libstdc++: Implement LWG 3481 change to ranges::viewable_range

libstdc++-v3/ChangeLog:

	* include/bits/ranges_base.h (viewable_range): Adjust as per
	LWG 3481.
	* testsuite/std/ranges/adaptors/all.cc (test07): New test.

(cherry picked from commit a2c2dcc6ca205a8c5c76b04ef2eb4fb097dcb069)

diff --git a/libstdc++-v3/include/bits/ranges_base.h b/libstdc++-v3/include/bits/ranges_base.h
index 48a9d0d95bb4c126d379131bbfab6c5fcfe201ec..87283b84028a4a6857abaec80e1e9a02aaba593f 100644 (file)
--- a/libstdc++-v3/include/bits/ranges_base.h
+++ b/libstdc++-v3/include/bits/ranges_base.h
@@ -664,7 +664,8 @@ namespace ranges
   /// A range which can be safely converted to a view.
   template<typename _Tp>
     concept viewable_range = range<_Tp>
-      && (borrowed_range<_Tp> || view<remove_cvref_t<_Tp>>);
+      && ((view<remove_cvref_t<_Tp>> && constructible_from<remove_cvref_t<_Tp>, _Tp>)
+         || (!view<remove_cvref_t<_Tp>> && borrowed_range<_Tp>));
 
   // [range.iter.ops] range iterator operations
 

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
index 42913ad38a303ce89cb97beca01d2ff3c673ae5f..5facaee7b371dc48636e27f8dc4a444cef2f2f64 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/all.cc
@@ -130,6 +130,20 @@ test05()
   static_assert(!requires { 0 | all; });
 }
 
+void
+test07()
+{
+  // LWG 3481
+  struct view_t : ranges::empty_view<int> { // move-only view
+    view_t(const view_t&) = delete;
+    view_t(view_t&&) = default;
+    view_t& operator=(const view_t&) = delete;
+    view_t& operator=(view_t&&) = default;
+  };
+  static_assert(std::movable<view_t> && !std::copyable<view_t>);
+  static_assert(!ranges::viewable_range<view_t&>);
+}
+
 int
 main()
 {
@@ -138,4 +152,5 @@ main()
   static_assert(test03());
   static_assert(test04());
   test05();
+  test07();
 }