Use let_else in even more places

compiler/rustc_codegen_llvm/src/debuginfo/metadata.rs

@@ -1493,7 +1493,7 @@ fn generator_layout_and_saved_local_names<'tcx>(
 
     let state_arg = mir::Local::new(1);
     for var in &body.var_debug_info {
-        let place = if let mir::VarDebugInfoContents::Place(p) = var.value { p } else { continue };
+        let mir::VarDebugInfoContents::Place(place) = &var.value else { continue };
         if place.local != state_arg {
             continue;
         }

compiler/rustc_codegen_llvm/src/lib.rs

@@ -7,6 +7,7 @@
 #![doc(html_root_url = "https://doc.rust-lang.org/nightly/nightly-rustc/")]
 #![feature(bool_to_option)]
 #![feature(crate_visibility_modifier)]
+#![feature(let_else)]
 #![feature(extern_types)]
 #![feature(nll)]
 #![recursion_limit = "256"]

compiler/rustc_interface/src/lib.rs

@@ -1,5 +1,6 @@
 #![feature(bool_to_option)]
 #![feature(box_patterns)]
+#![feature(let_else)]
 #![feature(internal_output_capture)]
 #![feature(thread_spawn_unchecked)]
 #![feature(nll)]

compiler/rustc_interface/src/util.rs

@@ -717,57 +717,57 @@ impl<'a, 'b> ReplaceBodyWithLoop<'a, 'b> {
     }
 
     fn should_ignore_fn(ret_ty: &ast::FnRetTy) -> bool {
-        if let ast::FnRetTy::Ty(ref ty) = ret_ty {
-            fn involves_impl_trait(ty: &ast::Ty) -> bool {
-                match ty.kind {
-                    ast::TyKind::ImplTrait(..) => true,
-                    ast::TyKind::Slice(ref subty)
-                    | ast::TyKind::Array(ref subty, _)
-                    | ast::TyKind::Ptr(ast::MutTy { ty: ref subty, .. })
-                    | ast::TyKind::Rptr(_, ast::MutTy { ty: ref subty, .. })
-                    | ast::TyKind::Paren(ref subty) => involves_impl_trait(subty),
-                    ast::TyKind::Tup(ref tys) => any_involves_impl_trait(tys.iter()),
-                    ast::TyKind::Path(_, ref path) => {
-                        path.segments.iter().any(|seg| match seg.args.as_deref() {
-                            None => false,
-                            Some(&ast::GenericArgs::AngleBracketed(ref data)) => {
-                                data.args.iter().any(|arg| match arg {
-                                    ast::AngleBracketedArg::Arg(arg) => match arg {
-                                        ast::GenericArg::Type(ty) => involves_impl_trait(ty),
-                                        ast::GenericArg::Lifetime(_)
-                                        | ast::GenericArg::Const(_) => false,
-                                    },
-                                    ast::AngleBracketedArg::Constraint(c) => match c.kind {
-                                        ast::AssocConstraintKind::Bound { .. } => true,
-                                        ast::AssocConstraintKind::Equality { ref term } => {
-                                            match term {
-                                                Term::Ty(ty) => involves_impl_trait(ty),
-                                                // FIXME(...): This should check if the constant
-                                                // involves a trait impl, but for now ignore.
-                                                Term::Const(_) => false,
-                                            }
+        let ast::FnRetTy::Ty(ref ty) = ret_ty else {
+            return false;
+        };
+        fn involves_impl_trait(ty: &ast::Ty) -> bool {
+            match ty.kind {
+                ast::TyKind::ImplTrait(..) => true,
+                ast::TyKind::Slice(ref subty)
+                | ast::TyKind::Array(ref subty, _)
+                | ast::TyKind::Ptr(ast::MutTy { ty: ref subty, .. })
+                | ast::TyKind::Rptr(_, ast::MutTy { ty: ref subty, .. })
+                | ast::TyKind::Paren(ref subty) => involves_impl_trait(subty),
+                ast::TyKind::Tup(ref tys) => any_involves_impl_trait(tys.iter()),
+                ast::TyKind::Path(_, ref path) => {
+                    path.segments.iter().any(|seg| match seg.args.as_deref() {
+                        None => false,
+                        Some(&ast::GenericArgs::AngleBracketed(ref data)) => {
+                            data.args.iter().any(|arg| match arg {
+                                ast::AngleBracketedArg::Arg(arg) => match arg {
+                                    ast::GenericArg::Type(ty) => involves_impl_trait(ty),
+                                    ast::GenericArg::Lifetime(_) | ast::GenericArg::Const(_) => {
+                                        false
+                                    }
+                                },
+                                ast::AngleBracketedArg::Constraint(c) => match c.kind {
+                                    ast::AssocConstraintKind::Bound { .. } => true,
+                                    ast::AssocConstraintKind::Equality { ref term } => {
+                                        match term {
+                                            Term::Ty(ty) => involves_impl_trait(ty),
+                                            // FIXME(...): This should check if the constant
+                                            // involves a trait impl, but for now ignore.
+                                            Term::Const(_) => false,
                                         }
-                                    },
-                                })
-                            }
-                            Some(&ast::GenericArgs::Parenthesized(ref data)) => {
-                                any_involves_impl_trait(data.inputs.iter())
-                                    || ReplaceBodyWithLoop::should_ignore_fn(&data.output)
-                            }
-                        })
-                    }
-                    _ => false,
+                                    }
+                                },
+                            })
+                        }
+                        Some(&ast::GenericArgs::Parenthesized(ref data)) => {
+                            any_involves_impl_trait(data.inputs.iter())
+                                || ReplaceBodyWithLoop::should_ignore_fn(&data.output)
+                        }
+                    })
                 }
+                _ => false,
             }
+        }
 
