Use let...else instead of match foo { ... _ => return }; and if let ... else return

Author: estebank

compiler/rustc_ast/src/ast.rs

@@ -1534,11 +1534,10 @@ impl Expr {
             // then type of result is trait object.
             // Otherwise we don't assume the result type.
             ExprKind::Binary(binop, lhs, rhs) if binop.node == BinOpKind::Add => {
-                if let (Some(lhs), Some(rhs)) = (lhs.to_bound(), rhs.to_bound()) {
-                    TyKind::TraitObject(vec![lhs, rhs], TraitObjectSyntax::None)
-                } else {
+                let (Some(lhs), Some(rhs)) = (lhs.to_bound(), rhs.to_bound()) else {
                     return None;
-                }
+                };
+                TyKind::TraitObject(vec![lhs, rhs], TraitObjectSyntax::None)
             }
 
             ExprKind::Underscore => TyKind::Infer,

compiler/rustc_ast/src/attr/mod.rs

@@ -402,20 +402,17 @@ impl MetaItem {
                     thin_vec![PathSegment::path_root(span)]
                 };
                 loop {
-                    if let Some(&TokenTree::Token(Token { kind: token::Ident(name, _), span }, _)) =
+                    let Some(&TokenTree::Token(Token { kind: token::Ident(name, _), span }, _)) =
                         iter.next().map(|tt| TokenTree::uninterpolate(tt)).as_deref()
-                    {
-                        segments.push(PathSegment::from_ident(Ident::new(name, span)));
-                    } else {
+                    else {
                         return None;
-                    }
-                    if let Some(TokenTree::Token(Token { kind: token::PathSep, .. }, _)) =
-                        iter.peek()
-                    {
-                        iter.next();
-                    } else {
+                    };
+                    segments.push(PathSegment::from_ident(Ident::new(name, span)));
+                    let Some(TokenTree::Token(Token { kind: token::PathSep, .. }, _)) = iter.peek()
+                    else {
                         break;
-                    }
+                    };
+                    iter.next();
                 }
                 let span = span.with_hi(segments.last().unwrap().ident.span.hi());
                 Path { span, segments, tokens: None }

compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -561,11 +561,8 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             VarDebugInfoContents::Place(ref p) => p == place,
             _ => false,
         });
-        let arg_name = if let Some(var_info) = var_info {
-            var_info.name
-        } else {
-            return;
-        };
+        let Some(var_info) = var_info else { return };
+        let arg_name = var_info.name;
         struct MatchArgFinder {
             expr_span: Span,
             match_arg_span: Option<Span>,

compiler/rustc_borrowck/src/diagnostics/explain_borrow.rs

@@ -850,16 +850,10 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, 'tcx> {
         // will only ever have one item at any given time, but by using a vector, we can pop from
         // it which simplifies the termination logic.
         let mut queue = vec![location];
-        let mut target =
-            if let Some(Statement { kind: StatementKind::Assign(box (place, _)), .. }) = stmt {
-                if let Some(local) = place.as_local() {
-                    local
-                } else {
-                    return false;
-                }
-            } else {
-                return false;
-            };
+        let Some(Statement { kind: StatementKind::Assign(box (place, _)), .. }) = stmt else {
+            return false;
+        };
+        let Some(mut target) = place.as_local() else { return false };
 
         debug!("was_captured_by_trait: target={:?} queue={:?}", target, queue);
         while let Some(current_location) = queue.pop() {

compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -1124,16 +1124,12 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         use self::UseSpans::*;
         debug!("borrow_spans: use_span={:?} location={:?}", use_span, location);
 
-        let target = match self.body[location.block].statements.get(location.statement_index) {
-            Some(Statement { kind: StatementKind::Assign(box (place, _)), .. }) => {
-                if let Some(local) = place.as_local() {
-                    local
-                } else {
-                    return OtherUse(use_span);
-                }
-            }
-            _ => return OtherUse(use_span),
+        let Some(Statement { kind: StatementKind::Assign(box (place, _)), .. }) =
+            self.body[location.block].statements.get(location.statement_index)
+        else {
+            return OtherUse(use_span);
         };
+        let Some(target) = place.as_local() else { return OtherUse(use_span) };
 
         if self.body.local_kind(target) != LocalKind::Temp {
             // operands are always temporaries.

compiler/rustc_borrowck/src/diagnostics/mutability_errors.rs

@@ -142,12 +142,11 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
                 } else {
                     item_msg = access_place_desc;
                     let local_info = self.body.local_decls[local].local_info();
-                    if let LocalInfo::StaticRef { def_id, .. } = *local_info {
-                        let static_name = &self.infcx.tcx.item_name(def_id);
-                        reason = format!(", as `{static_name}` is an immutable static item");
-                    } else {
+                    let LocalInfo::StaticRef { def_id, .. } = *local_info else {
                         bug!("is_ref_to_static return true, but not ref to static?");
-                    }
+                    };
+                    let static_name = &self.infcx.tcx.item_name(def_id);
+                    reason = format!(", as `{static_name}` is an immutable static item");
                 }
             }
             PlaceRef { local, projection: [proj_base @ .., ProjectionElem::Deref] } => {

compiler/rustc_borrowck/src/diagnostics/region_errors.rs

@@ -847,11 +847,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
             let fn_returns = self.infcx.tcx.return_type_impl_or_dyn_traits(suitable_region.scope);
 
