[gcc(refs/users/ppalka/heads/libstdcxx-constrained-algos)] Conditionally disable copyability of the test_range::iterator wrapper

[Patrick Palka]

https://gcc.gnu.org/g:05e7e7eec2f44a0bff12ded0c30bebdcc2d7f4ae

commit 05e7e7eec2f44a0bff12ded0c30bebdcc2d7f4ae
Author: Patrick Palka <ppalka@redhat.com>
Date:   Wed Jan 22 13:39:24 2020 -0500

    Conditionally disable copyability of the test_range::iterator wrapper
    
    As of P1207, input_iterators and output_iterators are no longer required to be
    copyable, but forward_iterators are.  Reflect these assumptions in the
    test_range::iterator wrapper by conditionally disabling its copyability.

Diff:
---
 libstdc++-v3/testsuite/util/testsuite_iterators.h | 23 ++++++++++++++++++++++-
 1 file changed, 22 insertions(+), 1 deletion(-)

diff --git a/libstdc++-v3/testsuite/util/testsuite_iterators.h b/libstdc++-v3/testsuite/util/testsuite_iterators.h
index 6667a3a..22fa3fd 100644
--- a/libstdc++-v3/testsuite/util/testsuite_iterators.h
+++ b/libstdc++-v3/testsuite/util/testsuite_iterators.h
@@ -654,12 +654,33 @@ namespace __gnu_test
       { return iter -= n; }
     };
 
+  template<bool active>
+  struct disable_copy { };
+
+  template<>
+  struct disable_copy<true>
+  {
+    disable_copy() noexcept = default;
+
+    disable_copy(disable_copy&&) noexcept = default;
+    disable_copy&
+    operator=(disable_copy&&) noexcept = default;
+
+    disable_copy(const disable_copy&) noexcept = delete;
+    disable_copy&
+    operator=(const disable_copy&) noexcept = delete;
+  };
+
+  template<>
+  struct disable_copy<false> { };
+
   // A type meeting the minimum std::range requirements
   template<typename T, template<typename> class Iter>
     class test_range
     {
       // Adds default constructor to Iter<T> if needed
-      struct iterator : Iter<T>
+      // and removes copyability if the iterator is not a forward iterator
+      struct iterator : Iter<T>, disable_copy<!std::forward_iterator<Iter<T>>>
       {
 	using Iter<T>::Iter;