[committed] libstdc++: Add std::is_scoped_enum for C++23

[committed] libstdc++: Add std::is_scoped_enum for C++23

[Jonathan Wakely]

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Implement this C++23 feature, as proposed by P1048R1.

This implementation assumes that a C++23 compiler supports concepts
already. I don't see any point in using preprocessor hacks to detect
compilers which define __cplusplus to a post-C++20 value but don't
support concepts yet.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (is_scoped_enum): Define.
	* include/std/version (__cpp_lib_is_scoped_enum): Define.
	* testsuite/20_util/is_scoped_enum/value.cc: New test.
	* testsuite/20_util/is_scoped_enum/version.cc: New test.

Tested powerpc64le-linux. Committed to trunk.


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commit b8ecdc772703729b75fba8b4bb94acfcb6f7cfae
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Fri Mar 19 19:42:18 2021

    libstdc++: Add std::is_scoped_enum for C++23
    
    Implement this C++23 feature, as proposed by P1048R1.
    
    This implementation assumes that a C++23 compiler supports concepts
    already. I don't see any point in using preprocessor hacks to detect
    compilers which define __cplusplus to a post-C++20 value but don't
    support concepts yet.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_scoped_enum): Define.
            * include/std/version (__cpp_lib_is_scoped_enum): Define.
            * testsuite/20_util/is_scoped_enum/value.cc: New test.
            * testsuite/20_util/is_scoped_enum/version.cc: New test.

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index ad2672d36a6..eeab1ca65fc 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3279,6 +3279,23 @@ template <typename _From, typename _To>
     inline constexpr bool is_unbounded_array_v
       = is_unbounded_array<_Tp>::value;
 
+#if __cplusplus > 202002L
+#define __cpp_lib_is_scoped_enum 202011L
+
+  template<typename _Tp>
+    struct is_scoped_enum
+    : false_type
+    { };
+
+  template<typename _Tp> requires __is_enum(_Tp)
+    struct is_scoped_enum<_Tp>
+    : __not_<is_convertible<_Tp, __underlying_type(_Tp)>>::type
+    { };
+
+  template<typename _Tp>
+    inline constexpr bool is_scoped_enum_v = is_scoped_enum<_Tp>::value;
+#endif // C++23
+
 #ifdef _GLIBCXX_HAVE_BUILTIN_IS_CONSTANT_EVALUATED
 
 #define __cpp_lib_is_constant_evaluated 201811L
diff --git a/libstdc++-v3/include/std/version b/libstdc++-v3/include/std/version
index e9eca06a72a..cb25148fca5 100644
--- a/libstdc++-v3/include/std/version
+++ b/libstdc++-v3/include/std/version
@@ -259,6 +259,7 @@
 
