[Bug c++/119026] New: Problem of const constexpr and maybe gcc 10 accepts invalid

[qurong at ios dot ac.cn via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=119026

            Bug ID: 119026
           Summary: Problem of const constexpr and maybe gcc 10 accepts
                    invalid
           Product: gcc
           Version: 10.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: qurong at ios dot ac.cn
  Target Milestone: ---

For this program:


template < typename T > const constexpr decltype (auto) b() {
    return 0;
}

int main() {
    const constexpr decltype (auto) a = b <int>();
    return 0;
}


This causes an error in clang、msvc and gcc≥11, but and gcc10 didn't report the
error. 

Compiler Explorer link: https://godbolt.org/z/cqM5Pn896