[Bug c++/107296] New: C++20 nested typename: non-template used as template, need typename

[Bug c++/107296] New: C++20 nested typename: non-template used as template, need typename

[tomaqa at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107296

            Bug ID: 107296
           Summary: C++20 nested typename: non-template used as template,
                    need typename
           Product: gcc
           Version: 12.2.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: tomaqa at gmail dot com
  Target Milestone: ---

Created attachment 53714
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53714&action=edit
.ii file

This is kind of related to this, but in the opposite way:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=102002

gcc -v -save-temps -c -std=c++20 nested_constructor.hpp

[Bug c++/107296] C++20 nested typename: non-template used as template, need typename

[tomaqa at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107296

--- Comment #1 from Tomáš K. <tomaqa at gmail dot com> ---
Created attachment 53715
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53715&action=edit
output

Output of the gcc command mentioned above

[Bug c++/107296] C++20 nested typename: non-template used as template, need typename

[marxin at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107296

Martin Liška <marxin at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jason at gcc dot gnu.org,
                   |                            |marxin at gcc dot gnu.org
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2022-10-17
           Keywords|                            |rejects-valid
     Ever confirmed|0                           |1

--- Comment #2 from Martin Liška <marxin at gcc dot gnu.org> ---
Likely started with r10-3735-gcb57504a55015891.

[Bug c++/107296] C++20 nested typename: non-template used as template, need typename

[tomaqa at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107296

--- Comment #3 from Tomáš K. <tomaqa at gmail dot com> ---
Created attachment 53716
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=53716&action=edit
minimal example

Description:

When `-std=c++20` option is used, it requires `typename` in definition of a
constructor of a template class that is nested in a nested class.
But it is not related to a typename in this case ...
I believe this is a consequence of c++20 new rules about treating `typename`.

The example works just fine if it is run with `-std=c++17`, with the very same
compiler.

[Bug c++/107296] C++20 nested typename: non-template used as template, need typename

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107296

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |mpolacek at gcc dot gnu.org

--- Comment #4 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
(In reply to Martin Liška from comment #2)
> Likely started with r10-3735-gcb57504a55015891.

Yes,
error: need ‘typename’ before ‘Mixin<B>::Nested::Mixin2’ because
‘Mixin<B>::Nested’ is a dependent scope
started with r10-3735-gcb57504a55015891,
error: non-template ‘Mixin2’ used as template
started with r12-4584-g1c690164668bda.