<type_traits>: Workaround for common_reference

stl/inc/concepts

@@ -40,7 +40,11 @@ concept derived_from = __is_base_of(_Base, _Derived)
     && __is_convertible_to(const volatile _Derived*, const volatile _Base*);
 
 template <class _From, class _To>
+#if !defined(__EDG__) && !defined(__clang__) // TRANSITION, DevCom-1627396
+concept convertible_to = is_convertible_v<_From, _To>
+#else // ^^^ workaround / no workaround vvv
 concept convertible_to = __is_convertible_to(_From, _To)
+#endif // ^^^ no workaround ^^^
     && requires {
         static_cast<_To>(_STD declval<_From>());
     };

stl/inc/type_traits

@@ -331,6 +331,32 @@ struct is_convertible : bool_constant<__is_convertible_to(_From, _To)> {
 template <class _From, class _To>
 _INLINE_VAR constexpr bool is_convertible_v = __is_convertible_to(_From, _To);
 
+#if !defined(__EDG__) && !defined(__clang__) // TRANSITION, DevCom-1627396
+template <class _Ty>
+struct is_convertible<_Ty&, volatile _Ty&> : true_type {};
+
+template <class _Ty>
+struct is_convertible<volatile _Ty&, volatile _Ty&> : true_type {};
+
+template <class _Ty>
+struct is_convertible<_Ty&, const volatile _Ty&> : true_type {};
+
+template <class _Ty>
+struct is_convertible<volatile _Ty&, const volatile _Ty&> : true_type {};
+
+template <class _Ty>
+_INLINE_VAR constexpr bool is_convertible_v<_Ty&, volatile _Ty&> = true;
+
+template <class _Ty>
+_INLINE_VAR constexpr bool is_convertible_v<volatile _Ty&, volatile _Ty&> = true;
+
+template <class _Ty>
+_INLINE_VAR constexpr bool is_convertible_v<_Ty&, const volatile _Ty&> = true;
+
+template <class _Ty>
+_INLINE_VAR constexpr bool is_convertible_v<volatile _Ty&, const volatile _Ty&> = true;
+#endif // ^^^ workaround
+
 template <class _Ty>
 struct is_enum : bool_constant<__is_enum(_Ty)> {}; // determine whether _Ty is an enumerated type
 
@@ -1179,10 +1205,6 @@ struct basic_common_reference {};
 template <class _Ty>
 _Ty _Returns_exactly() noexcept; // not defined
 
-template <class _Ty1, class _Ty2>
-using _Cond_res = // N4810 [meta.trans.other]/2.4
-    decltype(false ? _Returns_exactly<_Ty1>() : _Returns_exactly<_Ty2>());
-
 template <class _From>
 struct _Copy_cv_impl {
     template <class _To>
@@ -1223,6 +1245,34 @@ struct _Add_qualifiers<_Ty1&&> {
     using _Apply = add_rvalue_reference_t<_Copy_cv<_Ty1, _Ty2>>;
 };
 
+#if !defined(__EDG__) && !defined(__clang__) // TRANSITION, DevCom-876860
+template <class _Ty1, class _Ty2>
+using _Cond_res_if_right = // N4810 [meta.trans.other]/2.4
+    decltype(false ? _Returns_exactly<_Ty1>() : _Returns_exactly<_Ty2>());
+
+template <class _Ty>
+using _Is_scalar_or_array = disjunction<is_scalar<_Ty>, is_array<_Ty>>;
+
+template <class _Ty1, class _Ty2, class = void>
+struct _Cond_res_workaround {};
+
+template <class _Ty1, class _Ty2>
+struct _Cond_res_workaround<_Ty1, _Ty2, void_t<_Cond_res_if_right<_Ty1, _Ty2>>> {
+    using _Uty = remove_cvref_t<_Ty1>;
+    using type = conditional_t<conjunction_v<is_same<_Uty, remove_cvref_t<_Ty2>>, _Is_scalar_or_array<_Uty>,
+                                   disjunction<conjunction<is_lvalue_reference<_Ty1>, is_rvalue_reference<_Ty2>>,
+                                       conjunction<is_rvalue_reference<_Ty1>, is_lvalue_reference<_Ty2>>>>,
+        decay_t<_Copy_cv<remove_reference_t<_Ty1>, remove_reference_t<_Ty2>>>, _Cond_res_if_right<_Ty1, _Ty2>>;
+};
+
+template <class _Ty1, class _Ty2>
+using _Cond_res = typename _Cond_res_workaround<_Ty1, _Ty2>::type;
+#else // ^^^ workaround / no workaround vvv
+template <class _Ty1, class _Ty2>
+using _Cond_res = // N4810 [meta.trans.other]/2.4
+    decltype(false ? _Returns_exactly<_Ty1>() : _Returns_exactly<_Ty2>());
+#endif // ^^^ no workaround ^^^
+
 template <class...>
 struct common_reference;
 

