Auto merge of #109206 - matthiaskrgr:rollup-oev8ax6, r=matthiaskrgr

Rollup of 10 pull requests

Successful merges:

 - #108875 (rustdoc: fix type search for `Option` combinators)
 - #108971 (error-msg: impl better suggestion for `E0532`)
 - #109139 (rustdoc: DocFS: Replace rayon with threadpool and enable it for all targets)
 - #109151 (Assert def-kind is correct for alias types)
 - #109158 (error-msg: expand suggestion for `unused_def` lint)
 - #109166 (make `define_opaque_types` fully explicit)
 - #109171 (Some cleanups in our normalization logic)
 - #109180 (Unequal → Not equal)
 - #109185 (rustdoc: remove `std::` from primitive intra-doc link tooltips)
 - #109192 (Mention UEFI target promotion in release notes for 1.67.0)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

Cargo.lock

@@ -5458,13 +5458,13 @@ dependencies = [
  "itertools",
  "minifier",
  "once_cell",
- "rayon",
  "regex",
  "rustdoc-json-types",
  "serde",
  "serde_json",
  "smallvec",
  "tempfile",
+ "threadpool",
  "tracing",
  "tracing-subscriber",
  "tracing-tree",
@@ -6209,6 +6209,15 @@ dependencies = [
  "once_cell",
 ]
 
+[[package]]
+name = "threadpool"
+version = "1.8.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d050e60b33d41c19108b32cea32164033a9013fe3b46cbd4457559bfbf77afaa"
+dependencies = [
+ "num_cpus",
+]
+
 [[package]]
 name = "tidy"
 version = "0.1.0"

RELEASES.md

@@ -125,12 +125,13 @@ Compiler
 - [Optimize field ordering by grouping m\*2^n-sized fields with equivalently aligned ones.](https://github.com/rust-lang/rust/pull/102750/)
 - [Stabilize native library modifier `verbatim`.](https://github.com/rust-lang/rust/pull/104360/)
 
-Added and removed targets:
+Added, updated, and removed targets:
 
 - [Add a tier 3 target for PowerPC on AIX](https://github.com/rust-lang/rust/pull/102293/), `powerpc64-ibm-aix`.
 - [Add a tier 3 target for the Sony PlayStation 1](https://github.com/rust-lang/rust/pull/102689/), `mipsel-sony-psx`.
 - [Add tier 3 `no_std` targets for the QNX Neutrino RTOS](https://github.com/rust-lang/rust/pull/102701/),
   `aarch64-unknown-nto-qnx710` and `x86_64-pc-nto-qnx710`.
+- [Promote UEFI targets to tier 2](https://github.com/rust-lang/rust/pull/103933/), `aarch64-unknown-uefi`, `i686-unknown-uefi`, and `x86_64-unknown-uefi`.
 - [Remove tier 3 `linuxkernel` targets](https://github.com/rust-lang/rust/pull/104015/) (not used by the actual kernel).
 
 Refer to Rust's [platform support page][platform-support-doc]

compiler/rustc_borrowck/src/dataflow.rs

@@ -306,7 +306,7 @@ impl<'a, 'tcx> Borrows<'a, 'tcx> {
         }
 
         // By passing `PlaceConflictBias::NoOverlap`, we conservatively assume that any given
-        // pair of array indices are unequal, so that when `places_conflict` returns true, we
+        // pair of array indices are not equal, so that when `places_conflict` returns true, we
         // will be assured that two places being compared definitely denotes the same sets of
         // locations.
         let definitely_conflicting_borrows = other_borrows_of_local.filter(|&i| {

