improve syntax errors

[Daniel Marjamäki]

Hello!

I have used GCC for decades and would like to contribute a little. :-)

I would like to see if I can improve the syntax errors.

Here is one example code:

    int x = 3) + 0;

I have created this ugly experimental patch:

--- a/gcc/c/c-parser.c
+++ b/gcc/c/c-parser.c
@@ -2228,7 +2228,10 @@ c_parser_declaration_or_fndef (c_parser
*parser, bool fndef_ok,
            }
          else
            {
-             c_parser_error (parser, "expected %<,%> or %<;%>");
+             if (c_parser_next_token_is (parser, CPP_CLOSE_PAREN))
+               c_parser_error (parser, "extraneous )");
+             else
+               c_parser_error (parser, "expected %<,%> or %<;%>");
              c_parser_skip_to_end_of_block_or_statement (parser);
              return;
            }

Before my patch:
test1.c:3:12: error: expected ‘,’ or ‘;’ before ‘)’ token

After my patch:
test1.c:3:12: error: extraneous ) before ‘)’ token

That is not perfect neither.

I have 2 questions..
 * can somebody give me a hint how I improve the error message so it
does not say "before ) token"?
 * how do I run the tests?

Basically I want that when there is a unmatched extra ) or } or ] then
it should just say "extraneous .." instead of "expected ',' or ';'.
Adding a ',' or ';' in the example code will not fix the syntax error.

Best regards,
Daniel Marjamäki