P0466R5 Layout-Compatibility And Pointer-Interconvertibility Traits (#…

…1575)

Co-authored-by: Stephan T. Lavavej <stl@nuwen.net>

stl/inc/type_traits

@@ -1804,6 +1804,67 @@ inline constexpr bool is_nothrow_invocable_r_v =
     _Select_invoke_traits<_Callable, _Args...>::template _Is_nothrow_invocable_r<_Rx>::value;
 #endif // _HAS_CXX17
 
+#if _HAS_CXX20
+#ifndef __EDG__ // TRANSITION, VSO-1268984
+#ifndef __clang__ // TRANSITION, LLVM-48860
+// STRUCT TEMPLATE is_layout_compatible
+template <class _Ty1, class _Ty2>
+#ifdef _IS_LAYOUT_COMPATIBLE_SUPPORTED
+struct is_layout_compatible : bool_constant<__is_layout_compatible(_Ty1, _Ty2)> {
+#else // ^^^ _IS_LAYOUT_COMPATIBLE_SUPPORTED / !_IS_LAYOUT_COMPATIBLE_SUPPORTED vvv
+struct is_layout_compatible : bool_constant<__builtin_is_layout_compatible(_Ty1, _Ty2)> {
+#endif // _IS_LAYOUT_COMPATIBLE_SUPPORTED
+};
+
+template <class _Ty1, class _Ty2>
+#ifdef _IS_LAYOUT_COMPATIBLE_SUPPORTED
+inline constexpr bool is_layout_compatible_v = __is_layout_compatible(_Ty1, _Ty2);
+#else // ^^^ _IS_LAYOUT_COMPATIBLE_SUPPORTED / !_IS_LAYOUT_COMPATIBLE_SUPPORTED vvv
+inline constexpr bool is_layout_compatible_v = __builtin_is_layout_compatible(_Ty1, _Ty2);
+#endif // _IS_LAYOUT_COMPATIBLE_SUPPORTED
+
+// STRUCT TEMPLATE is_pointer_interconvertible_base_of
+template <class _Base, class _Derived>
+struct is_pointer_interconvertible_base_of
+#ifdef _IS_LAYOUT_COMPATIBLE_SUPPORTED
+    : bool_constant<__is_pointer_interconvertible_base_of(_Base, _Derived)> {
+};
+#else // ^^^ _IS_LAYOUT_COMPATIBLE_SUPPORTED / !_IS_LAYOUT_COMPATIBLE_SUPPORTED vvv
+    : bool_constant<__builtin_is_pointer_interconvertible_base_of(_Base, _Derived)> {
+};
+#endif // _IS_LAYOUT_COMPATIBLE_SUPPORTED
+
+template <class _Base, class _Derived>
+#ifdef _IS_LAYOUT_COMPATIBLE_SUPPORTED
+inline constexpr bool is_pointer_interconvertible_base_of_v = __is_pointer_interconvertible_base_of(_Base, _Derived);
+#else // ^^^ _IS_LAYOUT_COMPATIBLE_SUPPORTED / !_IS_LAYOUT_COMPATIBLE_SUPPORTED vvv
+inline constexpr bool is_pointer_interconvertible_base_of_v = __builtin_is_pointer_interconvertible_base_of(
+    _Base, _Derived);
+#endif // _IS_LAYOUT_COMPATIBLE_SUPPORTED
+
+// FUNCTION TEMPLATE is_pointer_interconvertible_with_class
+template <class _ClassTy, class _MemberTy>
+_NODISCARD constexpr bool is_pointer_interconvertible_with_class(_MemberTy _ClassTy::*_Pm) noexcept {
+#ifdef _IS_LAYOUT_COMPATIBLE_SUPPORTED
+    return __is_pointer_interconvertible_with_class(_ClassTy, _Pm);
+#else // ^^^ _IS_LAYOUT_COMPATIBLE_SUPPORTED / !_IS_LAYOUT_COMPATIBLE_SUPPORTED vvv
+    return __builtin_is_pointer_interconvertible_with_class(_ClassTy, _Pm);
+#endif // _IS_LAYOUT_COMPATIBLE_SUPPORTED
+}
+
+// FUNCTION TEMPLATE is_corresponding_member
+template <class _ClassTy1, class _ClassTy2, class _MemberTy1, class _MemberTy2>
+_NODISCARD constexpr bool is_corresponding_member(_MemberTy1 _ClassTy1::*_Pm1, _MemberTy2 _ClassTy2::*_Pm2) noexcept {
+#ifdef _IS_LAYOUT_COMPATIBLE_SUPPORTED
+    return __is_corresponding_member(_ClassTy1, _ClassTy2, _Pm1, _Pm2);
+#else // ^^^ _IS_LAYOUT_COMPATIBLE_SUPPORTED / !_IS_LAYOUT_COMPATIBLE_SUPPORTED vvv
+    return __builtin_is_corresponding_member(_ClassTy1, _ClassTy2, _Pm1, _Pm2);
+#endif // _IS_LAYOUT_COMPATIBLE_SUPPORTED
+}
+#endif // __clang__
+#endif // __EDG__
+#endif // _HAS_CXX20
+
 // ALIAS TEMPLATE _Weak_types
 template <class _Ty>
 struct _Function_args {}; // determine whether _Ty is a function