 #if __cplusplus > 202002L
 // c++2b
+#define __cpp_lib_is_scoped_enum 202011L
 #define __cpp_lib_string_contains 202011L
 #define __cpp_lib_to_underlying 202102L
 #endif // C++2b
diff --git a/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc b/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc
new file mode 100644
index 00000000000..bab7263ae4a
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc
@@ -0,0 +1,62 @@
+// Copyright (C) 2021 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++23" }
+// { dg-do compile { target c++23 } }
+
+#include <type_traits>
+
+#ifndef __cpp_lib_is_scoped_enum
+# error "Feature test macro for is_scoped_enum is missing in <type_traits>"
+#elif __cpp_lib_is_scoped_enum < 202011L
+# error "Feature test macro for is_scoped_enum has wrong value in <type_traits>"
+#endif
+
+#include <testsuite_tr1.h>
+
+template<typename T>
+  concept Is_scoped_enum
+    = __gnu_test::test_category<std::is_scoped_enum, T>(true);
+
+void
+test01()
+{
+  enum class E { e1, e2 };
+  static_assert( Is_scoped_enum<E> );
+  enum class Ec : char { e1, e2 };
+  static_assert( Is_scoped_enum<Ec> );
+
+  // negative tests
+  enum U { u1, u2 };
+  static_assert( ! Is_scoped_enum<U> );
+  enum F : int { f1, f2 };
+  static_assert( ! Is_scoped_enum<F> );
+  struct S { };
+  static_assert( ! Is_scoped_enum<S> );
+
+  static_assert( ! Is_scoped_enum<int> );
+  static_assert( ! Is_scoped_enum<int[]> );
+  static_assert( ! Is_scoped_enum<int[2]> );
+  static_assert( ! Is_scoped_enum<int[][2]> );
+  static_assert( ! Is_scoped_enum<int[2][3]> );
+  static_assert( ! Is_scoped_enum<int*> );
+  static_assert( ! Is_scoped_enum<int&> );
+  static_assert( ! Is_scoped_enum<int*&> );
+  static_assert( ! Is_scoped_enum<int()> );
+  static_assert( ! Is_scoped_enum<int(*)()> );
+  static_assert( ! Is_scoped_enum<int(&)()> );
+}
diff --git a/libstdc++-v3/testsuite/20_util/is_scoped_enum/version.cc b/libstdc++-v3/testsuite/20_util/is_scoped_enum/version.cc
new file mode 100644
index 00000000000..ed78fce5fbe
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/is_scoped_enum/version.cc
@@ -0,0 +1,27 @@
+// Copyright (C) 2021 Free Software Foundation, Inc.
+//
+// This file is part of the GNU ISO C++ Library.  This library is free
+// software; you can redistribute it and/or modify it under the
+// terms of the GNU General Public License as published by the
+// Free Software Foundation; either version 3, or (at your option)
+// any later version.
+
+// This library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+
+// You should have received a copy of the GNU General Public License along
+// with this library; see the file COPYING3.  If not see
+// <http://www.gnu.org/licenses/>.
+
+// { dg-options "-std=gnu++23" }
+// { dg-do compile { target c++23 } }
+
+#include <version>
+
+#ifndef __cpp_lib_is_scoped_enum
+# error "Feature test macro for is_scoped_enum is missing in <version>"
+#elif __cpp_lib_is_scoped_enum < 202011L
+# error "Feature test macro for is_scoped_enum has wrong value in <version>"
+#endif

Re: [committed] libstdc++: Add std::is_scoped_enum for C++23

[Tim Song]

On Fri, Mar 19, 2021 at 3:13 PM Jonathan Wakely via Libstdc++
<libstdc++@gcc.gnu.org> wrote:
>
> Implement this C++23 feature, as proposed by P1048R1.
>
> This implementation assumes that a C++23 compiler supports concepts
> already. I don't see any point in using preprocessor hacks to detect
> compilers which define __cplusplus to a post-C++20 value but don't
> support concepts yet.
>
> libstdc++-v3/ChangeLog:
>
>         * include/std/type_traits (is_scoped_enum): Define.
>         * include/std/version (__cpp_lib_is_scoped_enum): Define.
>         * testsuite/20_util/is_scoped_enum/value.cc: New test.
>         * testsuite/20_util/is_scoped_enum/version.cc: New test.
>
> Tested powerpc64le-linux. Committed to trunk.
>

Using __underlying_type breaks for incomplete enumeration types. GCC
doesn't have incomplete scoped enums due to
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89025 but unscoped ones
exist:

enum E {
    x = std::is_scoped_enum_v<E>
};

Re: [committed] libstdc++: Add std::is_scoped_enum for C++23

[Jonathan Wakely]

On Sat, 20 Mar 2021, 01:13 Tim Song via Libstdc++, <libstdc++@gcc.gnu.org>
wrote:

> On Fri, Mar 19, 2021 at 3:13 PM Jonathan Wakely via Libstdc++
> <libstdc++@gcc.gnu.org> wrote:
> >
> > Implement this C++23 feature, as proposed by P1048R1.
> >
> > This implementation assumes that a C++23 compiler supports concepts
> > already. I don't see any point in using preprocessor hacks to detect
> > compilers which define __cplusplus to a post-C++20 value but don't
> > support concepts yet.
> >
> > libstdc++-v3/ChangeLog:
> >
> >         * include/std/type_traits (is_scoped_enum): Define.
> >         * include/std/version (__cpp_lib_is_scoped_enum): Define.
> >         * testsuite/20_util/is_scoped_enum/value.cc: New test.
> >         * testsuite/20_util/is_scoped_enum/version.cc: New test.
> >
> > Tested powerpc64le-linux. Committed to trunk.
> >
>
> Using __underlying_type breaks for incomplete enumeration types. GCC
> doesn't have incomplete scoped enums due to
> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89025 but unscoped ones
> exist:
>
> enum E {
>     x = std::is_scoped_enum_v<E>
> };
>

Thanks, I'll just use int then. Maybe not until Monday though.

