl rustc_errors::IntoDiagnosticArg for Predicate<'_> {
     }
 }
 
+impl rustc_errors::IntoDiagnosticArg for Clause<'_> {
+    fn into_diagnostic_arg(self) -> rustc_errors::DiagnosticArgValue<'static> {
+        rustc_errors::DiagnosticArgValue::Str(std::borrow::Cow::Owned(self.to_string()))
+    }
+}
+
 /// A subset of predicates which can be assumed by the trait solver. They show up in
 /// an item's where clauses, hence the name `Clause`, and may either be user-written
 /// (such as traits) or may be inserted during lowering.
@@ -620,6 +626,10 @@ impl<'tcx> Clause<'tcx> {
             None
         }
     }
+
+    pub fn without_const(self, tcx: TyCtxt<'tcx>) -> Clause<'tcx> {
+        self.as_predicate().without_const(tcx).expect_clause()
+    }
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
@@ -651,6 +661,11 @@ pub enum ClauseKind<'tcx> {
 
     /// Constant initializer must evaluate successfully.
     ConstEvaluatable(ty::Const<'tcx>),
+
+    /// Represents a type found in the environment that we can use for implied bounds.
+    ///
+    /// Only used for Chalk.
+    TypeWellFormedFromEnv(Ty<'tcx>),
 }
 
 #[derive(Clone, Copy, PartialEq, Eq, Hash, TyEncodable, TyDecodable)]
@@ -687,11 +702,6 @@ pub enum PredicateKind<'tcx> {
     /// Constants must be equal. The first component is the const that is expected.
     ConstEquate(Const<'tcx>, Const<'tcx>),
 
-    /// Represents a type found in the environment that we can use for implied bounds.
-    ///
-    /// Only used for Chalk.
-    TypeWellFormedFromEnv(Ty<'tcx>),
-
     /// A marker predicate that is always ambiguous.
     /// Used for coherence to mark opaque types as possibly equal to each other but ambiguous.
     Ambiguous,
@@ -730,11 +740,10 @@ pub struct CratePredicatesMap<'tcx> {
     /// For each struct with outlive bounds, maps to a vector of the
     /// predicate of its outlive bounds. If an item has no outlives
     /// bounds, it will have no entry.
-    // FIXME(clause): should this be a `Clause`?
     pub predicates: FxHashMap<DefId, &'tcx [(Clause<'tcx>, Span)]>,
 }
 
-impl<'tcx> Predicate<'tcx> {
+impl<'tcx> Clause<'tcx> {
     /// Performs a substitution suitable for going from a
     /// poly-trait-ref to supertraits that must hold if that
     /// poly-trait-ref holds. This is slightly different from a normal
@@ -744,7 +753,7 @@ impl<'tcx> Predicate<'tcx> {
         self,
         tcx: TyCtxt<'tcx>,
         trait_ref: &ty::PolyTraitRef<'tcx>,
-    ) -> Predicate<'tcx> {
+    ) -> Clause<'tcx> {
         // The interaction between HRTB and supertraits is not entirely
         // obvious. Let me walk you (and myself) through an example.
         //
@@ -830,7 +839,13 @@ impl<'tcx> Predicate<'tcx> {
         // 3) ['x] + ['b] -> ['x, 'b]
         let bound_vars =
             tcx.mk_bound_variable_kinds_from_iter(trait_bound_vars.iter().chain(pred_bound_vars));
-        tcx.reuse_or_mk_predicate(self, ty::Binder::bind_with_vars(new, bound_vars))
+
+        // FIXME: Is it really perf sensitive to use reuse_or_mk_predicate here?
+        tcx.reuse_or_mk_predicate(
+            self.as_predicate(),
+            ty::Binder::bind_with_vars(PredicateKind::Clause(new), bound_vars),
+        )
+        .expect_clause()
     }
 }
 