stl/inc/yvals_core.h

@@ -146,6 +146,7 @@
 // P0457R2 starts_with()/ends_with() For basic_string/basic_string_view
 // P0458R2 contains() For Ordered And Unordered Associative Containers
 // P0463R1 endian
+// P0466R5 Layout-Compatibility And Pointer-Interconvertibility Traits
 // P0476R2 <bit> bit_cast
 // P0482R6 Library Support For char8_t
 //     (mbrtoc8 and c8rtomb not yet implemented)
@@ -1208,19 +1209,33 @@
 #define __cpp_lib_integer_comparison_functions 202002L
 #define __cpp_lib_interpolate                  201902L
 #define __cpp_lib_is_constant_evaluated        201811L
-#define __cpp_lib_is_nothrow_convertible       201806L
-#define __cpp_lib_jthread                      201911L
-#define __cpp_lib_latch                        201907L
-#define __cpp_lib_list_remove_return_type      201806L
-#define __cpp_lib_math_constants               201907L
-#define __cpp_lib_polymorphic_allocator        201902L
-#define __cpp_lib_remove_cvref                 201711L
-#define __cpp_lib_semaphore                    201907L
-#define __cpp_lib_shift                        201806L
-#define __cpp_lib_smart_ptr_for_overwrite      202002L
-#define __cpp_lib_span                         202002L
-#define __cpp_lib_ssize                        201902L
-#define __cpp_lib_starts_ends_with             201711L
+
+#ifndef __EDG__ // TRANSITION, VSO-1268984
+#ifndef __clang__ // TRANSITION, LLVM-48860
+#define __cpp_lib_is_layout_compatible 201907L
+#endif // __clang__
+#endif // __EDG__
+
+#define __cpp_lib_is_nothrow_convertible 201806L
+
+#ifndef __EDG__ // TRANSITION, VSO-1268984
+#ifndef __clang__ // TRANSITION, LLVM-48860
+#define __cpp_lib_is_pointer_interconvertible 201907L
+#endif // __clang__
+#endif // __EDG__
+
+#define __cpp_lib_jthread                 201911L
+#define __cpp_lib_latch                   201907L
+#define __cpp_lib_list_remove_return_type 201806L
+#define __cpp_lib_math_constants          201907L
+#define __cpp_lib_polymorphic_allocator   201902L
+#define __cpp_lib_remove_cvref            201711L
+#define __cpp_lib_semaphore               201907L
+#define __cpp_lib_shift                   201806L
+#define __cpp_lib_smart_ptr_for_overwrite 202002L
+#define __cpp_lib_span                    202002L
+#define __cpp_lib_ssize                   201902L
+#define __cpp_lib_starts_ends_with        201711L
 
 #ifdef __cpp_lib_concepts // TRANSITION, GH-395
 #define __cpp_lib_three_way_comparison 201711L

tests/std/test.lst

@@ -234,6 +234,7 @@ tests\P0414R2_shared_ptr_for_arrays
 tests\P0415R1_constexpr_complex
 tests\P0426R1_constexpr_char_traits
 tests\P0433R2_deduction_guides
+tests\P0466R5_layout_compatibility_and_pointer_interconvertibility_traits
 tests\P0476R2_bit_cast
 tests\P0487R1_fixing_operator_shl_basic_istream_char_pointer
 tests\P0513R0_poisoning_the_hash

tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\usual_latest_matrix.lst

tests/std/tests/P0466R5_layout_compatibility_and_pointer_interconvertibility_traits/test.cpp

