[Bug c++/64961] New: nested template implementation crossing namespace fails with access error

[Bug c++/64961] New: nested template implementation crossing namespace fails with access error

[eugene at hutorny dot in.ua]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

            Bug ID: 64961
           Summary: nested template implementation crossing namespace
                    fails with access error
           Product: gcc
           Version: 4.8.3
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: eugene at hutorny dot in.ua

Created attachment 34686
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34686&action=edit
code sample illustrating the issue

Consider a case:
a template with protected nested structure (Foo<>::Fo) is defined in one
namespace (foo),  and instantiated in another namespace (bar) via inheritance.

Specialization of nested templates methods fails with access error.
Compare to specialization of a outer template's method placed in exactly the
same scope and compiled with success.

[Bug c++/64961] nested template implementation crossing namespace fails with access error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Clang gives exactly the same error.

[Bug c++/64961] nested template implementation crossing namespace fails with access error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
And I think the code is invalid. If you want to define the function, don't use
a protected access path.

[Bug c++/64961] nested template implementation crossing namespace fails with access error

[eugene at hutorny dot in.ua]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

--- Comment #3 from Eugene <eugene at hutorny dot in.ua> ---
In the example method bar::Bar::Foo<1>::bar() is on the same access path and
its specialization gives no error. Is there an explanation for this difference?

[Bug c++/64961] nested template implementation crossing namespace fails with access error

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

--- Comment #4 from Jonathan Wakely <redi at gcc dot gnu.org> ---
No it isn't the same.

Foo<1> is a public member of bar::Bar ([class]/2 "For purposes of access
checking, the injected-class-name is treated as if it were a public member
name.")

Ba is a protected member of bar::Bar.

[Bug c++/64961] nested template implementation crossing namespace fails with access error

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64961

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever confirmed|0                           |1
   Last reconfirmed|                            |2021-12-10

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed. I think GCC is doing access checks too soon in this case. 

For a function definition, I don't think access checking applies.

bar::Bar::Ba::Fo::foo is the same as
Foo<1>::Fo::foo which should be valid to define in the foo namespace.
ICC, clang and MSVC all accept the code.