compiler/rustc_error_codes/src/error_codes/E0416.md

@@ -23,6 +23,6 @@ Or maybe did you mean to unify? Consider using a guard:
 # let (A, B, C) = (1, 2, 3);
 match (A, B, C) {
     (x, x2, see) if x == x2 => { /* A and B are equal, do one thing */ }
-    (y, z, see) => { /* A and B unequal; do another thing */ }
+    (y, z, see) => { /* A and B not equal; do another thing */ }
 }
 ```

compiler/rustc_expand/src/mbe/transcribe.rs

@@ -367,7 +367,7 @@ impl LockstepIterSize {
 ///
 /// Example: `$($($x $y)+*);+` -- we need to make sure that `x` and `y` repeat the same amount as
 /// each other at the given depth when the macro was invoked. If they don't it might mean they were
-/// declared at unequal depths or there was a compile bug. For example, if we have 3 repetitions of
+/// declared at depths which weren't equal or there was a compiler bug. For example, if we have 3 repetitions of
 /// the outer sequence and 4 repetitions of the inner sequence for `x`, we should have the same for
 /// `y`; otherwise, we can't transcribe them both at the given depth.
 fn lockstep_iter_size(

compiler/rustc_hir_analysis/src/coherence/builtin.rs

@@ -9,8 +9,8 @@ use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::ItemKind;
 use rustc_infer::infer::outlives::env::OutlivesEnvironment;
-use rustc_infer::infer::TyCtxtInferExt;
 use rustc_infer::infer::{self, RegionResolutionError};
+use rustc_infer::infer::{DefineOpaqueTypes, TyCtxtInferExt};
 use rustc_middle::ty::adjustment::CoerceUnsizedInfo;
 use rustc_middle::ty::{self, suggest_constraining_type_params, Ty, TyCtxt, TypeVisitableExt};
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
@@ -235,7 +235,8 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
     use rustc_type_ir::sty::TyKind::*;
     match (source.kind(), target.kind()) {
         (&Ref(r_a, _, mutbl_a), Ref(r_b, _, mutbl_b))
-            if infcx.at(&cause, param_env).eq(r_a, *r_b).is_ok() && mutbl_a == *mutbl_b => {}
+            if infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, r_a, *r_b).is_ok()
+                && mutbl_a == *mutbl_b => {}
         (&RawPtr(tm_a), &RawPtr(tm_b)) if tm_a.mutbl == tm_b.mutbl => (),
         (&Adt(def_a, substs_a), &Adt(def_b, substs_b))
             if def_a.is_struct() && def_b.is_struct() =>
@@ -278,7 +279,9 @@ fn visit_implementation_of_dispatch_from_dyn(tcx: TyCtxt<'_>, impl_did: LocalDef
                         }
                     }
 
-                    if let Ok(ok) = infcx.at(&cause, param_env).eq(ty_a, ty_b) {
+                    if let Ok(ok) =
+                        infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, ty_a, ty_b)
+                    {
                         if ok.obligations.is_empty() {
                             create_err(
                                 "the trait `DispatchFromDyn` may only be implemented \
@@ -504,7 +507,7 @@ pub fn coerce_unsized_info<'tcx>(tcx: TyCtxt<'tcx>, impl_did: DefId) -> CoerceUn
                     // we may have to evaluate constraint
                     // expressions in the course of execution.)
                     // See e.g., #41936.
-                    if let Ok(ok) = infcx.at(&cause, param_env).eq(a, b) {
+                    if let Ok(ok) = infcx.at(&cause, param_env).eq(DefineOpaqueTypes::No, a, b) {
                         if ok.obligations.is_empty() {
                             return None;
                         }

compiler/rustc_hir_analysis/src/lib.rs

@@ -102,7 +102,7 @@ use rustc_errors::ErrorGuaranteed;
 use rustc_errors::{DiagnosticMessage, SubdiagnosticMessage};
 use rustc_hir as hir;
 use rustc_hir::Node;
-use rustc_infer::infer::{InferOk, TyCtxtInferExt};
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk, TyCtxtInferExt};
 use rustc_macros::fluent_messages;
 use rustc_middle::middle;
 use rustc_middle::ty::query::Providers;
@@ -165,7 +165,7 @@ fn require_same_types<'tcx>(
 ) -> bool {
     let infcx = &tcx.infer_ctxt().build();
     let param_env = ty::ParamEnv::empty();
-    let errors = match infcx.at(cause, param_env).eq(expected, actual) {
+    let errors = match infcx.at(cause, param_env).eq(DefineOpaqueTypes::No, expected, actual) {
         Ok(InferOk { obligations, .. }) => traits::fully_solve_obligations(infcx, obligations),
         Err(err) => {
             infcx.err_ctxt().report_mismatched_types(cause, expected, actual, err).emit();

compiler/rustc_hir_typeck/src/closure.rs

@@ -8,7 +8,7 @@ use rustc_hir as hir;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir_analysis::astconv::AstConv;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::LateBoundRegionConversionTime;
+use rustc_infer::infer::{DefineOpaqueTypes, LateBoundRegionConversionTime};
 use rustc_infer::infer::{InferOk, InferResult};
 use rustc_macros::{TypeFoldable, TypeVisitable};
 use rustc_middle::ty::subst::InternalSubsts;
@@ -563,10 +563,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             ) {
                 // Check that E' = S'.
                 let cause = self.misc(hir_ty.span);
-                let InferOk { value: (), obligations } = self
-                    .at(&cause, self.param_env)
-                    .define_opaque_types(true)
-                    .eq(*expected_ty, supplied_ty)?;
+                let InferOk { value: (), obligations } = self.at(&cause, self.param_env).eq(
+                    DefineOpaqueTypes::Yes,
+                    *expected_ty,
+                    supplied_ty,
+                )?;
                 all_obligations.extend(obligations);
             }
 
@@ -576,10 +577,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 supplied_sig.output(),
             );
             let cause = &self.misc(decl.output.span());
-            let InferOk { value: (), obligations } = self
-                .at(cause, self.param_env)
-                .define_opaque_types(true)
-                .eq(expected_sigs.liberated_sig.output(), supplied_output_ty)?;
+            let InferOk { value: (), obligations } = self.at(cause, self.param_env).eq(
+                DefineOpaqueTypes::Yes,
+                expected_sigs.liberated_sig.output(),
+                supplied_output_ty,
+            )?;
             all_obligations.extend(obligations);
 
             let inputs = inputs.into_iter().map(|ty| self.resolve_vars_if_possible(ty));

compiler/rustc_hir_typeck/src/coercion.rs

@@ -45,7 +45,7 @@ use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::Expr;
 use rustc_hir_analysis::astconv::AstConv;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::{Coercion, InferOk, InferResult};
+use rustc_infer::infer::{Coercion, DefineOpaqueTypes, InferOk, InferResult};
 use rustc_infer::traits::Obligation;
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::ty::adjustment::{
@@ -143,11 +143,11 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
     fn unify(&self, a: Ty<'tcx>, b: Ty<'tcx>) -> InferResult<'tcx, Ty<'tcx>> {
         debug!("unify(a: {:?}, b: {:?}, use_lub: {})", a, b, self.use_lub);
         self.commit_if_ok(|_| {
-            let at = self.at(&self.cause, self.fcx.param_env).define_opaque_types(true);
+            let at = self.at(&self.cause, self.fcx.param_env);
             if self.use_lub {
-                at.lub(b, a)
+                at.lub(DefineOpaqueTypes::Yes, b, a)
             } else {
-                at.sup(b, a)
+                at.sup(DefineOpaqueTypes::Yes, b, a)
                     .map(|InferOk { value: (), obligations }| InferOk { value: a, obligations })
             }
         })
@@ -175,7 +175,7 @@ impl<'f, 'tcx> Coerce<'f, 'tcx> {
             // so this will have the side-effect of making sure we have no ambiguities
             // due to `[type error]` and `_` not coercing together.
             let _ = self.commit_if_ok(|_| {
-                self.at(&self.cause, self.param_env).define_opaque_types(true).eq(a, b)
+                self.at(&self.cause, self.param_env).eq(DefineOpaqueTypes::Yes, a, b)
             });
             return success(vec![], self.fcx.tcx.ty_error(guar), vec![]);
         }
@@ -1101,9 +1101,13 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                     (ty::FnDef(..), ty::FnDef(..)) => {
                         // Don't reify if the function types have a LUB, i.e., they
                         // are the same function and their parameters have a LUB.
-                        match self
-                            .commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
-                        {
+                        match self.commit_if_ok(|_| {
+                            self.at(cause, self.param_env).lub(
+                                DefineOpaqueTypes::No,
+                                prev_ty,
+                                new_ty,
+                            )
+                        }) {
                             // We have a LUB of prev_ty and new_ty, just return it.
                             Ok(ok) => return Ok(self.register_infer_ok_obligations(ok)),
                             Err(_) => {
@@ -1153,7 +1157,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let sig = self
                 .at(cause, self.param_env)
                 .trace(prev_ty, new_ty)
-                .lub(a_sig, b_sig)
+                .lub(DefineOpaqueTypes::No, a_sig, b_sig)
                 .map(|ok| self.register_infer_ok_obligations(ok))?;
 
             // Reify both sides and return the reified fn pointer type.
@@ -1237,7 +1241,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 );
 
                 return self
-                    .commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
+                    .commit_if_ok(|_| {
+                        self.at(cause, self.param_env).lub(DefineOpaqueTypes::No, prev_ty, new_ty)
+                    })
                     .map(|ok| self.register_infer_ok_obligations(ok));
             }
         }
@@ -1248,8 +1254,10 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                 if let Some(e) = first_error {
                     Err(e)
                 } else {
-                    self.commit_if_ok(|_| self.at(cause, self.param_env).lub(prev_ty, new_ty))
-                        .map(|ok| self.register_infer_ok_obligations(ok))
+                    self.commit_if_ok(|_| {
+                        self.at(cause, self.param_env).lub(DefineOpaqueTypes::No, prev_ty, new_ty)
+                    })
+                    .map(|ok| self.register_infer_ok_obligations(ok))
                 }
             }
             Ok(ok) => {
@@ -1487,8 +1495,12 @@ impl<'tcx, 'exprs, E: AsCoercionSite> CoerceMany<'tcx, 'exprs, E> {
             assert!(expression_ty.is_unit(), "if let hack without unit type");
             fcx.at(cause, fcx.param_env)
                 // needed for tests/ui/type-alias-impl-trait/issue-65679-inst-opaque-ty-from-val-twice.rs
-                .define_opaque_types(true)
-                .eq_exp(label_expression_as_expected, expression_ty, self.merged_ty())
+                .eq_exp(
+                    DefineOpaqueTypes::Yes,
+                    label_expression_as_expected,
+                    expression_ty,
+                    self.merged_ty(),
+                )
                 .map(|infer_ok| {
                     fcx.register_infer_ok_obligations(infer_ok);
                     expression_ty

compiler/rustc_hir_typeck/src/demand.rs

@@ -8,7 +8,7 @@ use rustc_hir::def::CtorKind;
 use rustc_hir::intravisit::Visitor;
 use rustc_hir::lang_items::LangItem;
 use rustc_hir::{is_range_literal, Node};
-use rustc_infer::infer::InferOk;
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_middle::lint::in_external_macro;
 use rustc_middle::middle::stability::EvalResult;
 use rustc_middle::ty::adjustment::AllowTwoPhase;
@@ -113,7 +113,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected: Ty<'tcx>,
         actual: Ty<'tcx>,
     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
-        match self.at(cause, self.param_env).define_opaque_types(true).sup(expected, actual) {
+        match self.at(cause, self.param_env).sup(DefineOpaqueTypes::Yes, expected, actual) {
             Ok(InferOk { obligations, value: () }) => {
                 self.register_predicates(obligations);
                 None
@@ -143,7 +143,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         expected: Ty<'tcx>,
         actual: Ty<'tcx>,
     ) -> Option<DiagnosticBuilder<'tcx, ErrorGuaranteed>> {
-        match self.at(cause, self.param_env).define_opaque_types(true).eq(expected, actual) {
+        match self.at(cause, self.param_env).eq(DefineOpaqueTypes::Yes, expected, actual) {
             Ok(InferOk { obligations, value: () }) => {
                 self.register_predicates(obligations);
                 None

compiler/rustc_hir_typeck/src/expr.rs

@@ -36,6 +36,7 @@ use rustc_hir_analysis::astconv::AstConv as _;
 use rustc_hir_analysis::check::ty_kind_suggestion;
 use rustc_infer::infer;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::infer::InferOk;
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::middle::stability;
@@ -1683,7 +1684,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
                             if let Some(_) = remaining_fields.remove(&ident) {
                                 let target_ty = self.field_ty(base_expr.span, f, substs);
                                 let cause = self.misc(base_expr.span);
-                                match self.at(&cause, self.param_env).sup(target_ty, fru_ty) {
+                                match self.at(&cause, self.param_env).sup(
+                                    DefineOpaqueTypes::No,
+                                    target_ty,
+                                    fru_ty,
+                                ) {
                                     Ok(InferOk { obligations, value: () }) => {
                                         self.register_predicates(obligations)
                                     }

compiler/rustc_hir_typeck/src/fn_ctxt/_impl.rs

@@ -19,7 +19,7 @@ use rustc_hir_analysis::astconv::{
 };
 use rustc_infer::infer::canonical::{Canonical, OriginalQueryValues, QueryResponse};
 use rustc_infer::infer::error_reporting::TypeAnnotationNeeded::E0282;
-use rustc_infer::infer::InferResult;
+use rustc_infer::infer::{DefineOpaqueTypes, InferResult};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, AutoBorrow, AutoBorrowMutability};
 use rustc_middle::ty::error::TypeError;
 use rustc_middle::ty::fold::TypeFoldable;
@@ -558,7 +558,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             let span = self.tcx.hir().body(body_id).value.span;
             let ok = self
                 .at(&self.misc(span), self.param_env)
-                .eq(interior, witness)
+                .eq(DefineOpaqueTypes::No, interior, witness)
                 .expect("Failed to unify generator interior type");
             let mut obligations = ok.obligations;
 
@@ -1341,7 +1341,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
             // This also occurs for an enum variant on a type alias.
             let impl_ty = self.normalize(span, tcx.type_of(impl_def_id).subst(tcx, substs));
             let self_ty = self.normalize(span, self_ty);
-            match self.at(&self.misc(span), self.param_env).eq(impl_ty, self_ty) {
+            match self.at(&self.misc(span), self.param_env).eq(
+                DefineOpaqueTypes::No,
+                impl_ty,
+                self_ty,
+            ) {
                 Ok(ok) => self.register_infer_ok_obligations(ok),
                 Err(_) => {
                     self.tcx.sess.delay_span_bug(

compiler/rustc_hir_typeck/src/fn_ctxt/checks.rs

@@ -24,8 +24,8 @@ use rustc_hir_analysis::structured_errors::StructuredDiagnostic;
 use rustc_index::vec::IndexVec;
 use rustc_infer::infer::error_reporting::{FailureCode, ObligationCauseExt};
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::InferOk;
 use rustc_infer::infer::TypeTrace;
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_middle::ty::adjustment::AllowTwoPhase;
 use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{self, IsSuggestable, Ty};
@@ -301,9 +301,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             // 3. Check if the formal type is a supertype of the checked one
             //    and register any such obligations for future type checks
-            let supertype_error = self
-                .at(&self.misc(provided_arg.span), self.param_env)
-                .sup(formal_input_ty, coerced_ty);
+            let supertype_error = self.at(&self.misc(provided_arg.span), self.param_env).sup(
+                DefineOpaqueTypes::No,
+                formal_input_ty,
+                coerced_ty,
+            );
             let subtyping_error = match supertype_error {
                 Ok(InferOk { obligations, value: () }) => {
                     self.register_predicates(obligations);
@@ -585,7 +587,9 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
             // Using probe here, since we don't want this subtyping to affect inference.
