From da6440b5b99d40f0540d7210ffeb4835e66a7f22 Mon Sep 17 00:00:00 2001
From: Erik Pilkington <erik.pilkington@gmail.com>
Date: Fri, 18 Jan 2019 21:33:23 +0000
Subject: [PATCH] [Sema] Suppress a warning about a forward-declared fixed enum
 in C mode

As of r343360, we support fixed-enums in C. This lead to some
warnings in project headers where a fixed enum is forward declared
then later defined. In C++, this is fine, the forward declaration is
treated as a complete type even though the definition isn't present.
We use this rule in C too, but still warn about the forward
declaration anyways. This patch suppresses the warning.

rdar://problem/47356469

Differential revision: https://reviews.llvm.org/D56879

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@351595 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp  |  3 +--
 test/Sema/fixed-enum.c | 23 ++++++++++++++++++++++-
 2 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 03061eab35..a5a4833a5c 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -14747,8 +14747,7 @@ CreateNewDecl:
     // If this is an undefined enum, warn.
     if (TUK != TUK_Definition && !Invalid) {
       TagDecl *Def;
-      if (IsFixed && (getLangOpts().CPlusPlus11 || getLangOpts().ObjC) &&
-          cast<EnumDecl>(New)->isFixed()) {
+      if (IsFixed && cast<EnumDecl>(New)->isFixed()) {
         // C++0x: 7.2p2: opaque-enum-declaration.
         // Conflicts are diagnosed above. Do nothing.
       }
diff --git a/test/Sema/fixed-enum.c b/test/Sema/fixed-enum.c
index 60a4bc474f..c77f5b0cbe 100644
--- a/test/Sema/fixed-enum.c
+++ b/test/Sema/fixed-enum.c
@@ -2,6 +2,7 @@
 // RUN: %clang_cc1 -Weverything -xc++ -std=c++03 -DCXX03 -verify %s
 // RUN: %clang_cc1 -Weverything -xobjective-c -DOBJC -verify %s
 // RUN: %clang_cc1 -Weverything -std=c11 -xc -DC11 -verify %s
+// RUN: %clang_cc1 -pedantic    -std=c11 -xc -DC11 -verify %s
 // RUN: %clang_cc1 -Weverything -std=c11 -xc -fms-extensions -DMS -verify %s
 
 enum X : int {e};
@@ -10,9 +11,29 @@ enum X : int {e};
 #elif defined(CXX03)
 // expected-warning@-4{{enumeration types with a fixed underlying type are a C++11 extension}}
 #elif defined(OBJC)
-// expected-no-diagnostics
+// No diagnostic
 #elif defined(C11)
 // expected-warning@-8{{enumeration types with a fixed underlying type are a Clang extension}}
 #elif defined(MS)
 // expected-warning@-10{{enumeration types with a fixed underlying type are a Microsoft extension}}
 #endif
+
+// Don't warn about the forward declaration in any language mode.
+enum Fwd : int;
+enum Fwd : int { e2 };
+#ifndef OBJC
+// expected-warning@-3 {{enumeration types with a fixed underlying type}}
+// expected-warning@-3 {{enumeration types with a fixed underlying type}}
+#endif
+
+// Always error on the incompatible redeclaration.
+enum BadFwd : int;
+#ifndef OBJC
+// expected-warning@-2 {{enumeration types with a fixed underlying type}}
+#endif
+// expected-note@-4 {{previous declaration is here}}
+enum BadFwd : char { e3 };
+#ifndef OBJC
+// expected-warning@-2 {{enumeration types with a fixed underlying type}}
+#endif
+// expected-error@-4 {{enumeration redeclared with different underlying type 'char' (was 'int')}}
-- 
2.50.1