tests/libcxx/expected_results.txt

@@ -262,17 +262,6 @@ std/atomics/atomics.types.generic/copy_semantics_traits.pass.cpp FAIL
 # DevCom-409222 "Constructing rvalue reference from non-reference-related lvalue reference"
 std/utilities/meta/meta.unary/meta.unary.prop/is_constructible.pass.cpp:0 FAIL
 
-# DevCom-876860 "conditional operator errors" blocks readable<volatile int*>.
-std/concepts/concepts.lang/concept.common/common_with.compile.pass.cpp:0 FAIL
-std/concepts/concepts.lang/concept.commonref/common_reference.compile.pass.cpp:0 FAIL
-std/containers/views/span.cons/iterator_sentinel.pass.cpp:0 FAIL
-std/iterators/iterator.requirements/iterator.concepts/iterator.concept.bidir/bidirectional_iterator.compile.pass.cpp:0 FAIL
-std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/contiguous_iterator.compile.pass.cpp:0 FAIL
-std/iterators/iterator.requirements/iterator.concepts/iterator.concept.readable/indirectly_readable.compile.pass.cpp:0 FAIL
-std/iterators/iterator.requirements/iterator.concepts/iterator.concept.forward/forward_iterator.compile.pass.cpp:0 FAIL
-std/iterators/iterator.requirements/iterator.concepts/iterator.concept.input/input_iterator.compile.pass.cpp:0 FAIL
-std/iterators/iterator.requirements/iterator.concepts/iterator.concept.random.access/random_access_iterator.compile.pass.cpp:0 FAIL
-
 # VSO-1271673 "static analyzer doesn't know about short-circuiting"
 std/algorithms/alg.sorting/alg.sort/partial.sort/partial_sort.pass.cpp:0 FAIL
 std/algorithms/alg.sorting/alg.sort/partial.sort/partial_sort_comp.pass.cpp:0 FAIL
@@ -290,9 +279,6 @@ std/utilities/utility/pairs/pairs.spec/three_way_comparison.pass.cpp:0 FAIL
 # DevCom-1626727: bogus "failure was caused by a conversion from void* to a pointer-to-object type" for conversion to void
 std/algorithms/robust_re_difference_type.compile.pass.cpp:0 FAIL
 
-# DevCom-1627396: C1XX's __is_convertible_to intrinsic mis-handles volatile array lvalues
-std/concepts/concepts.lang/concept.swappable/swappable_with.compile.pass.cpp:0 FAIL
-
 # DevCom-1628714: C1XX refuses nullptr_t == reference-to-function in a requires expression
 std/concepts/concepts.compare/concept.equalitycomparable/equality_comparable_with.compile.pass.cpp:0 FAIL
 

tests/libcxx/skipped_tests.txt

@@ -262,17 +262,6 @@ atomics\atomics.types.generic\copy_semantics_traits.pass.cpp
 # DevCom-409222 "Constructing rvalue reference from non-reference-related lvalue reference"
 utilities\meta\meta.unary\meta.unary.prop\is_constructible.pass.cpp
 
