Re: Ping^2: [PATCH v2] diagnostics: Honor #pragma GCC diagnostic in the preprocessor [PR53431]

[Lewis Hyatt <lhyatt@gmail.com>]

On Wed, Jul 6, 2022 at 2:17 PM Jason Merrill <jason@redhat.com> wrote:
>> On 7/6/22 10:23, Lewis Hyatt wrote:
> > Here is an updated patch addressing all your comments, thanks again for the
> > review. Regarding the idea about rewinding tokens, it seems potentially
> > problematic to try to make use of libcpp's backup token feature. I think there
> > can be pragmas which allow macro expansion, and then libcpp is not able to
> > step back through the expansion AFAIK. It would work fine for `#pragma GCC
> > diagnostic' but would break if a similar approach was added for some other
> > pragma allowing expansion in the future, and I think potentially also for
> > _Pragma. But it seems pretty tenable to handle this case just by providing an
> > interface in c-ppoutput.c to ask it to stream a given token that you have
> > lexed external to the token streaming process. That's how I set it up here,
> > it's much better than my first way IMHO, hopefully it looks OK?
> >
> > I also attached a diff of this version vs the previous version in case that
> > makes it easier to review. The C++ parts were not touched other than adding
> > the comment you suggested, the changes in this version are mostly in
> > c-ppoutput.cc and c-pragma.cc.
>
>
> > +/* When preprocessing only, pragma_lex() is not available, so obtain the tokens
> > +   directly from libcpp.  We also need to inform the token streamer about all
> > +   tokens we lex ourselves here, so it outputs them too; this is done by calling
> > +   c_pp_stream_token () for each.  */
>
> Let's add to this comment
>
> ??? If we need to support more pragmas in the future, maybe initialize
> this_parser with the pragma tokens and call pragma_lex?
>
> OK with that change.
>

Thank you very much, done.


-Lewis