-            fn any_involves_impl_trait<'a, I: Iterator<Item = &'a P<ast::Ty>>>(mut it: I) -> bool {
-                it.any(|subty| involves_impl_trait(subty))
-            }
-
-            involves_impl_trait(ty)
-        } else {
-            false
+        fn any_involves_impl_trait<'a, I: Iterator<Item = &'a P<ast::Ty>>>(mut it: I) -> bool {
+            it.any(|subty| involves_impl_trait(subty))
         }
+
+        involves_impl_trait(ty)
     }
 
     fn is_sig_const(sig: &ast::FnSig) -> bool {

compiler/rustc_mir_build/src/build/matches/mod.rs

@@ -1328,23 +1328,22 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
 
         let mut otherwise = None;
         for match_pair in match_pairs {
-            if let PatKind::Or { ref pats } = *match_pair.pattern.kind {
-                let or_span = match_pair.pattern.span;
-                let place = match_pair.place;
-
-                first_candidate.visit_leaves(|leaf_candidate| {
-                    self.test_or_pattern(
-                        leaf_candidate,
-                        &mut otherwise,
-                        pats,
-                        or_span,
-                        place.clone(),
-                        fake_borrows,
-                    );
-                });
-            } else {
+            let PatKind::Or { ref pats } = &*match_pair.pattern.kind else {
                 bug!("Or-patterns should have been sorted to the end");
-            }
+            };
+            let or_span = match_pair.pattern.span;
+            let place = match_pair.place;
+
+            first_candidate.visit_leaves(|leaf_candidate| {
+                self.test_or_pattern(
+                    leaf_candidate,
+                    &mut otherwise,
+                    pats,
+                    or_span,
+                    place.clone(),
+                    fake_borrows,
+                );
+            });
         }
 
         let remainder_start = otherwise.unwrap_or_else(|| self.cfg.start_new_block());

compiler/rustc_mir_build/src/build/matches/test.rs

@@ -88,11 +88,8 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         switch_ty: Ty<'tcx>,
         options: &mut FxIndexMap<&'tcx ty::Const<'tcx>, u128>,
     ) -> bool {
-        let match_pair = match candidate.match_pairs.iter().find(|mp| mp.place == *test_place) {
-            Some(match_pair) => match_pair,
-            _ => {
-                return false;
-            }
+        let Some(match_pair) = candidate.match_pairs.iter().find(|mp| mp.place == *test_place) else {
+            return false;
         };
 
         match *match_pair.pattern.kind {

compiler/rustc_resolve/src/late/diagnostics.rs

@@ -1162,9 +1162,7 @@ impl<'a: 'ast, 'ast> LateResolutionVisitor<'a, '_, 'ast> {
         ident: Symbol,
         kind: &AssocItemKind,
     ) -> Option<Symbol> {
-        let module = if let Some((module, _)) = self.current_trait_ref {
-            module
-        } else {
+        let Some((module, _)) = &self.current_trait_ref else {
             return None;
         };
         if ident == kw::Underscore {

compiler/rustc_resolve/src/late/lifetimes.rs

@@ -1000,46 +1000,45 @@ impl<'a, 'tcx> Visitor<'tcx> for LifetimeContext<'a, 'tcx> {
                 // `fn foo<'a>() -> MyAnonTy<'a> { ... }`
                 //          ^                 ^this gets resolved in the current scope
                 for lifetime in lifetimes {
-                    if let hir::GenericArg::Lifetime(lifetime) = lifetime {
-                        self.visit_lifetime(lifetime);
+                    let hir::GenericArg::Lifetime(lifetime) = lifetime else {
+                        continue
+                    };
+                    self.visit_lifetime(lifetime);
+
+                    // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
+                    // and ban them. Type variables instantiated inside binders aren't
+                    // well-supported at the moment, so this doesn't work.
+                    // In the future, this should be fixed and this error should be removed.
+                    let def = self.map.defs.get(&lifetime.hir_id).cloned();
+                    let Some(Region::LateBound(_, _, def_id, _)) = def else {
+                        continue
+                    };
+                    let Some(def_id) = def_id.as_local() else {
+                        continue
+                    };
+                    let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
+                    // Ensure that the parent of the def is an item, not HRTB
+                    let parent_id = self.tcx.hir().get_parent_node(hir_id);
+                    // FIXME(cjgillot) Can this check be replaced by
+                    // `let parent_is_item = parent_id.is_owner();`?
+                    let parent_is_item = if let Some(parent_def_id) = parent_id.as_owner() {
+                        matches!(self.tcx.hir().krate().owners.get(parent_def_id), Some(Some(_)),)
+                    } else {
+                        false
+                    };
 
