fix PR7943, a corner case with the GNU __VA_ARGS__ comma

swallowing extension.

llvm-svn: 111701

1 files changed, 7 insertions, 0 deletions

diff --git a/clang/lib/Lex/TokenLexer.cpp b/clang/lib/Lex/TokenLexer.cpp
index 49dc016590a..94719b0baa3 100644
--- a/clang/lib/Lex/TokenLexer.cpp
+++ b/clang/lib/Lex/TokenLexer.cpp
@@ -268,6 +268,13 @@ void TokenLexer::ExpandFunctionArguments() {
       // Remove the paste operator, report use of the extension.
       PP.Diag(ResultToks.back().getLocation(), diag::ext_paste_comma);
       ResultToks.pop_back();
+      
+      // If the comma was right after another paste (e.g. "X##,##__VA_ARGS__"),
+      // then removal of the comma should produce a placemarker token (in C99
+      // terms) which we model by popping off the previous ##, giving us a plain
+      // "X" when __VA_ARGS__ is empty.
+      if (!ResultToks.empty() && ResultToks.back().is(tok::hashhash))
+        ResultToks.pop_back();
     }
     continue;
   }