Lex arguments for __has_cpp_attribute and friends as expanded tokens
The C and C++ standards require the argument to __has_cpp_attribute and
__has_c_attribute to be expanded ([cpp.cond]p5). It would make little sense
to expand the argument to those operators but not expand the argument to
__has_attribute and __has_declspec, so those were both also changed in this
patch.
Note that it might make sense for the other builtins to also expand their
argument, but it wasn't as clear to me whether the behavior would be correct
there, and so they were left for a future revision.
diff --git a/clang/test/Preprocessor/has_c_attribute.c b/clang/test/Preprocessor/has_c_attribute.c
index 670e42a..36dd1c8 100644
--- a/clang/test/Preprocessor/has_c_attribute.c
+++ b/clang/test/Preprocessor/has_c_attribute.c
@@ -33,12 +33,45 @@
// CHECK: gnu::__warn_unused_result__: 201904L
C2x(gnu::__warn_unused_result__)
-// We do somewhat support the __clang__ vendor namespace, but it is a
-// predefined macro and thus we encourage users to use _Clang instead.
-// Because of this, we do not support __has_c_attribute for that
-// vendor namespace.
-//
-// Note, we can't use C2x here because it will expand __clang__ to 1
-// too early.
-// CHECK: 1::fallthrough: 0
-__clang__::fallthrough: __has_c_attribute(__clang__::fallthrough)
+// Test that macro expansion of the builtin argument works.
+#define C clang
+#define L likely
+#define CL clang::likely
+#define N nodiscard
+
+#if __has_c_attribute(N)
+int has_nodiscard;
+#endif
+// CHECK: int has_nodiscard;
+
+#if __has_c_attribute(C::L)
+int has_clang_likely_1;
+#endif
+// CHECK: int has_clang_likely_1;
+
+#if __has_c_attribute(clang::L)
+int has_clang_likely_2;
+#endif
+// CHECK: int has_clang_likely_2;
+
+#if __has_c_attribute(C::likely)
+int has_clang_likely_3;
+#endif
+// CHECK: int has_clang_likely_3;
+
+#if __has_c_attribute(CL)
+int has_clang_likely_4;
+#endif
+// CHECK: int has_clang_likely_4;
+
+#define FUNCLIKE1(x) clang::x
+#if __has_c_attribute(FUNCLIKE1(likely))
+int funclike_1;
+#endif
+// CHECK: int funclike_1;
+
+#define FUNCLIKE2(x) _Clang::x
+#if __has_c_attribute(FUNCLIKE2(likely))
+int funclike_2;
+#endif
+// CHECK: int funclike_2;
