[libc++] Fix ambiguity when using std::scoped_allocator constructor

[Rajveer100]

Resolves Issue #78754

[llvmbot]

@llvm/pr-subscribers-libcxx

Author: Rajveer Singh Bharadwaj (Rajveer100)

Changes

Resolves Issue #78754

---

Full diff: https://github.com/llvm/llvm-project/pull/80261.diff

2 Files Affected:

• (modified) libcxx/include/scoped_allocator (+2-2)
• (modified) libcxx/test/std/utilities/allocator.adaptor/allocator.adaptor.cnstr/allocs.pass.cpp (+8-1)

diff --git a/libcxx/include/scoped_allocator b/libcxx/include/scoped_allocator
index 6078906e92248..cfa2efe41456a 100644
--- a/libcxx/include/scoped_allocator
+++ b/libcxx/include/scoped_allocator
@@ -477,8 +477,8 @@ public:
 
 private:
   template <class _OuterA2, __enable_if_t<is_constructible<outer_allocator_type, _OuterA2>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI scoped_allocator_adaptor(_OuterA2&& __o, const inner_allocator_type& __i) _NOEXCEPT
-      : base(std::forward<_OuterA2>(__o), __i) {}
+  _LIBCPP_HIDE_FROM_ABI explicit scoped_allocator_adaptor(outer_allocator_type&& __o, inner_allocator_type&& __i) _NOEXCEPT
+      : base(std::move(__o), std::move(__i)) {}
 
   template <class _Tp, class... _Args>
   _LIBCPP_HIDE_FROM_ABI void __construct(integral_constant<int, 0>, _Tp* __p, _Args&&... __args) {
diff --git a/libcxx/test/std/utilities/allocator.adaptor/allocator.adaptor.cnstr/allocs.pass.cpp b/libcxx/test/std/utilities/allocator.adaptor/allocator.adaptor.cnstr/allocs.pass.cpp
index 2a9d7052eb655..d8135c6e7a1e7 100644
--- a/libcxx/test/std/utilities/allocator.adaptor/allocator.adaptor.cnstr/allocs.pass.cpp
+++ b/libcxx/test/std/utilities/allocator.adaptor/allocator.adaptor.cnstr/allocs.pass.cpp
@@ -107,13 +107,20 @@ int main(int, char**)
         assert((a.inner_allocator() ==
             std::scoped_allocator_adaptor<A2<int>, A3<int>>(A2<int>(5), A3<int>(6))));
     }
-//  Test for LWG2782
     {
+        //  Test for LWG2782
         static_assert(!std::is_convertible<A1<int>, A2<int>>::value, "");
         static_assert(!std::is_convertible<
              std::scoped_allocator_adaptor<A1<int>>,
              std::scoped_allocator_adaptor<A2<int>>>::value, "");
     }
+    {
+        // Test construction from convertible-to-allocator types
+        typedef std::scoped_allocator_adaptor<A1<int>, A1<int>> A;
+        A a(A1<char>(4), A1<char>(5));
+        assert(a.outer_allocator() == A1<int>(4));
+        assert(a.inner_allocator() == A1<int>(5));
+    }
 
   return 0;
 }

[github-actions]

✅ With the latest revision this PR passed the C/C++ code formatter.

[mordante]

This seems like a duplicate of #80020 is that correct?

[Rajveer100]

This seems like a duplicate of #80020 is that correct?

While it's for the same issue, the approach to resolve differs.

[ldionne]

I like this approach better than mine.