Re: [committed] libstdc++: Add std::is_scoped_enum for C++23

[Tim Song]

On Sat, Mar 20, 2021 at 3:58 AM Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>
>
>
> On Sat, 20 Mar 2021, 01:13 Tim Song via Libstdc++, <libstdc++@gcc.gnu.org> wrote:
>>
>> On Fri, Mar 19, 2021 at 3:13 PM Jonathan Wakely via Libstdc++
>> <libstdc++@gcc.gnu.org> wrote:
>> >
>> > Implement this C++23 feature, as proposed by P1048R1.
>> >
>> > This implementation assumes that a C++23 compiler supports concepts
>> > already. I don't see any point in using preprocessor hacks to detect
>> > compilers which define __cplusplus to a post-C++20 value but don't
>> > support concepts yet.
>> >
>> > libstdc++-v3/ChangeLog:
>> >
>> >         * include/std/type_traits (is_scoped_enum): Define.
>> >         * include/std/version (__cpp_lib_is_scoped_enum): Define.
>> >         * testsuite/20_util/is_scoped_enum/value.cc: New test.
>> >         * testsuite/20_util/is_scoped_enum/version.cc: New test.
>> >
>> > Tested powerpc64le-linux. Committed to trunk.
>> >
>>
>> Using __underlying_type breaks for incomplete enumeration types. GCC
>> doesn't have incomplete scoped enums due to
>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89025 but unscoped ones
>> exist:
>>
>> enum E {
>>     x = std::is_scoped_enum_v<E>
>> };
>
>
> Thanks, I'll just use int then. Maybe not until Monday though.
>
>

Using int avoids the hard error, but it appears to give the wrong
answer (presumably because the is_convertible check fails due to E
being incomplete). This may need to be handled explicitly?

Re: [committed] libstdc++: Add std::is_scoped_enum for C++23

[Jonathan Wakely]

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On 20/03/21 09:18 -0500, Tim Song wrote:
>On Sat, Mar 20, 2021 at 3:58 AM Jonathan Wakely <jwakely.gcc@gmail.com> wrote:
>>
>>
>>
>> On Sat, 20 Mar 2021, 01:13 Tim Song via Libstdc++, <libstdc++@gcc.gnu.org> wrote:
>>>
>>> On Fri, Mar 19, 2021 at 3:13 PM Jonathan Wakely via Libstdc++
>>> <libstdc++@gcc.gnu.org> wrote:
>>> >
>>> > Implement this C++23 feature, as proposed by P1048R1.
>>> >
>>> > This implementation assumes that a C++23 compiler supports concepts
>>> > already. I don't see any point in using preprocessor hacks to detect
>>> > compilers which define __cplusplus to a post-C++20 value but don't
>>> > support concepts yet.
>>> >
>>> > libstdc++-v3/ChangeLog:
>>> >
>>> >         * include/std/type_traits (is_scoped_enum): Define.
>>> >         * include/std/version (__cpp_lib_is_scoped_enum): Define.
>>> >         * testsuite/20_util/is_scoped_enum/value.cc: New test.
>>> >         * testsuite/20_util/is_scoped_enum/version.cc: New test.
>>> >
>>> > Tested powerpc64le-linux. Committed to trunk.
>>> >
>>>
>>> Using __underlying_type breaks for incomplete enumeration types. GCC
>>> doesn't have incomplete scoped enums due to
>>> https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89025 but unscoped ones
>>> exist:
>>>
>>> enum E {
>>>     x = std::is_scoped_enum_v<E>
>>> };
>>
>>
>> Thanks, I'll just use int then. Maybe not until Monday though.
>>
>>
>
>Using int avoids the hard error, but it appears to give the wrong
>answer (presumably because the is_convertible check fails due to E
>being incomplete). This may need to be handled explicitly?

This seems to work, at least until PR 89025 is fixed (because you
can't currently refer to an incomplete scoped enum type).

Tested powerpc64le-linux, pushed to trunk.




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commit 43ab1dc24abd6fded8d5bf6547f0de6851beb200
Author: Jonathan Wakely <jwakely@redhat.com>
Date:   Thu Apr 8 10:50:57 2021

    libstdc++: Make std::is_scoped_enum work with incomplete types
    
    Tim Song pointed out that using __underlying_type is ill-formed for
    incomplete enumeration types, and is_scoped_enum doesn't require a
    complete type. This changes the trait to check for conversion to int
    instead of to the underlying type.
    
