From 5e7b1eae1303a95061dab857dccb0ff15d5f943a Mon Sep 17 00:00:00 2001
From: Aaron Ballman <aaron@aaronballman.com>
Date: Tue, 23 Oct 2018 19:44:51 +0000
Subject: [PATCH] Change getRedeclContext() to support enumerations as another
 kind of transparent context in C.

This change fixes PR15071 and ensures that enumerators redefined in a struct cannot conflict with enumerators defined outside of the struct.

llvm-svn: 345073
---
 clang/lib/AST/DeclBase.cpp | 14 ++++++++++++--
 clang/test/Sema/enum.c     | 23 +++++++++++++++++++++++
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/clang/lib/AST/DeclBase.cpp b/clang/lib/AST/DeclBase.cpp
index f5de359..f65d306 100644
--- a/clang/lib/AST/DeclBase.cpp
+++ b/clang/lib/AST/DeclBase.cpp
@@ -1724,8 +1724,18 @@ void DeclContext::localUncachedLookup(DeclarationName Name,
 
 DeclContext *DeclContext::getRedeclContext() {
   DeclContext *Ctx = this;
-  // Skip through transparent contexts.
-  while (Ctx->isTransparentContext())
+
+  // In C, a record type is the redeclaration context for its fields only. If
+  // we arrive at a record context after skipping anything else, we should skip
+  // the record as well. Currently, this means skipping enumerations because
+  // they're the only transparent context that can exist within a struct or
+  // union.
+  bool SkipRecords = getDeclKind() == Decl::Kind::Enum &&
+                     !getParentASTContext().getLangOpts().CPlusPlus;
+
+  // Skip through contexts to get to the redeclaration context. Transparent
+  // contexts are always skipped.
+  while ((SkipRecords && Ctx->isRecord()) || Ctx->isTransparentContext())
     Ctx = Ctx->getParent();
   return Ctx;
 }
diff --git a/clang/test/Sema/enum.c b/clang/test/Sema/enum.c
index f9e4069..7681ebc 100644
--- a/clang/test/Sema/enum.c
+++ b/clang/test/Sema/enum.c
@@ -135,3 +135,26 @@ struct PR28903 {
   };
   int makeStructNonEmpty;
 };
+
+static int EnumRedecl; // expected-note 2 {{previous definition is here}}
+struct S {
+  enum {
+    EnumRedecl = 4 // expected-error {{redefinition of 'EnumRedecl'}}
+  } e;
+};
+
+union U {
+  enum {
+    EnumRedecl = 5 // expected-error {{redefinition of 'EnumRedecl'}}
+  } e;
+};
+
+enum PR15071 {
+  PR15071_One // expected-note {{previous definition is here}}
+};
+
+struct EnumRedeclStruct {
+  enum {
+    PR15071_One // expected-error {{redefinition of enumerator 'PR15071_One'}}
+  } e;
+};
-- 
2.7.4