[Bug c++/67829] New: Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[Bug c++/67829] New: Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[rs2740 at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67829

            Bug ID: 67829
           Summary: Bogus "ambiguous template instantiation" error with
                    partial specializations involving a template template
                    parameter
           Product: gcc
           Version: 6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: rs2740 at gmail dot com
  Target Milestone: ---

Repro:

template<class> class Purr { };

template<template<class> class, class>
class Meow;

template<template<class> class P>
class Meow<P, P<int>> { }; // 1

template<template<class> class P, class T>
class Meow<P, P<T>> { }; // 2

Meow<Purr, Purr<int>> kitty;

This should be unambiguous (and use #1), but GCC reports an ambiguity.

[Bug c++/67829] Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[paolo.carlini at oracle dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67829

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-10-22
     Ever confirmed|0                           |1

[Bug c++/67829] Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67829

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

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

[Bug c++/67829] Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67829

--- Comment #1 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:edec2660ff4890ecf8cc191f7c92cf527de51fe2

commit r12-1374-gedec2660ff4890ecf8cc191f7c92cf527de51fe2
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Jun 10 18:31:21 2021 -0400

    c++: matching deduced template template parameters [PR67829]

    During deduction, when the template of the argument for a bound ttp
    is a template template parameter, we need to consider the
    TEMPLATE_TEMPLATE_PARAMETER for matching rather than the TEMPLATE_DECL
    thereof, because the canonical form of a template template parameter as
    a template argument is the former tree, not the latter.

            PR c++/67829

    gcc/cp/ChangeLog:

            * pt.c (unify) <case BOUND_TEMPLATE_TEMPLATE_PARM>: When
            the TEMPLATE_DECL of a BOUND_TEMPLATE_TEMPLATE_PARM argument is
            a template template parameter, adjust to the
            TEMPLATE_TEMPLATE_PARAMETER before falling through.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/ttp34.C: New test.
            * g++.dg/template/ttp34a.C: New test.
            * g++.dg/template/ttp34b.C: New test.

[Bug c++/67829] Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67829

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|ASSIGNED                    |RESOLVED
         Resolution|---                         |FIXED
   Target Milestone|---                         |12.0
           Keywords|                            |rejects-valid

--- Comment #2 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12

[Bug c++/67829] Bogus "ambiguous template instantiation" error with partial specializations involving a template template parameter

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=67829

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |pyer4 at free dot fr

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 77335 has been marked as a duplicate of this bug. ***