On Wed, Aug 21, 2024 at 1:56 AM Jonathan Wakely <jwak...@redhat.com> wrote:
>
> Tested x86_64-linux. Pushed to trunk.
>
> Probably worth backporting too. It could potentially cause new errors
> for people using arrays in std::variant, but that's forbidden by the
> standard.
It might be worth mentioning in porting_to guide just in case. You
never know since we have gotten bug reports about broken code that was
also rejected by clang/MSVC due to a change in GCC.
Thanks,
Andrew
>
> -- >8 --
>
> libstdc++-v3/ChangeLog:
>
> PR libstdc++/116381
> * include/std/variant (variant): Fix conditions for
> static_assert to match the spec.
> * testsuite/20_util/variant/types_neg.cc: New test.
> ---
> libstdc++-v3/include/std/variant | 6 ++----
> .../testsuite/20_util/variant/types_neg.cc | 17 +++++++++++++++++
> 2 files changed, 19 insertions(+), 4 deletions(-)
> create mode 100644 libstdc++-v3/testsuite/20_util/variant/types_neg.cc
>
> diff --git a/libstdc++-v3/include/std/variant
> b/libstdc++-v3/include/std/variant
> index 12108d07f0b..5fb7770d889 100644
> --- a/libstdc++-v3/include/std/variant
> +++ b/libstdc++-v3/include/std/variant
> @@ -1457,10 +1457,8 @@ namespace __detail::__variant
>
> static_assert(sizeof...(_Types) > 0,
> "variant must have at least one alternative");
> - static_assert(!(std::is_reference_v<_Types> || ...),
> - "variant must have no reference alternative");
> - static_assert(!(std::is_void_v<_Types> || ...),
> - "variant must have no void alternative");
> + static_assert(((std::is_object_v<_Types> && !is_array_v<_Types>) &&
> ...),
> + "variant alternatives must be non-array object types");
>
> using _Base = __detail::__variant::_Variant_base<_Types...>;
>
> diff --git a/libstdc++-v3/testsuite/20_util/variant/types_neg.cc
> b/libstdc++-v3/testsuite/20_util/variant/types_neg.cc
> new file mode 100644
> index 00000000000..5cd3d02154b
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/variant/types_neg.cc
> @@ -0,0 +1,17 @@
> +// { dg-do compile { target c++17 } }
> +
> +# include <variant>
> +
> +std::variant<> v0; // { dg-error "here" }
> +// { dg-error "must have at least one alternative" "" { target *-*-* } 0 }
> +std::variant<int, void> v1; // { dg-error "here" }
> +std::variant<int, const void> v2; // { dg-error "here" }
> +std::variant<int, int&> v3; // { dg-error "here" }
> +std::variant<int, void()> v4; // { dg-error "here" }
> +std::variant<int, int[]> v5; // { dg-error "here" }
> +std::variant<int, int[1]> v6; // { dg-error "here" }
> +// { dg-error "must be non-array object types" "" { target *-*-* } 0 }
> +
> +// All of variant's base classes are instantiated before checking any
> +// static_assert, so we get lots of errors before the expected errors above.
> +// { dg-excess-errors "" }
> --
> 2.46.0
>
