[Bug fortran/56659] Segfault due to missing libcpp error handler for "gfortran -cpp"

["burnus at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=56659

--- Comment #10 from Tobias Burnus <burnus at gcc dot gnu.org> ---
(In reply to Manuel López-Ibáñez from comment #9)
> (In reply to Tobias Burnus from comment #8)
> >   f951: Warning: Include directory ‘foo/bar/’: Permission denied
> >   <built-in>: Error: foo/bar: Permission denied
> > (The <built-in> 
>
> Are you sure the Error is produced *after* entering the file (by entering I
> mean pushing the file into the include stack and thus updating the
> line-map).

I was too brief. It occurs between the two. The full version is:

If everything is not on the file stack 'f951' is printed, then the '<build-in>'
stuff happens, from "gfc_cpp_init":

    cpp_change_file (cpp_in, LC_RENAME, _("<built-in>"));
    ....
  cpp_change_file (cpp_in, LC_RENAME, _("<command-line>"));

(similar: c-family/c-opts.c: c_finish_options)

This could be undone (to print 'f951') by calling cpp_change_file with to_file
= NULL – but I am sure it won't have undesired side effect.


And only after the file has been successfully opened, linemap_add is called.
Thus, the '<built-in>' shows up between gfc_cpp_init() and linemap_add.

Or code wise, in gfc_init:

  if (!gfc_cpp_enabled ())
    {
      linemap_add (line_table, LC_ENTER, false, gfc_source_file, 1);
      linemap_add (line_table, LC_RENAME, false, "<built-in>", 0);
    }
  else
    gfc_cpp_init_0 ();
...
  if (gfc_cpp_enabled ())
    gfc_cpp_init ();
...
  gfc_new_file ();

with gfc_new_file:

  if (gfc_cpp_enabled ())
    {
      gfc_cpp_preprocess (gfc_source_file);
      if (!gfc_cpp_preprocess_only ())
        load_file (gfc_cpp_temporary_file (), gfc_source_file, true);
    }
  else
    load_file (gfc_source_file, NULL, true);

and in load_file:

        input = gfc_open_file (realfilename);

      if (input == NULL)
        gfc_fatal_error ("Cannot open file %qs", filename);
...
  f = get_file (filename, (initial && !preprocessed_p) ? LC_RENAME : LC_ENTER);

the latter then calls

  linemap_add (line_table, reason, false, f->filename, 1);

> In either case, this points to some mess in the line-map stack.

Suggestions how to improve the code above?