Re: C++ patch ping

[Jason Merrill <jason@redhat.com>]

On 9/1/21 4:11 PM, Jakub Jelinek wrote:
> 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.

Fair enough.  Go ahead without changes, then.

Jason