[Bug c++/100396] New: [11.1 regression] The template function overload is not selected correctly

["vopl at bk dot ru" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100396

            Bug ID: 100396
           Summary: [11.1 regression] The template function overload is
                    not selected correctly
           Product: gcc
           Version: 11.1.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: vopl at bk dot ru
  Target Milestone: ---

Regression in 11.1.0



$ cat src.cpp && echo EOFFFFFFF
/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
template<class F, class... Args>
constexpr bool valid = (0 < sizeof(F{}(Args{}...)));

/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
template<class F, class... Args>
void ovr(F f, Args... args)
requires valid<F, Args...> // external checker - fail, wrong Args formed
//requires (0 < sizeof(F{}(Args{}...))) // inline checker - ok (are wrong Args
compensated by SFINAE?)
{
    return ovr<F, Args...>(int{}, f, args...); // a second ovr is expected to
be called, but the compiler tries to call this ovr again. Collision between
'int' and 'F' is ignored, extra Args appended from 'f'
}

template<class F, class... Args> void ovr(int, F, Args...){}

/////////0/////////1/////////2/////////3/////////4/////////5/////////6/////////7
void use()
{
    ovr([]{return 'c';});
}

EOFFFFFFF



$ g++-11.1.0 -std=c++20 -c src.cpp 
src.cpp: In instantiation of 'constexpr const bool valid<use()::<lambda()>,
use()::<lambda()> >':
src.cpp:8:10:   required by substitution of 'template<class F, class ... Args>
void ovr(F, Args ...) requires  valid<F, Args ...> [with F = use()::<lambda()>;
Args = {use()::<lambda()>}]'
src.cpp:11:27:   required from 'void ovr(F, Args ...) requires  valid<F, Args
...> [with F = use()::<lambda()>; Args = {}]'
src.cpp:19:8:   required from here
src.cpp:3:39: error: no match for call to '(use()::<lambda()>)
(use()::<lambda()>)'
    3 | constexpr bool valid = (0 < sizeof(F{}(Args{}...)));
      |                                   ~~~~^~~~~~~~~~~~
src.cpp:3:39: note: candidate: 'char (*)()' (conversion)
src.cpp:3:39: note:   candidate expects 1 argument, 2 provided
src.cpp:19:9: note: candidate: 'use()::<lambda()>'
   19 |     ovr([]{return 'c';});
      |         ^
src.cpp:19:9: note:   candidate expects 0 arguments, 1 provided



$ g++-11.1.0 -v
Using built-in specs.
COLLECT_GCC=g++-11.1.0
COLLECT_LTO_WRAPPER=/usr/libexec/gcc/x86_64-pc-linux-gnu/11.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with:
/var/tmp/portage/sys-devel/gcc-11.1.0/work/gcc-11.1.0/configure
--host=x86_64-pc-linux-gnu --build=x86_64-pc-linux-gnu --prefix=/usr
--bindir=/usr/x86_64-pc-linux-gnu/gcc-bin/11.1.0
--includedir=/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/include
--datadir=/usr/share/gcc-data/x86_64-pc-linux-gnu/11.1.0
--mandir=/usr/share/gcc-data/x86_64-pc-linux-gnu/11.1.0/man
--infodir=/usr/share/gcc-data/x86_64-pc-linux-gnu/11.1.0/info
--with-gxx-include-dir=/usr/lib/gcc/x86_64-pc-linux-gnu/11.1.0/include/g++-v11
--with-python-dir=/share/gcc-data/x86_64-pc-linux-gnu/11.1.0/python
--enable-languages=c,c++,fortran --enable-obsolete --enable-secureplt
--disable-werror --with-system-zlib --disable-nls --enable-checking=release
--with-bugurl=https://bugs.gentoo.org/ --with-pkgversion='Gentoo 11.1.0 p1'
--disable-esp --enable-libstdcxx-time --with-build-config=bootstrap-lto
--enable-shared --enable-threads=posix --enable-__cxa_atexit
--enable-clocale=gnu --enable-multilib --with-multilib-list=m32,m64
--disable-fixed-point --enable-targets=all --enable-libgomp --disable-libssp
--disable-libada --enable-systemtap --disable-valgrind-annotations
--enable-vtable-verify --with-zstd --enable-lto --with-isl
--disable-isl-version-check --enable-default-pie --disable-default-ssp
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 11.1.0 (Gentoo 11.1.0 p1)