             let subtyping_error = self.probe(|_| {
-                self.at(&self.misc(arg_span), self.param_env).sup(formal_input_ty, coerced_ty).err()
+                self.at(&self.misc(arg_span), self.param_env)
+                    .sup(DefineOpaqueTypes::No, formal_input_ty, coerced_ty)
+                    .err()
             });
 
             // Same as above: if either the coerce type or the checked type is an error type,

compiler/rustc_hir_typeck/src/generator_interior/mod.rs

@@ -13,7 +13,7 @@ use rustc_hir::def_id::DefId;
 use rustc_hir::hir_id::HirIdSet;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_hir::{Arm, Expr, ExprKind, Guard, HirId, Pat, PatKind};
-use rustc_infer::infer::RegionVariableOrigin;
+use rustc_infer::infer::{DefineOpaqueTypes, RegionVariableOrigin};
 use rustc_middle::middle::region::{self, Scope, ScopeData, YieldData};
 use rustc_middle::ty::fold::FnMutDelegate;
 use rustc_middle::ty::{self, BoundVariableKind, RvalueScopes, Ty, TyCtxt, TypeVisitableExt};
@@ -327,7 +327,11 @@ pub fn resolve_interior<'a, 'tcx>(
     );
 
     // Unify the type variable inside the generator with the new witness
-    match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(interior, witness) {
+    match fcx.at(&fcx.misc(body.value.span), fcx.param_env).eq(
+        DefineOpaqueTypes::No,
+        interior,
+        witness,
+    ) {
         Ok(ok) => fcx.register_infer_ok_obligations(ok),
         _ => bug!("failed to relate {interior} and {witness}"),
     }

compiler/rustc_hir_typeck/src/method/confirm.rs

@@ -8,7 +8,7 @@ use rustc_hir_analysis::astconv::generics::{
     check_generic_arg_count_for_call, create_substs_for_generic_args,
 };
 use rustc_hir_analysis::astconv::{AstConv, CreateSubstsForGenericArgsCtxt, IsMethodCall};
-use rustc_infer::infer::{self, InferOk};
+use rustc_infer::infer::{self, DefineOpaqueTypes, InferOk};
 use rustc_middle::traits::{ObligationCauseCode, UnifyReceiverContext};
 use rustc_middle::ty::adjustment::{Adjust, Adjustment, PointerCast};
 use rustc_middle::ty::adjustment::{AllowTwoPhase, AutoBorrow, AutoBorrowMutability};
@@ -478,7 +478,7 @@ impl<'a, 'tcx> ConfirmContext<'a, 'tcx> {
                 substs,
             })),
         );
-        match self.at(&cause, self.param_env).sup(method_self_ty, self_ty) {
+        match self.at(&cause, self.param_env).sup(DefineOpaqueTypes::No, method_self_ty, self_ty) {
             Ok(InferOk { obligations, value: () }) => {
                 self.register_predicates(obligations);
             }

compiler/rustc_hir_typeck/src/method/probe.rs

@@ -13,6 +13,7 @@ use rustc_hir_analysis::astconv::InferCtxtExt as _;
 use rustc_hir_analysis::autoderef::{self, Autoderef};
 use rustc_infer::infer::canonical::OriginalQueryValues;
 use rustc_infer::infer::canonical::{Canonical, QueryResponse};
+use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::infer::{self, InferOk, TyCtxtInferExt};
 use rustc_middle::middle::stability;
 use rustc_middle::ty::fast_reject::TreatProjections;
@@ -930,7 +931,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 if let Some(self_ty) = self_ty {
                     if self
                         .at(&ObligationCause::dummy(), self.param_env)
-                        .sup(fty.inputs()[0], self_ty)
+                        .sup(DefineOpaqueTypes::No, fty.inputs()[0], self_ty)
                         .is_err()
                     {
                         return false;
@@ -1436,9 +1437,11 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 CandidateSource::Trait(candidate.item.container_id(self.tcx))
             }
             TraitCandidate(trait_ref) => self.probe(|_| {
-                let _ = self
-                    .at(&ObligationCause::dummy(), self.param_env)
-                    .sup(candidate.xform_self_ty, self_ty);
+                let _ = self.at(&ObligationCause::dummy(), self.param_env).sup(
+                    DefineOpaqueTypes::No,
+                    candidate.xform_self_ty,
+                    self_ty,
+                );
                 match self.select_trait_candidate(trait_ref) {
                     Ok(Some(traits::ImplSource::UserDefined(ref impl_data))) => {
                         // If only a single impl matches, make the error message point
@@ -1465,10 +1468,11 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
 
         self.probe(|_| {
             // First check that the self type can be related.
-            let sub_obligations = match self
-                .at(&ObligationCause::dummy(), self.param_env)
-                .sup(probe.xform_self_ty, self_ty)
-            {
+            let sub_obligations = match self.at(&ObligationCause::dummy(), self.param_env).sup(
+                DefineOpaqueTypes::No,
+                probe.xform_self_ty,
+                self_ty,
+            ) {
                 Ok(InferOk { obligations, value: () }) => obligations,
                 Err(err) => {
                     debug!("--> cannot relate self-types {:?}", err);
@@ -1683,7 +1687,7 @@ impl<'a, 'tcx> ProbeContext<'a, 'tcx> {
                 if let ProbeResult::Match = result
                     && self
                     .at(&ObligationCause::dummy(), self.param_env)
-                    .sup(return_ty, xform_ret_ty)
+                    .sup(DefineOpaqueTypes::No, return_ty, xform_ret_ty)
                     .is_err()
                 {
                     result = ProbeResult::BadReturnType;

compiler/rustc_infer/src/infer/at.rs

@@ -30,16 +30,20 @@ use super::*;
 use rustc_middle::ty::relate::{Relate, TypeRelation};
 use rustc_middle::ty::{Const, ImplSubject};
 
+/// Whether we should define opaque types or just treat them opaquely.
+///
+/// Currently only used to prevent predicate matching from matching anything
+/// against opaque types.
+#[derive(Debug, PartialEq, Eq, Clone, Copy)]
+pub enum DefineOpaqueTypes {
+    Yes,
+    No,
+}
+
 pub struct At<'a, 'tcx> {
     pub infcx: &'a InferCtxt<'tcx>,
     pub cause: &'a ObligationCause<'tcx>,
     pub param_env: ty::ParamEnv<'tcx>,
-    /// Whether we should define opaque types
-    /// or just treat them opaquely.
-    /// Currently only used to prevent predicate
-    /// matching from matching anything against opaque
-    /// types.
-    pub define_opaque_types: bool,
 }
 
 pub struct Trace<'a, 'tcx> {
@@ -55,7 +59,7 @@ impl<'tcx> InferCtxt<'tcx> {
         cause: &'a ObligationCause<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
     ) -> At<'a, 'tcx> {
-        At { infcx: self, cause, param_env, define_opaque_types: false }
+        At { infcx: self, cause, param_env }
     }
 
     /// Forks the inference context, creating a new inference context with the same inference
@@ -84,7 +88,6 @@ impl<'tcx> InferCtxt<'tcx> {
 
 pub trait ToTrace<'tcx>: Relate<'tcx> + Copy {
     fn to_trace(
-        tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -93,33 +96,21 @@ pub trait ToTrace<'tcx>: Relate<'tcx> + Copy {
 }
 
 impl<'a, 'tcx> At<'a, 'tcx> {
-    pub fn define_opaque_types(self, define_opaque_types: bool) -> Self {
-        Self { define_opaque_types, ..self }
-    }
-
-    /// Hacky routine for equating two impl headers in coherence.
-    pub fn eq_impl_headers(
-        self,
-        expected: &ty::ImplHeader<'tcx>,
-        actual: &ty::ImplHeader<'tcx>,
-    ) -> InferResult<'tcx, ()> {
-        debug!("eq_impl_header({:?} = {:?})", expected, actual);
-        match (expected.trait_ref, actual.trait_ref) {
-            (Some(a_ref), Some(b_ref)) => self.eq(a_ref, b_ref),
-            (None, None) => self.eq(expected.self_ty, actual.self_ty),
-            _ => bug!("mk_eq_impl_headers given mismatched impl kinds"),
-        }
-    }
-
     /// Makes `a <: b`, where `a` may or may not be expected.
     ///
     /// See [`At::trace_exp`] and [`Trace::sub`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn sub_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
+    pub fn sub_exp<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        a_is_expected: bool,
+        a: T,
+        b: T,
+    ) -> InferResult<'tcx, ()>
     where
         T: ToTrace<'tcx>,
     {
-        self.trace_exp(a_is_expected, a, b).sub(a, b)
+        self.trace_exp(a_is_expected, a, b).sub(define_opaque_types, a, b)
     }
 
     /// Makes `actual <: expected`. For example, if type-checking a
@@ -129,54 +120,81 @@ impl<'a, 'tcx> At<'a, 'tcx> {
     ///
     /// See [`At::trace`] and [`Trace::sub`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn sup<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
+    pub fn sup<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        expected: T,
+        actual: T,
+    ) -> InferResult<'tcx, ()>
     where
         T: ToTrace<'tcx>,
     {
-        self.sub_exp(false, actual, expected)
+        self.sub_exp(define_opaque_types, false, actual, expected)
     }
 
     /// Makes `expected <: actual`.
     ///
     /// See [`At::trace`] and [`Trace::sub`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn sub<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
+    pub fn sub<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        expected: T,
+        actual: T,
+    ) -> InferResult<'tcx, ()>
     where
         T: ToTrace<'tcx>,
     {
-        self.sub_exp(true, expected, actual)
+        self.sub_exp(define_opaque_types, true, expected, actual)
     }
 
     /// Makes `expected <: actual`.
     ///
     /// See [`At::trace_exp`] and [`Trace::eq`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn eq_exp<T>(self, a_is_expected: bool, a: T, b: T) -> InferResult<'tcx, ()>
+    pub fn eq_exp<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        a_is_expected: bool,
+        a: T,
+        b: T,
+    ) -> InferResult<'tcx, ()>
     where
         T: ToTrace<'tcx>,
     {
-        self.trace_exp(a_is_expected, a, b).eq(a, b)
+        self.trace_exp(a_is_expected, a, b).eq(define_opaque_types, a, b)
     }
 
     /// Makes `expected <: actual`.
     ///
     /// See [`At::trace`] and [`Trace::eq`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn eq<T>(self, expected: T, actual: T) -> InferResult<'tcx, ()>
+    pub fn eq<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        expected: T,
+        actual: T,
+    ) -> InferResult<'tcx, ()>
     where
         T: ToTrace<'tcx>,
     {
-        self.trace(expected, actual).eq(expected, actual)
+        self.trace(expected, actual).eq(define_opaque_types, expected, actual)
     }
 
-    pub fn relate<T>(self, expected: T, variance: ty::Variance, actual: T) -> InferResult<'tcx, ()>
+    pub fn relate<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        expected: T,
+        variance: ty::Variance,
+        actual: T,
+    ) -> InferResult<'tcx, ()>
     where
         T: ToTrace<'tcx>,
     {
         match variance {
-            ty::Variance::Covariant => self.sub(expected, actual),
-            ty::Variance::Invariant => self.eq(expected, actual),
-            ty::Variance::Contravariant => self.sup(expected, actual),
+            ty::Variance::Covariant => self.sub(define_opaque_types, expected, actual),
+            ty::Variance::Invariant => self.eq(define_opaque_types, expected, actual),
+            ty::Variance::Contravariant => self.sup(define_opaque_types, expected, actual),
 
             // We could make this make sense but it's not readily
             // exposed and I don't feel like dealing with it. Note
@@ -195,11 +213,16 @@ impl<'a, 'tcx> At<'a, 'tcx> {
     ///
     /// See [`At::trace`] and [`Trace::lub`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn lub<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
+    pub fn lub<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        expected: T,
+        actual: T,
+    ) -> InferResult<'tcx, T>
     where
         T: ToTrace<'tcx>,
     {
-        self.trace(expected, actual).lub(expected, actual)
+        self.trace(expected, actual).lub(define_opaque_types, expected, actual)
     }
 
     /// Computes the greatest-lower-bound, or mutual subtype, of two
@@ -208,11 +231,16 @@ impl<'a, 'tcx> At<'a, 'tcx> {
     ///
     /// See [`At::trace`] and [`Trace::glb`] for a version of
     /// this method that only requires `T: Relate<'tcx>`
-    pub fn glb<T>(self, expected: T, actual: T) -> InferResult<'tcx, T>
+    pub fn glb<T>(
+        self,
+        define_opaque_types: DefineOpaqueTypes,
+        expected: T,
+        actual: T,
+    ) -> InferResult<'tcx, T>
     where
         T: ToTrace<'tcx>,
     {
-        self.trace(expected, actual).glb(expected, actual)
+        self.trace(expected, actual).glb(define_opaque_types, expected, actual)
     }
 
     /// Sets the "trace" values that will be used for
@@ -233,7 +261,7 @@ impl<'a, 'tcx> At<'a, 'tcx> {
     where
         T: ToTrace<'tcx>,
     {
-        let trace = ToTrace::to_trace(self.infcx.tcx, self.cause, a_is_expected, a, b);
+        let trace = ToTrace::to_trace(self.cause, a_is_expected, a, b);
         Trace { at: self, trace, a_is_expected }
     }
 }
@@ -242,13 +270,13 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
     /// Makes `a <: b` where `a` may or may not be expected (if
     /// `a_is_expected` is true, then `a` is expected).
     #[instrument(skip(self), level = "debug")]
-    pub fn sub<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
+    pub fn sub<T>(self, define_opaque_types: DefineOpaqueTypes, a: T, b: T) -> InferResult<'tcx, ()>
     where
         T: Relate<'tcx>,
     {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
-            let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
+            let mut fields = at.infcx.combine_fields(trace, at.param_env, define_opaque_types);
             fields
                 .sub(a_is_expected)
                 .relate(a, b)
@@ -259,13 +287,13 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
     /// Makes `a == b`; the expectation is set by the call to
     /// `trace()`.
     #[instrument(skip(self), level = "debug")]
-    pub fn eq<T>(self, a: T, b: T) -> InferResult<'tcx, ()>
+    pub fn eq<T>(self, define_opaque_types: DefineOpaqueTypes, a: T, b: T) -> InferResult<'tcx, ()>
     where
         T: Relate<'tcx>,
     {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
-            let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
+            let mut fields = at.infcx.combine_fields(trace, at.param_env, define_opaque_types);
             fields
                 .equate(a_is_expected)
                 .relate(a, b)
@@ -274,13 +302,13 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
     }
 
     #[instrument(skip(self), level = "debug")]
-    pub fn lub<T>(self, a: T, b: T) -> InferResult<'tcx, T>
+    pub fn lub<T>(self, define_opaque_types: DefineOpaqueTypes, a: T, b: T) -> InferResult<'tcx, T>
     where
         T: Relate<'tcx>,
     {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
-            let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
+            let mut fields = at.infcx.combine_fields(trace, at.param_env, define_opaque_types);
             fields
                 .lub(a_is_expected)
                 .relate(a, b)
@@ -289,13 +317,13 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
     }
 
     #[instrument(skip(self), level = "debug")]
-    pub fn glb<T>(self, a: T, b: T) -> InferResult<'tcx, T>
+    pub fn glb<T>(self, define_opaque_types: DefineOpaqueTypes, a: T, b: T) -> InferResult<'tcx, T>
     where
         T: Relate<'tcx>,
     {
         let Trace { at, trace, a_is_expected } = self;
         at.infcx.commit_if_ok(|_| {
-            let mut fields = at.infcx.combine_fields(trace, at.param_env, at.define_opaque_types);
+            let mut fields = at.infcx.combine_fields(trace, at.param_env, define_opaque_types);
             fields
                 .glb(a_is_expected)
                 .relate(a, b)
@@ -306,7 +334,6 @@ impl<'a, 'tcx> Trace<'a, 'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
     fn to_trace(
-        tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -314,10 +341,10 @@ impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
     ) -> TypeTrace<'tcx> {
         match (a, b) {
             (ImplSubject::Trait(trait_ref_a), ImplSubject::Trait(trait_ref_b)) => {
-                ToTrace::to_trace(tcx, cause, a_is_expected, trait_ref_a, trait_ref_b)
+                ToTrace::to_trace(cause, a_is_expected, trait_ref_a, trait_ref_b)
             }
             (ImplSubject::Inherent(ty_a), ImplSubject::Inherent(ty_b)) => {
-                ToTrace::to_trace(tcx, cause, a_is_expected, ty_a, ty_b)
+                ToTrace::to_trace(cause, a_is_expected, ty_a, ty_b)
             }
             (ImplSubject::Trait(_), ImplSubject::Inherent(_))
             | (ImplSubject::Inherent(_), ImplSubject::Trait(_)) => {