@@ -0,0 +1,254 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+#include <assert.h>
+#include <type_traits>
+
+using namespace std;
+
+#define ASSERT(...) assert((__VA_ARGS__))
+
+struct S { // Must be declared at namespace scope due to static data member
+    static int s1;
+    int v1;
+    int v2;
+};
+
+constexpr bool test() {
+#ifndef __EDG__ // TRANSITION, VSO-1268984
+#ifndef __clang__ // TRANSITION, LLVM-48860
+    // is_layout_compatible tests
+    {
+        struct S0 {
+            int v1;
+            int v2;
+        };
+
+        struct S1 {
+            S0 s1;
+            int v3;
+        };
+
+        struct S2 {
+            S0 s1;
+            int v2;
+        };
+
+        struct S3 {
+            S0 s1;
+            int v2;
+            int v3;
+        };
+
+        struct S4 {
+            int v1;
+
+        private:
+            int v2;
+        };
+
+        struct S5 {
+            int v1;
+
+        private:
+            int v2;
+        };
+
+        enum E1 { e1, e2, e3, e4 };
+        enum E2 : int { e5 };
+        enum E3 : unsigned int { e6, e7, e8 };
+        enum class E4 : unsigned int { no, yes };
+        enum class E5 { zero, fortytwo = 42 };
+
+        ASSERT(is_layout_compatible_v<int, int>);
+        ASSERT(is_layout_compatible_v<const void, void>);
+        ASSERT(is_layout_compatible_v<S1, volatile S2>);
+        ASSERT(is_layout_compatible_v<S1, S2>);
+        ASSERT(is_layout_compatible_v<S4, S4>);
+        ASSERT(is_layout_compatible_v<const volatile S4, S4>);
+        ASSERT(is_layout_compatible_v<E1, E2>);
+        ASSERT(is_layout_compatible_v<E3, E4>);
+        ASSERT(is_layout_compatible_v<E5, E1>);
+        ASSERT(is_layout_compatible_v<const E1, E2>);
+        ASSERT(is_layout_compatible_v<volatile E3, const E4>);
+        ASSERT(is_layout_compatible_v<int[], int[]>);
+        ASSERT(is_layout_compatible_v<int[3], int[3]>);
+
+#if defined(__clang__) || defined(__EDG__) // TRANSITION, VSO-1269781
+        ASSERT(is_layout_compatible_v<const int[], int[]>);
+        ASSERT(is_layout_compatible_v<const int[3], int[3]>);
+        ASSERT(is_layout_compatible_v<int[], volatile int[]>);
+#endif // TRANSITION, VSO-1269781
+
+        ASSERT(!is_layout_compatible_v<int, char>);
+        ASSERT(!is_layout_compatible_v<int, void>);
+        ASSERT(!is_layout_compatible_v<S1, void>);
+        ASSERT(!is_layout_compatible_v<S1, S3>);
+        ASSERT(!is_layout_compatible_v<S4, S5>);
+        ASSERT(!is_layout_compatible_v<E1, void>);
+        ASSERT(!is_layout_compatible_v<E1, E3>);
+        ASSERT(!is_layout_compatible_v<E2, E4>);
+        ASSERT(!is_layout_compatible_v<int[], int[2]>);
+        ASSERT(!is_layout_compatible_v<int[3], int[1]>);
+    }
+
+    // is_pointer_interconvertible_base_of tests
+    {
+        class A {};
+        class B : public A {};
+        class C : public A {
+            int : 0;
+        };
+        class D : public C {};
+// Disable warning C4408: anonymous union did not declare any data members
+#pragma warning(push)
+#pragma warning(disable : 4408)
+        class E : public A {
+            union {};
+        };
+#pragma warning(pop)
+        class F : private A {}; // Non-public inheritance
+        class NS : public B, public C {}; // Non-standard layout
+        class I; // Incomplete
+
+        union U {
+            int i;
+            char c;
+        };
+
+        ASSERT(is_pointer_interconvertible_base_of_v<A, A>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, B>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, const B>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, C>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, volatile C>);
+        ASSERT(is_pointer_interconvertible_base_of_v<volatile A, const C>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, D>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, E>);
+        ASSERT(is_pointer_interconvertible_base_of_v<A, F>);
+        ASSERT(is_pointer_interconvertible_base_of_v<C, D>);
