only introduce a guard scope for arms with guards

5 files changed, 39 insertions, 23 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
index d43ac053758..f5770b7312d 100644
--- a/compiler/rustc_hir_analysis/src/check/region.rs
+++ b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -198,12 +198,12 @@ fn resolve_arm<'tcx>(visitor: &mut ScopeResolutionVisitor<'tcx>, arm: &'tcx hir:
     visitor.cx.var_parent = visitor.cx.parent;
 
     resolve_pat(visitor, arm.pat);
-    // We introduce a new scope to contain bindings and temporaries from `if let` guards, to
-    // ensure they're dropped before the arm's pattern's bindings. This extends to the end of
-    // the arm body and is the scope of its locals as well.
-    visitor.enter_scope(Scope { local_id: arm.hir_id.local_id, data: ScopeData::MatchGuard });
-    visitor.cx.var_parent = visitor.cx.parent;
     if let Some(guard) = arm.guard {
+        // We introduce a new scope to contain bindings and temporaries from `if let` guards, to
+        // ensure they're dropped before the arm's pattern's bindings. This extends to the end of
+        // the arm body and is the scope of its locals as well.
+        visitor.enter_scope(Scope { local_id: arm.hir_id.local_id, data: ScopeData::MatchGuard });
+        visitor.cx.var_parent = visitor.cx.parent;
         resolve_cond(visitor, guard);
     }
     resolve_expr(visitor, arm.body, false);
diff --git a/compiler/rustc_mir_build/src/builder/matches/mod.rs b/compiler/rustc_mir_build/src/builder/matches/mod.rs
index c9a561fc54a..d5822a65b17 100644
--- a/compiler/rustc_mir_build/src/builder/matches/mod.rs
+++ b/compiler/rustc_mir_build/src/builder/matches/mod.rs
@@ -434,12 +434,14 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                 let arm_source_info = self.source_info(arm.span);
                 let arm_scope = (arm.scope, arm_source_info);
                 let match_scope = self.local_scope();
+                let guard_scope = arm
+                    .guard
+                    .map(|_| region::Scope { data: region::ScopeData::MatchGuard, ..arm.scope });
                 self.in_scope(arm_scope, arm.lint_level, |this| {
-                    let guard_scope =
-                        region::Scope { data: region::ScopeData::MatchGuard, ..arm.scope };
-                    this.in_scope((guard_scope, arm_source_info), LintLevel::Inherited, |this| {
+                    this.opt_in_scope(guard_scope.map(|scope| (scope, arm_source_info)), |this| {
+                        // `if let` guard temps needing deduplicating will be in the guard scope.
                         let old_dedup_scope =
-                            mem::replace(&mut this.fixed_temps_scope, Some(guard_scope));
+                            mem::replace(&mut this.fixed_temps_scope, guard_scope);
 
                         // `try_to_place` may fail if it is unable to resolve the given
                         // `PlaceBuilder` inside a closure. In this case, we don't want to include
diff --git a/compiler/rustc_mir_build/src/builder/scope.rs b/compiler/rustc_mir_build/src/builder/scope.rs
index 403e7167a69..96659873622 100644
--- a/compiler/rustc_mir_build/src/builder/scope.rs
+++ b/compiler/rustc_mir_build/src/builder/scope.rs
@@ -697,6 +697,20 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         block.and(rv)
     }
 