@@ -329,7 +356,6 @@ impl<'tcx> ToTrace<'tcx> for ImplSubject<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -344,7 +370,6 @@ impl<'tcx> ToTrace<'tcx> for Ty<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -356,7 +381,6 @@ impl<'tcx> ToTrace<'tcx> for ty::Region<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for Const<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -371,7 +395,6 @@ impl<'tcx> ToTrace<'tcx> for Const<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::GenericArg<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -399,7 +422,6 @@ impl<'tcx> ToTrace<'tcx> for ty::GenericArg<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -411,7 +433,6 @@ impl<'tcx> ToTrace<'tcx> for ty::Term<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -426,7 +447,6 @@ impl<'tcx> ToTrace<'tcx> for ty::TraitRef<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
@@ -441,24 +461,17 @@ impl<'tcx> ToTrace<'tcx> for ty::PolyTraitRef<'tcx> {
 
 impl<'tcx> ToTrace<'tcx> for ty::AliasTy<'tcx> {
     fn to_trace(
-        tcx: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,
         b: Self,
     ) -> TypeTrace<'tcx> {
-        let a_ty = tcx.mk_projection(a.def_id, a.substs);
-        let b_ty = tcx.mk_projection(b.def_id, b.substs);
-        TypeTrace {
-            cause: cause.clone(),
-            values: Terms(ExpectedFound::new(a_is_expected, a_ty.into(), b_ty.into())),
-        }
+        TypeTrace { cause: cause.clone(), values: Aliases(ExpectedFound::new(a_is_expected, a, b)) }
     }
 }
 
 impl<'tcx> ToTrace<'tcx> for ty::FnSig<'tcx> {
     fn to_trace(
-        _: TyCtxt<'tcx>,
         cause: &ObligationCause<'tcx>,
         a_is_expected: bool,
         a: Self,

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

@@ -14,7 +14,7 @@ use crate::infer::canonical::{
 };
 use crate::infer::nll_relate::{TypeRelating, TypeRelatingDelegate};
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
-use crate::infer::{InferCtxt, InferOk, InferResult, NllRegionVariableOrigin};
+use crate::infer::{DefineOpaqueTypes, InferCtxt, InferOk, InferResult, NllRegionVariableOrigin};
 use crate::traits::query::{Fallible, NoSolution};
 use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use crate::traits::{PredicateObligations, TraitEngine, TraitEngineExt};
@@ -510,7 +510,7 @@ impl<'tcx> InferCtxt<'tcx> {
             let b = substitute_value(self.tcx, &result_subst, b);
             debug!(?a, ?b, "constrain opaque type");
             obligations
-                .extend(self.at(cause, param_env).define_opaque_types(true).eq(a, b)?.obligations);
+                .extend(self.at(cause, param_env).eq(DefineOpaqueTypes::Yes, a, b)?.obligations);
         }
 
         Ok(InferOk { value: result_subst, obligations })
@@ -603,8 +603,11 @@ impl<'tcx> InferCtxt<'tcx> {
 
                 match (value1.unpack(), value2.unpack()) {
                     (GenericArgKind::Type(v1), GenericArgKind::Type(v2)) => {
-                        obligations
-                            .extend(self.at(cause, param_env).eq(v1, v2)?.into_obligations());
+                        obligations.extend(
+                            self.at(cause, param_env)
+                                .eq(DefineOpaqueTypes::Yes, v1, v2)?
+                                .into_obligations(),
+                        );
                     }
                     (GenericArgKind::Lifetime(re1), GenericArgKind::Lifetime(re2))
                         if re1.is_erased() && re2.is_erased() =>
@@ -612,11 +615,14 @@ impl<'tcx> InferCtxt<'tcx> {
                         // no action needed
                     }
                     (GenericArgKind::Lifetime(v1), GenericArgKind::Lifetime(v2)) => {
-                        obligations
-                            .extend(self.at(cause, param_env).eq(v1, v2)?.into_obligations());
+                        obligations.extend(
+                            self.at(cause, param_env)
+                                .eq(DefineOpaqueTypes::Yes, v1, v2)?
+                                .into_obligations(),
+                        );
                     }
                     (GenericArgKind::Const(v1), GenericArgKind::Const(v2)) => {
-                        let ok = self.at(cause, param_env).eq(v1, v2)?;
+                        let ok = self.at(cause, param_env).eq(DefineOpaqueTypes::Yes, v1, v2)?;
                         obligations.extend(ok.into_obligations());
                     }
                     _ => {

compiler/rustc_infer/src/infer/combine.rs

@@ -27,7 +27,7 @@ use super::glb::Glb;
 use super::lub::Lub;
 use super::sub::Sub;
 use super::type_variable::TypeVariableValue;
-use super::{InferCtxt, MiscVariable, TypeTrace};
+use super::{DefineOpaqueTypes, InferCtxt, MiscVariable, TypeTrace};
 use crate::traits::{Obligation, PredicateObligations};
 use rustc_data_structures::sso::SsoHashMap;
 use rustc_hir::def_id::DefId;
@@ -52,12 +52,7 @@ pub struct CombineFields<'infcx, 'tcx> {
     pub cause: Option<ty::relate::Cause>,
     pub param_env: ty::ParamEnv<'tcx>,
     pub obligations: PredicateObligations<'tcx>,
-    /// Whether we should define opaque types
-    /// or just treat them opaquely.
-    /// Currently only used to prevent predicate
-    /// matching from matching anything against opaque
-    /// types.
-    pub define_opaque_types: bool,
+    pub define_opaque_types: DefineOpaqueTypes,
 }
 
 #[derive(Copy, Clone, Debug)]

compiler/rustc_infer/src/infer/equate.rs

@@ -1,3 +1,4 @@
+use crate::infer::DefineOpaqueTypes;
 use crate::traits::PredicateObligations;
 
 use super::combine::{CombineFields, ObligationEmittingRelation, RelationDir};
@@ -110,7 +111,8 @@ impl<'tcx> TypeRelation<'tcx> for Equate<'_, '_, 'tcx> {
             }
             (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
             | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
-                if self.fields.define_opaque_types && def_id.is_local() =>
+                if self.fields.define_opaque_types == DefineOpaqueTypes::Yes
+                    && def_id.is_local() =>
             {
                 self.fields.obligations.extend(
                     infcx

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

@@ -1568,6 +1568,9 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
                     ValuePairs::TraitRefs(_) | ValuePairs::PolyTraitRefs(_) => {
                         (false, Mismatch::Fixed("trait"))
                     }
+                    ValuePairs::Aliases(infer::ExpectedFound { expected, .. }) => {
+                        (false, Mismatch::Fixed(self.tcx.def_descr(expected.def_id)))
+                    }
                     ValuePairs::Regions(_) => (false, Mismatch::Fixed("lifetime")),
                 };
                 let Some(vals) = self.values_str(values) else {
@@ -2124,6 +2127,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
         match values {
             infer::Regions(exp_found) => self.expected_found_str(exp_found),
             infer::Terms(exp_found) => self.expected_found_str_term(exp_found),
+            infer::Aliases(exp_found) => self.expected_found_str(exp_found),
             infer::TraitRefs(exp_found) => {
                 let pretty_exp_found = ty::error::ExpectedFound {
                     expected: exp_found.expected.print_only_trait_path(),

compiler/rustc_infer/src/infer/glb.rs

@@ -2,8 +2,8 @@
 
 use super::combine::{CombineFields, ObligationEmittingRelation};
 use super::lattice::{self, LatticeDir};
-use super::InferCtxt;
 use super::Subtype;
+use super::{DefineOpaqueTypes, InferCtxt};
 
 use crate::traits::{ObligationCause, PredicateObligations};
 use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
@@ -142,7 +142,7 @@ impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Glb<'combine, 'infcx,
         Ok(())
     }
 
-    fn define_opaque_types(&self) -> bool {
+    fn define_opaque_types(&self) -> DefineOpaqueTypes {
         self.fields.define_opaque_types
     }
 }

compiler/rustc_infer/src/infer/lattice.rs

@@ -19,7 +19,7 @@
 
 use super::combine::ObligationEmittingRelation;
 use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use super::InferCtxt;
+use super::{DefineOpaqueTypes, InferCtxt};
 
 use crate::traits::ObligationCause;
 use rustc_middle::ty::relate::RelateResult;
@@ -36,7 +36,7 @@ pub trait LatticeDir<'f, 'tcx>: ObligationEmittingRelation<'tcx> {
 
     fn cause(&self) -> &ObligationCause<'tcx>;
 
-    fn define_opaque_types(&self) -> bool;
+    fn define_opaque_types(&self) -> DefineOpaqueTypes;
 
     // Relates the type `v` to `a` and `b` such that `v` represents
     // the LUB/GLB of `a` and `b` as appropriate.
@@ -110,7 +110,7 @@ where
         ) if a_def_id == b_def_id => infcx.super_combine_tys(this, a, b),
         (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
         | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
-            if this.define_opaque_types() && def_id.is_local() =>
+            if this.define_opaque_types() == DefineOpaqueTypes::Yes && def_id.is_local() =>
         {
             this.register_obligations(
                 infcx

compiler/rustc_infer/src/infer/lub.rs

@@ -2,8 +2,8 @@
 
 use super::combine::{CombineFields, ObligationEmittingRelation};
 use super::lattice::{self, LatticeDir};
-use super::InferCtxt;
 use super::Subtype;
+use super::{DefineOpaqueTypes, InferCtxt};
 
 use crate::traits::{ObligationCause, PredicateObligations};
 use rustc_middle::ty::relate::{Relate, RelateResult, TypeRelation};
@@ -142,7 +142,7 @@ impl<'combine, 'infcx, 'tcx> LatticeDir<'infcx, 'tcx> for Lub<'combine, 'infcx,
         Ok(())
     }
 
-    fn define_opaque_types(&self) -> bool {
+    fn define_opaque_types(&self) -> DefineOpaqueTypes {
         self.fields.define_opaque_types
     }
 }

compiler/rustc_infer/src/infer/mod.rs

@@ -1,3 +1,4 @@
+pub use self::at::DefineOpaqueTypes;
 pub use self::freshen::TypeFreshener;
 pub use self::lexical_region_resolve::RegionResolutionError;
 pub use self::LateBoundRegionConversionTime::*;
@@ -338,6 +339,7 @@ pub struct InferCtxt<'tcx> {
 pub enum ValuePairs<'tcx> {
     Regions(ExpectedFound<ty::Region<'tcx>>),
     Terms(ExpectedFound<ty::Term<'tcx>>),
+    Aliases(ExpectedFound<ty::AliasTy<'tcx>>),
     TraitRefs(ExpectedFound<ty::TraitRef<'tcx>>),
     PolyTraitRefs(ExpectedFound<ty::PolyTraitRef<'tcx>>),
     Sigs(ExpectedFound<ty::FnSig<'tcx>>),
@@ -729,7 +731,7 @@ impl<'tcx> InferCtxt<'tcx> {
         &'a self,
         trace: TypeTrace<'tcx>,
         param_env: ty::ParamEnv<'tcx>,
-        define_opaque_types: bool,
+        define_opaque_types: DefineOpaqueTypes,
     ) -> CombineFields<'a, 'tcx> {
         CombineFields {
             infcx: self,
@@ -864,7 +866,7 @@ impl<'tcx> InferCtxt<'tcx> {
         T: at::ToTrace<'tcx>,
     {
         let origin = &ObligationCause::dummy();
-        self.probe(|_| self.at(origin, param_env).sub(a, b).is_ok())
+        self.probe(|_| self.at(origin, param_env).sub(DefineOpaqueTypes::No, a, b).is_ok())
     }
 
     pub fn can_eq<T>(&self, param_env: ty::ParamEnv<'tcx>, a: T, b: T) -> bool
@@ -872,7 +874,7 @@ impl<'tcx> InferCtxt<'tcx> {
         T: at::ToTrace<'tcx>,
     {
         let origin = &ObligationCause::dummy();
-        self.probe(|_| self.at(origin, param_env).eq(a, b).is_ok())
+        self.probe(|_| self.at(origin, param_env).eq(DefineOpaqueTypes::No, a, b).is_ok())
     }
 
     #[instrument(skip(self), level = "debug")]
@@ -967,7 +969,8 @@ impl<'tcx> InferCtxt<'tcx> {
             let ty::SubtypePredicate { a_is_expected, a, b } =
                 self.instantiate_binder_with_placeholders(predicate);
 
-            let ok = self.at(cause, param_env).sub_exp(a_is_expected, a, b)?;
+            let ok =
+                self.at(cause, param_env).sub_exp(DefineOpaqueTypes::No, a_is_expected, a, b)?;
 
             Ok(ok.unit())
         }))

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -1,3 +1,5 @@
+use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
+use super::{DefineOpaqueTypes, InferResult};
 use crate::errors::OpaqueHiddenTypeDiag;
 use crate::infer::{DefiningAnchor, InferCtxt, InferOk};
 use crate::traits;
@@ -16,18 +18,13 @@ use rustc_middle::ty::{
     TypeVisitable, TypeVisitableExt, TypeVisitor,
 };
 use rustc_span::Span;
-
 use std::ops::ControlFlow;
 
-pub type OpaqueTypeMap<'tcx> = VecMap<OpaqueTypeKey<'tcx>, OpaqueTypeDecl<'tcx>>;
-
 mod table;
 
+pub type OpaqueTypeMap<'tcx> = VecMap<OpaqueTypeKey<'tcx>, OpaqueTypeDecl<'tcx>>;
 pub use table::{OpaqueTypeStorage, OpaqueTypeTable};
 
-use super::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use super::InferResult;
-
 /// Information about the opaque types whose values we
 /// are inferring in this function (these are the `impl Trait` that
 /// appear in the return type).
@@ -547,8 +544,7 @@ impl<'tcx> InferCtxt<'tcx> {
         if let Some(prev) = prev {
             obligations = self
                 .at(&cause, param_env)
-                .define_opaque_types(true)
-                .eq_exp(a_is_expected, prev, hidden_ty)?
+                .eq_exp(DefineOpaqueTypes::Yes, a_is_expected, prev, hidden_ty)?
                 .obligations;
         }
 

compiler/rustc_infer/src/infer/sub.rs

@@ -1,5 +1,5 @@
 use super::combine::{CombineFields, RelationDir};
-use super::{ObligationEmittingRelation, SubregionOrigin};
+use super::{DefineOpaqueTypes, ObligationEmittingRelation, SubregionOrigin};
 
 use crate::traits::{Obligation, PredicateObligations};
 use rustc_middle::ty::relate::{Cause, Relate, RelateResult, TypeRelation};
@@ -138,7 +138,8 @@ impl<'tcx> TypeRelation<'tcx> for Sub<'_, '_, 'tcx> {
             }
             (&ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }), _)
             | (_, &ty::Alias(ty::Opaque, ty::AliasTy { def_id, .. }))
-                if self.fields.define_opaque_types && def_id.is_local() =>
+                if self.fields.define_opaque_types == DefineOpaqueTypes::Yes
+                    && def_id.is_local() =>
             {
                 self.fields.obligations.extend(
                     infcx

compiler/rustc_lint/src/lints.rs

@@ -1390,7 +1390,7 @@ pub struct UnusedOp<'a> {
     pub op: &'a str,
     #[label]
     pub label: Span,
-    #[suggestion(style = "verbose", code = "let _ = ", applicability = "machine-applicable")]
+    #[suggestion(style = "verbose", code = "let _ = ", applicability = "maybe-incorrect")]
     pub suggestion: Span,
 }
 
@@ -1434,17 +1434,15 @@ pub struct UnusedDef<'a, 'b> {
 }
 
 #[derive(Subdiagnostic)]
-pub enum UnusedDefSuggestion {
-    #[suggestion(
-        lint_suggestion,
-        style = "verbose",
-        code = "let _ = ",
-        applicability = "machine-applicable"
-    )]
-    Default {
-        #[primary_span]
-        span: Span,
-    },
+#[suggestion(
+    lint_suggestion,
+    style = "verbose",
+    code = "let _ = ",
+    applicability = "maybe-incorrect"
+)]
+pub struct UnusedDefSuggestion {
+    #[primary_span]
+    pub span: Span,
 }
 
 // Needed because of def_path_str

compiler/rustc_lint/src/unused.rs

@@ -123,7 +123,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
         let must_use_result = is_ty_must_use(cx, ty, &expr, expr.span);
         let type_lint_emitted_or_suppressed = match must_use_result {
             Some(path) => {
-                emit_must_use_untranslated(cx, &path, "", "", 1);
+                emit_must_use_untranslated(cx, &path, "", "", 1, false);
                 true
             }
             None => false,
@@ -358,6 +358,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                         descr_pre_path,
                         descr_post_path,
                         1,
+                        false,
                     )
                 })
                 .is_some()
@@ -370,6 +371,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
             descr_pre: &str,
             descr_post: &str,
             plural_len: usize,
+            is_inner: bool,
         ) {
             let plural_suffix = pluralize!(plural_len);
 
@@ -377,20 +379,22 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                 MustUsePath::Suppressed => {}
                 MustUsePath::Boxed(path) => {
                     let descr_pre = &format!("{}boxed ", descr_pre);
-                    emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len);
+                    emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true);
                 }
                 MustUsePath::Opaque(path) => {
                     let descr_pre = &format!("{}implementer{} of ", descr_pre, plural_suffix);
-                    emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len);
+                    emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true);
                 }
                 MustUsePath::TraitObject(path) => {
                     let descr_post = &format!(" trait object{}{}", plural_suffix, descr_post);
-                    emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len);
+                    emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len, true);
                 }
                 MustUsePath::TupleElement(elems) => {
                     for (index, path) in elems {
                         let descr_post = &format!(" in tuple element {}", index);
