[libcxx] r296561 - Fix PR32097 - is_abstract doesn't work on class templates.

[Eric Fiselier via cfe-commits]

@Hans Where are we in the release process? I would like to merge this into
4.0.

Although it's not a regression, it is a significant bug. This patch fixes
the bug by
forwarding to a compiler builtin, which is strictly better than what we
have. I'm
confident this patch is safe.

/Eric

On Tue, Feb 28, 2017 at 6:27 PM, Eric Fiselier via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: ericwf
> Date: Tue Feb 28 19:27:14 2017
> New Revision: 296561
>
> URL: http://llvm.org/viewvc/llvm-project?rev=296561&view=rev
> Log:
> Fix PR32097 - is_abstract doesn't work on class templates.
>
> This patch fixes llvm.org/PR32097 by using the __is_abstract
> builtin type-trait instead of the previous library-only implementation.
>
> All supported compilers provide this trait. I've tested as far
> back as Clang 3.2, GCC 4.6 and MSVC trunk.
>
> Modified:
>     libcxx/trunk/include/type_traits
>     libcxx/trunk/test/std/utilities/meta/meta.unary/
> meta.unary.prop/is_abstract.pass.cpp
>
> Modified: libcxx/trunk/include/type_traits
> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/
> type_traits?rev=296561&r1=296560&r2=296561&view=diff
> ============================================================
> ==================
> --- libcxx/trunk/include/type_traits (original)
> +++ libcxx/trunk/include/type_traits Tue Feb 28 19:27:14 2017
> @@ -1297,18 +1297,8 @@ template <class _Tp> using decay_t = typ
>
>  // is_abstract
>
> -namespace __is_abstract_imp
> -{
> -template <class _Tp> char  __test(_Tp (*)[1]);
> -template <class _Tp> __two __test(...);
> -}
> -
> -template <class _Tp, bool = is_class<_Tp>::value>
> -struct __libcpp_abstract : public integral_constant<bool,
> sizeof(__is_abstract_imp::__test<_Tp>(0)) != 1> {};
> -
> -template <class _Tp> struct __libcpp_abstract<_Tp, false> : public
> false_type {};
> -
> -template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_abstract : public
> __libcpp_abstract<_Tp> {};
> +template <class _Tp> struct _LIBCPP_TEMPLATE_VIS is_abstract
> +    : public integral_constant<bool, __is_abstract(_Tp)> {};
>
>  #if _LIBCPP_STD_VER > 14 && !defined(_LIBCPP_HAS_NO_VARIABLE_TEMPLATES)
>  template <class _Tp> _LIBCPP_CONSTEXPR bool is_abstract_v
>
> Modified: libcxx/trunk/test/std/utilities/meta/meta.unary/
> meta.unary.prop/is_abstract.pass.cpp
> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/std/
> utilities/meta/meta.unary/meta.unary.prop/is_abstract.
> pass.cpp?rev=296561&r1=296560&r2=296561&view=diff
> ============================================================
> ==================
> --- libcxx/trunk/test/std/utilities/meta/meta.unary/
> meta.unary.prop/is_abstract.pass.cpp (original)
> +++ libcxx/trunk/test/std/utilities/meta/meta.unary/
> meta.unary.prop/is_abstract.pass.cpp Tue Feb 28 19:27:14 2017
> @@ -65,6 +65,14 @@ class Abstract
>      virtual ~Abstract() = 0;
>  };
>
> +template <class>
> +struct AbstractTemplate {
> +  virtual void test() = 0;
> +};
> +
> +template <>
> +struct AbstractTemplate<double> {};
> +
>  int main()
>  {
>      test_is_not_abstract<void>();
> @@ -81,4 +89,6 @@ int main()
>      test_is_not_abstract<NotEmpty>();
>
>      test_is_abstract<Abstract>();
> +    test_is_abstract<AbstractTemplate<int> >();
> +    test_is_not_abstract<AbstractTemplate<double> >();
>  }
>
>
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