+    /// Convenience wrapper that executes `f` either within the current scope or a new scope.
+    /// Used for pattern matching, which introduces an additional scope for patterns with guards.
+    pub(crate) fn opt_in_scope<R>(
+        &mut self,
+        opt_region_scope: Option<(region::Scope, SourceInfo)>,
+        f: impl FnOnce(&mut Builder<'a, 'tcx>) -> BlockAnd<R>,
+    ) -> BlockAnd<R> {
+        if let Some(region_scope) = opt_region_scope {
+            self.in_scope(region_scope, LintLevel::Inherited, f)
+        } else {
+            f(self)
+        }
+    }
+
     /// Push a scope onto the stack. You can then build code in this
     /// scope and call `pop_scope` afterwards. Note that these two
     /// calls must be paired; using `in_scope` as a convenience
diff --git a/tests/ui/thir-print/thir-tree-loop-match.stdout b/tests/ui/thir-print/thir-tree-loop-match.stdout
index 86d37e987e2..5c4c50cb156 100644
--- a/tests/ui/thir-print/thir-tree-loop-match.stdout
+++ b/tests/ui/thir-print/thir-tree-loop-match.stdout
@@ -129,7 +129,7 @@ body:
                                                                                                 body: 
                                                                                                     Expr {
                                                                                                         ty: bool
-                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(16)), backwards_incompatible: None }
+                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(16)), backwards_incompatible: None }
                                                                                                         span: $DIR/thir-tree-loop-match.rs:12:25: 15:18 (#0)
                                                                                                         kind: 
                                                                                                             Scope {
@@ -138,14 +138,14 @@ body:
                                                                                                                 value:
                                                                                                                     Expr {
                                                                                                                         ty: bool
-                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(16)), backwards_incompatible: None }
+                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(16)), backwards_incompatible: None }
                                                                                                                         span: $DIR/thir-tree-loop-match.rs:12:25: 15:18 (#0)
                                                                                                                         kind: 
                                                                                                                             NeverToAny {
                                                                                                                                 source:
                                                                                                                                     Expr {
                                                                                                                                         ty: !
-                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(16)), backwards_incompatible: None }
+                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(16)), backwards_incompatible: None }
                                                                                                                                         span: $DIR/thir-tree-loop-match.rs:12:25: 15:18 (#0)
                                                                                                                                         kind: 
                                                                                                                                             Block {
@@ -227,7 +227,7 @@ body:
                                                                                                 body: 
                                                                                                     Expr {
                                                                                                         ty: bool
-                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(24)), backwards_incompatible: None }
+                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(24)), backwards_incompatible: None }
                                                                                                         span: $DIR/thir-tree-loop-match.rs:16:26: 16:38 (#0)
                                                                                                         kind: 
                                                                                                             Scope {
@@ -236,21 +236,21 @@ body:
                                                                                                                 value:
                                                                                                                     Expr {
                                                                                                                         ty: bool
-                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(24)), backwards_incompatible: None }
+                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(24)), backwards_incompatible: None }
                                                                                                                         span: $DIR/thir-tree-loop-match.rs:16:26: 16:38 (#0)
                                                                                                                         kind: 
                                                                                                                             NeverToAny {
                                                                                                                                 source:
                                                                                                                                     Expr {
                                                                                                                                         ty: !
-                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(24)), backwards_incompatible: None }
+                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(24)), backwards_incompatible: None }
                                                                                                                                         span: $DIR/thir-tree-loop-match.rs:16:26: 16:38 (#0)
                                                                                                                                         kind: 
                                                                                                                                             Return {
                                                                                                                                                 value:
                                                                                                                                                     Expr {
                                                                                                                                                         ty: bool
-                                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(24)), backwards_incompatible: None }
+                                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(24)), backwards_incompatible: None }
                                                                                                                                                         span: $DIR/thir-tree-loop-match.rs:16:33: 16:38 (#0)
                                                                                                                                                         kind: 
                                                                                                                                                             Scope {
@@ -259,7 +259,7 @@ body:
                                                                                                                                                                 value:
                                                                                                                                                                     Expr {
                                                                                                                                                                         ty: bool
-                                                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(24)), backwards_incompatible: None }
+                                                                                                                                                                        temp_lifetime: TempLifetime { temp_lifetime: Some(Node(24)), backwards_incompatible: None }
                                                                                                                                                                         span: $DIR/thir-tree-loop-match.rs:16:33: 16:38 (#0)
                                                                                                                                                                         kind: 
                                                                                                                                                                             VarRef {
diff --git a/tests/ui/thir-print/thir-tree-match.stdout b/tests/ui/thir-print/thir-tree-match.stdout
index 31b9b3b9995..2049c531abd 100644
--- a/tests/ui/thir-print/thir-tree-match.stdout
+++ b/tests/ui/thir-print/thir-tree-match.stdout
@@ -123,7 +123,7 @@ body:
                                                                         body: 
                                                                             Expr {
                                                                                 ty: bool
-                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(14)), backwards_incompatible: None }
+                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(Node(14)), backwards_incompatible: None }
                                                                                 span: $DIR/thir-tree-match.rs:17:36: 17:40 (#0)
                                                                                 kind: 
                                                                                     Scope {
@@ -132,7 +132,7 @@ body:
                                                                                         value:
                                                                                             Expr {
                                                                                                 ty: bool
-                                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(14)), backwards_incompatible: None }
+                                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(Node(14)), backwards_incompatible: None }
                                                                                                 span: $DIR/thir-tree-match.rs:17:36: 17:40 (#0)
                                                                                                 kind: 
                                                                                                     Literal( lit: Spanned { node: Bool(true), span: $DIR/thir-tree-match.rs:17:36: 17:40 (#0) }, neg: false)
@@ -175,7 +175,7 @@ body:
                                                                         body: 
                                                                             Expr {
                                                                                 ty: bool
-                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(20)), backwards_incompatible: None }
+                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(Node(20)), backwards_incompatible: None }
                                                                                 span: $DIR/thir-tree-match.rs:18:27: 18:32 (#0)
                                                                                 kind: 
                                                                                     Scope {
@@ -184,7 +184,7 @@ body:
                                                                                         value:
                                                                                             Expr {
                                                                                                 ty: bool
-                                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(20)), backwards_incompatible: None }
+                                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(Node(20)), backwards_incompatible: None }
                                                                                                 span: $DIR/thir-tree-match.rs:18:27: 18:32 (#0)
                                                                                                 kind: 
                                                                                                     Literal( lit: Spanned { node: Bool(false), span: $DIR/thir-tree-match.rs:18:27: 18:32 (#0) }, neg: false)
@@ -219,7 +219,7 @@ body:
                                                                         body: 
                                                                             Expr {
                                                                                 ty: bool
-                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(26)), backwards_incompatible: None }
+                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(Node(26)), backwards_incompatible: None }
                                                                                 span: $DIR/thir-tree-match.rs:19:24: 19:28 (#0)
                                                                                 kind: 
                                                                                     Scope {
@@ -228,7 +228,7 @@ body:
                                                                                         value:
                                                                                             Expr {
                                                                                                 ty: bool
-                                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(MatchGuard(26)), backwards_incompatible: None }
+                                                                                                temp_lifetime: TempLifetime { temp_lifetime: Some(Node(26)), backwards_incompatible: None }
                                                                                                 span: $DIR/thir-tree-match.rs:19:24: 19:28 (#0)
                                                                                                 kind: 
                                                                                                     Literal( lit: Spanned { node: Bool(true), span: $DIR/thir-tree-match.rs:19:24: 19:28 (#0) }, neg: false)