[Bug c++/112908] New: __reference_{converts,constructs}_from_temporary checks for move constructor when binding prvalue to reference of the same type

[Bug c++/112908] New: __reference_{converts,constructs}_from_temporary checks for move constructor when binding prvalue to reference of the same type

[mital at mitalashok dot co.uk]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112908

            Bug ID: 112908
           Summary: __reference_{converts,constructs}_from_temporary
                    checks for move constructor when binding prvalue to
                    reference of the same type
           Product: gcc
           Version: 14.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: mital at mitalashok dot co.uk
  Target Milestone: ---

The following compiles on trunk:

    struct NonMovable {
      NonMovable() = default;
      NonMovable(NonMovable&&) = delete;
    };

    static_assert( __reference_converts_from_temporary(int&&, int));
    static_assert(!__reference_converts_from_temporary(NonMovable&&,
NonMovable));
    static_assert( __reference_constructs_from_temporary(int&&, int));
    static_assert(!__reference_constructs_from_temporary(NonMovable&&,
NonMovable));

When the NonMovable assertions should fail because there *is* a temporary being
bound to a reference (in exactly the same way as the int case).

We can observe it instantiating constructors that shouldn't be too:

    template<typename T>
    struct S {
      template<typename U = T>
      S(const S&&) noexcept(U()) {}
    };

    static_assert(__reference_converts_from_temporary(const S<bool>&&, const
S<bool>));
    static_assert(__reference_converts_from_temporary(const S<void*>&&, const
S<void*>));

Which complains about a conversion from void* to bool even though constructors
shouldn't be looked at.

[Bug c++/112908] __reference_{converts,constructs}_from_temporary checks for move constructor when binding prvalue to reference of the same type

[ppalka at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112908

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

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|                            |2023-12-20
              Alias|                            |lwg3819
     Ever confirmed|0                           |1
             Status|UNCONFIRMED                 |NEW
                 CC|                            |ppalka at gcc dot gnu.org

--- Comment #1 from Patrick Palka <ppalka at gcc dot gnu.org> ---
This seems to be https://cplusplus.github.io/LWG/issue3819

[Bug c++/112908] __reference_{converts,constructs}_from_temporary checks for move constructor when binding prvalue to reference of the same type

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112908

Marek Polacek <mpolacek at gcc dot gnu.org> changed:

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