@@ -1301,6 +1316,14 @@ impl<'tcx> ToPredicate<'tcx, Clause<'tcx>> for TraitRef<'tcx> {
     }
 }
 
+impl<'tcx> ToPredicate<'tcx, Clause<'tcx>> for TraitPredicate<'tcx> {
+    #[inline(always)]
+    fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Clause<'tcx> {
+        let p: Predicate<'tcx> = self.to_predicate(tcx);
+        p.expect_clause()
+    }
+}
+
 impl<'tcx> ToPredicate<'tcx> for Binder<'tcx, TraitRef<'tcx>> {
     #[inline(always)]
     fn to_predicate(self, tcx: TyCtxt<'tcx>) -> Predicate<'tcx> {
@@ -1402,7 +1425,7 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(..))
             | PredicateKind::ConstEquate(..)
             | PredicateKind::Ambiguous
-            | PredicateKind::TypeWellFormedFromEnv(..) => None,
+            | PredicateKind::Clause(ClauseKind::TypeWellFormedFromEnv(..)) => None,
         }
     }
 
@@ -1423,7 +1446,7 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(..))
             | PredicateKind::ConstEquate(..)
             | PredicateKind::Ambiguous
-            | PredicateKind::TypeWellFormedFromEnv(..) => None,
+            | PredicateKind::Clause(ClauseKind::TypeWellFormedFromEnv(..)) => None,
         }
     }
 
@@ -1444,7 +1467,7 @@ impl<'tcx> Predicate<'tcx> {
             | PredicateKind::Clause(ClauseKind::ConstEvaluatable(..))
             | PredicateKind::ConstEquate(..)
             | PredicateKind::Ambiguous
-            | PredicateKind::TypeWellFormedFromEnv(..) => None,
+            | PredicateKind::Clause(ClauseKind::TypeWellFormedFromEnv(..)) => None,
         }
     }
 
@@ -1456,12 +1479,11 @@ impl<'tcx> Predicate<'tcx> {
         }
     }
 
-    /// Turns a predicate into a clause without checking that it is a `PredicateKind::Clause`
+    /// Assert that the predicate is a clause.
-    /// first. This will ICE when methods are called on `Clause`.
     pub fn expect_clause(self) -> Clause<'tcx> {
         match self.kind().skip_binder() {
             PredicateKind::Clause(..) => Clause(self.0),
-            _ => bug!(),
+            _ => bug!("{self} is not a clause"),
         }
     }
 }
@@ -1487,7 +1509,7 @@ impl<'tcx> Predicate<'tcx> {
 /// [usize:Bar<isize>]]`.
 #[derive(Clone, Debug, TypeFoldable, TypeVisitable)]
 pub struct InstantiatedPredicates<'tcx> {
-    pub predicates: Vec<Predicate<'tcx>>,
+    pub predicates: Vec<Clause<'tcx>>,
     pub spans: Vec<Span>,
 }
 
@@ -1506,9 +1528,9 @@ impl<'tcx> InstantiatedPredicates<'tcx> {
 }
 
 impl<'tcx> IntoIterator for InstantiatedPredicates<'tcx> {
-    type Item = (Predicate<'tcx>, Span);
+    type Item = (Clause<'tcx>, Span);
 
-    type IntoIter = std::iter::Zip<std::vec::IntoIter<Predicate<'tcx>>, std::vec::IntoIter<Span>>;
+    type IntoIter = std::iter::Zip<std::vec::IntoIter<Clause<'tcx>>, std::vec::IntoIter<Span>>;
 
     fn into_iter(self) -> Self::IntoIter {
         debug_assert_eq!(self.predicates.len(), self.spans.len());
@@ -1517,10 +1539,10 @@ impl<'tcx> IntoIterator for InstantiatedPredicates<'tcx> {
 }
 
 impl<'a, 'tcx> IntoIterator for &'a InstantiatedPredicates<'tcx> {
-    type Item = (Predicate<'tcx>, Span);
+    type Item = (Clause<'tcx>, Span);
 
     type IntoIter = std::iter::Zip<
-        std::iter::Copied<std::slice::Iter<'a, Predicate<'tcx>>>,
+        std::iter::Copied<std::slice::Iter<'a, Clause<'tcx>>>,
         std::iter::Copied<std::slice::Iter<'a, Span>>,
     >;
 
