Implement P2538R1 ADL-Proof projected

stl/inc/xutility

@@ -864,22 +864,40 @@ _EXPORT_STD template <class _Fn, class... _Its>
     requires (indirectly_readable<_Its> && ...) && invocable<_Fn, iter_reference_t<_Its>...>
 using indirect_result_t = invoke_result_t<_Fn, iter_reference_t<_Its>...>;
 
-_EXPORT_STD template <indirectly_readable _It, indirectly_regular_unary_invocable<_It> _Proj>
-struct projected {
-    using value_type = remove_cvref_t<indirect_result_t<_Proj&, _It>>;
-    indirect_result_t<_Proj&, _It> operator*() const {
-        _CSTD abort();
-    }
+template <class _It>
+struct _Projected_difference_type_impl {
+    struct _Base {};
+};
+
+template <weakly_incrementable _It>
+struct _Projected_difference_type_impl<_It> {
+    struct _Base {
+        using difference_type = iter_difference_t<_It>;
+    };
 };
 
 template <class _It, class _Proj>
-struct _Indirect_value_impl<projected<_It, _Proj>> {
-    using type = invoke_result_t<_Proj&, _Indirect_value_t<_It>>;
+struct _Projected_impl {
+    struct _Type : _Projected_difference_type_impl<_It>::_Base {
+        using _Iterator   = _It;
+        using _Projection = _Proj;
+
+        using value_type = remove_cvref_t<indirect_result_t<_Proj&, _It>>;
+        indirect_result_t<_Proj&, _It> operator*() const {
+            _CSTD abort();
+        }
+    };
 };
 
-template <weakly_incrementable _It, class _Proj>
-struct incrementable_traits<projected<_It, _Proj>> {
-    using difference_type = iter_difference_t<_It>;
+_EXPORT_STD template <indirectly_readable _It, indirectly_regular_unary_invocable<_It> _Proj>
+using projected = _Projected_impl<_It, _Proj>::_Type;
+
+template <class _Ty>
+concept _Projected_specialization = same_as<_Ty, projected<typename _Ty::_Iterator, typename _Ty::_Projection>>;
+
+template <_Projected_specialization _ProjTy>
+struct _Indirect_value_impl<_ProjTy> {
+    using type = invoke_result_t<typename _ProjTy::_Projection&, _Indirect_value_t<typename _ProjTy::_Iterator>>;
 };
 
 _EXPORT_STD template <class _In, class _Out>

stl/inc/yvals_core.h

@@ -285,6 +285,7 @@
 // P2432R1 Fix istream_view
 // P2508R1 basic_format_string, format_string, wformat_string
 // P2520R0 move_iterator<T*> Should Be A Random-Access Iterator
+// P2538R1 ADL-Proof projected
 // P2572R1 std::format Fill Character Allowances
 // P2588R3 barrier's Phase Completion Guarantees
 // P2602R2 Poison Pills Are Too Toxic

tests/std/test.lst

@@ -618,6 +618,7 @@ tests\P2474R2_views_repeat_death
 tests\P2494R2_move_only_range_adaptors
 tests\P2505R5_monadic_functions_for_std_expected
 tests\P2517R1_apply_conditional_noexcept
+tests\P2538R1_adl_proof_std_projected
 tests\P2609R3_relaxing_ranges_just_a_smidge
 tests\VSO_0000000_allocator_propagation
 tests\VSO_0000000_any_calling_conventions

tests/std/tests/P2538R1_adl_proof_std_projected/env.lst

@@ -0,0 +1,4 @@
+# Copyright (c) Microsoft Corporation.
+# SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+RUNALL_INCLUDE ..\concepts_20_matrix.lst

tests/std/tests/P2538R1_adl_proof_std_projected/test.compile.pass.cpp

@@ -0,0 +1,52 @@
+// Copyright (c) Microsoft Corporation.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+
+#include <cassert>
+#include <functional>
+#include <iterator>
+#include <ranges>
+#include <utility>
+
+using namespace std;
+
+// TRANSITION, GH-1596, should use ranges::count
+struct my_count_fn {
+    template <input_iterator I, sentinel_for<I> S, class T, class Proj = identity>
+        requires indirect_binary_predicate<ranges::equal_to, projected<I, Proj>, const T*>
+    constexpr iter_difference_t<I> operator()(I first, S last, const T& value, Proj proj = {}) const {
+        iter_difference_t<I> counter = 0;
+        for (; first != last; ++first) {
+            if (std::invoke(proj, *first) == value) { // intentionally qualified to avoid ADL
+                ++counter;
+            }
+        }
+        return counter;
+    }
+
+    template <ranges::input_range R, class T, class Proj = identity>
+        requires indirect_binary_predicate<ranges::equal_to, projected<ranges::iterator_t<R>, Proj>, const T*>
+    constexpr ranges::range_difference_t<R> operator()(R&& r, const T& value, Proj proj = {}) const {
+        return (*this)(ranges::begin(r), ranges::end(r), value, ref(proj));
+    }
+};
+
+inline constexpr my_count_fn my_count;
+
+template <class T>
+struct Holder {
+    T t;
+};
+struct Incomplete;
+
+static_assert(equality_comparable<Holder<Incomplete>*>);
+static_assert(indirectly_comparable<Holder<Incomplete>**, Holder<Incomplete>**, equal_to<>>);
+static_assert(sortable<Holder<Incomplete>**>);
+
+constexpr bool test() {
+    Holder<Incomplete>* a[10] = {};
+    assert(my_count(a, a + 10, nullptr) == 10);
+    assert(my_count(a, nullptr) == 10);
+    return true;
+}
+
+static_assert(test());

tests/std/tests/P2609R3_relaxing_ranges_just_a_smidge/env.lst

@@ -1,4 +1,4 @@
 # Copyright (c) Microsoft Corporation.
 # SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 
-RUNALL_INCLUDE ..\concepts_latest_matrix.lst
+RUNALL_INCLUDE ..\concepts_20_matrix.lst