Adopt let_else in even more places

compiler/rustc_borrowck/src/diagnostics/bound_region_errors.rs

@@ -142,11 +142,9 @@ trait TypeOpInfo<'tcx> {
         let tcx = mbcx.infcx.tcx;
         let base_universe = self.base_universe();
 
-        let adjusted_universe = if let Some(adjusted) =
+        let Some(adjusted_universe) =
             placeholder.universe.as_u32().checked_sub(base_universe.as_u32())
-        {
-            adjusted
-        } else {
+        else {
             mbcx.buffer_error(self.fallback_error(tcx, cause.span));
             return;
         };

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -892,15 +892,14 @@ impl<'cx, 'tcx> MirBorrowckCtxt<'cx, 'tcx> {
             kind: TerminatorKind::Call { fn_span, from_hir_call, .. }, ..
         }) = &self.body[location.block].terminator
         {
-            let (method_did, method_substs) = if let Some(info) =
+            let Some((method_did, method_substs)) =
                 rustc_const_eval::util::find_self_call(
                     self.infcx.tcx,
                     &self.body,
                     target_temp,
                     location.block,
-                ) {
-                info
-            } else {
+                )
+            else {
                 return normal_ret;
             };
 

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -639,11 +639,9 @@ impl<'a, 'tcx> MirBorrowckCtxt<'a, 'tcx> {
         let hir_map = self.infcx.tcx.hir();
         let my_def = self.body.source.def_id();
         let my_hir = hir_map.local_def_id_to_hir_id(my_def.as_local().unwrap());
-        let td = if let Some(a) =
+        let Some(td) =
             self.infcx.tcx.impl_of_method(my_def).and_then(|x| self.infcx.tcx.trait_id_of_impl(x))
-        {
-            a
-        } else {
+        else {
             return (false, None);
         };
         (

compiler/rustc_builtin_macros/src/concat_bytes.rs

@@ -6,9 +6,7 @@ use rustc_expand::base::{self, DummyResult};
 
 /// Emits errors for literal expressions that are invalid inside and outside of an array.
 fn invalid_type_err(cx: &mut base::ExtCtxt<'_>, expr: &P<rustc_ast::Expr>, is_nested: bool) {
-    let lit = if let ast::ExprKind::Lit(lit) = &expr.kind {
-        lit
-    } else {
+    let ast::ExprKind::Lit(lit) = &expr.kind else {
         unreachable!();
     };
     match lit.kind {

compiler/rustc_builtin_macros/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(decl_macro)]
 #![feature(is_sorted)]
 #![feature(nll)]
+#![feature(let_else)]
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_quote)]
 #![recursion_limit = "256"]

compiler/rustc_codegen_ssa/src/back/link.rs

@@ -216,17 +216,18 @@ pub fn each_linked_rlib(
         }
         let name = &info.crate_name[&cnum];
         let used_crate_source = &info.used_crate_source[&cnum];
-        let path = if let Some((path, _)) = &used_crate_source.rlib {
-            path
-        } else if used_crate_source.rmeta.is_some() {
-            return Err(format!(
-                "could not find rlib for: `{}`, found rmeta (metadata) file",
-                name
-            ));
+        if let Some((path, _)) = &used_crate_source.rlib {
+            f(cnum, &path);
         } else {
-            return Err(format!("could not find rlib for: `{}`", name));
-        };
-        f(cnum, &path);
+            if used_crate_source.rmeta.is_some() {
+                return Err(format!(
+                    "could not find rlib for: `{}`, found rmeta (metadata) file",
+                    name
+                ));
+            } else {
+                return Err(format!("could not find rlib for: `{}`", name));
+            }
+        }
     }
     Ok(())
 }

compiler/rustc_codegen_ssa/src/back/metadata.rs

@@ -200,9 +200,7 @@ fn create_object_file(sess: &Session) -> Option<write::Object<'static>> {
 //   `SHF_EXCLUDE` flag we can set on sections in an object file to get
 //   automatically removed from the final output.
 pub fn create_rmeta_file(sess: &Session, metadata: &[u8]) -> Vec<u8> {
-    let mut file = if let Some(file) = create_object_file(sess) {
-        file
-    } else {
+    let Some(mut file) = create_object_file(sess) else {
         // This is used to handle all "other" targets. This includes targets
         // in two categories:
         //
@@ -262,9 +260,7 @@ pub fn create_compressed_metadata_file(
 ) -> Vec<u8> {
     let mut compressed = rustc_metadata::METADATA_HEADER.to_vec();
     FrameEncoder::new(&mut compressed).write_all(metadata.raw_data()).unwrap();
-    let mut file = if let Some(file) = create_object_file(sess) {
-        file
-    } else {
+    let Some(mut file) = create_object_file(sess) else {
         return compressed.to_vec();
     };
     let section = file.add_section(

