Support __has_c_attribute

[aaron.ballman]

Summary

We have the has_cpp_attribute builtin macro to determine when an attribute is supported with C++ [[]] syntax, and this patch adds the analogous has_c_attribute builtin macro so that users can test whether a given [[]] attribute is available in C when -fdouble-square-bracket-attributes is specified.

[aaron.ballman]

Ping

[aaron.ballman]

Ping

[aaron.ballman]

Ping

[rsmith]

Please update the documentation and the release notes.

[aaron.ballman]

Commit in r320088.

clang/include/clang/Lex/Preprocessor.h

class Preprocessor {
   IdentifierInfo *Ident__has_attribute;            // __has_attribute
   IdentifierInfo *Ident__has_include;              // __has_include
   IdentifierInfo *Ident__has_include_next;         // __has_include_next
   IdentifierInfo *Ident__has_warning;              // __has_warning
   IdentifierInfo *Ident__is_identifier;            // __is_identifier
   IdentifierInfo *Ident__building_module;          // __building_module
   IdentifierInfo *Ident__MODULE__;                 // __MODULE__
   IdentifierInfo *Ident__has_cpp_attribute;        // __has_cpp_attribute
+  IdentifierInfo *Ident__has_c_attribute;          // __has_c_attribute
   IdentifierInfo *Ident__has_declspec;             // __has_declspec_attribute
 
   SourceLocation DATELoc, TIMELoc;
   unsigned CounterValue;  // Next __COUNTER__ value.
 
   enum {
     /// \brief Maximum depth of \#includes.
     MaxAllowedIncludeStackDepth = 200

clang/lib/Lex/PPMacroExpansion.cpp

if (LangOpts.MicrosoftExt) {
     Ident__pragma = nullptr;
   }
 
   // Clang Extensions.
   Ident__has_feature      = RegisterBuiltinMacro(*this, "__has_feature");
   Ident__has_extension    = RegisterBuiltinMacro(*this, "__has_extension");
   Ident__has_builtin      = RegisterBuiltinMacro(*this, "__has_builtin");
   Ident__has_attribute    = RegisterBuiltinMacro(*this, "__has_attribute");
+  Ident__has_c_attribute  = RegisterBuiltinMacro(*this, "__has_c_attribute");
   Ident__has_declspec = RegisterBuiltinMacro(*this, "__has_declspec_attribute");
   Ident__has_include      = RegisterBuiltinMacro(*this, "__has_include");
   Ident__has_include_next = RegisterBuiltinMacro(*this, "__has_include_next");
   Ident__has_warning      = RegisterBuiltinMacro(*this, "__has_warning");
   Ident__is_identifier    = RegisterBuiltinMacro(*this, "__is_identifier");
 
   // Modules.
   Ident__building_module  = RegisterBuiltinMacro(*this, "__building_module");
void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
   } else if (II == Ident__has_declspec) {
     EvaluateFeatureLikeBuiltinMacro(OS, Tok, II, *this,
       [this](Token &Tok, bool &HasLexedNextToken) -> int {
         IdentifierInfo *II = ExpectFeatureIdentifierInfo(Tok, *this,
                                            diag::err_feature_check_malformed);
         return II ? hasAttribute(AttrSyntax::Declspec, nullptr, II,
                                  getTargetInfo(), getLangOpts()) : 0;
       });
-  } else if (II == Ident__has_cpp_attribute) {
-    EvaluateFeatureLikeBuiltinMacro(OS, Tok, II, *this,
-      [this](Token &Tok, bool &HasLexedNextToken) -> int {
+  } else if (II == Ident__has_cpp_attribute ||
+             II == Ident__has_c_attribute) {
+    bool IsCXX = II == Ident__has_cpp_attribute;
+    EvaluateFeatureLikeBuiltinMacro(
+        OS, Tok, II, *this, [&](Token &Tok, bool &HasLexedNextToken) -> int {
           IdentifierInfo *ScopeII = nullptr;
-        IdentifierInfo *II = ExpectFeatureIdentifierInfo(Tok, *this,
-                                           diag::err_feature_check_malformed);
+          IdentifierInfo *II = ExpectFeatureIdentifierInfo(
+              Tok, *this, diag::err_feature_check_malformed);
           if (!II)
             return false;
 
           // It is possible to receive a scope token.  Read the "::", if it is
           // available, and the subsequent identifier.
           LexUnexpandedToken(Tok);
           if (Tok.isNot(tok::coloncolon))
             HasLexedNextToken = true;
           else {
             ScopeII = II;
             LexUnexpandedToken(Tok);
             II = ExpectFeatureIdentifierInfo(Tok, *this,
                                              diag::err_feature_check_malformed);
           }
 
-        return II ? hasAttribute(AttrSyntax::CXX, ScopeII, II,
-                                 getTargetInfo(), getLangOpts()) : 0;
+          AttrSyntax Syntax = IsCXX ? AttrSyntax::CXX : AttrSyntax::C;
+          return II ? hasAttribute(Syntax, ScopeII, II, getTargetInfo(),
+                                   getLangOpts())
+                    : 0;
         });
   } else if (II == Ident__has_include ||
              II == Ident__has_include_next) {
     // The argument to these two builtins should be a parenthesized
     // file name string literal using angle brackets (<>) or
     // double-quotes ("").
     bool Value;
     if (II == Ident__has_include)
       Value = EvaluateHasInclude(Tok, II, *this);

clang/test/Preprocessor/has_c_attribute.c

+// RUN: %clang_cc1 -fdouble-square-bracket-attributes -std=c11 -E %s -o - | FileCheck %s
+
+// CHECK: has_fallthrough
+#if __has_c_attribute(fallthrough)
+  int has_fallthrough();
+#endif
+
+// CHECK: does_not_have_selectany
+#if !__has_c_attribute(selectany)
+  int does_not_have_selectany();
+#endif
+