[Bug c++/107278] New: fails to correctly parse template default function declarations.

["ky4ct at arrl dot net" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107278

            Bug ID: 107278
           Summary: fails to correctly parse template default function
                    declarations.
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: ky4ct at arrl dot net
  Target Milestone: ---

Created attachment 53709
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53709&action=edit
minimal source code to reproduce the error.

This is specific to the -std=C++20 and -std=C++2b switches. The following
compiles fine by default and under C++ 11 and 14.

kd5eax@KY4CT UCRT64 ~
$ cat test.cpp
template<typename T>
class foo
{
        foo<T>(foo<T> const&) = delete;
        foo<T>(foo<T> const&&) = default;

};

int main()
{
        return 0;
};
kd5eax@KY4CT UCRT64 ~
$ g++ -std=c++20 test.cpp
test.cpp:4:22: error: expected ')' before 'const'
    4 |         foo<T>(foo<T> const&) = delete;
      |               ~      ^~~~~~
      |                      )
test.cpp:5:22: error: expected ')' before 'const'
    5 |         foo<T>(foo<T> const&&) = default;
      |               ~      ^~~~~~
      |                      )

kd5eax@KY4CT UCRT64 ~
$ g++ -v
Using built-in specs.
COLLECT_GCC=E:\msys64\ucrt64\bin\g++.exe
COLLECT_LTO_WRAPPER=E:/msys64/ucrt64/bin/../lib/gcc/x86_64-w64-mingw32/12.2.0/lto-wrapper.exe
Target: x86_64-w64-mingw32
Configured with: ../gcc-12.2.0/configure --prefix=/ucrt64
--with-local-prefix=/ucrt64/local --build=x86_64-w64-mingw32
--host=x86_64-w64-mingw32 --target=x86_64-w64-mingw32
--with-native-system-header-dir=/ucrt64/include --libexecdir=/ucrt64/lib
--enable-bootstrap --enable-checking=release --with-arch=x86-64
--with-tune=generic --enable-languages=c,lto,c++,fortran,ada,objc,obj-c++,jit
--enable-shared --enable-static --enable-libatomic --enable-threads=posix
--enable-graphite --enable-fully-dynamic-string
--enable-libstdcxx-filesystem-ts --enable-libstdcxx-time
--disable-libstdcxx-pch --enable-lto --enable-libgomp --disable-multilib
--disable-rpath --disable-win32-registry --disable-nls --disable-werror
--disable-symvers --with-libiconv --with-system-zlib --with-gmp=/ucrt64
--with-mpfr=/ucrt64 --with-mpc=/ucrt64 --with-isl=/ucrt64
--with-pkgversion='Rev1, Built by MSYS2 project'
--with-bugurl=https://github.com/msys2/MINGW-packages/issues --with-gnu-as
--with-gnu-ld --disable-libstdcxx-debug --with-boot-ldflags=-static-libstdc++
--with-stage1-ldflags=-static-libstdc++
Thread model: posix
Supported LTO compression algorithms: zlib zstd
gcc version 12.2.0 (Rev1, Built by MSYS2 project)