libstdc++: Fix views::transform(move_only_fn{}) forwarding [PR118413]

The range adaptor perfect forwarding simplification mechanism is currently
only enabled for trivially copyable bound arguments, to prevent undesirable
copies of complex objects.  But "trivially copyable" is the wrong property
to check for here, since a move-only type with a trivial move constructor
is considered trivially copyable, and after P2492R2 we can't assume copy
constructibility of the bound arguments.  This patch makes the mechanism
more specifically check for trivial copy constructibility instead so
that it's properly disabled for move-only bound arguments.

	PR libstdc++/118413

libstdc++-v3/ChangeLog:

	* include/std/ranges (views::__adaptor::_Partial): Adjust
	constraints on the "simple" partial specializations to require
	is_trivially_copy_constructible_v instead of
	is_trivially_copyable_v.
	* testsuite/std/ranges/adaptors/adjacent_transform/1.cc (test04):
	Extend P2494R2 test.
	* testsuite/std/ranges/adaptors/transform.cc (test09): Likewise.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
(cherry picked from commit 09d1cbee10b8c51aed48f047f30717f622d6f811)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index eba539176848c3c5fd4f89e604c9e05253fff914..a966699479bb39697ff04e498b4d31caf1592d23 100644 (file)
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1122,7 +1122,7 @@ namespace views::__adaptor
   // which makes overload resolution failure diagnostics more concise.
   template<typename _Adaptor, typename... _Args>
     requires __adaptor_has_simple_extra_args<_Adaptor, _Args...>
-      && (is_trivially_copyable_v<_Args> && ...)
+      && (is_trivially_copy_constructible_v<_Args> && ...)
     struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>>
     {
       tuple<_Args...> _M_args;
@@ -1153,7 +1153,7 @@ namespace views::__adaptor
   // where _Adaptor accepts a single extra argument.
   template<typename _Adaptor, typename _Arg>
     requires __adaptor_has_simple_extra_args<_Adaptor, _Arg>
-      && is_trivially_copyable_v<_Arg>
+      && is_trivially_copy_constructible_v<_Arg>
     struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>>
     {
       _Arg _M_arg;

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/adjacent_transform/1.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/adjacent_transform/1.cc
index a5791b3da702a2b511091bdf7c1faf368f89409a..772e4b3b6a0d15d15eeca317b370d541e8e23cd2 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/adjacent_transform/1.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/adjacent_transform/1.cc
@@ -110,6 +110,7 @@ test04()
   };
   // P2494R2 Relaxing range adaptors to allow for move only types
   static_assert( requires { views::pairwise_transform(x, move_only{}); } );
+  static_assert( requires { x | views::pairwise_transform(move_only{}); } );
 }
 
 int

diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
index e1b74353e6327dec87ef0dd83868e880d7de792d..783b0fba7e1e6b97e809f2390c8ad933684427a0 100644 (file)
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/transform.cc
@@ -191,8 +191,10 @@ test09()
 #if __cpp_lib_ranges >= 202207L
   // P2494R2 Relaxing range adaptors to allow for move only types
   static_assert( requires { transform(x, move_only{}); } );
+  static_assert( requires { x | transform(move_only{}); } ); // PR libstdc++/118413
 #else
   static_assert( ! requires { transform(x, move_only{}); } );
+  static_assert( ! requires { x | transform(move_only{}); } );
 #endif
 }