-                        emit_must_use_untranslated(cx, path, descr_pre, descr_post, plural_len);
+                        emit_must_use_untranslated(
+                            cx, path, descr_pre, descr_post, plural_len, true,
+                        );
                     }
                 }
                 MustUsePath::Array(path, len) => {
@@ -401,6 +405,7 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                         descr_pre,
                         descr_post,
                         plural_len.saturating_add(usize::try_from(*len).unwrap_or(usize::MAX)),
+                        true,
                     );
                 }
                 MustUsePath::Closure(span) => {
@@ -418,19 +423,6 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                     );
                 }
                 MustUsePath::Def(span, def_id, reason) => {
-                    let suggestion = if matches!(
-                        cx.tcx.get_diagnostic_name(*def_id),
-                        Some(sym::add)
-                            | Some(sym::sub)
-                            | Some(sym::mul)
-                            | Some(sym::div)
-                            | Some(sym::rem)
-                            | Some(sym::neg),
-                    ) {
-                        Some(UnusedDefSuggestion::Default { span: span.shrink_to_lo() })
-                    } else {
-                        None
-                    };
                     cx.emit_spanned_lint(
                         UNUSED_MUST_USE,
                         *span,
@@ -440,7 +432,8 @@ impl<'tcx> LateLintPass<'tcx> for UnusedResults {
                             cx,
                             def_id: *def_id,
                             note: *reason,
-                            suggestion,
+                            suggestion: (!is_inner)
+                                .then_some(UnusedDefSuggestion { span: span.shrink_to_lo() }),
                         },
                     );
                 }

compiler/rustc_middle/src/mir/syntax.rs

@@ -1081,7 +1081,7 @@ pub enum Rvalue<'tcx> {
     /// Same as `BinaryOp`, but yields `(T, bool)` with a `bool` indicating an error condition.
     ///
     /// For addition, subtraction, and multiplication on integers the error condition is set when
-    /// the infinite precision result would be unequal to the actual result.
+    /// the infinite precision result would not be equal to the actual result.
     ///
     /// Other combinations of types and operators are unsupported.
     CheckedBinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),

compiler/rustc_middle/src/query/mod.rs

@@ -2215,7 +2215,7 @@ rustc_queries! {
     }
 
     /// Used in `super_combine_consts` to ICE if the type of the two consts are definitely not going to end up being
-    /// equal to eachother. This might return `Ok` even if the types are unequal, but will never return `Err` if
+    /// equal to eachother. This might return `Ok` even if the types are not equal, but will never return `Err` if
     /// the types might be equal.
     query check_tys_might_be_eq(arg: Canonical<'tcx, (ty::ParamEnv<'tcx>, Ty<'tcx>, Ty<'tcx>)>) -> Result<(), NoSolution> {
         desc { "check whether two const param are definitely not equal to eachother"}

compiler/rustc_middle/src/ty/consts/int.rs

@@ -237,7 +237,7 @@ impl ScalarInt {
     }
 
     /// Tries to convert the `ScalarInt` to an unsigned integer of the given size.
-    /// Fails if the size of the `ScalarInt` is unequal to `size` and returns the
+    /// Fails if the size of the `ScalarInt` is not equal to `size` and returns the
     /// `ScalarInt`s size in that case.
     #[inline]
     pub fn try_to_uint(self, size: Size) -> Result<u128, Size> {
@@ -297,7 +297,7 @@ impl ScalarInt {
     }
 
     /// Tries to convert the `ScalarInt` to a signed integer of the given size.
-    /// Fails if the size of the `ScalarInt` is unequal to `size` and returns the
+    /// Fails if the size of the `ScalarInt` is not equal to `size` and returns the
     /// `ScalarInt`s size in that case.
     #[inline]
     pub fn try_to_int(self, size: Size) -> Result<i128, Size> {
@@ -306,35 +306,35 @@ impl ScalarInt {
     }
 
     /// Tries to convert the `ScalarInt` to i8.
-    /// Fails if the size of the `ScalarInt` is unequal to `Size { raw: 1 }`
+    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 1 }`
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i8(self) -> Result<i8, Size> {
         self.try_to_int(Size::from_bits(8)).map(|v| i8::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i16.
-    /// Fails if the size of the `ScalarInt` is unequal to `Size { raw: 2 }`
+    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 2 }`
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i16(self) -> Result<i16, Size> {
         self.try_to_int(Size::from_bits(16)).map(|v| i16::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i32.
-    /// Fails if the size of the `ScalarInt` is unequal to `Size { raw: 4 }`
+    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 4 }`
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i32(self) -> Result<i32, Size> {
         self.try_to_int(Size::from_bits(32)).map(|v| i32::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i64.
-    /// Fails if the size of the `ScalarInt` is unequal to `Size { raw: 8 }`
+    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 8 }`
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i64(self) -> Result<i64, Size> {
         self.try_to_int(Size::from_bits(64)).map(|v| i64::try_from(v).unwrap())
     }
 
     /// Tries to convert the `ScalarInt` to i128.
-    /// Fails if the size of the `ScalarInt` is unequal to `Size { raw: 16 }`
+    /// Fails if the size of the `ScalarInt` is not equal to `Size { raw: 16 }`
     /// and returns the `ScalarInt`s size in that case.
     pub fn try_to_i128(self) -> Result<i128, Size> {
         self.try_to_int(Size::from_bits(128)).map(|v| i128::try_from(v).unwrap())

compiler/rustc_middle/src/ty/context.rs

@@ -71,6 +71,7 @@ use rustc_type_ir::WithCachedTypeInfo;
 use rustc_type_ir::{CollectAndApply, DynKind, Interner, TypeFlags};
 
 use std::any::Any;
+use std::assert_matches::debug_assert_matches;
 use std::borrow::Borrow;
 use std::cmp::Ordering;
 use std::fmt;
@@ -2049,6 +2050,12 @@ impl<'tcx> TyCtxt<'tcx> {
 
     #[inline]
     pub fn mk_alias(self, kind: ty::AliasKind, alias_ty: ty::AliasTy<'tcx>) -> Ty<'tcx> {
+        debug_assert_matches!(
+            (kind, self.def_kind(alias_ty.def_id)),
+            (ty::Opaque, DefKind::OpaqueTy)
+                | (ty::Projection, DefKind::AssocTy)
+                | (ty::Opaque | ty::Projection, DefKind::ImplTraitPlaceholder)
+        );
         self.mk_ty_from_kind(Alias(kind, alias_ty))
     }
 

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1289,25 +1289,41 @@ impl<'a: 'ast, 'ast, 'tcx> LateResolutionVisitor<'a, '_, 'ast, 'tcx> {
                 PathSource::Expr(_) | PathSource::TupleStruct(..) | PathSource::Pat => {
                     let span = find_span(&source, err);
                     err.span_label(self.r.def_span(def_id), &format!("`{path_str}` defined here"));
-                    let (tail, descr, applicability) = match source {
-                        PathSource::Pat | PathSource::TupleStruct(..) => {
-                            ("", "pattern", Applicability::MachineApplicable)
-                        }
-                        _ => (": val", "literal", Applicability::HasPlaceholders),
-                    };
 
+                    let (tail, descr, applicability, old_fields) = match source {
+                        PathSource::Pat => ("", "pattern", Applicability::MachineApplicable, None),
+                        PathSource::TupleStruct(_, args) => (
+                            "",
+                            "pattern",
+                            Applicability::MachineApplicable,
+                            Some(
+                                args.iter()
+                                    .map(|a| self.r.tcx.sess.source_map().span_to_snippet(*a).ok())
+                                    .collect::<Vec<Option<String>>>(),
+                            ),
+                        ),
+                        _ => (": val", "literal", Applicability::HasPlaceholders, None),
+                    };
                     let field_ids = self.r.field_def_ids(def_id);
                     let (fields, applicability) = match field_ids {
-                        Some(field_ids) => (
-                            field_ids
-                                .iter()
-                                .map(|&field_id| {
-                                    format!("{}{tail}", self.r.tcx.item_name(field_id))
-                                })
-                                .collect::<Vec<String>>()
-                                .join(", "),
-                            applicability,
-                        ),
+                        Some(field_ids) => {
+                            let fields = field_ids.iter().map(|&id| self.r.tcx.item_name(id));
+
+                            let fields = if let Some(old_fields) = old_fields {
+                                fields
+                                    .enumerate()
+                                    .map(|(idx, new)| (new, old_fields.get(idx)))
+                                    .map(|(new, old)| {
+                                        let new = new.to_ident_string();
+                                        if let Some(Some(old)) = old && new != *old { format!("{}: {}", new, old) } else { new }
+                                    })
+                                    .collect::<Vec<String>>()
+                            } else {
+                                fields.map(|f| format!("{f}{tail}")).collect::<Vec<String>>()
+                            };
+
+                            (fields.join(", "), applicability)
+                        }
                         None => ("/* fields */".to_string(), Applicability::HasPlaceholders),
                     };
                     let pad = match field_ids {

compiler/rustc_trait_selection/src/solve/eval_ctxt.rs

@@ -2,7 +2,7 @@ use rustc_hir::def_id::DefId;
 use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::CanonicalVarValues;
 use rustc_infer::infer::type_variable::{TypeVariableOrigin, TypeVariableOriginKind};
-use rustc_infer::infer::{InferCtxt, InferOk, LateBoundRegionConversionTime};
+use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk, LateBoundRegionConversionTime};
 use rustc_infer::traits::query::NoSolution;
 use rustc_infer::traits::ObligationCause;
 use rustc_middle::infer::unify_key::{ConstVariableOrigin, ConstVariableOriginKind};
@@ -144,7 +144,7 @@ impl<'tcx> EvalCtxt<'_, 'tcx> {
     ) -> Result<Vec<Goal<'tcx, ty::Predicate<'tcx>>>, NoSolution> {
         self.infcx
             .at(&ObligationCause::dummy(), param_env)
-            .eq(lhs, rhs)
+            .eq(DefineOpaqueTypes::No, lhs, rhs)
             .map(|InferOk { value: (), obligations }| {
                 obligations.into_iter().map(|o| o.into()).collect()
             })

compiler/rustc_trait_selection/src/solve/mod.rs

@@ -19,7 +19,7 @@ use std::mem;
 
 use rustc_hir::def_id::DefId;
 use rustc_infer::infer::canonical::{Canonical, CanonicalVarValues};
-use rustc_infer::infer::{InferCtxt, InferOk, TyCtxtInferExt};
+use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk, TyCtxtInferExt};
 use rustc_infer::traits::query::NoSolution;
 use rustc_middle::traits::solve::{
     CanonicalGoal, CanonicalResponse, Certainty, ExternalConstraints, ExternalConstraintsData,
@@ -268,7 +268,7 @@ impl<'a, 'tcx> EvalCtxt<'a, 'tcx> {
             let InferOk { value: (), obligations } = self
                 .infcx
                 .at(&ObligationCause::dummy(), goal.param_env)
-                .sub(goal.predicate.a, goal.predicate.b)?;
+                .sub(DefineOpaqueTypes::No, goal.predicate.a, goal.predicate.b)?;
             self.evaluate_all_and_make_canonical_response(
                 obligations.into_iter().map(|pred| pred.into()).collect(),
             )

compiler/rustc_trait_selection/src/traits/auto_trait.rs

@@ -7,6 +7,7 @@ use crate::errors::UnableToConstructConstantValue;
 use crate::infer::region_constraints::{Constraint, RegionConstraintData};
 use crate::infer::InferCtxt;
 use crate::traits::project::ProjectAndUnifyResult;
+use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_middle::mir::interpret::ErrorHandled;
 use rustc_middle::ty::fold::{TypeFolder, TypeSuperFoldable};
 use rustc_middle::ty::visit::TypeVisitableExt;
@@ -814,7 +815,7 @@ impl<'tcx> AutoTraitFinder<'tcx> {
 
                     match (evaluate(c1), evaluate(c2)) {
                         (Ok(c1), Ok(c2)) => {
-                            match selcx.infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
+                            match selcx.infcx.at(&obligation.cause, obligation.param_env).eq(DefineOpaqueTypes::No,c1, c2)
                             {
                                 Ok(_) => (),
                                 Err(_) => return false,

compiler/rustc_trait_selection/src/traits/coherence.rs

@@ -17,7 +17,7 @@ use crate::traits::{
 use rustc_data_structures::fx::FxIndexSet;
 use rustc_errors::Diagnostic;
 use rustc_hir::def_id::{DefId, CRATE_DEF_ID, LOCAL_CRATE};
-use rustc_infer::infer::{DefiningAnchor, InferCtxt, TyCtxtInferExt};
+use rustc_infer::infer::{DefineOpaqueTypes, DefiningAnchor, InferCtxt, TyCtxtInferExt};
 use rustc_infer::traits::util;
 use rustc_middle::traits::specialization_graph::OverlapMode;
 use rustc_middle::ty::fast_reject::{DeepRejectCtxt, TreatParams};
@@ -181,7 +181,7 @@ fn overlap_within_probe<'cx, 'tcx>(
     let impl1_header = with_fresh_ty_vars(selcx, param_env, impl1_def_id);
     let impl2_header = with_fresh_ty_vars(selcx, param_env, impl2_def_id);
 
-    let obligations = equate_impl_headers(selcx, &impl1_header, &impl2_header)?;
+    let obligations = equate_impl_headers(selcx.infcx, &impl1_header, &impl2_header)?;
     debug!("overlap: unification check succeeded");
 
     if overlap_mode.use_implicit_negative() {
@@ -207,20 +207,25 @@ fn overlap_within_probe<'cx, 'tcx>(
     Some(OverlapResult { impl_header, intercrate_ambiguity_causes, involves_placeholder })
 }
 
-fn equate_impl_headers<'cx, 'tcx>(
-    selcx: &mut SelectionContext<'cx, 'tcx>,
-    impl1_header: &ty::ImplHeader<'tcx>,
-    impl2_header: &ty::ImplHeader<'tcx>,
+#[instrument(level = "debug", skip(infcx), ret)]
+fn equate_impl_headers<'tcx>(
+    infcx: &InferCtxt<'tcx>,
+    impl1: &ty::ImplHeader<'tcx>,
+    impl2: &ty::ImplHeader<'tcx>,
 ) -> Option<PredicateObligations<'tcx>> {
-    // Do `a` and `b` unify? If not, no overlap.
-    debug!("equate_impl_headers(impl1_header={:?}, impl2_header={:?}", impl1_header, impl2_header);
-    selcx
-        .infcx
-        .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
-        .define_opaque_types(true)
-        .eq_impl_headers(impl1_header, impl2_header)
-        .map(|infer_ok| infer_ok.obligations)
-        .ok()
+    let result = match (impl1.trait_ref, impl2.trait_ref) {
+        (Some(impl1_ref), Some(impl2_ref)) => infcx
+            .at(&ObligationCause::dummy(), ty::ParamEnv::empty())
+            .eq(DefineOpaqueTypes::Yes, impl1_ref, impl2_ref),
+        (None, None) => infcx.at(&ObligationCause::dummy(), ty::ParamEnv::empty()).eq(
+            DefineOpaqueTypes::Yes,
+            impl1.self_ty,
+            impl2.self_ty,
+        ),
+        _ => bug!("mk_eq_impl_headers given mismatched impl kinds"),
+    };
+
+    result.map(|infer_ok| infer_ok.obligations).ok()
 }
 
 /// Given impl1 and impl2 check if both impls can be satisfied by a common type (including
@@ -325,7 +330,7 @@ fn equate<'tcx>(
 ) -> bool {
     // do the impls unify? If not, not disjoint.
     let Ok(InferOk { obligations: more_obligations, .. }) =
-        infcx.at(&ObligationCause::dummy(), impl_env).eq(subject1, subject2)
+        infcx.at(&ObligationCause::dummy(), impl_env).eq(DefineOpaqueTypes::No,subject1, subject2)
     else {
         debug!("explicit_disjoint: {:?} does not unify with {:?}", subject1, subject2);
         return true;

compiler/rustc_trait_selection/src/traits/engine.rs

@@ -11,7 +11,7 @@ use rustc_infer::infer::at::ToTrace;
 use rustc_infer::infer::canonical::{
     Canonical, CanonicalQueryResponse, CanonicalVarValues, QueryResponse,
 };
-use rustc_infer::infer::{InferCtxt, InferOk};
+use rustc_infer::infer::{DefineOpaqueTypes, InferCtxt, InferOk};
 use rustc_infer::traits::query::Fallible;
 use rustc_infer::traits::{
     FulfillmentError, Obligation, ObligationCause, PredicateObligation, TraitEngineExt as _,
@@ -128,8 +128,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
     {
         self.infcx
             .at(cause, param_env)
-            .define_opaque_types(true)
-            .eq_exp(a_is_expected, a, b)
+            .eq_exp(DefineOpaqueTypes::Yes, a_is_expected, a, b)