+        ASSERT(is_pointer_interconvertible_base_of_v<I, I>);
+        ASSERT(is_pointer_interconvertible_base_of_v<const I, I>);
+
+        ASSERT(!is_pointer_interconvertible_base_of_v<int, int>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<void, void>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<A, int>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<B, C>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<A, NS>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<B, NS>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<int, I>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<U, U>);
+        ASSERT(!is_pointer_interconvertible_base_of_v<U, I>);
+    }
+
+    // is_corresponding_member tests
+    {
+        struct S1 {
+            int v1;
+            int v2;
+        };
+
+        struct S2 {
+            int w1;
+            int w2;
+        };
+
+        struct S3 {
+            int v1;
+            int v2;
+            int v3;
+        };
+
+        struct S4 {
+            char v1;
+            int v2;
+            int v3;
+        };
+
+        struct S5 {
+            int v1;
+            int v2;
+            void* v3;
+        };
+
+        struct S6 {
+            int v1;
+            int v2;
+            double v3;
+        };
+
+        struct S7 {
+            int f1() {
+                return 0;
+            }
+        };
+
+        struct NS : S1, S2 {}; // Non-standard layout
+
+        ASSERT(is_corresponding_member(&S1::v1, &S::v1));
+        ASSERT(is_corresponding_member(&S1::v2, &S::v2));
+        ASSERT(is_corresponding_member(&S1::v1, &S1::v1));
+        ASSERT(is_corresponding_member(&S1::v2, &S1::v2));
+        ASSERT(is_corresponding_member(&S1::v1, &S2::w1));
+        ASSERT(is_corresponding_member(&S1::v2, &S2::w2));
+        ASSERT(is_corresponding_member(&S1::v1, &S3::v1));
+        ASSERT(is_corresponding_member(&S1::v2, &S3::v2));
+        ASSERT(is_corresponding_member(&S5::v1, &S6::v1));
+        ASSERT(is_corresponding_member(&S5::v2, &S6::v2));
+
+        ASSERT(!is_corresponding_member(&S1::v1, &S1::v2));
+        ASSERT(!is_corresponding_member(&S1::v2, &S1::v1));
+        ASSERT(!is_corresponding_member(&S1::v2, &S2::w1));
+        ASSERT(!is_corresponding_member(&S1::v1, &S4::v1));
+        ASSERT(!is_corresponding_member(&S1::v2, &S4::v2));
+        ASSERT(!is_corresponding_member(&S3::v1, &S4::v1));
+        ASSERT(!is_corresponding_member(&S3::v2, &S4::v2));
+        ASSERT(!is_corresponding_member(&S5::v1, &S6::v2));
+        ASSERT(!is_corresponding_member(&S5::v2, &S6::v1));
+        ASSERT(!is_corresponding_member(&S5::v3, &S6::v3));
+        ASSERT(!is_corresponding_member<NS, NS>(&NS::v1, &NS::w1));
+        ASSERT(!is_corresponding_member(&S7::f1, &S7::f1));
+        ASSERT(!is_corresponding_member(static_cast<int S1::*>(nullptr), static_cast<int S2::*>(nullptr)));
+        ASSERT(!is_corresponding_member(&S1::v1, static_cast<int S2::*>(nullptr)));
+    }
+
+    // is_pointer_interconvertible_with_class tests
+    {
+        struct A {
+            int a;
+        };
+
+        struct B {
+            int b;
+        };
+
+        struct C {
+            int f1() {
+                return 0;
+            }
+        };
+
+        struct NS : A, B {}; // Non-standard layout
+
+        union U {
+            int v1;
+            char v2;
+        };
+
+        ASSERT(is_pointer_interconvertible_with_class(&A::a));
+        ASSERT(is_pointer_interconvertible_with_class(&NS::b));
+        ASSERT(is_pointer_interconvertible_with_class(&U::v1));
+        ASSERT(is_pointer_interconvertible_with_class(&U::v2));
+
+        ASSERT(!is_pointer_interconvertible_with_class<NS>(&NS::a));
+        ASSERT(!is_pointer_interconvertible_with_class<NS>(&NS::b));
+        ASSERT(!is_pointer_interconvertible_with_class(&C::f1));
+        ASSERT(!is_pointer_interconvertible_with_class(static_cast<int A::*>(nullptr)));
+    }
+#endif // __clang__
+#endif // __EDG__
+    return true;
+}
+
+int main() {
+    static_assert(test());
+    test();
+}