[PATCH] D56879: [Sema] Suppress a warning about a forward-declared fixed enum in C mode

[Erik Pilkington via Phabricator via cfe-commits]

erik.pilkington created this revision.
erik.pilkington added reviewers: rsmith, aaron.ballman, arphaman.
Herald added subscribers: dexonsmith, jkorous.

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

Thanks for taking a look!
Erik


Repository:
  rC Clang

https://reviews.llvm.org/D56879

Files:
  clang/lib/Sema/SemaDecl.cpp
  clang/test/Sema/fixed-enum.c


Index: clang/test/Sema/fixed-enum.c
===================================================================
--- clang/test/Sema/fixed-enum.c
+++ clang/test/Sema/fixed-enum.c
@@ -10,9 +10,29 @@
 #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')}}
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -14743,8 +14743,7 @@
     // 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.
       }



Index: clang/test/Sema/fixed-enum.c
===================================================================
--- clang/test/Sema/fixed-enum.c
+++ clang/test/Sema/fixed-enum.c
@@ -10,9 +10,29 @@
 #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')}}
Index: clang/lib/Sema/SemaDecl.cpp
===================================================================
--- clang/lib/Sema/SemaDecl.cpp
+++ clang/lib/Sema/SemaDecl.cpp
@@ -14743,8 +14743,7 @@
     // 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.
       }

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