[Bug c++/65308] New: [C++14] auto-returning function template used inside function template has problems with being assigned to auto

[Bug c++/65308] New: [C++14] auto-returning function template used inside function template has problems with being assigned to auto

[jvp4846 at g dot rit.edu]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65308

            Bug ID: 65308
           Summary: [C++14] auto-returning function template used inside
                    function template has problems with being assigned to
                    auto
           Product: gcc
           Version: 5.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: jvp4846 at g dot rit.edu

Created attachment 34945
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34945&action=edit
Sample

I'm 99% sure this is valid C++14, but there's always the chance I misunderstood
something. If you call a function template (`make_thing` in the sample) that
returns auto from another function template (`foo` in the sample), and try to
use a template member function from that return value, GCC emits the following
diagnostic:

  test.cpp: In function 'void foo()':
  test.cpp:12:26: error: expected primary-expression before 'int'
     make_thing<int>().func<int>();

This error doesn't occur if `make_thing` is defined to return `thing`, or if
`make_thing` is not a template, or if `foo` is not a template. Adding
`template` before the call to `func` also fixes this, but that shouldn't be
necessary.

I've reproduced this under GCC 4.9.2 and the GCC 5.0 snapshot from Debian. Here
are their exact versions:

  g++ (Ubuntu 4.9.2-0ubuntu1~14.04) 4.9.2

  g++ (Debian 20150225-1) 5.0.0 20150225 (experimental) [trunk revision 220970]

[Bug c++/65308] [C++14] auto-returning function template used inside function template doesn't allow template members to be called

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65308

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-03-04
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
It compiles OK if you change it to:

  make_thing<int>().template func<int>();

which I would have thought is necessary, but EDG and Clang don't require it.

Maybe there's some defect report that changed whether the "template" keyword is
required there, and G++ doesn't implement that yet.

[Bug c++/65308] [C++14] auto-returning function template used inside function template doesn't allow template members to be called

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65308

Jonathan Wakely <redi at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Actually no, the 'template' keyword is not required there, but maybe G++ is
confused into thinking that the expression is dependent because of the deduced
return type for make_thing<int>()

[Bug c++/65308] [C++14] auto-returning function template used inside function template doesn't allow template members to be called

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65308

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
         Resolution|---                         |DUPLICATE
             Status|NEW                         |RESOLVED
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #4 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Looks like this same bug was reported much later as PR81045 and fixed for GCC 8
and 7.2.  Thanks for the bug report and ping.

*** This bug has been marked as a duplicate of bug 81045 ***