use if let instead of single match arm expressions

compiler/rustc_infer/src/infer/error_reporting/nice_region_error/static_impl_trait.rs

@@ -488,18 +488,16 @@ impl<'tcx> Visitor<'tcx> for HirTraitObjectVisitor {
     }
 
     fn visit_ty(&mut self, t: &'tcx hir::Ty<'tcx>) {
-        match t.kind {
-            TyKind::TraitObject(
-                poly_trait_refs,
-                Lifetime { name: LifetimeName::ImplicitObjectLifetimeDefault, .. },
-            ) => {
-                for ptr in poly_trait_refs {
-                    if Some(self.1) == ptr.trait_ref.trait_def_id() {
-                        self.0.push(ptr.span);
-                    }
+        if let TyKind::TraitObject(
+            poly_trait_refs,
+            Lifetime { name: LifetimeName::ImplicitObjectLifetimeDefault, .. },
+        ) = t.kind
+        {
+            for ptr in poly_trait_refs {
+                if Some(self.1) == ptr.trait_ref.trait_def_id() {
+                    self.0.push(ptr.span);
                 }
             }
-            _ => {}
         }
         walk_ty(self, t);
     }

compiler/rustc_middle/src/ty/error.rs

@@ -832,14 +832,11 @@ fn foo(&self) -> Self::T { String::new() }
                 kind: hir::ItemKind::Impl { items, .. }, ..
             })) => {
                 for item in &items[..] {
-                    match item.kind {
-                        hir::AssocItemKind::Type => {
-                            if self.type_of(self.hir().local_def_id(item.id.hir_id)) == found {
-                                db.span_label(item.span, "expected this associated type");
-                                return true;
-                            }
+                    if let hir::AssocItemKind::Type = item.kind {
+                        if self.type_of(self.hir().local_def_id(item.id.hir_id)) == found {
+                            db.span_label(item.span, "expected this associated type");
+                            return true;
                         }
-                        _ => {}
                     }
                 }
             }

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

@@ -2125,17 +2125,10 @@ fn for_each_def(tcx: TyCtxt<'_>, mut collect_fn: impl for<'b> FnMut(&'b Ident, N
     // Iterate all local crate items no matter where they are defined.
     let hir = tcx.hir();
     for item in hir.krate().items.values() {
-        if item.ident.name.as_str().is_empty() {
+        if item.ident.name.as_str().is_empty() || matches!(item.kind, ItemKind::Use(_, _)) {
             continue;
         }
 
-        match item.kind {
-            ItemKind::Use(_, _) => {
-                continue;
-            }
-            _ => {}
-        }
-
         if let Some(local_def_id) = hir.definitions().opt_hir_id_to_local_def_id(item.hir_id) {
             let def_id = local_def_id.to_def_id();
             let ns = tcx.def_kind(def_id).ns().unwrap_or(Namespace::TypeNS);

compiler/rustc_mir/src/transform/promote_consts.rs

@@ -242,11 +242,8 @@ impl<'tcx> Visitor<'tcx> for Collector<'_, 'tcx> {
             }
             TerminatorKind::InlineAsm { ref operands, .. } => {
                 for (index, op) in operands.iter().enumerate() {
-                    match op {
-                        InlineAsmOperand::Const { .. } => {
-                            self.candidates.push(Candidate::InlineAsm { bb: location.block, index })
-                        }
-                        _ => {}
+                    if let InlineAsmOperand::Const { .. } = op {
+                        self.candidates.push(Candidate::InlineAsm { bb: location.block, index })
                     }
                 }
             }
@@ -612,12 +609,9 @@ impl<'tcx> Validator<'_, 'tcx> {
                 let operand_ty = operand.ty(self.body, self.tcx);
                 let cast_in = CastTy::from_ty(operand_ty).expect("bad input type for cast");
                 let cast_out = CastTy::from_ty(cast_ty).expect("bad output type for cast");
-                match (cast_in, cast_out) {
-                    (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) => {
-                        // ptr-to-int casts are not possible in consts and thus not promotable
-                        return Err(Unpromotable);
-                    }
-                    _ => {}
+                if let (CastTy::Ptr(_) | CastTy::FnPtr, CastTy::Int(_)) = (cast_in, cast_out) {
+                    // ptr-to-int casts are not possible in consts and thus not promotable
+                    return Err(Unpromotable);
                 }
             }
 

compiler/rustc_parse/src/lexer/tokentrees.rs

@@ -149,12 +149,9 @@ impl<'a> TokenTreesReader<'a> {
                             }
                         }
 
-                        match (open_brace, delim) {
-                            //only add braces
-                            (DelimToken::Brace, DelimToken::Brace) => {
-                                self.matching_block_spans.push((open_brace_span, close_brace_span));
-                            }
-                            _ => {}
+                        //only add braces
+                        if let (DelimToken::Brace, DelimToken::Brace) = (open_brace, delim) {
+                            self.matching_block_spans.push((open_brace_span, close_brace_span));
                         }
 
                         if self.open_braces.is_empty() {

compiler/rustc_parse_format/src/lib.rs

@@ -527,12 +527,9 @@ impl<'a> Parser<'a> {
 
         // fill character
         if let Some(&(_, c)) = self.cur.peek() {
-            match self.cur.clone().nth(1) {
-                Some((_, '>' | '<' | '^')) => {
-                    spec.fill = Some(c);
-                    self.cur.next();
-                }
-                _ => {}
+            if let Some((_, '>' | '<' | '^')) = self.cur.clone().nth(1) {
+                spec.fill = Some(c);
+                self.cur.next();
             }
         }
         // Alignment

compiler/rustc_resolve/src/lib.rs

@@ -534,11 +534,8 @@ impl<'a> ModuleData<'a> {
                 if ns != TypeNS {
                     return;
                 }
-                match binding.res() {
-                    Res::Def(DefKind::Trait | DefKind::TraitAlias, _) => {
-                        collected_traits.push((name, binding))
-                    }
-                    _ => (),
+                if let Res::Def(DefKind::Trait | DefKind::TraitAlias, _) = binding.res() {
+                    collected_traits.push((name, binding))
                 }
             });
             *traits = Some(collected_traits.into_boxed_slice());

compiler/rustc_symbol_mangling/src/v0.rs

@@ -152,11 +152,8 @@ impl SymbolMangler<'tcx> {
         let _ = write!(self.out, "{}", ident.len());
 
         // Write a separating `_` if necessary (leading digit or `_`).
-        match ident.chars().next() {
-            Some('_' | '0'..='9') => {
-                self.push("_");
-            }
-            _ => {}
+        if let Some('_' | '0'..='9') = ident.chars().next() {
+            self.push("_");
         }
 
         self.push(ident);