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 
@@ -142,8 +141,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
     ) -> Result<(), TypeError<'tcx>> {
         self.infcx
             .at(cause, param_env)
-            .define_opaque_types(true)
-            .eq(expected, actual)
+            .eq(DefineOpaqueTypes::Yes, expected, actual)
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 
@@ -157,8 +155,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
     ) -> Result<(), TypeError<'tcx>> {
         self.infcx
             .at(cause, param_env)
-            .define_opaque_types(true)
-            .sub(expected, actual)
+            .sub(DefineOpaqueTypes::Yes, expected, actual)
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 
@@ -172,8 +169,7 @@ impl<'a, 'tcx> ObligationCtxt<'a, 'tcx> {
     ) -> Result<(), TypeError<'tcx>> {
         self.infcx
             .at(cause, param_env)
-            .define_opaque_types(true)
-            .sup(expected, actual)
+            .sup(DefineOpaqueTypes::Yes, expected, actual)
             .map(|infer_ok| self.register_infer_ok_obligations(infer_ok))
     }
 

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -2,6 +2,7 @@ use crate::infer::{InferCtxt, TyOrConstInferVar};
 use rustc_data_structures::obligation_forest::ProcessResult;
 use rustc_data_structures::obligation_forest::{Error, ForestObligation, Outcome};
 use rustc_data_structures::obligation_forest::{ObligationForest, ObligationProcessor};
+use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::traits::ProjectionCacheKey;
 use rustc_infer::traits::{SelectionError, TraitEngine, TraitObligation};
 use rustc_middle::mir::interpret::ErrorHandled;
@@ -515,7 +516,7 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                                 if let Ok(new_obligations) = infcx
                                     .at(&obligation.cause, obligation.param_env)
                                     .trace(c1, c2)
-                                    .eq(a.substs, b.substs)
+                                    .eq(DefineOpaqueTypes::No, a.substs, b.substs)
                                 {
                                     return ProcessResult::Changed(mk_pending(
                                         new_obligations.into_obligations(),
@@ -524,8 +525,9 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                             }
                             (_, Unevaluated(_)) | (Unevaluated(_), _) => (),
                             (_, _) => {
-                                if let Ok(new_obligations) =
-                                    infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
+                                if let Ok(new_obligations) = infcx
+                                    .at(&obligation.cause, obligation.param_env)
+                                    .eq(DefineOpaqueTypes::No, c1, c2)
                                 {
                                     return ProcessResult::Changed(mk_pending(
                                         new_obligations.into_obligations(),
@@ -565,12 +567,11 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
 
                     match (evaluate(c1), evaluate(c2)) {
                         (Ok(c1), Ok(c2)) => {
-                            match self
-                                .selcx
-                                .infcx
-                                .at(&obligation.cause, obligation.param_env)
-                                .eq(c1, c2)
-                            {
+                            match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
+                                DefineOpaqueTypes::No,
+                                c1,
+                                c2,
+                            ) {
                                 Ok(inf_ok) => {
                                     ProcessResult::Changed(mk_pending(inf_ok.into_obligations()))
                                 }
@@ -610,12 +611,11 @@ impl<'a, 'tcx> ObligationProcessor for FulfillProcessor<'a, 'tcx> {
                     bug!("AliasEq is only used for new solver")
                 }
                 ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
-                    match self
-                        .selcx
-                        .infcx
-                        .at(&obligation.cause, obligation.param_env)
-                        .eq(ct.ty(), ty)
-                    {
+                    match self.selcx.infcx.at(&obligation.cause, obligation.param_env).eq(
+                        DefineOpaqueTypes::No,
+                        ct.ty(),
+                        ty,
+                    ) {
                         Ok(inf_ok) => ProcessResult::Changed(mk_pending(inf_ok.into_obligations())),
                         Err(_) => ProcessResult::Error(FulfillmentErrorCode::CodeSelectionError(
                             SelectionError::Unimplemented,

compiler/rustc_trait_selection/src/traits/project.rs

@@ -28,6 +28,7 @@ use rustc_hir::def::DefKind;
 use rustc_hir::lang_items::LangItem;
 use rustc_infer::infer::at::At;
 use rustc_infer::infer::resolve::OpportunisticRegionResolver;
+use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::traits::ImplSourceBuiltinData;
 use rustc_middle::traits::select::OverflowError;
 use rustc_middle::ty::fold::{TypeFoldable, TypeFolder, TypeSuperFoldable};
@@ -285,12 +286,12 @@ fn project_and_unify_type<'cx, 'tcx>(
         );
     obligations.extend(new);
 
-    match infcx
-        .at(&obligation.cause, obligation.param_env)
-        // This is needed to support nested opaque types like `impl Fn() -> impl Trait`
-        .define_opaque_types(true)
-        .eq(normalized, actual)
-    {
+    // Need to define opaque types to support nested opaque types like `impl Fn() -> impl Trait`
+    match infcx.at(&obligation.cause, obligation.param_env).eq(
+        DefineOpaqueTypes::Yes,
+        normalized,
+        actual,
+    ) {
         Ok(InferOk { obligations: inferred_obligations, value: () }) => {
             obligations.extend(inferred_obligations);
             ProjectAndUnifyResult::Holds(obligations)
@@ -467,6 +468,11 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
             return ty;
         }
 
+        let (kind, data) = match *ty.kind() {
+            ty::Alias(kind, alias_ty) => (kind, alias_ty),
+            _ => return ty.super_fold_with(self),
+        };
+
         // We try to be a little clever here as a performance optimization in
         // cases where there are nested projections under binders.
         // For example:
@@ -490,13 +496,11 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
         // replace bound vars if the current type is a `Projection` and we need
         // to make sure we don't forget to fold the substs regardless.
 
-        match *ty.kind() {
+        match kind {
             // This is really important. While we *can* handle this, this has
             // severe performance implications for large opaque types with
             // late-bound regions. See `issue-88862` benchmark.
-            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. })
-                if !substs.has_escaping_bound_vars() =>
-            {
+            ty::Opaque if !data.substs.has_escaping_bound_vars() => {
                 // Only normalize `impl Trait` outside of type inference, usually in codegen.
                 match self.param_env.reveal() {
                     Reveal::UserFacing => ty.super_fold_with(self),
@@ -512,8 +516,8 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
                             );
                         }
 
-                        let substs = substs.fold_with(self);
-                        let generic_ty = self.interner().type_of(def_id);
+                        let substs = data.substs.fold_with(self);
+                        let generic_ty = self.interner().type_of(data.def_id);
                         let concrete_ty = generic_ty.subst(self.interner(), substs);
                         self.depth += 1;
                         let folded_ty = self.fold_ty(concrete_ty);
@@ -522,8 +526,9 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
                     }
                 }
             }
+            ty::Opaque => ty.super_fold_with(self),
 
-            ty::Alias(ty::Projection, data) if !data.has_escaping_bound_vars() => {
+            ty::Projection if !data.has_escaping_bound_vars() => {
                 // This branch is *mostly* just an optimization: when we don't
                 // have escaping bound vars, we don't need to replace them with
                 // placeholders (see branch below). *Also*, we know that we can
@@ -562,7 +567,7 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
                 normalized_ty.ty().unwrap()
             }
 
-            ty::Alias(ty::Projection, data) => {
+            ty::Projection => {
                 // If there are escaping bound vars, we temporarily replace the
                 // bound vars with placeholders. Note though, that in the case
                 // that we still can't project for whatever reason (e.g. self
@@ -611,8 +616,6 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx
                 );
                 normalized_ty
             }
-
-            _ => ty.super_fold_with(self),
         }
     }
 
@@ -2064,7 +2067,11 @@ fn confirm_param_env_candidate<'cx, 'tcx>(
 
     debug!(?cache_projection, ?obligation_projection);
 
-    match infcx.at(cause, param_env).eq(cache_projection, obligation_projection) {
+    match infcx.at(cause, param_env).eq(
+        DefineOpaqueTypes::No,
+        cache_projection,
+        obligation_projection,
+    ) {
         Ok(InferOk { value: _, obligations }) => {
             nested_obligations.extend(obligations);
             assoc_ty_own_obligations(selcx, obligation, &mut nested_obligations);

compiler/rustc_trait_selection/src/traits/query/normalize.rs

@@ -197,23 +197,30 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
             return Ok(*ty);
         }
 
+        let (kind, data) = match *ty.kind() {
+            ty::Alias(kind, data) => (kind, data),
+            _ => {
+                let res = ty.try_super_fold_with(self)?;
+                self.cache.insert(ty, res);
+                return Ok(res);
+            }
+        };
+
         // See note in `rustc_trait_selection::traits::project` about why we
         // wait to fold the substs.
 
         // Wrap this in a closure so we don't accidentally return from the outer function
-        let res = match *ty.kind() {
+        let res = match kind {
             // This is really important. While we *can* handle this, this has
             // severe performance implications for large opaque types with
             // late-bound regions. See `issue-88862` benchmark.
-            ty::Alias(ty::Opaque, ty::AliasTy { def_id, substs, .. })
-                if !substs.has_escaping_bound_vars() =>
-            {
+            ty::Opaque if !data.substs.has_escaping_bound_vars() => {
                 // Only normalize `impl Trait` outside of type inference, usually in codegen.
                 match self.param_env.reveal() {
                     Reveal::UserFacing => ty.try_super_fold_with(self)?,
 
                     Reveal::All => {
-                        let substs = substs.try_fold_with(self)?;
+                        let substs = data.substs.try_fold_with(self)?;
                         let recursion_limit = self.interner().recursion_limit();
                         if !recursion_limit.value_within_limit(self.anon_depth) {
                             // A closure or generator may have itself as in its upvars.
@@ -228,7 +235,7 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                             return ty.try_super_fold_with(self);
                         }
 
-                        let generic_ty = self.interner().type_of(def_id);
+                        let generic_ty = self.interner().type_of(data.def_id);
                         let concrete_ty = generic_ty.subst(self.interner(), substs);
                         self.anon_depth += 1;
                         if concrete_ty == ty {
@@ -248,62 +255,22 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                 }
             }
 
-            ty::Alias(ty::Projection, data) if !data.has_escaping_bound_vars() => {
-                // This branch is just an optimization: when we don't have escaping bound vars,
-                // we don't need to replace them with placeholders (see branch below).
+            ty::Opaque => ty.try_super_fold_with(self)?,
 
-                let tcx = self.infcx.tcx;
-                let data = data.try_fold_with(self)?;
-
-                let mut orig_values = OriginalQueryValues::default();
-                // HACK(matthewjasper) `'static` is special-cased in selection,
-                // so we cannot canonicalize it.
-                let c_data = self
-                    .infcx
-                    .canonicalize_query_keep_static(self.param_env.and(data), &mut orig_values);
-                debug!("QueryNormalizer: c_data = {:#?}", c_data);
-                debug!("QueryNormalizer: orig_values = {:#?}", orig_values);
-                let result = tcx.normalize_projection_ty(c_data)?;
-                // We don't expect ambiguity.
-                if result.is_ambiguous() {
-                    // Rustdoc normalizes possibly not well-formed types, so only
-                    // treat this as a bug if we're not in rustdoc.
-                    if !tcx.sess.opts.actually_rustdoc {
-                        tcx.sess.delay_span_bug(
-                            DUMMY_SP,
-                            format!("unexpected ambiguity: {:?} {:?}", c_data, result),
-                        );
-                    }
-                    return Err(NoSolution);
-                }
-                let InferOk { value: result, obligations } =
-                    self.infcx.instantiate_query_response_and_region_obligations(
-                        self.cause,
-                        self.param_env,
-                        &orig_values,
-                        result,
-                    )?;
-                debug!("QueryNormalizer: result = {:#?}", result);
-                debug!("QueryNormalizer: obligations = {:#?}", obligations);
-                self.obligations.extend(obligations);
-
-                let res = result.normalized_ty;
-                // `tcx.normalize_projection_ty` may normalize to a type that still has
-                // unevaluated consts, so keep normalizing here if that's the case.
-                if res != ty && res.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION) {
-                    res.try_super_fold_with(self)?
-                } else {
-                    res
-                }
-            }
-
-            ty::Alias(ty::Projection, data) => {
+            ty::Projection => {
                 // See note in `rustc_trait_selection::traits::project`
 
                 let tcx = self.infcx.tcx;
                 let infcx = self.infcx;
-                let (data, mapped_regions, mapped_types, mapped_consts) =
-                    BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
+                // Just an optimization: When we don't have escaping bound vars,
+                // we don't need to replace them with placeholders.
+                let (data, maps) = if data.has_escaping_bound_vars() {
+                    let (data, mapped_regions, mapped_types, mapped_consts) =
+                        BoundVarReplacer::replace_bound_vars(infcx, &mut self.universes, data);
+                    (data, Some((mapped_regions, mapped_types, mapped_consts)))
+                } else {
+                    (data, None)
+                };
                 let data = data.try_fold_with(self)?;
 
                 let mut orig_values = OriginalQueryValues::default();
@@ -337,14 +304,18 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                 debug!("QueryNormalizer: result = {:#?}", result);
                 debug!("QueryNormalizer: obligations = {:#?}", obligations);
                 self.obligations.extend(obligations);
-                let res = PlaceholderReplacer::replace_placeholders(
-                    infcx,
-                    mapped_regions,
-                    mapped_types,
-                    mapped_consts,
-                    &self.universes,
-                    result.normalized_ty,
-                );
+                let res = if let Some((mapped_regions, mapped_types, mapped_consts)) = maps {
+                    PlaceholderReplacer::replace_placeholders(
+                        infcx,
+                        mapped_regions,
+                        mapped_types,
+                        mapped_consts,
+                        &self.universes,
+                        result.normalized_ty,
+                    )
+                } else {
+                    result.normalized_ty
+                };
