[Bug c++/108347] New: Incorrect error: ambiguous template instantiation

[Bug c++/108347] New: Incorrect error: ambiguous template instantiation

[CoachHagins at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108347

            Bug ID: 108347
           Summary: Incorrect error: ambiguous template instantiation
           Product: gcc
           Version: 13.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: CoachHagins at gmail dot com
  Target Milestone: ---

Created attachment 54222
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54222&action=edit
C++ source - no include directives

The attached code is a single .cpp file, as it contains no #include directives.

I have also posted on compiler explorer here: https://godbolt.org/z/jjEPKdx8Y

The code compiles fine with all versions of clang from 7 up through the latest
branch on CE.

The code FAILS to compile with gcc, all versions from 7 up through the latest
branch on CE.

There are THREE #defines in the included code, which provide three different
"fixes" to make the code compile.

The command

    g++ -std=c++17 -DFIX0=0 -DFIX1=0 -DFIX2=0

will fail to compile with an ambiguous template instantiation error.  However,
all of the following will allow the code to compile.  Hopefully, the various
"fixes" will help identify the underlying issue(s).

    g++ -std=c++17 -DFIX0=0 -DFIX1=0 -DFIX2=1
    g++ -std=c++17 -DFIX0=0 -DFIX1=1 -DFIX2=0
    g++ -std=c++17 -DFIX0=0 -DFIX1=1 -DFIX2=1
    g++ -std=c++17 -DFIX0=1 -DFIX1=0 -DFIX2=0
    g++ -std=c++17 -DFIX0=1 -DFIX1=0 -DFIX2=1
    g++ -std=c++17 -DFIX0=1 -DFIX1=1 -DFIX2=0
    g++ -std=c++17 -DFIX0=1 -DFIX1=1 -DFIX2=1

[Bug c++/108347] Incorrect error: ambiguous template instantiation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108347

--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Well MSVC has an internal compiler error  with this code.

[Bug c++/108347] Incorrect error: ambiguous template instantiation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108347

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Created attachment 54223
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54223&action=edit
testcase that removes the C++17isms and convert it over to C++11

[Bug c++/108347] Incorrect error: ambiguous template instantiation

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108347

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #2)
> Created attachment 54223 [details]
> testcase that removes the C++17isms and convert it over to C++11

The reason why I did this is because I wanted to see if older versions of GCC
rejected this code and they do in a similar fashion. (MSVC still ICEs).

[Bug c++/108347] Incorrect error: ambiguous template instantiation

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108347

--- Comment #4 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:a6ac1fc64c3caed19da65c2e6b12f8ddaf551231

commit r14-4110-ga6ac1fc64c3caed19da65c2e6b12f8ddaf551231
Author: Patrick Palka <ppalka@redhat.com>
Date:   Mon Sep 18 14:41:07 2023 -0400

    c++: unifying identical tmpls from current inst [PR108347]

    Here more_specialized_partial_spec wrongly considers the two partial
    specializations to be unordered ultimately because unify for identical
    parm=arg=A<T>::C returns failure due to C being dependent.

    This patch fixes this by relaxing unify's early-exit identity test to
    also accept dependent decls; we can't deduce anything further from them
    anyway.  In passing this patch removes the CONST_DECL case of unify:
    we should never see the CONST_DECL version of a template parameter here,
    and for other CONST_DECLs (such as enumerators) it seems we can rely on
    them to already have been folded to their DECL_INITIAL.

            PR c++/108347

    gcc/cp/ChangeLog:

            * pt.cc (unify): Return unify_success for identical dependent
            DECL_P 'arg' and 'parm'.
            <case CONST_DECL>: Remove handling.

    gcc/testsuite/ChangeLog:

            * g++.dg/template/ttp41.C: New test.

[Bug c++/108347] Incorrect error: ambiguous template instantiation

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108347

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
   Target Milestone|---                         |14.0
           Assignee|unassigned at gcc dot gnu.org      |ppalka at gcc dot gnu.org
         Resolution|---                         |FIXED
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 14, thanks for the bug report.