@@ -1670,7 +1692,7 @@ pub struct ParamEnv<'tcx> {
     /// want `Reveal::All`.
     ///
     /// Note: This is packed, use the reveal() method to access it.
-    packed: CopyTaggedPtr<&'tcx List<Predicate<'tcx>>, ParamTag, true>,
+    packed: CopyTaggedPtr<&'tcx List<Clause<'tcx>>, ParamTag, true>,
 }
 
 #[derive(Copy, Clone)]
@@ -1736,7 +1758,7 @@ impl<'tcx> ParamEnv<'tcx> {
     }
 
     #[inline]
-    pub fn caller_bounds(self) -> &'tcx List<Predicate<'tcx>> {
+    pub fn caller_bounds(self) -> &'tcx List<Clause<'tcx>> {
         self.packed.pointer()
     }
 
@@ -1770,7 +1792,7 @@ impl<'tcx> ParamEnv<'tcx> {
     /// Construct a trait environment with the given set of predicates.
     #[inline]
     pub fn new(
-        caller_bounds: &'tcx List<Predicate<'tcx>>,
+        caller_bounds: &'tcx List<Clause<'tcx>>,
         reveal: Reveal,
         constness: hir::Constness,
     ) -> Self {

compiler/rustc_middle/src/ty/print/pretty.rs

@@ -2864,20 +2864,38 @@ define_print_and_forward_display! {
         p!(print(binder))
     }
 
+    ty::Clause<'tcx> {
+        p!(print(self.kind()))
+    }
+
+    ty::ClauseKind<'tcx> {
+        match *self {
+            ty::ClauseKind::Trait(ref data) => {
+                p!(print(data))
+            }
+            ty::ClauseKind::RegionOutlives(predicate) => p!(print(predicate)),
+            ty::ClauseKind::TypeOutlives(predicate) => p!(print(predicate)),
+            ty::ClauseKind::Projection(predicate) => p!(print(predicate)),
+            ty::ClauseKind::ConstArgHasType(ct, ty) => {
+                p!("the constant `", print(ct), "` has type `", print(ty), "`")
+            },
+            ty::ClauseKind::WellFormed(arg) => p!(print(arg), " well-formed"),
+            ty::ClauseKind::ConstEvaluatable(ct) => {
+                p!("the constant `", print(ct), "` can be evaluated")
+            }
+            ty::ClauseKind::TypeWellFormedFromEnv(ty) => {
+                p!("the type `", print(ty), "` is found in the environment")
+            }
+        }
+    }
+
     ty::PredicateKind<'tcx> {
         match *self {
-            ty::PredicateKind::Clause(ty::ClauseKind::Trait(ref data)) => {
+            ty::PredicateKind::Clause(data) => {
                 p!(print(data))
             }
             ty::PredicateKind::Subtype(predicate) => p!(print(predicate)),
             ty::PredicateKind::Coerce(predicate) => p!(print(predicate)),
-            ty::PredicateKind::Clause(ty::ClauseKind::RegionOutlives(predicate)) => p!(print(predicate)),
-            ty::PredicateKind::Clause(ty::ClauseKind::TypeOutlives(predicate)) => p!(print(predicate)),
-            ty::PredicateKind::Clause(ty::ClauseKind::Projection(predicate)) => p!(print(predicate)),
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstArgHasType(ct, ty)) => {
-                p!("the constant `", print(ct), "` has type `", print(ty), "`")
-            },
-            ty::PredicateKind::Clause(ty::ClauseKind::WellFormed(arg)) => p!(print(arg), " well-formed"),
             ty::PredicateKind::ObjectSafe(trait_def_id) => {
                 p!("the trait `", print_def_path(trait_def_id, &[]), "` is object-safe")
             }
@@ -2886,15 +2904,9 @@ define_print_and_forward_display! {
                 print_value_path(closure_def_id, &[]),
                 write("` implements the trait `{}`", kind)
             ),
-            ty::PredicateKind::Clause(ty::ClauseKind::ConstEvaluatable(ct)) => {
-                p!("the constant `", print(ct), "` can be evaluated")
-            }
             ty::PredicateKind::ConstEquate(c1, c2) => {
                 p!("the constant `", print(c1), "` equals `", print(c2), "`")
             }
-            ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
-                p!("the type `", print(ty), "` is found in the environment")
-            }
             ty::PredicateKind::Ambiguous => p!("ambiguous"),
             ty::PredicateKind::AliasRelate(t1, t2, dir) => p!(print(t1), write(" {} ", dir), print(t2)),
         }