-            let param = if let Some(param) =
+            let Some(param) =
                 find_param_with_region(self.infcx.tcx, self.mir_def_id(), f, outlived_f)
-            {
-                param
-            } else {
+            else {
                 return;
             };
 
@@ -930,37 +928,27 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
 
         let tcx = self.infcx.tcx;
 
-        let instance = if let ConstraintCategory::CallArgument(Some(func_ty)) = category {
-            let (fn_did, args) = match func_ty.kind() {
-                ty::FnDef(fn_did, args) => (fn_did, args),
-                _ => return,
-            };
-            debug!(?fn_did, ?args);
+        let ConstraintCategory::CallArgument(Some(func_ty)) = category else { return };
+        let ty::FnDef(fn_did, args) = func_ty.kind() else { return };
+        debug!(?fn_did, ?args);
 
-            // Only suggest this on function calls, not closures
-            let ty = tcx.type_of(fn_did).instantiate_identity();
-            debug!("ty: {:?}, ty.kind: {:?}", ty, ty.kind());
-            if let ty::Closure(_, _) = ty.kind() {
-                return;
-            }
-
-            if let Ok(Some(instance)) = ty::Instance::try_resolve(
-                tcx,
-                self.infcx.typing_env(self.infcx.param_env),
-                *fn_did,
-                self.infcx.resolve_vars_if_possible(args),
-            ) {
-                instance
-            } else {
-                return;
-            }
-        } else {
+        // Only suggest this on function calls, not closures
+        let ty = tcx.type_of(fn_did).instantiate_identity();
+        debug!("ty: {:?}, ty.kind: {:?}", ty, ty.kind());
+        if let ty::Closure(_, _) = ty.kind() {
+            return;
+        }
+        let Ok(Some(instance)) = ty::Instance::try_resolve(
+            tcx,
+            self.infcx.typing_env(self.infcx.param_env),
+            *fn_did,
+            self.infcx.resolve_vars_if_possible(args),
+        ) else {
             return;
         };
 
-        let param = match find_param_with_region(tcx, self.mir_def_id(), f, o) {
-            Some(param) => param,
-            None => return,
+        let Some(param) = find_param_with_region(tcx, self.mir_def_id(), f, o) else {
+            return;
         };
         debug!(?param);
 

compiler/rustc_borrowck/src/polonius/legacy/accesses.rs

@@ -67,12 +67,11 @@ impl<'a, 'tcx> Visitor<'tcx> for AccessFactsExtractor<'a, 'tcx> {
         match context {
             PlaceContext::NonMutatingUse(_)
             | PlaceContext::MutatingUse(MutatingUseContext::Borrow) => {
-                let path = match self.move_data.rev_lookup.find(place.as_ref()) {
-                    LookupResult::Exact(path) | LookupResult::Parent(Some(path)) => path,
-                    _ => {
-                        // There's no path access to emit.
-                        return;
-                    }
+                let (LookupResult::Exact(path) | LookupResult::Parent(Some(path))) =
+                    self.move_data.rev_lookup.find(place.as_ref())
+                else {
+                    // There's no path access to emit.
+                    return;
                 };
                 debug!("AccessFactsExtractor - emit path access ({path:?}, {location:?})");
                 self.facts.path_accessed_at_base.push((path, self.location_to_index(location)));

compiler/rustc_codegen_cranelift/src/debuginfo/unwind.rs

@@ -130,11 +130,9 @@ impl UnwindContext {
             return;
         }
 
-        let unwind_info = if let Some(unwind_info) =
+        let Some(unwind_info) =
             context.compiled_code().unwrap().create_unwind_info(module.isa()).unwrap()
-        {
-            unwind_info
-        } else {
+        else {
             return;
         };
 

compiler/rustc_codegen_cranelift/src/optimize/peephole.rs

@@ -29,11 +29,7 @@ pub(crate) fn maybe_known_branch_taken(
     arg: Value,
     test_zero: bool,
 ) -> Option<bool> {
-    let arg_inst = if let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) {
-        arg_inst
-    } else {
-        return None;
-    };
+    let ValueDef::Result(arg_inst, 0) = bcx.func.dfg.value_def(arg) else { return None };
 
     match bcx.func.dfg.insts[arg_inst] {
         InstructionData::UnaryImm { opcode: Opcode::Iconst, imm } => {