Fix -Wshadow false positives with function-local classes.

Summary:
Fixes http://llvm.org/PR33947.

https://godbolt.org/g/54XRMT

void f(int a) {
  struct A {
    void g(int a) {}
    A() { int a; }
  };
}

3 : <source>:3:16: warning: declaration shadows a local variable [-Wshadow]
    void g(int a) {}
               ^
1 : <source>:1:12: note: previous declaration is here
void f(int a) {
           ^
4 : <source>:4:15: warning: declaration shadows a local variable [-Wshadow]
    A() { int a; }
              ^
1 : <source>:1:12: note: previous declaration is here
void f(int a) {
           ^
2 warnings generated.

The local variable `a` of the function `f` can't be accessed from a method of
the function-local class A, thus no shadowing occurs and no diagnostic is
needed.

Reviewers: rnk, rsmith, arphaman, Quuxplusone

Reviewed By: rnk, Quuxplusone

Subscribers: Quuxplusone, cfe-commits

Differential Revision: https://reviews.llvm.org/D35941

llvm-svn: 309569

1 files changed, 15 insertions, 0 deletions

diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp
index 31b24f91c1d..6bcb0231743 100644
--- a/clang/lib/Sema/SemaDecl.cpp
+++ b/clang/lib/Sema/SemaDecl.cpp
@@ -6999,6 +6999,21 @@ void Sema::CheckShadow(NamedDecl *D, NamedDecl *ShadowedDecl,
           return;
         }
       }
+
+      if (cast<VarDecl>(ShadowedDecl)->hasLocalStorage()) {
+        // A variable can't shadow a local variable in an enclosing scope, if
+        // they are separated by a non-capturing declaration context.
+        for (DeclContext *ParentDC = NewDC;
+             ParentDC && !ParentDC->Equals(OldDC);
+             ParentDC = getLambdaAwareParentOfDeclContext(ParentDC)) {
+          // Only block literals, captured statements, and lambda expressions
+          // can capture; other scopes don't.
+          if (!isa<BlockDecl>(ParentDC) && !isa<CapturedDecl>(ParentDC) &&
+              !isLambdaCallOperator(ParentDC)) {
+            return;
+          }
+        }
+      }
     }
   }