compiler/rustc_middle/src/ty/structural_impls.rs

@@ -189,6 +189,9 @@ impl<'tcx> fmt::Debug for ty::ClauseKind<'tcx> {
             ty::ClauseKind::ConstEvaluatable(ct) => {
                 write!(f, "ConstEvaluatable({ct:?})")
             }
+            ty::ClauseKind::TypeWellFormedFromEnv(ty) => {
+                write!(f, "TypeWellFormedFromEnv({:?})", ty)
+            }
         }
     }
 }
@@ -206,9 +209,6 @@ impl<'tcx> fmt::Debug for ty::PredicateKind<'tcx> {
                 write!(f, "ClosureKind({:?}, {:?}, {:?})", closure_def_id, closure_substs, kind)
             }
             ty::PredicateKind::ConstEquate(c1, c2) => write!(f, "ConstEquate({:?}, {:?})", c1, c2),
-            ty::PredicateKind::TypeWellFormedFromEnv(ty) => {
-                write!(f, "TypeWellFormedFromEnv({:?})", ty)
-            }
             ty::PredicateKind::Ambiguous => write!(f, "Ambiguous"),
             ty::PredicateKind::AliasRelate(t1, t2, dir) => {
                 write!(f, "AliasRelate({t1:?}, {dir:?}, {t2:?})")
@@ -701,15 +701,6 @@ impl<'tcx> TypeSuperVisitable<TyCtxt<'tcx>> for ty::Predicate<'tcx> {
     }
 }
 
-impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<ty::Predicate<'tcx>> {
-    fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
-        self,
-        folder: &mut F,
-    ) -> Result<Self, F::Error> {
-        ty::util::fold_list(self, folder, |tcx, v| tcx.mk_predicates(v))
-    }
-}
-
 impl<'tcx> TypeFoldable<TyCtxt<'tcx>> for &'tcx ty::List<ty::Clause<'tcx>> {
     fn try_fold_with<F: FallibleTypeFolder<TyCtxt<'tcx>>>(
         self,

compiler/rustc_middle/src/ty/sty.rs

@@ -715,7 +715,7 @@ impl<'tcx> PolyExistentialPredicate<'tcx> {
     /// Given an existential predicate like `?Self: PartialEq<u32>` (e.g., derived from `dyn PartialEq<u32>`),
     /// and a concrete type `self_ty`, returns a full predicate where the existentially quantified variable `?Self`
     /// has been replaced with `self_ty` (e.g., `self_ty: PartialEq<u32>`, in our example).
-    pub fn with_self_ty(&self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ty::Predicate<'tcx> {
+    pub fn with_self_ty(&self, tcx: TyCtxt<'tcx>, self_ty: Ty<'tcx>) -> ty::Clause<'tcx> {
         use crate::ty::ToPredicate;
         match self.skip_binder() {
             ExistentialPredicate::Trait(tr) => {