Improved error recovery for _Pragma

Summary:
Currently, if the argument to _Pragma is not a parenthesised string
literal, the bad token will be consumed, as well as the ')', if present.
If additional bad tokens are passed to the _Pragma, this results in
extra error messages which may distract from the true problem.

The proposed patch causes all tokens to be consumed until the closing
')' or a new line, whichever is reached first.

Reviewers: hfinkel, rsmith

Subscribers: hubert.reinterpretcast, fraggamuffin, rnk, cfe-commits

Differential Revision: http://reviews.llvm.org/D8308

Patch by Rachel Craik!


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@243692 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Lex/Pragma.cpp

@@ -191,9 +191,13 @@ void Preprocessor::Handle_Pragma(Token &Tok) {
   Lex(Tok);
   if (!tok::isStringLiteral(Tok.getKind())) {
     Diag(PragmaLoc, diag::err__Pragma_malformed);
-    // Skip this token, and the ')', if present.
+    // Skip bad tokens, and the ')', if present.
     if (Tok.isNot(tok::r_paren) && Tok.isNot(tok::eof))
       Lex(Tok);
+    while (Tok.isNot(tok::r_paren) &&
+           !Tok.isAtStartOfLine() &&
+           Tok.isNot(tok::eof))
+      Lex(Tok);
     if (Tok.is(tok::r_paren))
       Lex(Tok);
     return _PragmaLexing.failed();

test/Preprocessor/_Pragma.c

@@ -12,4 +12,8 @@ _Pragma("message(\"foo \\\\\\\\ bar\")") // expected-warning {{foo \\ bar}}
 #error #define invalid
 #endif
 
+_Pragma(unroll 1 // expected-error{{_Pragma takes a parenthesized string literal}}
+
+_Pragma(clang diagnostic push) // expected-error{{_Pragma takes a parenthesized string literal}}
+
 _Pragma( // expected-error{{_Pragma takes a parenthesized string literal}}