Re: C++ patch ping

[Jakub Jelinek <jakub@redhat.com>]

On Wed, Sep 01, 2021 at 03:25:17PM -0400, Jason Merrill wrote:
> On 8/30/21 3:11 AM, Jakub Jelinek wrote:
> > Hi!
> > 
> > I'd like to ping the following patches
> > 
> > libcpp: __VA_OPT__ p1042r1 placemarker changes [PR101488]
> > https://gcc.gnu.org/pipermail/gcc-patches/2021-July/575621.html
> > together with your
> > https://gcc.gnu.org/pipermail/gcc-patches/2021-August/577602.html
> > incremental patch (successfully tested on x86_64-linux and i686-linux).
> 
> OK, thanks.

Thanks, committed both patches.

> My reply to that patch approved it with a suggestion for a tweak to
> ucn_valid_in_identifier.  Quoting it here:
>
> > I might check invalid_start_flags first, and return 1 if not set, then
> > check all the other flags when not pedantic, and finally return 2 if
> > nothing matches.  OK with or without this change.

Sorry for missing this, didn't scroll down enough.

I don't think something like:
  if (CPP_OPTION (pfile, cxx23_identifiers))
    invalid_start_flags = NXX23;
  else if (CPP_OPTION (pfile, c11_identifiers))
    invalid_start_flags = N11;
  else if (CPP_OPTION (pfile, c99))
    invalid_start_flags = N99;
  else
    invalid_start_flags = 0;

  /* In C99, UCN digits may not begin identifiers.  In C11 and C++11,
     UCN combining characters may not begin identifiers.  */
  if ((ucnranges[mn].flags & invalid_start_flags) == 0)
    return 1;

  /* If not -pedantic, accept as character that may
     begin an identifier a union of characters allowed
     at that position in each of the character sets.  */
  if (!CPP_PEDANTIC (pfile)
      && ((ucnranges[mn].flags & (C99 | N99)) == C99
          || (ucnranges[mn].flags & CXX) != 0
          || (ucnranges[mn].flags & (C11 | N11)) == C11
          || (ucnranges[mn].flags & (CXX23 | NXX23)) == CXX23))
    return 1;

  return 2;
would work, e.g. for C++98 invalid_start_flags is 0, so it would return
always 1, while the previous patch returned 2 for non-pedantic if the char
wasn't in the CXX set but was e.g. in the C99 set that wasn't allowed
as the first char (i.e. in & (C99 | N99) == (C99 | N99) set) etc.
While all C99 | N99 characters are C11 | 0, e.g.
\u0304 (and many others) are not in C99 at all, not in CXX, and in
C11 | N11 and in CXX23 | NXX23.  So they are never valid as start
characters.  There are also some characters like
\u1dfa which are not in C99 at all, not in CXX, not in CXX23 and in
C11 | N11, so again not valid as start character in any of the pedantic
modes.  IMHO we want to return 2 for them in non-pedantic.
And testing first
  if (ucnranges[mn].flags & invalid_start_flags)
    return 2;
and then doing the if !CPP_PEDANTIC stuff wouldn't work either, e.g.
\U0001d18b is in CXX23 | NXX23 and in C11 | 0, so we IMHO want to return
1 for that (allowed as start character in -pedantic -std=c++20, disallowed
as start character in -pedantic -std=c++23) but we would return 2
in -std=c++23 mode.

	Jakub