[libcxx-commits] [libcxx] [libc++] LWG 3821 uses_allocator_construction_args should have overload for pair-like (PR #66939)

[Louis Dionne via libcxx-commits]

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@@ -132,19 +133,48 @@ constexpr bool test() {
   }
 #endif
   {
-    ConvertibleToPair ctp {};
-    auto ret = test_uses_allocator_construction_args<std::pair<int, int>>(a, ctp);
+    ConvertibleToPair ctp{};
+    auto ret              = test_uses_allocator_construction_args<std::pair<int, int>>(a, ctp);
     std::pair<int, int> v = std::get<0>(ret);
     assert(std::get<0>(v) == 1);
     assert(std::get<1>(v) == 2);
   }
   {
-    ConvertibleToPair ctp {};
-    auto ret = test_uses_allocator_construction_args<std::pair<int, int>>(a, std::move(ctp));
+    ConvertibleToPair ctp{};
+    auto ret              = test_uses_allocator_construction_args<std::pair<int, int>>(a, std::move(ctp));
     std::pair<int, int> v = std::get<0>(ret);
     assert(std::get<0>(v) == 1);
     assert(std::get<1>(v) == 2);
   }
+#if TEST_STD_VER >= 23
+  // LWG 3821
+  // uses_allocator_construction_args should have overload for pair-like
+  {
+    // pair-like with explicit ctr should work
+    struct Foo {
+      int i = 5;
+    };
+    struct Bar {
+      int i;
+      constexpr explicit Bar(Foo foo) : i(foo.i) {}
+    };
+
+    std::tuple<Foo, Foo> pair_like;
+    auto ret  = test_uses_allocator_construction_args<std::pair<Bar, Bar>>(a, pair_like);
+    auto pair = std::make_from_tuple<std::pair<Bar, Bar>>(std::move(ret));
+    assert(pair.first.i == 5);
+    assert(pair.second.i == 5);
+  }
+  {
+    // subrange should work
+    int i = 5;
+    std::ranges::subrange<int*, int*> r{&i, &i};
+    auto ret  = std::__uses_allocator_construction_args<std::pair<int*, int*>>(a, r);
----------------
ldionne wrote:

We shouldn't be using the private version here! I guess you should be using `test_uses_allocator_construction_args` here instead.

https://github.com/llvm/llvm-project/pull/66939