Rollup merge of rust-lang#91481 - est31:let_else, r=jackh726

Use let_else in some more places in rustc_lint

Follow-up of rust-lang#91018 and rust-lang#89933 . Also cc rust-lang#90985 which added the first let_else uses to rustc_lint.

compiler/rustc_lint/src/array_into_iter.rs

@@ -79,9 +79,8 @@ impl<'tcx> LateLintPass<'tcx> for ArrayIntoIter {
             let receiver_ty = cx.typeck_results().expr_ty(receiver_arg);
             let adjustments = cx.typeck_results().expr_adjustments(receiver_arg);
 
-            let target = match adjustments.last() {
-                Some(Adjustment { kind: Adjust::Borrow(_), target }) => target,
-                _ => return,
+            let Some(Adjustment { kind: Adjust::Borrow(_), target }) = adjustments.last() else {
+                return
             };
 
             let types =

compiler/rustc_lint/src/builtin.rs

@@ -609,14 +609,12 @@ impl<'tcx> LateLintPass<'tcx> for MissingDoc {
                 // If the trait is private, add the impl items to `private_traits` so they don't get
                 // reported for missing docs.
                 let real_trait = trait_ref.path.res.def_id();
-                if let Some(def_id) = real_trait.as_local() {
-                    let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
-                    if let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) {
-                        if let hir::VisibilityKind::Inherited = item.vis.node {
-                            for impl_item_ref in items {
-                                self.private_traits.insert(impl_item_ref.id.hir_id());
-                            }
-                        }
+                let Some(def_id) = real_trait.as_local() else { return };
+                let hir_id = cx.tcx.hir().local_def_id_to_hir_id(def_id);
+                let Some(Node::Item(item)) = cx.tcx.hir().find(hir_id) else { return };
+                if let hir::VisibilityKind::Inherited = item.vis.node {
+                    for impl_item_ref in items {
+                        self.private_traits.insert(impl_item_ref.id.hir_id());
                     }
                 }
                 return;
@@ -829,9 +827,8 @@ impl<'tcx> LateLintPass<'tcx> for MissingDebugImplementations {
             _ => return,
         }
 
-        let debug = match cx.tcx.get_diagnostic_item(sym::Debug) {
-            Some(debug) => debug,
-            None => return,
+        let Some(debug) = cx.tcx.get_diagnostic_item(sym::Debug) else {
+            return
         };
 
         if self.impling_types.is_none() {
@@ -1509,9 +1506,8 @@ impl TypeAliasBounds {
 
 impl<'tcx> LateLintPass<'tcx> for TypeAliasBounds {
     fn check_item(&mut self, cx: &LateContext<'_>, item: &hir::Item<'_>) {
-        let (ty, type_alias_generics) = match item.kind {
-            hir::ItemKind::TyAlias(ref ty, ref generics) => (&*ty, generics),
-            _ => return,
+        let hir::ItemKind::TyAlias(ty, type_alias_generics) = &item.kind else {
+            return
         };
         if let hir::TyKind::OpaqueDef(..) = ty.kind {
             // Bounds are respected for `type X = impl Trait`
@@ -2266,16 +2262,15 @@ impl<'tcx> LateLintPass<'tcx> for ExplicitOutlivesRequirements {
                         // and should check for them here.
                         match predicate.bounded_ty.kind {
                             hir::TyKind::Path(hir::QPath::Resolved(None, ref path)) => {
-                                if let Res::Def(DefKind::TyParam, def_id) = path.res {
-                                    let index = ty_generics.param_def_id_to_index[&def_id];
-                                    (
-                                        Self::lifetimes_outliving_type(inferred_outlives, index),
-                                        &predicate.bounds,
-                                        predicate.span,
-                                    )
-                                } else {
-                                    continue;
-                                }
+                                let Res::Def(DefKind::TyParam, def_id) = path.res else {
+                                    continue
+                                };
+                                let index = ty_generics.param_def_id_to_index[&def_id];
+                                (
+                                    Self::lifetimes_outliving_type(inferred_outlives, index),
+                                    &predicate.bounds,
+                                    predicate.span,
+                                )
                             }
                             _ => {
                                 continue;
@@ -3216,18 +3211,17 @@ impl<'tcx> LateLintPass<'tcx> for NamedAsmLabels {
                     for (idx, _) in statement.match_indices(':') {
                         let possible_label = statement[start_idx..idx].trim();
                         let mut chars = possible_label.chars();
-                        if let Some(c) = chars.next() {
-                            // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
-                            if (c.is_alphabetic() || matches!(c, '.' | '_'))
-                                && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
-                            {
-                                found_labels.push(possible_label);
-                            } else {
-                                // If we encounter a non-label, there cannot be any further labels, so stop checking
-                                break;
-                            }
-                        } else {
+                        let Some(c) = chars.next() else {
                             // Empty string means a leading ':' in this section, which is not a label
+                            break
+                        };
+                        // A label starts with an alphabetic character or . or _ and continues with alphanumeric characters, _, or $
+                        if (c.is_alphabetic() || matches!(c, '.' | '_'))
+                            && chars.all(|c| c.is_alphanumeric() || matches!(c, '_' | '$'))
+                        {
+                            found_labels.push(possible_label);
+                        } else {
+                            // If we encounter a non-label, there cannot be any further labels, so stop checking
                             break;
                         }
 

compiler/rustc_lint/src/levels.rs

@@ -227,14 +227,12 @@ impl<'s> LintLevelsBuilder<'s> {
         let sess = self.sess;
         let bad_attr = |span| struct_span_err!(sess, span, E0452, "malformed lint attribute input");
         for attr in attrs {
-            let level = match Level::from_symbol(attr.name_or_empty()) {
-                None => continue,
-                Some(lvl) => lvl,
+            let Some(level) = Level::from_symbol(attr.name_or_empty()) else {
+                continue
             };
 