                 // `tcx.normalize_projection_ty` may normalize to a type that still has
                 // unevaluated consts, so keep normalizing here if that's the case.
                 if res != ty && res.has_type_flags(ty::TypeFlags::HAS_CT_PROJECTION) {
@@ -353,8 +324,6 @@ impl<'cx, 'tcx> FallibleTypeFolder<TyCtxt<'tcx>> for QueryNormalizer<'cx, 'tcx>
                     res
                 }
             }
-
-            _ => ty.try_super_fold_with(self)?,
         };
 
         self.cache.insert(ty, res);

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -8,8 +8,8 @@
 //! https://rustc-dev-guide.rust-lang.org/traits/resolution.html#confirmation
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_hir::lang_items::LangItem;
-use rustc_infer::infer::InferOk;
 use rustc_infer::infer::LateBoundRegionConversionTime::HigherRankedType;
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk};
 use rustc_middle::ty::{
     self, Binder, GenericParamDefKind, InternalSubsts, SubstsRef, ToPolyTraitRef, ToPredicate,
     TraitRef, Ty, TyCtxt, TypeVisitableExt,
@@ -177,7 +177,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         obligations.extend(self.infcx.commit_if_ok(|_| {
             self.infcx
                 .at(&obligation.cause, obligation.param_env)
-                .sup(placeholder_trait_predicate, candidate)
+                .sup(DefineOpaqueTypes::No, placeholder_trait_predicate, candidate)
                 .map(|InferOk { obligations, .. }| obligations)
                 .map_err(|_| Unimplemented)
         })?);
@@ -462,7 +462,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         nested.extend(self.infcx.commit_if_ok(|_| {
             self.infcx
                 .at(&obligation.cause, obligation.param_env)
-                .sup(obligation_trait_ref, upcast_trait_ref)
+                .sup(DefineOpaqueTypes::No, obligation_trait_ref, upcast_trait_ref)
                 .map(|InferOk { obligations, .. }| obligations)
                 .map_err(|_| Unimplemented)
         })?);
@@ -827,11 +827,10 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 )
             });
 
+        // needed to define opaque types for tests/ui/type-alias-impl-trait/assoc-projection-ice.rs
         self.infcx
             .at(&obligation.cause, obligation.param_env)
-            // needed for tests/ui/type-alias-impl-trait/assoc-projection-ice.rs
-            .define_opaque_types(true)
-            .sup(obligation_trait_ref, expected_trait_ref)
+            .sup(DefineOpaqueTypes::Yes, obligation_trait_ref, expected_trait_ref)
             .map(|InferOk { mut obligations, .. }| {
                 obligations.extend(nested);
                 obligations
@@ -896,7 +895,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let InferOk { obligations, .. } = self
                     .infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .sup(target, source_trait)
+                    .sup(DefineOpaqueTypes::No, target, source_trait)
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
 
@@ -995,7 +994,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let InferOk { obligations, .. } = self
                     .infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .sup(target, source_trait)
+                    .sup(DefineOpaqueTypes::No, target, source_trait)
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
 
@@ -1066,7 +1065,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let InferOk { obligations, .. } = self
                     .infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .eq(b, a)
+                    .eq(DefineOpaqueTypes::No, b, a)
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
             }
@@ -1114,7 +1113,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let InferOk { obligations, .. } = self
                     .infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .eq(target, new_struct)
+                    .eq(DefineOpaqueTypes::No, target, new_struct)
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
 
@@ -1144,7 +1143,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 let InferOk { obligations, .. } = self
                     .infcx
                     .at(&obligation.cause, obligation.param_env)
-                    .eq(target, new_tuple)
+                    .eq(DefineOpaqueTypes::No, target, new_tuple)
                     .map_err(|_| Unimplemented)?;
                 nested.extend(obligations);
 

compiler/rustc_trait_selection/src/traits/select/mod.rs

@@ -38,6 +38,7 @@ use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_errors::Diagnostic;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
+use rustc_infer::infer::DefineOpaqueTypes;
 use rustc_infer::infer::LateBoundRegionConversionTime;
 use rustc_infer::traits::TraitEngine;
 use rustc_infer::traits::TraitEngineExt;
@@ -912,7 +913,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                     .infcx
                                     .at(&obligation.cause, obligation.param_env)
                                     .trace(c1, c2)
-                                    .eq(a.substs, b.substs)
+                                    .eq(DefineOpaqueTypes::No, a.substs, b.substs)
                                 {
                                     let mut obligations = new_obligations.obligations;
                                     self.add_depth(
@@ -930,7 +931,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                                 if let Ok(new_obligations) = self
                                     .infcx
                                     .at(&obligation.cause, obligation.param_env)
-                                    .eq(c1, c2)
+                                    .eq(DefineOpaqueTypes::No, c1, c2)
                                 {
                                     let mut obligations = new_obligations.obligations;
                                     self.add_depth(
@@ -964,8 +965,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
 
                     match (evaluate(c1), evaluate(c2)) {
                         (Ok(c1), Ok(c2)) => {
-                            match self.infcx.at(&obligation.cause, obligation.param_env).eq(c1, c2)
-                            {
+                            match self.infcx.at(&obligation.cause, obligation.param_env).eq(
+                                DefineOpaqueTypes::No,
+                                c1,
+                                c2,
+                            ) {
                                 Ok(inf_ok) => self.evaluate_predicates_recursively(
                                     previous_stack,
                                     inf_ok.into_obligations(),
@@ -993,7 +997,11 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                 }
                 ty::PredicateKind::Ambiguous => Ok(EvaluatedToAmbig),
                 ty::PredicateKind::Clause(ty::Clause::ConstArgHasType(ct, ty)) => {
-                    match self.infcx.at(&obligation.cause, obligation.param_env).eq(ct.ty(), ty) {
+                    match self.infcx.at(&obligation.cause, obligation.param_env).eq(
+                        DefineOpaqueTypes::No,
+                        ct.ty(),
+                        ty,
+                    ) {
                         Ok(inf_ok) => self.evaluate_predicates_recursively(
                             previous_stack,
                             inf_ok.into_obligations(),
@@ -1751,7 +1759,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         });
         self.infcx
             .at(&obligation.cause, obligation.param_env)
-            .sup(ty::Binder::dummy(placeholder_trait_ref), trait_bound)
+            .sup(DefineOpaqueTypes::No, ty::Binder::dummy(placeholder_trait_ref), trait_bound)
             .map(|InferOk { obligations: _, value: () }| {
                 // This method is called within a probe, so we can't have
                 // inference variables and placeholders escape.
@@ -1813,7 +1821,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         let is_match = self
             .infcx
             .at(&obligation.cause, obligation.param_env)
-            .sup(obligation.predicate, infer_projection)
+            .sup(DefineOpaqueTypes::No, obligation.predicate, infer_projection)
             .map_or(false, |InferOk { obligations, value: () }| {
                 self.evaluate_predicates_recursively(
                     TraitObligationStackList::empty(&ProvisionalEvaluationCache::default()),
@@ -2534,7 +2542,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
         let InferOk { obligations, .. } = self
             .infcx
             .at(&cause, obligation.param_env)
-            .eq(placeholder_obligation_trait_ref, impl_trait_ref)
+            .eq(DefineOpaqueTypes::No, placeholder_obligation_trait_ref, impl_trait_ref)
             .map_err(|e| {
                 debug!("match_impl: failed eq_trait_refs due to `{}`", e.to_string(self.tcx()))
             })?;
@@ -2584,7 +2592,7 @@ impl<'tcx> SelectionContext<'_, 'tcx> {
     ) -> Result<Vec<PredicateObligation<'tcx>>, ()> {
         self.infcx
             .at(&obligation.cause, obligation.param_env)
-            .sup(obligation.predicate.to_poly_trait_ref(), poly_trait_ref)
+            .sup(DefineOpaqueTypes::No, obligation.predicate.to_poly_trait_ref(), poly_trait_ref)
             .map(|InferOk { obligations, .. }| obligations)
             .map_err(|_| ())
     }

compiler/rustc_trait_selection/src/traits/specialize/mod.rs

@@ -10,6 +10,7 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/traits/specialization.html
 
 pub mod specialization_graph;
+use rustc_infer::infer::DefineOpaqueTypes;
 use specialization_graph::GraphExt;
 
 use crate::errors::NegativePositiveConflict;
@@ -193,7 +194,7 @@ fn fulfill_implication<'tcx>(
 
     // do the impls unify? If not, no specialization.
     let Ok(InferOk { obligations: more_obligations, .. }) =
-        infcx.at(&ObligationCause::dummy(), param_env).eq(source_trait, target_trait)
+        infcx.at(&ObligationCause::dummy(), param_env, ).eq(DefineOpaqueTypes::No,source_trait, target_trait)
     else {
         debug!(
             "fulfill_implication: {:?} does not unify with {:?}",

compiler/rustc_trait_selection/src/traits/util.rs

@@ -1,15 +1,14 @@
+use super::NormalizeExt;
+use super::{Obligation, ObligationCause, PredicateObligation, SelectionContext};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::Diagnostic;
+use rustc_hir::def_id::DefId;
+use rustc_infer::infer::InferOk;
+use rustc_middle::ty::{self, ImplSubject, ToPredicate, Ty, TyCtxt, TypeVisitableExt};
+use rustc_middle::ty::{GenericArg, SubstsRef};
 use rustc_span::Span;
 use smallvec::SmallVec;
 
-use rustc_data_structures::fx::FxHashSet;
-use rustc_hir::def_id::DefId;
-use rustc_middle::ty::{self, ImplSubject, ToPredicate, Ty, TyCtxt, TypeVisitableExt};
-use rustc_middle::ty::{GenericArg, SubstsRef};
-
-use super::NormalizeExt;
-use super::{Obligation, ObligationCause, PredicateObligation, SelectionContext};
-use rustc_infer::infer::InferOk;
 pub use rustc_infer::traits::{self, util::*};
 
 ///////////////////////////////////////////////////////////////////////////
@@ -201,6 +200,7 @@ pub fn impl_subject_and_oblig<'a, 'tcx>(
 ) -> (ImplSubject<'tcx>, impl Iterator<Item = PredicateObligation<'tcx>>) {
     let subject = selcx.tcx().bound_impl_subject(impl_def_id);
     let subject = subject.subst(selcx.tcx(), impl_substs);
+
     let InferOk { value: subject, obligations: normalization_obligations1 } =
         selcx.infcx.at(&ObligationCause::dummy(), param_env).normalize(subject);
 

library/alloc/src/rc.rs

@@ -1738,11 +1738,11 @@ impl<T: ?Sized + PartialEq> PartialEq for Rc<T> {
 
     /// Inequality for two `Rc`s.
     ///
-    /// Two `Rc`s are unequal if their inner values are unequal.
+    /// Two `Rc`s are not equal if their inner values are not equal.
     ///
     /// If `T` also implements `Eq` (implying reflexivity of equality),
     /// two `Rc`s that point to the same allocation are
-    /// never unequal.
+    /// always equal.
     ///
     /// # Examples
     ///

library/alloc/src/sync.rs

@@ -2475,10 +2475,10 @@ impl<T: ?Sized + PartialEq> PartialEq for Arc<T> {
 
     /// Inequality for two `Arc`s.
     ///
-    /// Two `Arc`s are unequal if their inner values are unequal.
+    /// Two `Arc`s are not equal if their inner values are not equal.
     ///
     /// If `T` also implements `Eq` (implying reflexivity of equality),
-    /// two `Arc`s that point to the same value are never unequal.
+    /// two `Arc`s that point to the same value are always equal.
     ///
     /// # Examples
     ///

library/core/src/hash/mod.rs

@@ -158,7 +158,7 @@ mod sip;
 ///
 /// Implementations of `hash` should ensure that the data they
 /// pass to the `Hasher` are prefix-free. That is,
-/// unequal values should cause two different sequences of values to be written,
+/// values which are not equal should cause two different sequences of values to be written,
 /// and neither of the two sequences should be a prefix of the other.
 ///
 /// For example, the standard implementation of [`Hash` for `&str`][impl] passes an extra

library/core/src/iter/traits/iterator.rs

@@ -3721,7 +3721,7 @@ pub trait Iterator {
         }
     }
 
-    /// Determines if the elements of this [`Iterator`] are unequal to those of
+    /// Determines if the elements of this [`Iterator`] are not equal to those of
     /// another.
     ///
     /// # Examples

library/core/src/primitive_docs.rs

@@ -1110,7 +1110,7 @@ impl<T: Copy> Copy for (T,) {
 /// - [NaN (not a number)](#associatedconstant.NAN): this value results from
 ///   calculations like `(-1.0).sqrt()`. NaN has some potentially unexpected
 ///   behavior:
-///   - It is unequal to any float, including itself! This is the reason `f32`
+///   - It is not equal to any float, including itself! This is the reason `f32`
 ///     doesn't implement the `Eq` trait.
 ///   - It is also neither smaller nor greater than any float, making it
 ///     impossible to sort by the default comparison operation, which is the

library/std/src/primitive_docs.rs

@@ -1110,7 +1110,7 @@ impl<T: Copy> Copy for (T,) {
 /// - [NaN (not a number)](#associatedconstant.NAN): this value results from
 ///   calculations like `(-1.0).sqrt()`. NaN has some potentially unexpected
 ///   behavior:
-///   - It is unequal to any float, including itself! This is the reason `f32`
+///   - It is not equal to any float, including itself! This is the reason `f32`
 ///     doesn't implement the `Eq` trait.
 ///   - It is also neither smaller nor greater than any float, making it
 ///     impossible to sort by the default comparison operation, which is the

library/std/src/sync/remutex.rs

@@ -35,7 +35,7 @@ use crate::sys::locks as sys;
 /// `owner` can be checked by other threads that want to see if they already
 /// hold the lock, so needs to be atomic. If it compares equal, we're on the
 /// same thread that holds the mutex and memory access can use relaxed ordering
-/// since we're not dealing with multiple threads. If it compares unequal,
+/// since we're not dealing with multiple threads. If it's not equal,
 /// synchronization is left to the mutex, making relaxed memory ordering for
 /// the `owner` field fine in all cases.
 pub struct ReentrantMutex<T> {

src/librustdoc/Cargo.toml

@@ -20,15 +20,13 @@ smallvec = "1.8.1"
 tempfile = "3"
 tracing = "0.1"
 tracing-tree = "0.2.0"
+threadpool = "1.8.1"
 
 [dependencies.tracing-subscriber]
 version = "0.3.3"
 default-features = false
 features = ["fmt", "env-filter", "smallvec", "parking_lot", "ansi"]
 
-[target.'cfg(windows)'.dependencies]
-rayon = "1.5.1"
-
 [dev-dependencies]
 expect-test = "1.4.0"
 

src/librustdoc/clean/blanket_impl.rs

@@ -1,6 +1,6 @@
 use crate::rustc_trait_selection::traits::query::evaluate_obligation::InferCtxtExt;
 use rustc_hir as hir;
-use rustc_infer::infer::{InferOk, TyCtxtInferExt};
+use rustc_infer::infer::{DefineOpaqueTypes, InferOk, TyCtxtInferExt};
 use rustc_infer::traits;
 use rustc_middle::ty::ToPredicate;
 use rustc_span::DUMMY_SP;
@@ -47,8 +47,7 @@ impl<'a, 'tcx> BlanketImplFinder<'a, 'tcx> {
 
                 // Require the type the impl is implemented on to match
                 // our type, and ignore the impl if there was a mismatch.
-                let cause = traits::ObligationCause::dummy();
-                let Ok(eq_result) = infcx.at(&cause, param_env).eq(impl_trait_ref.self_ty(), impl_ty) else {
+                let Ok(eq_result) = infcx.at(&traits::ObligationCause::dummy(), param_env).eq(DefineOpaqueTypes::No, impl_trait_ref.self_ty(), impl_ty) else {
                         continue
                     };
                 let InferOk { value: (), obligations } = eq_result;

src/librustdoc/docfs.rs

@@ -2,18 +2,20 @@
 //!
 //! On Windows this indirects IO into threads to work around performance issues
 //! with Defender (and other similar virus scanners that do blocking operations).
-//! On other platforms this is a thin shim to fs.
 //!
