Accept __has_feature(__feature__) as a synonym for __has_feature(feature) (and

likewise for __has_extension). Patch by Jonathan Sauer!

llvm-svn: 151445

clang/docs/LanguageExtensions.html

@@ -228,6 +228,11 @@ not related to the language standard, such as e.g.
 
 <p>The feature tag is described along with the language feature below.</p>
 
+<p>The feature name or extension name can also be specified with a preceding and
+following <code>__</code> (double underscore) to avoid interference from a macro
+with the same name. For instance, <code>__always_inline__</code> can be used
+instead of <code>always_inline</code>.</p>
+
 <!-- ======================================================================= -->
 <h3><a name="__has_attribute">__has_attribute</a></h3>
 <!-- ======================================================================= -->

clang/lib/Lex/PPMacroExpansion.cpp

@@ -589,8 +589,13 @@ static void ComputeDATE_TIME(SourceLocation &DATELoc, SourceLocation &TIMELoc,
 /// specified by the identifier as a standard language feature.
 static bool HasFeature(const Preprocessor &PP, const IdentifierInfo *II) {
   const LangOptions &LangOpts = PP.getLangOptions();
+  StringRef Feature = II->getName();
 
-  return llvm::StringSwitch<bool>(II->getName())
+  // Normalize the feature name, __foo__ becomes foo.
+  if (Feature.startswith("__") && Feature.endswith("__") && Feature.size() >= 4)
+    Feature = Feature.substr(2, Feature.size() - 4);
+
+  return llvm::StringSwitch<bool>(Feature)
            .Case("address_sanitizer", LangOpts.AddressSanitizer)
            .Case("attribute_analyzer_noreturn", true)
            .Case("attribute_availability", true)
@@ -724,10 +729,16 @@ static bool HasExtension(const Preprocessor &PP, const IdentifierInfo *II) {
     return false;
 
   const LangOptions &LangOpts = PP.getLangOptions();
+  StringRef Extension = II->getName();
+
+  // Normalize the extension name, __foo__ becomes foo.
+  if (Extension.startswith("__") && Extension.endswith("__") &&
+      Extension.size() >= 4)
+    Extension = Extension.substr(2, Extension.size() - 4);
 
   // Because we inherit the feature list from HasFeature, this string switch
   // must be less restrictive than HasFeature's.
-  return llvm::StringSwitch<bool>(II->getName())
+  return llvm::StringSwitch<bool>(Extension)
            // C11 features supported by other languages as extensions.
            .Case("c_alignas", true)
            .Case("c_atomic", true)

clang/lib/Sema/AttributeList.cpp

@@ -101,7 +101,8 @@ AttributeList::Kind AttributeList::getKind(const IdentifierInfo *Name) {
   StringRef AttrName = Name->getName();
 
   // Normalize the attribute name, __foo__ becomes foo.
-  if (AttrName.startswith("__") && AttrName.endswith("__"))
+  if (AttrName.startswith("__") && AttrName.endswith("__") &&
+      AttrName.size() >= 4)
     AttrName = AttrName.substr(2, AttrName.size() - 4);
 
   return llvm::StringSwitch<AttributeList::Kind>(AttrName)

clang/test/Lexer/has_extension.c

@@ -36,3 +36,9 @@ int has_c_alignas();
 int no_c_alignas();
 #endif
 
+// Arbitrary feature to test that the extension name can be surrounded with
+// double underscores.
+// CHECK-PED-NONE: has_double_underscores
+#if __has_extension(__c_alignas__)
+int has_double_underscores();
+#endif

clang/test/Preprocessor/feature_tests.c

@@ -21,7 +21,9 @@
 #error Clang should not have this
 #endif
 
-
+#if !__has_feature(__attribute_deprecated_with_message__)
+#error Feature name in double underscores does not work
+#endif
 
 // Make sure we have x86 builtins only (forced with target triple).