From d1d8fa55394d99ba9a36a7bc8a2eee0490df67b9 Mon Sep 17 00:00:00 2001
From: Argiris Kirtzidis <akyrtzi@gmail.com>
Date: Mon, 31 Jan 2011 07:04:41 +0000
Subject: [PATCH] 'extern' variables in functions don't shadow externs in
 global scope. Fixes rdar://8883302.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124578 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp   | 13 +++++++++++++
 test/Sema/warn-shadow.c |  6 ++++++
 2 files changed, 19 insertions(+)

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 1c487b811..bcc67b2e9 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -3117,6 +3117,19 @@ void Sema::CheckShadow(Scope *S, VarDecl *D, const LookupResult& R) {
 
   DeclContext *OldDC = ShadowedDecl->getDeclContext();
 
+  // Don't warn for this case:
+  //
+  // @code
+  // extern int bob;
+  // void f() {
+  //   extern int bob;
+  // }
+  // @endcode
+  if (D->isExternC() && NewDC->isFunctionOrMethod())
+    if (VarDecl *shadowedVar = dyn_cast<VarDecl>(ShadowedDecl))
+      if (shadowedVar->isExternC())
+        return;
+
   // Only warn about certain kinds of shadowing for class members.
   if (NewDC && NewDC->isRecord()) {
     // In particular, don't warn about shadowing non-class members.
diff --git a/test/Sema/warn-shadow.c b/test/Sema/warn-shadow.c
index a112210c9..c77bb0c45 100644
--- a/test/Sema/warn-shadow.c
+++ b/test/Sema/warn-shadow.c
@@ -48,3 +48,9 @@ void test4(int i) { // expected-warning {{declaration shadows a variable in the
 void test5(int i);
 void test6(void (*f)(int i)) {}
 void test7(void *context, void (*callback)(void *context)) {}
+
+// rdar://8883302
+extern int bob;
+void rdar8883302() {
+  extern int bob; // don't warn for shadowing.
+}
-- 
2.11.4.GIT