Re: MinGW cross compilation failure on Debian trixie

On Fri, Sep 19, 2025 at 8:13 PM Nazir Bilal Yavuz <byavuz81(at)gmail(dot)com> wrote::
> pg_locale_libc.c: In function ‘wc_isdigit_libc_mb’:
> ../../../../src/include/port/win32_port.h:438:20: error: implicit
> declaration of function ‘_iswctype_l’; did you mean ‘_isctype_l’?
> [-Wimplicit-function-declaration]
> 438 | #define iswdigit_l _iswdigit_l
> | ^~~~~~~~~~~
> pg_locale_libc.c:178:16: note: in expansion of macro ‘iswdigit_l’
> 178 | return iswdigit_l((wint_t) wc, locale->info.lt);
> | ^~~~~~~~~~

It looks like version 12 of mingw-w64-x86-64-dev, currently shipping
in Debian trixie and sid, must have broken something that worked in
version 8 from bullseye. Several different headers apparently compete
to provide that family of functions, with a common guard
_WCTYPE_DEFINED:

https://github.com/mingw-w64/mingw-w64/blob/v12.x/mingw-w64-headers/crt/ctype.h
https://github.com/mingw-w64/mingw-w64/blob/v12.x/mingw-w64-headers/crt/wchar.h
https://github.com/mingw-w64/mingw-w64/blob/v12.x/mingw-w64-headers/crt/wctype.h

I suspect that if you define _CTYPE_DISABLE_MACROS (for example in
CPPFLAGS) then it might work. Assuming <ctype.h> wins (I guess so,
it's included at the top of port.h), then I suppose it must use this
definition, hiding the function of the same name:

#define _iswdigit_l(_c,_p) (_iswctype_l(_c,_DIGIT,_p))

But _iswctype_l is only declared if:

#if __MSVCRT_VERSION__ >= 0x800

It looks like the default __MSVCRT_VERSION__ is 0x700
(/usr/x86_64-w64-mingw32/include/_mingw.h). Hmm, so does UCRT
make the problem go away? We wanted to do that already -- see
pgql-bugs #18940. Try installing gcc-mingw-w64-ucrt64 and
g++-mingw-w64-ucrt64 on the CI image, and changing the compilers like
this, perhaps?

- CC="ccache x86_64-w64-mingw32-gcc" \
- CXX="ccache x86_64-w64-mingw32-g++"
+ CC="ccache x86_64-w64-mingw32ucrt-gcc" \
+ CXX="ccache x86_64-w64-mingw32ucrt-g++"