[Bug c++/107408] New: Inaccurate "error: too many template-parameter-lists" diagnostic for missing template argument list

[redi at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107408

            Bug ID: 107408
           Summary: Inaccurate "error: too many template-parameter-lists"
                    diagnostic for missing template argument list
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Keywords: diagnostic
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: redi at gcc dot gnu.org
  Target Milestone: ---

template<class T> struct S
{
  template<class U> S(U);
};

template<class T> template<class U> S::S(U) { }

This prints:

t.C:6:38: error: too many template-parameter-lists
    6 | template<class T> template<class U> S::S(U) { }
      |                                      ^~


The caret is in the right location, but the diagnostic message is misleading.
The problem is a missing template argument list, it should be S<T>::S(U)