[Bug c/110654] New: inconsistent error message in presence of unexpected encoded characters

[Bug c/110654] New: inconsistent error message in presence of unexpected encoded characters

[drepper.fsp+rhbz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110654

            Bug ID: 110654
           Summary: inconsistent error message in presence of unexpected
                    encoded characters
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c
          Assignee: unassigned at gcc dot gnu.org
          Reporter: drepper.fsp+rhbz at gmail dot com
  Target Milestone: ---

Take this code which in a similar form was taken from a text document where the
smart quote handling used the U201c and U201d characters instead of simple
ASCII double quotes.  Note, this text should be encoded in UTF-8 and the
environment of the compiler must use UTF-8 as well.

#include <stdio.h>
int main() {
  puts(“hello world”);
  return 0;
}

Compiling this with a recent gcc 13 or older versions leads to these error
messages:

u.c: In function ‘main’:
u.c:3:8: error: stray ‘\342’ in program
    3 |   puts(<U+201C>hello world<U+201D>);
      |        ^~~~~~~~
u.c:3:9: error: ‘hello’ undeclared (first use in this function); did you mean
‘ftello’?
    3 |   puts(“hello world”);
      |         ^~~~~
      |         ftello
u.c:3:9: note: each undeclared identifier is reported only once for each
function it appears in
u.c:3:14: error: expected ‘)’ before ‘world’
    3 |   puts(“hello world”);
      |       ~      ^~~~~~
      |              )
u.c:3:20: error: stray ‘\342’ in program
    3 |   puts(<U+201C>hello world<U+201D>);
      |                           ^~~~~~~~

The problem is the initial message about "stray ‘\342’" and the notation used
in the context line.  In the later the byte is correctly recognized as being
part on an UTF-8 character.

Note that this is in contrast to the C++ frontend which handles this correctly.
 It shows:

u.c:3:8: error: extended character “ is not valid in an identifier
    3 |   puts(“hello world”);
      |        ^

The C frontend should adopt the same code as the C++ frontend.

[Bug c/110654] inconsistent error message in presence of unexpected encoded characters

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110654

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
libccp has:
          /* In C++, this is an error for invalid character in an identifier
             because logically, the UTF-8 was converted to a UCN during
             translation phase 1 (even though we don't physically do it that
             way).  In C, this byte rather becomes grammatically a separate
             token.  */

          if (CPP_OPTION (pfile, cplusplus))
            cpp_error (pfile, CPP_DL_ERROR,
                       "extended character %.*s is not valid in an identifier",
                       (int) (*pstr - base), base);
          else
            {
              *pstr = base;
              return false;
            }


So this is due to differences in the languages themselves rather than due to C
vs C++ front-end ...

[Bug c/110654] inconsistent error message in presence of unexpected encoded characters

[drepper.fsp+rhbz at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110654

--- Comment #2 from Ulrich Drepper <drepper.fsp+rhbz at gmail dot com> ---
(In reply to Andrew Pinski from comment #1)
> So this is due to differences in the languages themselves rather than due to
> C vs C++ front-end ...

This is certainly true for the validation.

But the standard never says anything about how an error should be reported.  I
don't think there is a reason to make this more obscure than necessary.