-            let mut metas = match attr.meta_item_list() {
-                Some(x) => x,
-                None => continue,
+            let Some(mut metas) = attr.meta_item_list() else {
+                continue
             };
 
             if metas.is_empty() {
@@ -481,9 +479,8 @@ impl<'s> LintLevelsBuilder<'s> {
                     continue;
                 }
 
-                let (lint_attr_name, lint_attr_span) = match *src {
-                    LintLevelSource::Node(name, span, _) => (name, span),
-                    _ => continue,
+                let LintLevelSource::Node(lint_attr_name, lint_attr_span, _) = *src else {
+                    continue
                 };
 
                 let lint = builtin::UNUSED_ATTRIBUTES;

compiler/rustc_lint/src/noop_method_call.rs

@@ -40,9 +40,8 @@ declare_lint_pass!(NoopMethodCall => [NOOP_METHOD_CALL]);
 impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
         // We only care about method calls.
-        let (call, elements) = match expr.kind {
-            ExprKind::MethodCall(call, _, elements, _) => (call, elements),
-            _ => return,
+        let ExprKind::MethodCall(call, _, elements, _) = &expr.kind else {
+            return
         };
         // We only care about method calls corresponding to the `Clone`, `Deref` and `Borrow`
         // traits and ignore any other method call.
@@ -70,9 +69,8 @@ impl<'tcx> LateLintPass<'tcx> for NoopMethodCall {
         }
         let param_env = cx.tcx.param_env(trait_id);
         // Resolve the trait method instance.
-        let i = match ty::Instance::resolve(cx.tcx, param_env, did, substs) {
-            Ok(Some(i)) => i,
-            _ => return,
+        let Ok(Some(i)) = ty::Instance::resolve(cx.tcx, param_env, did, substs) else {
+            return
         };
         // (Re)check that it implements the noop diagnostic.
         let Some(name) = cx.tcx.get_diagnostic_name(i.def_id()) else { return };

compiler/rustc_lint/src/traits.rs

@@ -91,9 +91,8 @@ impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
 
         let predicates = cx.tcx.explicit_predicates_of(item.def_id);
         for &(predicate, span) in predicates.predicates {
-            let trait_predicate = match predicate.kind().skip_binder() {
-                Trait(trait_predicate) => trait_predicate,
-                _ => continue,
+            let Trait(trait_predicate) = predicate.kind().skip_binder() else {
+                continue
             };
             if trait_predicate.constness == ty::BoundConstness::ConstIfConst {
                 // `~const Drop` definitely have meanings so avoid linting here.
@@ -106,9 +105,8 @@ impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
                     continue;
                 }
                 cx.struct_span_lint(DROP_BOUNDS, span, |lint| {
-                    let needs_drop = match cx.tcx.get_diagnostic_item(sym::needs_drop) {
-                        Some(needs_drop) => needs_drop,
-                        None => return,
+                    let Some(needs_drop) = cx.tcx.get_diagnostic_item(sym::needs_drop) else {
+                        return
                     };
                     let msg = format!(
                         "bounds on `{}` are most likely incorrect, consider instead \
@@ -123,17 +121,15 @@ impl<'tcx> LateLintPass<'tcx> for DropTraitConstraints {
     }
 
     fn check_ty(&mut self, cx: &LateContext<'_>, ty: &'tcx hir::Ty<'tcx>) {
-        let bounds = match &ty.kind {
-            hir::TyKind::TraitObject(bounds, _lifetime, _syntax) => bounds,
-            _ => return,
+        let hir::TyKind::TraitObject(bounds, _lifetime, _syntax) = &ty.kind else {
+            return
         };
         for bound in &bounds[..] {
             let def_id = bound.trait_ref.trait_def_id();
             if cx.tcx.lang_items().drop_trait() == def_id {
                 cx.struct_span_lint(DYN_DROP, bound.span, |lint| {
-                    let needs_drop = match cx.tcx.get_diagnostic_item(sym::needs_drop) {
-                        Some(needs_drop) => needs_drop,
-                        None => return,
+                    let Some(needs_drop) = cx.tcx.get_diagnostic_item(sym::needs_drop) else {
+                        return
                     };
                     let msg = format!(
                         "types that do not implement `Drop` can still have drop glue, consider \

compiler/rustc_lint/src/types.rs

@@ -1342,11 +1342,10 @@ impl<'tcx> LateLintPass<'tcx> for VariantSizeDifferences {
                     | ty::layout::LayoutError::NormalizationFailure(_, _),
                 ) => return,
             };
-            let (variants, tag) = match layout.variants {
-                Variants::Multiple {
+            let Variants::Multiple {
                     tag_encoding: TagEncoding::Direct, tag, ref variants, ..
-                } => (variants, tag),
-                _ => return,
+                } = &layout.variants else {
+                return
             };
 
             let tag_size = tag.value.size(&cx.tcx).bytes();