-                        // Check for predicates like `impl for<'a> Trait<impl OtherTrait<'a>>`
-                        // and ban them. Type variables instantiated inside binders aren't
-                        // well-supported at the moment, so this doesn't work.
-                        // In the future, this should be fixed and this error should be removed.
-                        let def = self.map.defs.get(&lifetime.hir_id).cloned();
-                        if let Some(Region::LateBound(_, _, def_id, _)) = def {
-                            if let Some(def_id) = def_id.as_local() {
-                                let hir_id = self.tcx.hir().local_def_id_to_hir_id(def_id);
-                                // Ensure that the parent of the def is an item, not HRTB
-                                let parent_id = self.tcx.hir().get_parent_node(hir_id);
-                                // FIXME(cjgillot) Can this check be replaced by
-                                // `let parent_is_item = parent_id.is_owner();`?
-                                let parent_is_item =
-                                    if let Some(parent_def_id) = parent_id.as_owner() {
-                                        matches!(
-                                            self.tcx.hir().krate().owners.get(parent_def_id),
-                                            Some(Some(_)),
-                                        )
-                                    } else {
-                                        false
-                                    };
-
-                                if !parent_is_item {
-                                    if !self.trait_definition_only {
-                                        struct_span_err!(
-                                            self.tcx.sess,
-                                            lifetime.span,
-                                            E0657,
-                                            "`impl Trait` can only capture lifetimes \
-                                                bound at the fn or impl level"
-                                        )
-                                        .emit();
-                                    }
-                                    self.uninsert_lifetime_on_error(lifetime, def.unwrap());
-                                }
-                            }
+                    if !parent_is_item {
+                        if !self.trait_definition_only {
+                            struct_span_err!(
+                                self.tcx.sess,
+                                lifetime.span,
+                                E0657,
+                                "`impl Trait` can only capture lifetimes \
+                                    bound at the fn or impl level"
+                            )
+                            .emit();
                         }
+                        self.uninsert_lifetime_on_error(lifetime, def.unwrap());
                     }
                 }
 

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

@@ -840,39 +840,38 @@ impl<'a, 'tcx> InferCtxtExt<'tcx> for InferCtxt<'a, 'tcx> {
             };
 
             for refs_remaining in 0..refs_number {
-                if let ty::Ref(_, inner_ty, _) = suggested_ty.kind() {
-                    suggested_ty = inner_ty;
+                let ty::Ref(_, inner_ty, _) = suggested_ty.kind() else {
+                    break;
+                };
+                suggested_ty = inner_ty;
 
-                    let new_obligation = self.mk_trait_obligation_with_new_self_ty(
-                        obligation.param_env,
-                        trait_ref,
-                        suggested_ty,
-                    );
+                let new_obligation = self.mk_trait_obligation_with_new_self_ty(
+                    obligation.param_env,
+                    trait_ref,
+                    suggested_ty,
+                );
 
-                    if self.predicate_may_hold(&new_obligation) {
-                        let sp = self
-                            .tcx
-                            .sess
-                            .source_map()
-                            .span_take_while(span, |c| c.is_whitespace() || *c == '&');
+                if self.predicate_may_hold(&new_obligation) {
+                    let sp = self
+                        .tcx
+                        .sess
+                        .source_map()
+                        .span_take_while(span, |c| c.is_whitespace() || *c == '&');
 
-                        let remove_refs = refs_remaining + 1;
+                    let remove_refs = refs_remaining + 1;
 
-                        let msg = if remove_refs == 1 {
-                            "consider removing the leading `&`-reference".to_string()
-                        } else {
-                            format!("consider removing {} leading `&`-references", remove_refs)
-                        };
+                    let msg = if remove_refs == 1 {
+                        "consider removing the leading `&`-reference".to_string()
+                    } else {
+                        format!("consider removing {} leading `&`-references", remove_refs)
+                    };
 
-                        err.span_suggestion_short(
-                            sp,
-                            &msg,
-                            String::new(),
-                            Applicability::MachineApplicable,
-                        );
-                        break;
-                    }
-                } else {
+                    err.span_suggestion_short(
+                        sp,
+                        &msg,
+                        String::new(),
+                        Applicability::MachineApplicable,
+                    );
                     break;
                 }
             }