 //! Only calls needed to permit this workaround have been abstracted: thus
 //! fs::read is still done directly via the fs module; if in future rustdoc
 //! needs to read-after-write from a file, then it would be added to this
 //! abstraction.
 
+use std::cmp::max;
 use std::fs;
 use std::io;
 use std::path::{Path, PathBuf};
 use std::string::ToString;
 use std::sync::mpsc::Sender;
+use std::thread::available_parallelism;
+use threadpool::ThreadPool;
 
 pub(crate) trait PathError {
     fn new<S, P: AsRef<Path>>(e: S, path: P) -> Self
@@ -24,11 +26,21 @@ pub(crate) trait PathError {
 pub(crate) struct DocFS {
     sync_only: bool,
     errors: Option<Sender<String>>,
+    pool: ThreadPool,
 }
 
 impl DocFS {
     pub(crate) fn new(errors: Sender<String>) -> DocFS {
-        DocFS { sync_only: false, errors: Some(errors) }
+        const MINIMUM_NB_THREADS: usize = 2;
+        DocFS {
+            sync_only: false,
+            errors: Some(errors),
+            pool: ThreadPool::new(
+                available_parallelism()
+                    .map(|nb| max(nb.get(), MINIMUM_NB_THREADS))
+                    .unwrap_or(MINIMUM_NB_THREADS),
+            ),
+        }
     }
 
     pub(crate) fn set_sync_only(&mut self, sync_only: bool) {
@@ -54,12 +66,11 @@ impl DocFS {
     where
         E: PathError,
     {
-        #[cfg(windows)]
         if !self.sync_only {
             // A possible future enhancement after more detailed profiling would
             // be to create the file sync so errors are reported eagerly.
             let sender = self.errors.clone().expect("can't write after closing");
-            rayon::spawn(move || {
+            self.pool.execute(move || {
                 fs::write(&path, contents).unwrap_or_else(|e| {
                     sender.send(format!("\"{}\": {}", path.display(), e)).unwrap_or_else(|_| {
                         panic!("failed to send error on \"{}\"", path.display())
@@ -70,9 +81,12 @@ impl DocFS {
             fs::write(&path, contents).map_err(|e| E::new(e, path))?;
         }
 
-        #[cfg(not(windows))]
-        fs::write(&path, contents).map_err(|e| E::new(e, path))?;
-
         Ok(())
     }
 }
+
+impl Drop for DocFS {
+    fn drop(&mut self) {
+        self.pool.join();
+    }
+}

src/librustdoc/html/format.rs

@@ -771,6 +771,12 @@ pub(crate) fn link_tooltip(did: DefId, fragment: &Option<UrlFragment>, cx: &Cont
         .or_else(|| cache.external_paths.get(&did))
         else { return String::new() };
     let mut buf = Buffer::new();
+    let fqp = if *shortty == ItemType::Primitive {
+        // primitives are documented in a crate, but not actually part of it
+        &fqp[fqp.len() - 1..]
+    } else {
+        &fqp
+    };
     if let &Some(UrlFragment::Item(id)) = fragment {
         write!(buf, "{} ", cx.tcx().def_descr(id));
         for component in fqp {

src/librustdoc/html/render/search_index.rs

@@ -486,7 +486,7 @@ fn add_generics_and_bounds_as_types<'tcx, 'a>(
     }
 
     // First, check if it's "Self".
-    let arg = if let Some(self_) = self_ {
+    let mut arg = if let Some(self_) = self_ {
         match &*arg {
             Type::BorrowedRef { type_, .. } if type_.is_self_type() => self_,
             type_ if type_.is_self_type() => self_,
@@ -496,11 +496,16 @@ fn add_generics_and_bounds_as_types<'tcx, 'a>(
         arg
     };
 
+    // strip references from the argument type
+    while let Type::BorrowedRef { type_, .. } = &*arg {
+        arg = &*type_;
+    }
+
     // If this argument is a type parameter and not a trait bound or a type, we need to look
     // for its bounds.
     if let Type::Generic(arg_s) = *arg {
         // First we check if the bounds are in a `where` predicate...
-        if let Some(where_pred) = generics.where_predicates.iter().find(|g| match g {
+        for where_pred in generics.where_predicates.iter().filter(|g| match g {
             WherePredicate::BoundPredicate { ty: Type::Generic(ty_s), .. } => *ty_s == arg_s,
             _ => false,
         }) {

tests/rustdoc-js-std/option-type-signatures.js

@@ -1,7 +1,18 @@
-const QUERY = 'option, fnonce -> option';
+const QUERY = [
+    'option, fnonce -> option',
+    'option -> default',
+];
 
-const EXPECTED = {
-    'others': [
-        { 'path': 'std::option::Option', 'name': 'map' },
-    ],
-};
+const EXPECTED = [
+    {
+        'others': [
+            { 'path': 'std::option::Option', 'name': 'map' },
+        ],
+    },
+    {
+        'others': [
+            { 'path': 'std::option::Option', 'name': 'unwrap_or_default' },
+            { 'path': 'std::option::Option', 'name': 'get_or_insert_default' },
+        ],
+    },
+];

tests/rustdoc-js/where-clause.js

@@ -1,4 +1,4 @@
-const QUERY = ['trait<nested>', '-> trait<nested>', 't1, t2'];
+const QUERY = ['trait<nested>', '-> trait<nested>', 't1, t2', '-> shazam', 'drizzel -> shazam'];
 
 const EXPECTED = [
     {
@@ -16,4 +16,15 @@ const EXPECTED = [
             { 'path': 'where_clause', 'name': 'presto' },
         ],
     },
+    {
+        'others': [
+            { 'path': 'where_clause', 'name': 'bippety' },
+            { 'path': 'where_clause::Drizzel', 'name': 'boppety' },
+        ],
+    },
+    {
+        'others': [
+            { 'path': 'where_clause::Drizzel', 'name': 'boppety' },
+        ],
+    },
 ];

tests/rustdoc-js/where-clause.rs

@@ -14,3 +14,17 @@ pub trait T2<'a, T> {
 }
 
 pub fn presto<A, B>(_: A, _: B) where A: T1, B: for <'b> T2<'b, Nested> {}
+
+pub trait Shazam {}
+
+pub fn bippety<X>() -> &'static X where X: Shazam {
+    panic!()
+}
+
+pub struct Drizzel<T>(T);
+
+impl<T> Drizzel<T> {
+    pub fn boppety(&self) -> &T where T: Shazam {
+        panic!();
+    }
+}

tests/rustdoc/intra-doc/prim-methods.rs

@@ -2,6 +2,8 @@
 
 // @has prim_methods/index.html
 // @has - '//*[@id="main-content"]//a[@href="{{channel}}/std/primitive.char.html"]' 'char'
+// @has - '//*[@id="main-content"]//a[@href="{{channel}}/std/primitive.char.html"]/@title' 'primitive char'
 // @has - '//*[@id="main-content"]//a[@href="{{channel}}/std/primitive.char.html#method.len_utf8"]' 'char::len_utf8'
+// @has - '//*[@id="main-content"]//a[@href="{{channel}}/std/primitive.char.html#method.len_utf8"]/@title' 'method char::len_utf8'
 
 //! A [`char`] and its [`char::len_utf8`].

tests/ui/conditional-compilation/cfg-attr-multi-true.stderr

@@ -35,6 +35,10 @@ note: the lint level is defined here
    |
 LL | #![warn(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = MustUseDeprecated::new();
+   |     +++++++
 
 warning: 5 warnings emitted
 

tests/ui/issues/issue-19086.stderr

@@ -5,7 +5,7 @@ LL |     FooB { x: i32, y: i32 }
    |     ----------------------- `FooB` defined here
 ...
 LL |         FooB(a, b) => println!("{} {}", a, b),
-   |         ^^^^^^^^^^ help: use struct pattern syntax instead: `FooB { x, y }`
+   |         ^^^^^^^^^^ help: use struct pattern syntax instead: `FooB { x: a, y: b }`
 
 error: aborting due to previous error
 

tests/ui/lint/fn_must_use.stderr

@@ -10,12 +10,21 @@ note: the lint level is defined here
    |
 LL | #![warn(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = need_to_use_this_value();
+   |     +++++++
 
 warning: unused return value of `MyStruct::need_to_use_this_method_value` that must be used
   --> $DIR/fn_must_use.rs:60:5
    |
 LL |     m.need_to_use_this_method_value();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = m.need_to_use_this_method_value();
+   |     +++++++
 
 warning: unused return value of `EvenNature::is_even` that must be used
   --> $DIR/fn_must_use.rs:61:5
@@ -24,24 +33,43 @@ LL |     m.is_even(); // trait method!
    |     ^^^^^^^^^^^
    |
    = note: no side effects
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = m.is_even(); // trait method!
+   |     +++++++
 
 warning: unused return value of `MyStruct::need_to_use_this_associated_function_value` that must be used
   --> $DIR/fn_must_use.rs:64:5
    |
 LL |     MyStruct::need_to_use_this_associated_function_value();
    |     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = MyStruct::need_to_use_this_associated_function_value();
+   |     +++++++
 
 warning: unused return value of `std::cmp::PartialEq::eq` that must be used
   --> $DIR/fn_must_use.rs:70:5
    |
 LL |     2.eq(&3);
    |     ^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = 2.eq(&3);
+   |     +++++++
 
 warning: unused return value of `std::cmp::PartialEq::eq` that must be used
   --> $DIR/fn_must_use.rs:71:5
    |
 LL |     m.eq(&n);
    |     ^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = m.eq(&n);
+   |     +++++++
 
 warning: unused comparison that must be used
   --> $DIR/fn_must_use.rs:74:5

tests/ui/lint/unused/must-use-box-from-raw.stderr

@@ -10,6 +10,10 @@ note: the lint level is defined here
    |
 LL | #![warn(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = Box::from_raw(ptr);
+   |     +++++++
 
 warning: 1 warning emitted
 

tests/ui/lint/unused/must_use-unit.stderr

@@ -9,12 +9,21 @@ note: the lint level is defined here
    |
 LL | #![deny(unused_must_use)]
    |         ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo();
+   |     +++++++
 
 error: unused return value of `bar` that must be used
   --> $DIR/must_use-unit.rs:15:5
    |
 LL |     bar();
    |     ^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = bar();
+   |     +++++++
 
 error: aborting due to 2 previous errors
 

tests/ui/lint/unused/unused-async.stderr

@@ -16,12 +16,22 @@ error: unused return value of `foo` that must be used
    |
 LL |     foo();
    |     ^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo();
+   |     +++++++
 
 error: unused output of future returned by `foo` that must be used
   --> $DIR/unused-async.rs:33:5
    |
 LL |     foo().await;
    |     ^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo().await;
+   |     +++++++
 
 error: unused implementer of `Future` that must be used
   --> $DIR/unused-async.rs:34:5
@@ -36,12 +46,22 @@ error: unused return value of `bar` that must be used
    |
 LL |     bar();
    |     ^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = bar();
+   |     +++++++
 
 error: unused output of future returned by `bar` that must be used
   --> $DIR/unused-async.rs:36:5
    |
 LL |     bar().await;
    |     ^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = bar().await;
+   |     +++++++
 
 error: unused implementer of `Future` that must be used
   --> $DIR/unused-async.rs:37:5

tests/ui/lint/unused/unused-result.stderr

@@ -9,6 +9,10 @@ note: the lint level is defined here
    |
 LL | #![deny(unused_results, unused_must_use)]
    |                         ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo::<MustUse>();
+   |     +++++++
 
 error: unused `MustUseMsg` that must be used
   --> $DIR/unused-result.rs:22:5
@@ -17,6 +21,10 @@ LL |     foo::<MustUseMsg>();
    |     ^^^^^^^^^^^^^^^^^^^
    |
    = note: some message
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo::<MustUseMsg>();
+   |     +++++++
 
 error: unused result of type `isize`
   --> $DIR/unused-result.rs:34:5
@@ -35,6 +43,11 @@ error: unused `MustUse` that must be used
    |
 LL |     foo::<MustUse>();
    |     ^^^^^^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo::<MustUse>();
+   |     +++++++
 
 error: unused `MustUseMsg` that must be used
   --> $DIR/unused-result.rs:36:5
@@ -43,6 +56,10 @@ LL |     foo::<MustUseMsg>();
    |     ^^^^^^^^^^^^^^^^^^^
    |
    = note: some message
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo::<MustUseMsg>();
+   |     +++++++
 
 error: aborting due to 5 previous errors
 

tests/ui/lint/unused/unused_attributes-must_use.stderr

@@ -146,42 +146,76 @@ note: the lint level is defined here
    |
 LL | #![deny(unused_attributes, unused_must_use)]
    |                            ^^^^^^^^^^^^^^^
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = X;
+   |     +++++++
 
 error: unused `Y` that must be used
   --> $DIR/unused_attributes-must_use.rs:104:5
    |
 LL |     Y::Z;
    |     ^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = Y::Z;
+   |     +++++++
 
 error: unused `U` that must be used
   --> $DIR/unused_attributes-must_use.rs:105:5
    |
 LL |     U { unit: () };
    |     ^^^^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = U { unit: () };
+   |     +++++++
 
 error: unused return value of `U::method` that must be used
   --> $DIR/unused_attributes-must_use.rs:106:5
    |
 LL |     U::method();
    |     ^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = U::method();
+   |     +++++++
 
 error: unused return value of `foo` that must be used
   --> $DIR/unused_attributes-must_use.rs:107:5
    |
 LL |     foo();
    |     ^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = foo();
+   |     +++++++
 
 error: unused return value of `foreign_foo` that must be used
   --> $DIR/unused_attributes-must_use.rs:110:9
    |
 LL |         foreign_foo();
    |         ^^^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |         let _ = foreign_foo();
+   |         +++++++
 
 error: unused return value of `Use::get_four` that must be used
   --> $DIR/unused_attributes-must_use.rs:118:5
    |
 LL |     ().get_four();
    |     ^^^^^^^^^^^^^
+   |
+help: use `let _ = ...` to ignore the resulting value
+   |
+LL |     let _ = ().get_four();
+   |     +++++++
 
 error: aborting due to 28 previous errors
 

tests/ui/pattern/issue-106862.fixed

@@ -0,0 +1,44 @@
+// run-rustfix
+
+#![allow(unused)]
+
+use Foo::{FooB, FooA};
+
+enum Foo {
+    FooA { opt_x: Option<i32>, y: i32 },
+    FooB { x: i32, y: i32 }
+}
+
+fn main() {
+    let f = FooB { x: 3, y: 4 };
+
+    match f {
+        FooB { x: a, y: b } => println!("{} {}", a, b),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+
+    match f {
+        FooB { x, y } => println!("{} {}", x, y),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+
+    match f {
+        FooA { opt_x: Some(x), y } => println!("{} {}", x, y),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooA`
+        _ => (),
+    }
+
+    match f {
+        FooB { x: a, y: _ } => println!("{}", a),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+
+    match f {
+        FooB { x, y } => (),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+}

tests/ui/pattern/issue-106862.rs

@@ -0,0 +1,44 @@
+// run-rustfix
+
+#![allow(unused)]
+
+use Foo::{FooB, FooA};
+
+enum Foo {
+    FooA { opt_x: Option<i32>, y: i32 },
+    FooB { x: i32, y: i32 }
+}
+
+fn main() {
+    let f = FooB { x: 3, y: 4 };
+
+    match f {
+        FooB(a, b) => println!("{} {}", a, b),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+
+    match f {
+        FooB(x, y) => println!("{} {}", x, y),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+
+    match f {
+        FooA(Some(x), y) => println!("{} {}", x, y),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooA`
+        _ => (),
+    }
+
+    match f {
+        FooB(a, _, _) => println!("{}", a),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+
+    match f {
+        FooB() => (),
+        //~^ ERROR expected tuple struct or tuple variant, found variant `FooB`
+        _ => (),
+    }
+}

tests/ui/pattern/issue-106862.stderr

@@ -0,0 +1,48 @@
+error[E0532]: expected tuple struct or tuple variant, found variant `FooB`
+  --> $DIR/issue-106862.rs:16:9
+   |
+LL |     FooB { x: i32, y: i32 }
+   |     ----------------------- `FooB` defined here
+...
+LL |         FooB(a, b) => println!("{} {}", a, b),
+   |         ^^^^^^^^^^ help: use struct pattern syntax instead: `FooB { x: a, y: b }`
+
+error[E0532]: expected tuple struct or tuple variant, found variant `FooB`
+  --> $DIR/issue-106862.rs:22:9
+   |
+LL |     FooB { x: i32, y: i32 }
+   |     ----------------------- `FooB` defined here
+...
+LL |         FooB(x, y) => println!("{} {}", x, y),
+   |         ^^^^^^^^^^ help: use struct pattern syntax instead: `FooB { x, y }`
+
+error[E0532]: expected tuple struct or tuple variant, found variant `FooA`
+  --> $DIR/issue-106862.rs:28:9
+   |
+LL |     FooA { opt_x: Option<i32>, y: i32 },
+   |     ----------------------------------- `FooA` defined here
+...
+LL |         FooA(Some(x), y) => println!("{} {}", x, y),
+   |         ^^^^^^^^^^^^^^^^ help: use struct pattern syntax instead: `FooA { opt_x: Some(x), y }`
+
+error[E0532]: expected tuple struct or tuple variant, found variant `FooB`
+  --> $DIR/issue-106862.rs:34:9
+   |
+LL |     FooB { x: i32, y: i32 }
+   |     ----------------------- `FooB` defined here
+...
+LL |         FooB(a, _, _) => println!("{}", a),
+   |         ^^^^^^^^^^^^^ help: use struct pattern syntax instead: `FooB { x: a, y: _ }`
+
+error[E0532]: expected tuple struct or tuple variant, found variant `FooB`
+  --> $DIR/issue-106862.rs:40:9
+   |
+LL |     FooB { x: i32, y: i32 }
+   |     ----------------------- `FooB` defined here
+...
+LL |         FooB() => (),
+   |         ^^^^^^ help: use struct pattern syntax instead: `FooB { x, y }`
+
+error: aborting due to 5 previous errors
+
+For more information about this error, try `rustc --explain E0532`.