[Bug c++/108848] New: Accessing class static member of non-dependent expression using member syntax in dependent context is rejected

[Bug c++/108848] New: Accessing class static member of non-dependent expression using member syntax in dependent context is rejected

[eric.niebler at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

            Bug ID: 108848
           Summary: Accessing class static member of non-dependent
                    expression using member syntax in dependent context is
                    rejected
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eric.niebler at gmail dot com
  Target Milestone: ---

Clang accepts the following, gcc thinks the expression in the line marked
"HERE" should be `tag<int>.template smbr<void>`.

    template <class T>
    struct tag_t {
      template <class Sig>
      static constexpr const Sig* smbr = nullptr; 
      int i = 0;
    };

    template <class T>
    inline constexpr tag_t<T> tag {};

    // This is OK
    using X = decltype(tag<int>.smbr<void>);

    template <class U>
    struct S {
      // This is incorrectly rejected by gcc
      using Y = decltype(tag<int>.smbr<void>);

      // This is OK
      using Z = decltype(tag_t<int>::smbr<void>);
    };

https://godbolt.org/z/9GoPYTYa1

[Bug c++/108848] template keyword incorreclty required to access template class static member of non-dependent expression using member syntax in dependent context

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

Andrew Pinski <pinskia at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2023-02-20
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=67965
     Ever confirmed|0                           |1
            Summary|Accessing class static      |template keyword
                   |member of non-dependent     |incorreclty required to
                   |expression using member     |access template class
                   |syntax in dependent context |static member of
                   |is rejected                 |non-dependent expression
                   |                            |using member syntax in
                   |                            |dependent context

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Reduced testcase to show it is not an issue with decltype:

template <class T>
struct tag_t {
        template <class Sig>
        static constexpr const Sig* smbr = nullptr; 
};

template <class T>
inline constexpr tag_t<T> tag {};
template<class T>
void f()
{
  auto t = tag<int>.smbr<void>;
}

[Bug c++/108848] [10/11/12/13 Regression] template keyword incorreclty required to access template class static member of non-dependent expression using member syntax in dependent context

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
            Summary|template keyword            |[10/11/12/13 Regression]
                   |incorreclty required to     |template keyword
                   |access template class       |incorreclty required to
                   |static member of            |access template class
                   |non-dependent expression    |static member of
                   |using member syntax in      |non-dependent expression
                   |dependent context           |using member syntax in
                   |                            |dependent context
      Known to work|                            |5.1.0
      Known to fail|                            |10.4.0, 11.3.0, 12.2.0,
                   |                            |13.0, 5.2.0
   Target Milestone|---                         |10.5

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Testcase exhibiting a regression relative to GCC 5.1:

template <class T>
struct tag_t {
        template <class Sig>
        static const Sig* smbr();
};

template <class T>
constexpr tag_t<T> tag {};

template<class T>
void f()
{
  auto t = tag<int>.smbr<void>();
}

Started with r226642.

[Bug c++/108848] [10/11/12/13 Regression] template keyword incorreclty required to access template class static member of non-dependent expression using member syntax in dependent context

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Priority|P3                          |P2

[Bug c++/108848] [10/11/12/13 Regression] template keyword incorreclty required to access template class static member of non-dependent expression using member syntax in dependent context

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
             Status|NEW                         |ASSIGNED

[Bug c++/108848] [10/11/12/13 Regression] template keyword incorreclty required to access template class static member of non-dependent expression using member syntax in dependent context

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

--- Comment #3 from CVS Commits <cvs-commit at gcc dot gnu.org> ---
The master branch has been updated by Patrick Palka <ppalka@gcc.gnu.org>:

https://gcc.gnu.org/g:d3d205ab440886164b6de2be2a2efa10cac95b66

commit r13-6380-gd3d205ab440886164b6de2be2a2efa10cac95b66
Author: Patrick Palka <ppalka@redhat.com>
Date:   Tue Feb 28 15:05:30 2023 -0500

    c++: non-dependent variable template-id [PR108848]

    Here we're treating deeming the non-dependent variable template-id
    tag<int> as dependent ever since r226642 gave variable TEMPLATE_ID_EXPR
    an empty type, which causes the call to finish_template_variable from
    finish_id_expression_1 to be unreachable at template parse time.  Thus
    we're led into thinking tag<int>.var<void> refers to a dependent name.

    This patch fixes this by making finish_id_expression_1 instantiate a
    variable template-id as long as it's not dependent according to the
    dependence test in lookup_and_finish_template_variable rather than
    according to type_dependent_expression_p.

            PR c++/108848

    gcc/cp/ChangeLog:

            * pt.cc (finish_template_variable): Move dependence check
            to here from ...
            (lookup_and_finish_template_variable): ... here.
            * semantics.cc (finish_id_expression_1): Call
            finish_template_variable sooner, before (and regardless of) the
            type_dependent_expression_p test.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp1y/noexcept1.C: Don't expect a bogus "different
            exception specifier" error.  Expect a separate "not usable
            in a constant expression" error.
            * g++.dg/cpp1y/var-templ75.C: New test.
            * g++.dg/cpp1y/var-templ76.C: New test.

[Bug c++/108848] [10/11/12 Regression] template keyword incorreclty required to access template class static member of non-dependent expression using member syntax in dependent context

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

Patrick Palka <ppalka at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
      Known to work|                            |13.0
      Known to fail|13.0                        |
            Summary|[10/11/12/13 Regression]    |[10/11/12 Regression]
                   |template keyword            |template keyword
                   |incorreclty required to     |incorreclty required to
                   |access template class       |access template class
                   |static member of            |static member of
                   |non-dependent expression    |non-dependent expression
                   |using member syntax in      |using member syntax in
                   |dependent context           |dependent context

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 13 so far

[Bug c++/108848] [11/12 Regression] template keyword incorrectly required to access template class static member of non-dependent expression using member syntax in dependent context

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108848

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Target Milestone|10.5                        |11.5

--- Comment #5 from Richard Biener <rguenth at gcc dot gnu.org> ---
GCC 10 branch is being closed.