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From: "services+gccbugs at vasama dot org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug c++/110006] New: friend function template with NTTP and
 constraint doesn't match existing declaration
Date: Sat, 27 May 2023 17:33:10 +0000
X-Bugzilla-Reason: CC
X-Bugzilla-Type: new
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X-Bugzilla-Product: gcc
X-Bugzilla-Component: c++
X-Bugzilla-Version: 14.0
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X-Bugzilla-Severity: normal
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X-Bugzilla-Status: UNCONFIRMED
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X-Bugzilla-Priority: P3
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D110006

            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);
}=