[Bug c++/65396] New: Function template default template arguments not merged

[Bug c++/65396] New: Function template default template arguments not merged

[david at stellarscience dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

            Bug ID: 65396
           Summary: Function template default template arguments not
                    merged
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: david at stellarscience dot com

template <typename T, T *> void f();

template <typename T, T * = nullptr> void f() {}

int main() { f<int>(); }

------------------------

gcc inaccurately rejects this program, which is violating the following
sentence from [C++11 14.1 p10]

The set of default template-arguments available for use with a template
declaration or definition is obtained by merging the default arguments from the
definition (if in scope) and all declarations in scope in the same way default
function arguments are (8.3.6).

[Bug c++/65396] Function template default template arguments not merged

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
           Keywords|                            |rejects-valid
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2015-03-12
     Ever confirmed|0                           |1

--- Comment #1 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Presumably this rule was never implemented for function templates when they
started being allowed default template arguments.

[Bug c++/65396] Function template default template arguments not merged

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |devgs at ukr dot net

--- Comment #5 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 80771 has been marked as a duplicate of this bug. ***

[Bug c++/65396] Function template default template arguments not merged

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |Predelnik at gmail dot com

--- Comment #6 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 93415 has been marked as a duplicate of this bug. ***

[Bug c++/65396] Function template default template arguments not merged

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
The testcase from PR 93415 shows this can produce wrong code too:
template <bool B>
void f (int);
template <bool B = true>
void f (int) {}

template <bool B = true>
void f (char) { __builtin_abort (); }

int main ()
{
    f (0);
    return 0;
}

[Bug c++/65396] Function template default template arguments not merged

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |sp2danny at gmail dot com

--- Comment #8 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
*** Bug 87279 has been marked as a duplicate of this bug. ***

[Bug c++/65396] Function template default template arguments not merged

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

--- Comment #9 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Another simplified testcase:

template<class T> void f();
template<class T=int> void f() {}
int main() { f(); }

[Bug c++/65396] Function template default template arguments not merged

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

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

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

[Bug c++/65396] Function template default template arguments not merged

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

--- Comment #10 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:fe548eb8436f3906e6a3c6e3e8707d24e60ec0fa

commit r12-7562-gfe548eb8436f3906e6a3c6e3e8707d24e60ec0fa
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Mar 9 08:42:19 2022 -0500

    c++: merge default targs for function templates [PR65396]

    We currently merge default template arguments for class templates, but
    not for function templates.  This patch fixes this by factoring out the
    argument merging logic in redeclare_class_template into a separate
    function and using it in duplicate_decls as well.

            PR c++/65396

    gcc/cp/ChangeLog:

            * cp-tree.h (merge_default_template_args): Declare.
            * decl.cc (merge_default_template_args): Define, factored out
            from redeclare_class_template.
            (duplicate_decls): Use it when merging member function template
            and free function declarations.
            * pt.cc (redeclare_class_template): Factor out default argument
            merging logic into merge_default_template_args.  Improve location
            of a note when there's a template parameter kind mismatch.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp0x/vt-34314.C: Adjust expected location of
            "redeclared here" note.
            * g++.dg/template/pr92440.C: Likewise.
            * g++.old-deja/g++.pt/redecl1.C: Adjust expected location of
            "redefinition of default argument" error.
            * g++.dg/template/defarg23.C: New test.
            * g++.dg/template/defarg23a.C: New test.

[Bug c++/65396] Function template default template arguments not merged

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=65396

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

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

--- Comment #11 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 12.