compiler/rustc_index/src/bit_set.rs

@@ -852,11 +852,7 @@ impl<T: Idx> HybridBitSet<T> {
             Bound::Excluded(end) => end.index(),
             Bound::Unbounded => self.domain_size() - 1,
         };
-        let len = if let Some(l) = end.checked_sub(start) {
-            l
-        } else {
-            return;
-        };
+        let Some(len) = end.checked_sub(start) else { return };
         match self {
             HybridBitSet::Sparse(sparse) if sparse.len() + len < SPARSE_MAX => {
                 // The set is sparse and has space for `elems`.

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

@@ -553,8 +553,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let ty_msg = match (local_visitor.found_node_ty, local_visitor.found_exact_method_call) {
             (_, Some(_)) => String::new(),
             (Some(ty), _) if ty.is_closure() => {
-                let substs =
-                    if let ty::Closure(_, substs) = *ty.kind() { substs } else { unreachable!() };
+                let ty::Closure(_, substs) = *ty.kind() else { unreachable!() };
                 let fn_sig = substs.as_closure().sig();
                 let args = closure_args(&fn_sig);
                 let ret = fn_sig.output().skip_binder().to_string();
@@ -597,8 +596,7 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
         let param_type = arg_data.kind.descr();
         let suffix = match local_visitor.found_node_ty {
             Some(ty) if ty.is_closure() => {
-                let substs =
-                    if let ty::Closure(_, substs) = *ty.kind() { substs } else { unreachable!() };
+                let ty::Closure(_, substs) = *ty.kind() else { unreachable!() };
                 let fn_sig = substs.as_closure().sig();
                 let ret = fn_sig.output().skip_binder().to_string();
 

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -982,7 +982,7 @@ impl<'a, 'tcx> EncodeContext<'a, 'tcx> {
         for local_id in hir.iter_local_def_id() {
             let def_id = local_id.to_def_id();
             let def_kind = tcx.opt_def_kind(local_id);
-            let def_kind = if let Some(def_kind) = def_kind { def_kind } else { continue };
+            let Some(def_kind) = def_kind else { continue };
             record!(self.tables.def_kind[def_id] <- match def_kind {
                 // Replace Ctor by the enclosing object to avoid leaking details in children crates.
                 DefKind::Ctor(CtorOf::Struct, _) => DefKind::Struct,

compiler/rustc_middle/src/dep_graph/mod.rs

@@ -61,7 +61,7 @@ impl rustc_query_system::dep_graph::DepKind for DepKind {
         OP: for<'a> FnOnce(TaskDepsRef<'a>),
     {
         ty::tls::with_context_opt(|icx| {
-            let icx = if let Some(icx) = icx { icx } else { return };
+            let Some(icx) = icx else { return };
             op(icx.task_deps)
         })
     }

compiler/rustc_mir_transform/src/generator.rs

@@ -1241,9 +1241,7 @@ impl<'tcx> MirPass<'tcx> for StateTransform {
     }
 
     fn run_pass(&self, tcx: TyCtxt<'tcx>, body: &mut Body<'tcx>) {
-        let yield_ty = if let Some(yield_ty) = body.yield_ty() {
-            yield_ty
-        } else {
+        let Some(yield_ty) = body.yield_ty() else {
             // This only applies to generators
             return;
         };

compiler/rustc_mir_transform/src/normalize_array_len.rs

@@ -211,12 +211,7 @@ fn normalize_array_len_call<'tcx>(
                         let Some(local) = place.as_local() else { return };
                         match operand {
                             Operand::Copy(place) | Operand::Move(place) => {
-                                let operand_local =
-                                    if let Some(local) = place.local_or_deref_local() {
-                                        local
-                                    } else {
-                                        return;
-                                    };
+                                let Some(operand_local) = place.local_or_deref_local() else { return; };
                                 if !interesting_locals.contains(operand_local) {
                                     return;
                                 }