    In order to give the correct result when the trait is used in the
    enumerator-list of an incomplete type the partial specialization for
    enums has an additional check that fails for incomplete types. This
    assumes that an incompelte enumeration type must be an unscoped
    enumeration, and so the primary template (with a std::false_type base
    characteristic) can be used. This isn't necessarily true, but it is not
    currently possible to refer to a scoped enumeration type before its type
    is complete (PR c++/89025).
    
    It should be possible to use requires(remove_cv_t<_Tp> __t) in the
    partial specialization's assignablility check, but that currently gives
    an ICE (PR c++/99968) so there is an extra partial specialization of
    is_scoped_enum<const _Tp> to handle const types.
    
    libstdc++-v3/ChangeLog:
    
            * include/std/type_traits (is_scoped_enum<T>): Constrain partial
            specialization to not match incomplete enum types. Use a
            requires-expression instead of instantiating is_convertible.
            (is_scoped_enum<const T>): Add as workaround for PR c++/99968.
            * testsuite/20_util/is_scoped_enum/value.cc: Check with
            incomplete types and opaque-enum-declarations.

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index eeab1ca65fc..1f8b57b04a0 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -3287,9 +3287,20 @@ template <typename _From, typename _To>
     : false_type
     { };
 
-  template<typename _Tp> requires __is_enum(_Tp)
+  template<typename _Tp>
+    requires __is_enum(_Tp)
+    && requires(_Tp __t) { __t = __t; } // fails if incomplete
     struct is_scoped_enum<_Tp>
-    : __not_<is_convertible<_Tp, __underlying_type(_Tp)>>::type
+    : bool_constant<!requires(_Tp __t, void(*__f)(int)) { __f(__t); }>
+    { };
+
+  // FIXME remove this partial specialization and use remove_cv_t<_Tp> above
+  // when PR c++/99968 is fixed.
+  template<typename _Tp>
+    requires __is_enum(_Tp)
+    && requires(_Tp __t) { __t = __t; } // fails if incomplete
+    struct is_scoped_enum<const _Tp>
+    : bool_constant<!requires(_Tp __t, void(*__f)(int)) { __f(__t); }>
     { };
 
   template<typename _Tp>
diff --git a/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc b/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc
index bab7263ae4a..2cef857a042 100644
--- a/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc
+++ b/libstdc++-v3/testsuite/20_util/is_scoped_enum/value.cc
@@ -32,6 +32,8 @@ template<typename T>
   concept Is_scoped_enum
     = __gnu_test::test_category<std::is_scoped_enum, T>(true);
 
+struct Incomplete_struct;
+
 void
 test01()
 {
@@ -45,6 +47,9 @@ test01()
   static_assert( ! Is_scoped_enum<U> );
   enum F : int { f1, f2 };
   static_assert( ! Is_scoped_enum<F> );
+  static_assert( ! Is_scoped_enum<Incomplete_struct> );
+  struct S;
+  static_assert( ! Is_scoped_enum<S> );
   struct S { };
   static_assert( ! Is_scoped_enum<S> );
 
@@ -60,3 +65,36 @@ test01()
   static_assert( ! Is_scoped_enum<int(*)()> );
   static_assert( ! Is_scoped_enum<int(&)()> );
 }
+
+enum opaque_unscoped : short;
+enum class opaque_scoped;
+enum class opaque_scoped_with_base : long;
+
+static_assert( ! Is_scoped_enum<opaque_unscoped> );
+static_assert( Is_scoped_enum<opaque_scoped> );
+static_assert( Is_scoped_enum<opaque_scoped_with_base> );
+
+void
+test02()
+{
+  enum unscoped {
+    u_is_enum = std::is_enum_v<unscoped>,
+    u_is_scoped = std::is_scoped_enum_v<unscoped>,
+  };
+  static_assert( unscoped::u_is_enum );
+  static_assert( ! unscoped::u_is_scoped );
+
+  enum unscoped_fixed : char {
+    uf_is_enum = std::is_enum_v<unscoped_fixed>,
+    uf_is_scoped = std::is_scoped_enum_v<unscoped_fixed>,
+  };
+  static_assert( unscoped_fixed::uf_is_enum);
+  static_assert( ! unscoped_fixed::uf_is_scoped );
+
+  enum class scoped {
+    is_enum = std::is_enum_v<scoped>,
+    is_scoped = std::is_scoped_enum_v<scoped>,
+  };
+  static_assert( (bool) scoped::is_enum );
+  static_assert( (bool) scoped::is_scoped );
+}