-# DevCom-876860 "conditional operator errors" blocks readable<volatile int*>.
-concepts\concepts.lang\concept.common\common_with.compile.pass.cpp
-concepts\concepts.lang\concept.commonref\common_reference.compile.pass.cpp
-containers\views\span.cons\iterator_sentinel.pass.cpp
-iterators\iterator.requirements\iterator.concepts\iterator.concept.bidir\bidirectional_iterator.compile.pass.cpp
-iterators\iterator.requirements\iterator.concepts\iterator.concept.random.access\contiguous_iterator.compile.pass.cpp
-iterators\iterator.requirements\iterator.concepts\iterator.concept.readable\indirectly_readable.compile.pass.cpp
-iterators\iterator.requirements\iterator.concepts\iterator.concept.forward\forward_iterator.compile.pass.cpp
-iterators\iterator.requirements\iterator.concepts\iterator.concept.input\input_iterator.compile.pass.cpp
-iterators\iterator.requirements\iterator.concepts\iterator.concept.random.access\random_access_iterator.compile.pass.cpp
-
 # VSO-1271673 "static analyzer doesn't know about short-circuiting"
 algorithms\alg.sorting\alg.sort\partial.sort\partial_sort.pass.cpp
 algorithms\alg.sorting\alg.sort\partial.sort\partial_sort_comp.pass.cpp
@@ -290,9 +279,6 @@ utilities\utility\pairs\pairs.spec\three_way_comparison.pass.cpp
 # DevCom-1626727: bogus "failure was caused by a conversion from void* to a pointer-to-object type" for conversion to void
 algorithms\robust_re_difference_type.compile.pass.cpp
 
-# DevCom-1627396: C1XX's __is_convertible_to intrinsic mis-handles volatile array lvalues
-concepts\concepts.lang\concept.swappable\swappable_with.compile.pass.cpp
-
 # DevCom-1628714: C1XX refuses nullptr_t == reference-to-function in a requires expression
 concepts\concepts.compare\concept.equalitycomparable\equality_comparable_with.compile.pass.cpp
 

tests/std/test.lst

@@ -192,6 +192,7 @@ tests\GH_002039_byte_is_not_trivially_swappable
 tests\GH_002058_debug_iterator_race
 tests\GH_002120_streambuf_seekpos_and_seekoff
 tests\GH_002488_promise_not_default_constructible_types
+tests\GH_002581_common_reference_workaround
 tests\LWG2597_complex_branch_cut
 tests\LWG3018_shared_ptr_function
 tests\LWG3146_excessive_unwrapping_ref_cref

tests/std/tests/GH_002581_common_reference_workaround/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\strict_concepts_20_matrix.lst

tests/std/tests/GH_002581_common_reference_workaround/test.compile.pass.cpp

@@ -0,0 +1,45 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cstddef>
+#include <iterator>
+
+using namespace std;
+
+struct Test {};
+enum Unscoped {};
+enum class Scoped {};
+
+// Tests for raw pointers
+static_assert(contiguous_iterator<volatile int*>);
+static_assert(contiguous_iterator<const volatile int*>);
+static_assert(contiguous_iterator<volatile double*>);
+static_assert(contiguous_iterator<const volatile double*>);
+static_assert(contiguous_iterator<volatile nullptr_t*>);
+static_assert(contiguous_iterator<const volatile nullptr_t*>);
+static_assert(contiguous_iterator<volatile Unscoped*>);
+static_assert(contiguous_iterator<const volatile Unscoped*>);
+static_assert(contiguous_iterator<volatile Scoped*>);
+static_assert(contiguous_iterator<const volatile Scoped*>);
+static_assert(contiguous_iterator<Test* volatile*>);
+static_assert(contiguous_iterator<Test* const volatile*>);
+static_assert(contiguous_iterator<int Test::*volatile*>);
+static_assert(contiguous_iterator<int Test::*const volatile*>);
+
+// Tests for move_iterator specializations
+static_assert(input_iterator<move_iterator<volatile int*>>);
+static_assert(input_iterator<move_iterator<const volatile int*>>);
+static_assert(input_iterator<move_iterator<volatile double*>>);
+static_assert(input_iterator<move_iterator<const volatile double*>>);
+static_assert(input_iterator<move_iterator<volatile nullptr_t*>>);
+static_assert(input_iterator<move_iterator<const volatile nullptr_t*>>);
+static_assert(input_iterator<move_iterator<volatile Unscoped*>>);
+static_assert(input_iterator<move_iterator<const volatile Unscoped*>>);
+static_assert(input_iterator<move_iterator<volatile Scoped*>>);
+static_assert(input_iterator<move_iterator<const volatile Scoped*>>);
+static_assert(input_iterator<move_iterator<Test* volatile*>>);
+static_assert(input_iterator<move_iterator<Test* const volatile*>>);
+static_assert(input_iterator<move_iterator<int Test::*volatile*>>);
+static_assert(input_iterator<move_iterator<int Test::*const volatile*>>);
+
+int main() {} // COMPILE-ONLY