[preprocessor] Don't warn about "disabled expansion of recursive macro"

for "#define X X".

This is a pattern that, for example, stdbool.h uses.
rdar://12435773

llvm-svn: 173952

clang/lib/Lex/PPMacroExpansion.cpp

@@ -459,7 +459,10 @@ bool Preprocessor::HandleMacroExpandedIdentifier(Token &Identifier,
       if (MacroInfo *NewMI = getMacroInfo(NewII))
         if (!NewMI->isEnabled() || NewMI == MI) {
           Identifier.setFlag(Token::DisableExpand);
-          Diag(Identifier, diag::pp_disabled_macro_expansion);
+          // Don't warn for "#define X X" like "#define bool bool" from
+          // stdbool.h.
+          if (NewMI != MI)
+            Diag(Identifier, diag::pp_disabled_macro_expansion);
         }
     }
 

clang/test/Headers/stdbool.cpp

@@ -1,5 +1,6 @@
 // RUN: %clang_cc1 -E -dM %s | FileCheck --check-prefix=CHECK-GNU-COMPAT %s
 // RUN: %clang_cc1 -std=c++98 -E -dM %s | FileCheck --check-prefix=CHECK-CONFORMING %s
+// RUN: %clang_cc1 -fsyntax-only -std=gnu++98 -verify -Weverything %s
 #include <stdbool.h>
 #define zzz
 
@@ -12,3 +13,7 @@
 // CHECK-CONFORMING: #define __CHAR_BIT__
 // CHECK-CONFORMING-NOT: #define false false
 // CHECK-CONFORMING: #define zzz
+
+zzz
+// expected-no-diagnostics
+extern bool x;

clang/test/Preprocessor/warn-disabled-macro-expansion.c

@@ -16,7 +16,7 @@
 
 #define z(x) (z)(x)
 
-p // expected-warning {{recursive macro}}
+p // no warning
 
 a // expected-warning {{recursive macro}}