Re: [RFC PATCH] parse #pragma GCC diagnostic in libcpp

["Manuel López-Ibáñez" <lopezibanez@gmail.com>]

On 25 September 2015 at 17:14, Dodji Seketeli <dodji@redhat.com> wrote:
> The caller of do_pragma(), which is destringize_and_run() then detects
> that pfile->directive_result.type is set, and then puts the tokens of
> the pragma back into the input stream again.  So next time the FE
> requests more tokens, it's going to get the same pragma tokens.
>
> So, maybe you could alter pragma_entry::is_deferred; change it into a
> flag which type is an enum that says how the the pragma is to be
> handled; either internally and its tokens shouldn't be visible to the FE
> (this is what the current pragma_entry::is_internal means), internally
> and the tokens would be visible to the FE, or deferred.
>
> Then do do_pragma() would be adjusted to change the if (p->is_deferred)
> clause to allow the third handling kind I just talked about.

I could not make it work by touching directive_result.type. However,
behaving as if the pragma was unknown did work:

@@ -1414,11 +1435,11 @@ do_pragma (cpp_reader *pfile)
        }
     }

   if (p)
     {
-      if (p->is_deferred)
+      if (p->type == DEFERRED)
        {
          pfile->directive_result.src_loc = pragma_token_virt_loc;
          pfile->directive_result.type = CPP_PRAGMA;
          pfile->directive_result.flags = pragma_token->flags;
          pfile->directive_result.val.pragma = p->u.ident;
@@ -1439,11 +1460,12 @@ do_pragma (cpp_reader *pfile)
          (*p->u.handler) (pfile);
          if (p->allow_expansion)
            pfile->state.prevent_expansion++;
        }
     }
-  else if (pfile->cb.def_pragma)
+
+  if ((!p || p->type == INTERNAL_VISIBLE) && pfile->cb.def_pragma)
     {
       if (count == 1 || pfile->context->prev == NULL)
        _cpp_backup_tokens (pfile, count);
       else
        {

Yet, there is another problem. Now the FE sees the pragma and it warns
with -Wunknown-pragma. But if we register the pragma in the FE to
ignore it, then we get

cc1plus: internal compiler error: #pragma GCC diagnostic is already registered

Cheers,

Manuel.