add a scope for `if let` guard temporaries and bindings

This ensures `if let` guard temporaries and bindings are dropped before
the match arm's pattern's bindings.

1 files changed, 5 insertions, 0 deletions

diff --git a/compiler/rustc_hir_analysis/src/check/region.rs b/compiler/rustc_hir_analysis/src/check/region.rs
index 95f6fba6487..d43ac053758 100644
--- a/compiler/rustc_hir_analysis/src/check/region.rs
+++ b/compiler/rustc_hir_analysis/src/check/region.rs
@@ -198,6 +198,11 @@ 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 {
         resolve_cond(visitor, guard);
     }