[Bug c++/105848] New: undefined reference for default template argument of function type

["dk.1995-fast at yandex dot ru" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105848

            Bug ID: 105848
           Summary: undefined reference for default template argument of
                    function type
           Product: gcc
           Version: 12.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: dk.1995-fast at yandex dot ru
  Target Milestone: ---

Following code produces link-time error in new version of GCC.

$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-pc-linux-gnu/12.1.0/lto-wrapper
Target: x86_64-pc-linux-gnu
Configured with: /build/gcc/src/gcc/configure
--enable-languages=c,c++,ada,fortran,go,lto,objc,obj-c++ --enable-bootstrap
--prefix=/usr --libdir=/usr/lib --libexecdir=/usr/lib --mandir=/usr/share/man
--infodir=/usr/share/info --with-bugurl=https://bugs.archlinux.org/
--with-linker-hash-style=gnu --with-system-zlib --enable-__cxa_atexit
--enable-cet=auto --enable-checking=release --enable-clocale=gnu
--enable-default-pie --enable-default-ssp --enable-gnu-indirect-function
--enable-gnu-unique-object --enable-linker-build-id --enable-lto
--enable-multilib --enable-plugin --enable-shared --enable-threads=posix
--disable-libssp --disable-libstdcxx-pch --disable-werror
--with-build-config=bootstrap-lto --enable-link-serialization=1
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.1.0 (GCC)

$ cat main.cpp
template<typename T>
void def()
{}

template<void (*foobar)() = def<int>>
void bar()
{
    foobar();
}

template<typename T>
void foo()
{
    bar();
}

int main()
{
    foo<int>();
}

$ gcc main.cpp
/usr/bin/ld: /tmp/ccbVvQNJ.o: in function `void bar<&(void def<int>())>()':
main.cpp:(.text._Z3barIXadL_Z3defIiEvvEEEvv[_Z3barIXadL_Z3defIiEvvEEEvv]+0x5):
undefined reference to `void def<int>()'
collect2: error: ld returned 1 exit status