Test that correct value category is used in scoped_allocator_adaptor::construct

[zoecarver]

Summary

This patch fixes 2586. Just tests; NFC.

[zoecarver]

For the pair section of the issue, I ran into a few problems. The genesis of the problem is the fact that this compiles (and I can't figure out why):

struct Foo
{
	typedef std::allocator<Foo> allocator_type;
	
	Foo(std::allocator_arg_t, allocator_type&&) { }
	Foo(allocator_type&) { }
};

int main()
{
	using Alloc1 = std::allocator<pair<Foo, Foo>>;
	using Alloc2 = std::allocator<Foo>;
	static_assert( std::is_constructible<Foo, std::allocator_arg_t, Alloc1&>::value);
	static_assert(!std::is_constructible<Foo, std::allocator_arg_t, Alloc2&>::value);
}

[zoecarver]

It doesn't compile because Alloc1 is convertible to Alloc2, and when it makes the conversion it can turn into either value category (thanks to Eric for explaining). Anyhow, given that bit of information I do not see how the pair portion of this issue can be tested (or how the change matters for pairs).

[zoecarver]

• Rebase off master

[zoecarver]

Friendly ping. This patch just tests so its a non-functional change.

test/std/utilities/allocator.adaptor/allocator.adaptor.members/construct.pass.cpp

explicit F(int i, int j, const allocator_type& a)
         assert(j == 2);
         assert(a.id() == 50);
         constructed = true;
     }
 };
 
 bool F::constructed = false;
 
+struct G
+{
+    static bool constructed;
+
+    typedef std::allocator<G> allocator_type;
+
+    G(std::allocator_arg_t, allocator_type&&) { assert(false); }
+    G(allocator_type&) { constructed = true; }
+};
+
+bool G::constructed = false;
+
 int main(int, char**)
 {
 
     {
         typedef std::scoped_allocator_adaptor<A1<std::string>> A;
         A a;
         char buf[100];
         typedef std::string S;
int main(int, char**)
         S* s = (S*)buf;
         A3<F>::constructed = false;
         a.construct(s, 1, 2);
         assert(!S::constructed);
         assert(A3<F>::constructed);
         s->~S();
     }
 
+    // LWG 2586
+    // test that is_constructible uses an lvalue ref so the correct constructor is picked
+    {
+        std::scoped_allocator_adaptor<G::allocator_type> sa;
+        G* ptr = sa.allocate(1);
+        sa.construct(ptr);
+        assert(G::constructed);
+        sa.deallocate(ptr, 1);
+    }
+
   return 0;
 }

www/cxx1z_status.html

<!--   <I>Note: "NAD" means that the issue was deemed "Not a defect"</I> -->
   <tr><td><a href="https://wg21.link/LWG2575">2575</a></td><td>[fund.ts.v2] <tt>experimental::function::assign</tt> should be removed</td><td>Jacksonville</td><td></td></tr>
   <tr><td><a href="https://wg21.link/LWG2576">2576</a></td><td><tt>istream_iterator</tt> and <tt>ostream_iterator</tt> should use <tt>std::addressof</tt></td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2577">2577</a></td><td><tt>{shared,unique}_lock</tt> should use <tt>std::addressof</tt></td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2579">2579</a></td><td>Inconsistency wrt Allocators in <tt>basic_string</tt> assignment vs. <tt>basic_string::assign</tt></td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2581">2581</a></td><td>Specialization of <tt>&lt;type_traits&gt;</tt> variable templates should be prohibited</td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2582">2582</a></td><td>&sect;[res.on.functions]/2's prohibition against incomplete types shouldn't apply to type traits</td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2583">2583</a></td><td>There is no way to supply an allocator for <tt>basic_string(str, pos)</tt></td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2585">2585</a></td><td><tt>forward_list::resize(size_type, const value_type&amp;)</tt> effects incorrect</td><td>Jacksonville</td><td>Complete</td></tr>
-  <tr><td><a href="https://wg21.link/LWG2586">2586</a></td><td>Wrong value category used in <tt>scoped_allocator_adaptor::construct()</tt></td><td>Jacksonville</td><td></td></tr>
+  <tr><td><a href="https://wg21.link/LWG2586">2586</a></td><td>Wrong value category used in <tt>scoped_allocator_adaptor::construct()</tt></td><td>Jacksonville</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2590">2590</a></td><td>Aggregate initialization for <tt>std::array</tt></td><td>Jacksonville</td><td>Complete</td></tr>
    <tr><td></td><td></td><td></td><td></td></tr>
   <tr><td><a href="https://wg21.link/LWG2181">2181</a></td><td>Exceptions from seed sequence operations</td><td>Oulu</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2309">2309</a></td><td>mutex::lock() should not throw device_or_resource_busy</td><td>Oulu</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2310">2310</a></td><td>Public exposition only member in std::array</td><td>Oulu</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2312">2312</a></td><td>tuple's constructor constraints need to be phrased more precisely</td><td>Oulu</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2328">2328</a></td><td>Rvalue stream extraction should use perfect forwarding</td><td>Oulu</td><td>Complete</td></tr>
   <tr><td><a href="https://wg21.link/LWG2393">2393</a></td><td>std::function's Callable definition is broken</td><td>Oulu</td><td>Complete</td></tr>