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

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

[redi at gcc dot gnu.org]

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)

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

[redi at gcc dot gnu.org]

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

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Clang prints three errors. The first one hints at the real problem, but the
next two are bogus:

t.C:6:37: error: 'S' is not a class, namespace, or enumeration
template<class T> template<class U> S::S(U) { }
                                    ^
t.C:1:26: note: 'S' declared here
template<class T> struct S
                         ^
t.C:6:1: error: extraneous template parameter list in template specialization
or out-of-line template definition
template<class T> template<class U> S::S(U) { }
^~~~~~~~~~~~~~~~~
t.C:6:48: error: expected ';' at end of declaration
template<class T> template<class U> S::S(U) { }
                                               ^
                                               ;
3 errors generated.

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

[redi at gcc dot gnu.org]

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

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
EDG gets it right:

"t.C", line 6: error: name followed by "::" must be a class or namespace name
  template<class T> template<class U> S::S(U) { }
                                      ^

"t.C", line 6: error: argument list for class template "S" is missing
  template<class T> template<class U> S::S(U) { }
                                      ^

2 errors detected in the compilation of "t.C".