Allow a double-underscore spelling of Clang attributes using double square bracket syntax.

This matches a similar behavior with GCC accepting [[gnu::__attr__]] as a alias for [[gnu::attr]] in that clang attributes can now be spelled with two leading and trailing underscores.

I had always intended for this to work, but missed the critical bit. We already had an existing test in test/Preprocessor/has_attribute.cpp for [[clang::__fallthrough__]] but using that spelling would still give an "unknown attribute" diagnostic.

llvm-svn: 346547

1 files changed, 15 insertions, 0 deletions

diff --git a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
index 9540b1ff288..6ccac122cff 100644
--- a/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
+++ b/clang/test/SemaCXX/switch-implicit-fallthrough.cpp
@@ -314,3 +314,18 @@ int fallthrough_targets(int n) {
   }
   return n;
 }
+
+int fallthrough_alt_spelling(int n) {
+  switch (n) {
+  case 0:
+    n++;
+    [[clang::fallthrough]];
+  case 1:
+    n++;
+    [[clang::__fallthrough__]];
+  case 2:
+    n++;
+    break;
+  }
+  return n;
+}