[Clang] Improve type traits recognition in __has_builtin (#111516)

`__has_builtin` was relying on reversible identifiers and string
matching to recognize builtin-type traits, leading to some newer type
traits not being recognized.

Fixes #111477

Author: cor3ntin

clang/docs/ReleaseNotes.rst

@@ -408,6 +408,8 @@ Bug Fixes to Compiler Builtins
 
 - ``__noop`` can now be used in a constant expression. (#GH102064)
 
+- Fix ``__has_builtin`` incorrectly returning ``false`` for some C++ type traits. (#GH111477)
+
 Bug Fixes to Attribute Support
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 

clang/include/clang/Basic/TokenKinds.def

@@ -64,6 +64,10 @@
 #ifndef EXPRESSION_TRAIT
 #define EXPRESSION_TRAIT(I,E,K) KEYWORD(I,K)
 #endif
+#ifndef TRANSFORM_TYPE_TRAIT_DEF
+#define TRANSFORM_TYPE_TRAIT_DEF(K, Trait) KEYWORD(__##Trait, KEYCXX)
+#endif
+
 #ifndef ALIAS
 #define ALIAS(X,Y,Z)
 #endif
@@ -534,7 +538,6 @@ TYPE_TRAIT_1(__has_unique_object_representations,
 TYPE_TRAIT_2(__is_layout_compatible, IsLayoutCompatible, KEYCXX)
 TYPE_TRAIT_2(__is_pointer_interconvertible_base_of, IsPointerInterconvertibleBaseOf, KEYCXX)
 
-#define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) KEYWORD(__##Trait, KEYCXX)
 #include "clang/Basic/TransformTypeTraits.def"
 
 // Clang-only C++ Type Traits

clang/lib/Lex/PPMacroExpansion.cpp

@@ -1616,6 +1616,34 @@ asm("_ZNKSt8time_putIcSt19ostreambuf_iteratorIcSt11char_traitsIcEEE3putES3_"
     "RSt8ios_basecPK2tmPKcSB_");
 #endif
 
+static bool IsBuiltinTrait(Token &Tok) {
+
+#define TYPE_TRAIT_1(Spelling, Name, Key)                                      \
+  case tok::kw_##Spelling:                                                     \
+    return true;
+#define TYPE_TRAIT_2(Spelling, Name, Key)                                      \
+  case tok::kw_##Spelling:                                                     \
+    return true;
+#define TYPE_TRAIT_N(Spelling, Name, Key)                                      \
+  case tok::kw_##Spelling:                                                     \
+    return true;
+#define ARRAY_TYPE_TRAIT(Spelling, Name, Key)                                  \
+  case tok::kw_##Spelling:                                                     \
+    return true;
+#define EXPRESSION_TRAIT(Spelling, Name, Key)                                  \
+  case tok::kw_##Spelling:                                                     \
+    return true;
+#define TRANSFORM_TYPE_TRAIT_DEF(K, Spelling)                                  \
+  case tok::kw___##Spelling:                                                   \
+    return true;
+
+  switch (Tok.getKind()) {
+  default:
+    return false;
+#include "clang/Basic/TokenKinds.def"
+  }
+}
+
 /// ExpandBuiltinMacro - If an identifier token is read that is to be expanded
 /// as a builtin macro, handle it and return the next token as 'Tok'.
 void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
@@ -1814,25 +1842,11 @@ void Preprocessor::ExpandBuiltinMacro(Token &Tok) {
                 getTargetInfo().getTargetOpts().FeatureMap);
           }
           return true;
-        } else if (II->getTokenID() != tok::identifier ||
-                   II->hasRevertedTokenIDToIdentifier()) {
-          // Treat all keywords that introduce a custom syntax of the form
-          //
-          //   '__some_keyword' '(' [...] ')'
-          //
-          // as being "builtin functions", even if the syntax isn't a valid
-          // function call (for example, because the builtin takes a type
-          // argument).
-          if (II->getName().starts_with("__builtin_") ||
-              II->getName().starts_with("__is_") ||
-              II->getName().starts_with("__has_"))
-            return true;
-          return llvm::StringSwitch<bool>(II->getName())
-              .Case("__array_rank", true)
-              .Case("__array_extent", true)
-#define TRANSFORM_TYPE_TRAIT_DEF(_, Trait) .Case("__" #Trait, true)
-#include "clang/Basic/TransformTypeTraits.def"
-              .Default(false);
+        } else if (IsBuiltinTrait(Tok)) {
+          return true;
+        } else if (II->getTokenID() != tok::identifier &&
+                   II->getName().starts_with("__builtin_")) {
+          return true;
         } else {
           return llvm::StringSwitch<bool>(II->getName())
               // Report builtin templates as being builtins.

clang/test/Preprocessor/feature_tests.cpp

@@ -31,7 +31,11 @@
     !__has_builtin(__underlying_type) || \
     !__has_builtin(__is_trivial) || \
     !__has_builtin(__is_same_as) || \
-    !__has_builtin(__has_unique_object_representations)
+    !__has_builtin(__has_unique_object_representations) || \
+    !__has_builtin(__is_trivially_equality_comparable) || \
+    !__has_builtin(__reference_constructs_from_temporary) || \
+    !__has_builtin(__reference_binds_to_temporary) || \
+    !__has_builtin(__reference_converts_from_temporary)
 #error Clang should have these
 #endif