If a comma operator is followed by a token which unambiguously indicates the

start of a statement or the end of a compound-statement, diagnose the comma as
a typo for a semicolon. Patch by Ahmed Bougacha! Additional test cases and
minor refactoring by me.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@164085 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 22 insertions, 0 deletions

diff --git a/lib/Parse/ParseExpr.cpp b/lib/Parse/ParseExpr.cpp
index af3389532e..9b95641f46 100644
--- a/lib/Parse/ParseExpr.cpp
+++ b/lib/Parse/ParseExpr.cpp
@@ -265,6 +265,17 @@ ExprResult Parser::ParseConstantExpression(TypeCastState isTypeCast) {
   return Actions.ActOnConstantExpression(Res);
 }
 
+bool Parser::isNotExpressionStart() {
+  tok::TokenKind K = Tok.getKind();
+  if (K == tok::l_brace || K == tok::r_brace  ||
+      K == tok::kw_for  || K == tok::kw_while ||
+      K == tok::kw_if   || K == tok::kw_else  ||
+      K == tok::kw_goto || K == tok::kw_try)
+    return true;
+  // If this is a decl-specifier, we can't be at the start of an expression.
+  return isKnownToBeDeclarationSpecifier();
+}
+
 /// \brief Parse a binary expression that starts with \p LHS and has a
 /// precedence of at least \p MinPrec.
 ExprResult
@@ -285,6 +296,17 @@ Parser::ParseRHSOfBinaryExpression(ExprResult LHS, prec::Level MinPrec) {
     Token OpToken = Tok;
     ConsumeToken();
 
+    // Bail out when encountering a comma followed by a token which can't
+    // possibly be the start of an expression. For instance:
+    //   int f() { return 1, }
+    // We can't do this before consuming the comma, because
+    // isNotExpressionStart() looks at the token stream.
+    if (OpToken.is(tok::comma) && isNotExpressionStart()) {
+      PP.EnterToken(Tok);
+      Tok = OpToken;
+      return LHS;
+    }
+
     // Special case handling for the ternary operator.
     ExprResult TernaryMiddle(true);
     if (NextTokPrec == prec::Conditional) {