compiler/rustc_monomorphize/src/collector.rs

@@ -947,9 +947,7 @@ fn visit_instance_use<'tcx>(
 /// Returns `true` if we should codegen an instance in the local crate, or returns `false` if we
 /// can just link to the upstream crate and therefore don't need a mono item.
 fn should_codegen_locally<'tcx>(tcx: TyCtxt<'tcx>, instance: &Instance<'tcx>) -> bool {
-    let def_id = if let Some(def_id) = instance.def.def_id_if_not_guaranteed_local_codegen() {
-        def_id
-    } else {
+    let Some(def_id) = instance.def.def_id_if_not_guaranteed_local_codegen() else {
         return true;
     };
 

compiler/rustc_monomorphize/src/util.rs

@@ -8,13 +8,11 @@ use std::io::prelude::*;
 /// During the same compile all closures dump the information in the same file
 /// "closure_profile_XXXXX.csv", which is created in the directory where the compiler is invoked.
 crate fn dump_closure_profile<'tcx>(tcx: TyCtxt<'tcx>, closure_instance: Instance<'tcx>) {
-    let mut file = if let Ok(file) = OpenOptions::new()
+    let Ok(mut file) = OpenOptions::new()
         .create(true)
         .append(true)
         .open(&format!("closure_profile_{}.csv", std::process::id()))
-    {
-        file
-    } else {
+    else {
         eprintln!("Cound't open file for writing closure profile");
         return;
     };

compiler/rustc_parse/src/lexer/mod.rs

@@ -158,9 +158,7 @@ impl<'a> StringReader<'a> {
         Some(match token {
             rustc_lexer::TokenKind::LineComment { doc_style } => {
                 // Skip non-doc comments
-                let doc_style = if let Some(doc_style) = doc_style {
-                    doc_style
-                } else {
+                let Some(doc_style) = doc_style else {
                     self.lint_unicode_text_flow(start);
                     return None;
                 };
@@ -185,9 +183,7 @@ impl<'a> StringReader<'a> {
                 }
 
                 // Skip non-doc comments
-                let doc_style = if let Some(doc_style) = doc_style {
-                    doc_style
-                } else {
+                let Some(doc_style) = doc_style else {
                     self.lint_unicode_text_flow(start);
                     return None;
                 };

compiler/rustc_parse/src/lib.rs

@@ -4,6 +4,7 @@
 #![feature(crate_visibility_modifier)]
 #![feature(if_let_guard)]
 #![feature(box_patterns)]
+#![feature(let_else)]
 #![recursion_limit = "256"]
 
 #[macro_use]

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -704,7 +704,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         ) = &bounded_ty.kind
         {
             // use this to verify that ident is a type param.
-            let partial_res = if let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
+            let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
                 bounded_ty.id,
                 None,
                 &Segment::from_path(path),
@@ -712,9 +712,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                 span,
                 true,
                 CrateLint::No,
-            ) {
-                partial_res
-            } else {
+            ) else {
                 return false;
             };
             if !(matches!(
@@ -731,7 +729,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
 
         if let ast::TyKind::Path(None, type_param_path) = &ty.peel_refs().kind {
             // Confirm that the `SelfTy` is a type parameter.
-            let partial_res = if let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
+            let Ok(Some(partial_res)) = self.resolve_qpath_anywhere(
                 bounded_ty.id,
                 None,
                 &Segment::from_path(type_param_path),
@@ -739,9 +737,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
                 span,
                 true,
                 CrateLint::No,
-            ) {
-                partial_res
-            } else {
+            ) else {
                 return false;
             };
             if !(matches!(

compiler/rustc_trait_selection/src/traits/error_reporting/suggestions.rs

@@ -1099,9 +1099,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             _ => return false,
         };
 
-        let ret_ty = if let hir::FnRetTy::Return(ret_ty) = sig.decl.output {
-            ret_ty
-        } else {
+        let hir::FnRetTy::Return(ret_ty) = sig.decl.output else {
             return false;
         };
 
