From c8fd2dae17a0fc631a07ab7b66c9d3ebe90a0cc6 Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Tue, 27 Apr 2010 16:26:47 +0000
Subject: [PATCH] When checking the redeclaration context of a typedef that
 refers to a tag of the same name, compare the lookup contexts rather than the
 actual contexts. Fixes PR6923.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@102437 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp           |  3 ++-
 test/SemaCXX/typedef-redecl.cpp | 11 +++++++++++
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index d9696d9ed5..fcee68d474 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -5029,7 +5029,8 @@ Sema::DeclPtrTy Sema::ActOnTag(Scope *S, unsigned TagSpec, TagUseKind TUK,
         if (const TagType *TT = TD->getUnderlyingType()->getAs<TagType>()) {
           TagDecl *Tag = TT->getDecl();
           if (Tag->getDeclName() == Name &&
-              Tag->getDeclContext()->Equals(TD->getDeclContext())) {
+              Tag->getDeclContext()->getLookupContext()
+                          ->Equals(TD->getDeclContext()->getLookupContext())) {
             PrevDecl = Tag;
             Previous.clear();
             Previous.addDecl(Tag);
diff --git a/test/SemaCXX/typedef-redecl.cpp b/test/SemaCXX/typedef-redecl.cpp
index 2acf6757fa..49e1f3aa79 100644
--- a/test/SemaCXX/typedef-redecl.cpp
+++ b/test/SemaCXX/typedef-redecl.cpp
@@ -37,3 +37,14 @@ namespace test1 {
   using namespace a; 
   foo x;
 }
+
+namespace PR6923 {
+  struct A;
+
+  extern "C" {
+    struct A;
+    typedef struct A A;
+  }
+
+  struct A;
+}