[Bug libstdc++/90165] std::variant constructs wrong alternative

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90165

--- Comment #3 from Jonathan Wakely <redi at gcc dot gnu.org> ---
Author: redi
Date: Tue Apr 23 12:48:18 2019
New Revision: 270509

URL: https://gcc.gnu.org/viewcvs?rev=270509&root=gcc&view=rev
Log:
PR libstdc++/90165 constrain variant(T&&) constructor

Also refactor some constraints slightly to be more readable.

        PR libstdc++/90165
        * include/std/variant (variant::__not_self): New helper for the
        is_same_v<remove_cvref_t<T>, variant>==false constraints.
        (variant::__to_type_impl): Remove.
        (variant::__to_type): Add default argument to check pack size, instead
        of using __to_type_impl.
        (variant::__accepted_type): Add default argument using __not_self.
        (variant::__is_in_place_tag, variant::__not_in_place_tag): New helpers
        for variant(T&&) constructor constraint.
        (variant::variant(T&&)): Use __not_in_place_tag in constraints.
        Extract __accepted_type into a named template parameter for reuse in
        other constraints and in the exception specification.
        (variant::variant(in_place_type_t<T>, Args&&...))
        (variant::variant(in_place_type_t<T>, initializer_list<U>, Args&&...))
        (variant::variant(in_place_index_t<T>, Args&&...))
        (variant::variant(in_place_index_t<T>, initializer_list<U>, Args&&...))
        (variant::operator=T&&)): Remove redundant && from trait arguments.
        * testsuite/20_util/variant/compile.cc: Check variant(T&&) constructor
        isn't used for in_place_type or in_place_index arguments.

Modified:
    trunk/libstdc++-v3/ChangeLog
    trunk/libstdc++-v3/include/std/variant
    trunk/libstdc++-v3/testsuite/20_util/variant/compile.cc