@@ -1168,7 +1166,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             };
 
         let sm = self.tcx.sess.source_map();
-        let snippet = if let (true, hir::TyKind::TraitObject(..), Ok(snippet), true) = (
+        let (true, hir::TyKind::TraitObject(..), Ok(snippet), true) = (
             // Verify that we're dealing with a return `dyn Trait`
             ret_ty.span.overlaps(span),
             &ret_ty.kind,
@@ -1176,9 +1174,7 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             // If any of the return types does not conform to the trait, then we can't
             // suggest `impl Trait` nor trait objects: it is a type mismatch error.
             all_returns_conform_to_trait,
-        ) {
-            snippet
-        } else {
+        ) else {
             return false;
         };
         err.code(error_code!(E0746));

compiler/rustc_typeck/src/check/expr.rs

@@ -1318,10 +1318,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         base_expr: &'tcx Option<&'tcx hir::Expr<'tcx>>,
     ) -> Ty<'tcx> {
         // Find the relevant variant
-        let (variant, adt_ty) = if let Some(variant_ty) = self.check_struct_path(qpath, expr.hir_id)
-        {
-            variant_ty
-        } else {
+        let Some((variant, adt_ty)) = self.check_struct_path(qpath, expr.hir_id) else {
             self.check_struct_fields_on_error(fields, base_expr);
             return self.tcx.ty_error();
         };

src/librustdoc/clean/simplify.rs

@@ -51,9 +51,7 @@ crate fn where_clauses(cx: &DocContext<'_>, clauses: Vec<WP>) -> Vec<WP> {
     // Look for equality predicates on associated types that can be merged into
     // general bound predicates
     equalities.retain(|&(ref lhs, ref rhs)| {
-        let (self_, trait_did, name) = if let Some(p) = lhs.projection() {
-            p
-        } else {
+        let Some((self_, trait_did, name)) = lhs.projection() else {
             return true;
         };
         let generic = match self_ {

src/librustdoc/html/markdown.rs

@@ -236,9 +236,7 @@ impl<'a, I: Iterator<Item = Event<'a>>> Iterator for CodeBlocks<'_, 'a, I> {
         let should_panic;
         let ignore;
         let edition;
-        let kind = if let Some(Event::Start(Tag::CodeBlock(kind))) = event {
-            kind
-        } else {
+        let Some(Event::Start(Tag::CodeBlock(kind))) = event else {
             return event;
         };
 

src/librustdoc/html/render/print_item.rs

@@ -1752,9 +1752,7 @@ fn document_type_layout(w: &mut Buffer, cx: &Context<'_>, ty_def_id: DefId) {
                             <ul>",
                     );
 
-                    let adt = if let Adt(adt, _) = ty_layout.ty.kind() {
-                        adt
-                    } else {
+                    let Adt(adt, _) = ty_layout.ty.kind() else {
                         span_bug!(tcx.def_span(ty_def_id), "not an adt")
                     };
 

src/librustdoc/passes/collect_intra_doc_links.rs

@@ -1226,9 +1226,7 @@ impl LinkCollector<'_, '_> {
         let base_node =
             if item.is_mod() && inner_docs { self.mod_ids.last().copied() } else { parent_node };
 
-        let mut module_id = if let Some(id) = base_node {
-            id
-        } else {
+        let Some(mut module_id) = base_node else {
             // This is a bug.
             debug!("attempting to resolve item without parent module: {}", path_str);
             resolution_failure(
@@ -1977,9 +1975,7 @@ fn resolution_failure(
                     // If so, report it and say the first which failed; if not, say the first path segment didn't resolve.
                     let mut name = path_str;
                     'outer: loop {
-                        let (start, end) = if let Some(x) = split(name) {
-                            x
-                        } else {
+                        let Some((start, end)) = split(name) else {
                             // avoid bug that marked [Quux::Z] as missing Z, not Quux
                             if partial_res.is_none() {
                                 *unresolved = name.into();

src/librustdoc/scrape_examples.rs

@@ -152,9 +152,7 @@ where
             }
             hir::ExprKind::MethodCall(_, _, span) => {
                 let types = tcx.typeck(ex.hir_id.owner);
-                let def_id = if let Some(def_id) = types.type_dependent_def_id(ex.hir_id) {
-                    def_id
-                } else {
+                let Some(def_id) = types.type_dependent_def_id(ex.hir_id) else {
                     trace!("type_dependent_def_id({}) = None", ex.hir_id);
                     return;
                 };

src/librustdoc/visit_ast.rs

@@ -188,9 +188,7 @@ impl<'a, 'tcx> RustdocVisitor<'a, 'tcx> {
         debug!("maybe_inline_local res: {:?}", res);
 
         let tcx = self.cx.tcx;
-        let res_did = if let Some(did) = res.opt_def_id() {
-            did
-        } else {
+        let Some(res_did) = res.opt_def_id() else {
             return false;
         };