[Bug c++/110006] New: friend function template with NTTP and constraint doesn't match existing declaration

[Bug c++/110006] New: friend function template with NTTP and constraint doesn't match existing declaration

[services+gccbugs at vasama dot org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

            Bug ID: 110006
           Summary: friend function template with NTTP and constraint
                    doesn't match existing declaration
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: services+gccbugs at vasama dot org
  Target Milestone: ---

// https://godbolt.org/z/jWo6ve9fh

template<typename T>
class s;

template<typename T>
void constraint(s<T> const&, int&);

template<typename U, typename T2>
U function(s<T2> const x)
        requires requires (U& u) { constraint(x, u); }
{
        return {};
}

template<typename T>
class s
{
        template<typename U, typename T2>
        friend U function(s<T2> const x)
                requires requires (U& u) { constraint(x, u); };
};

int f(s<int> q)
{
        // error: call of overloaded 'function<int>(s<int>&)' is ambiguous
        return function<int>(q);
}

[Bug c++/110006] friend function template with constraint doesn't match existing declaration

[waffl3x at protonmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

waffl3x <waffl3x at protonmail dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |waffl3x at protonmail dot com

--- Comment #1 from waffl3x <waffl3x at protonmail dot com> ---
I am pretty certain Bug 110291 is a duplicate of this one

[Bug c++/110006] [11/12/13/14 Regression] friend function template with constraint doesn't match existing declaration

[pinskia at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-07-10
      Known to fail|                            |11.1.0
     Ever confirmed|0                           |1
            Summary|friend function template    |[11/12/13/14 Regression]
                   |with constraint doesn't     |friend function template
                   |match existing declaration  |with constraint doesn't
                   |                            |match existing declaration
      Known to work|                            |10.4.0
           Keywords|                            |needs-bisection
             Status|UNCONFIRMED                 |NEW
           See Also|                            |https://gcc.gnu.org/bugzill
                   |                            |a/show_bug.cgi?id=110291
   Target Milestone|---                         |11.5

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to waffl3x from comment #1)
> I am pretty certain Bug 110291 is a duplicate of this one

It is at least related.

Confirmed.

[Bug c++/110006] [11/12/13/14 Regression] friend function template with constraint doesn't match existing declaration

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ppalka at gcc dot gnu.org
           Keywords|needs-bisection             |

--- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Started with r11-3261-gb28b621ac67bee

[Bug c++/110006] [11/12/13/14 Regression] friend function template with constraint doesn't match existing declaration

[rguenth at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

Richard Biener <rguenth at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2023-07-10 00:00:00         |2024-1-12
           Priority|P3                          |P2

[Bug c++/110006] [11/12/13/14 Regression] friend function template with constraint doesn't match existing declaration

[cvs-commit at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

--- Comment #4 from GCC 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:686b5eb9c9ee623a604dde5c49fa11c23f384c62

commit r14-8770-g686b5eb9c9ee623a604dde5c49fa11c23f384c62
Author: Patrick Palka <ppalka@redhat.com>
Date:   Fri Feb 2 19:07:08 2024 -0500

    c++: requires-exprs and partial constraint subst [PR110006]

    In r11-3261-gb28b621ac67bee we made tsubst_requires_expr never partially
    substitute into a requires-expression so as to avoid checking its
    requirements out of order during e.g. generic lambda regeneration.

    These PRs however illustrate that we still sometimes do need to
    partially substitute into a requires-expression, in particular when it
    appears in associated constraints that we're directly substituting for
    sake of declaration matching or dguide constraint rewriting.  In these
    cases we're being called from tsubst_constraint during which
    processing_constraint_expression_p is true, so this patch checks this
    predicate to control whether we defer substitution or partially
    substitute.

    In turn, we now need to propagate semantic tsubst flags through
    tsubst_requires_expr rather than just using tf_none, notably for sake of
    dguide constraint rewriting which sets tf_dguide.

            PR c++/110006
            PR c++/112769

    gcc/cp/ChangeLog:

            * constraint.cc (subst_info::quiet): Accomodate non-diagnostic
            tsubst flags.
            (tsubst_valid_expression_requirement): Likewise.
            (tsubst_simple_requirement): Return a substituted _REQ node when
            processing_template_decl.
            (tsubst_type_requirement_1): Accomodate non-diagnostic tsubst
            flags.
            (tsubst_type_requirement): Return a substituted _REQ node when
            processing_template_decl.
            (tsubst_compound_requirement): Likewise.  Accomodate non-diagnostic
            tsubst flags.
            (tsubst_nested_requirement): Likewise.
            (tsubst_requires_expr): Don't defer partial substitution when
            processing_constraint_expression_p is true, in which case return
            a substituted REQUIRES_EXPR.
            * pt.cc (tsubst_expr) <case REQUIRES_EXPR>: Accomodate
            non-diagnostic tsubst flags.

    gcc/testsuite/ChangeLog:

            * g++.dg/cpp2a/class-deduction-alias18.C: New test.
            * g++.dg/cpp2a/concepts-friend16.C: New test.

    Reviewed-by: Jason Merrill <jason@redhat.com>

[Bug c++/110006] [11/12/13 Regression] friend function template with constraint doesn't match existing declaration

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13/14 Regression]    |[11/12/13 Regression]
                   |friend function template    |friend function template
                   |with constraint doesn't     |with constraint doesn't
                   |match existing declaration  |match existing declaration

--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Fixed for GCC 14 so far.

[Bug c++/110006] [11/12/13 Regression] friend function template with constraint doesn't match existing declaration

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

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

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

[Bug c++/110006] [11/12 Regression] friend function template with constraint doesn't match existing declaration

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=110006

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
            Summary|[11/12/13 Regression]       |[11/12 Regression] friend
                   |friend function template    |function template with
                   |with constraint doesn't     |constraint doesn't match
                   |match existing declaration  |existing declaration

--- Comment #6 from Patrick Palka <ppalka at gcc dot gnu.org> ---
Now also backported for GCC 13.3 as r13-8608-g38c2679ff9330d and
r13-8609-g265f207a46bc38.