From 444e8412950ee28cafb4d32a8c8598c81a98d6da Mon Sep 17 00:00:00 2001
From: Argiris Kirtzidis <akyrtzi@gmail.com>
Date: Mon, 31 Jan 2011 07:04:50 +0000
Subject: [PATCH] Fix the diagnostic when we are shadowing an external variable
 and there exists a locally scoped extern with the same name.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@124580 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp   | 37 ++++++++++++++++++++++++-------------
 test/Sema/warn-shadow.c |  7 ++++++-
 2 files changed, 30 insertions(+), 14 deletions(-)

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 24307c98a..253f1dcde 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -3129,21 +3129,32 @@ void Sema::CheckShadow(Scope *S, VarDecl *D, const LookupResult& R) {
   if (!isa<VarDecl>(ShadowedDecl) && !isa<FieldDecl>(ShadowedDecl))
     return;
 
-  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())
+  if (VarDecl *shadowedVar = dyn_cast<VarDecl>(ShadowedDecl))
+    if (shadowedVar->isExternC()) {
+      // Don't warn for this case:
+      //
+      // @code
+      // extern int bob;
+      // void f() {
+      //   extern int bob;
+      // }
+      // @endcode
+      if (D->isExternC())
         return;
 
+      // For shadowing external vars, make sure that we point to the global
+      // declaration, not a locally scoped extern declaration.
+      for (VarDecl::redecl_iterator
+             I = shadowedVar->redecls_begin(), E = shadowedVar->redecls_end();
+           I != E; ++I)
+        if (I->isFileVarDecl()) {
+          ShadowedDecl = *I;
+          break;
+        }
+    }
+
+  DeclContext *OldDC = ShadowedDecl->getDeclContext();
+
   // 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 c77bb0c45..32aca8d61 100644
--- a/test/Sema/warn-shadow.c
+++ b/test/Sema/warn-shadow.c
@@ -49,8 +49,13 @@ void test5(int i);
 void test6(void (*f)(int i)) {}
 void test7(void *context, void (*callback)(void *context)) {}
 
+extern int bob; // expected-note {{previous declaration is here}}
+
 // rdar://8883302
-extern int bob;
 void rdar8883302() {
   extern int bob; // don't warn for shadowing.
 }
+
+void test8() {
+  int bob; // expected-warning {{declaration shadows a variable in the global scope}}
+}
-- 
2.11.4.GIT