libstdc++: Implement P2609R3 changes to the indirect invocability concepts

This implements the changes of this C++23 paper as a DR against C++20.

Note that after the later P2538R1 "ADL-proof std::projected" (which we
already implement), we can't use a simple partial specialization to match
specializations of the 'projected' alias template.  So instead we identify
such specializations using a pair of distinguishing member aliases.

libstdc++-v3/ChangeLog:

	* include/bits/iterator_concepts.h (__detail::__indirect_value):
	Define.
	(__indirect_value_t): Define as per P2609R3.
	(iter_common_reference_t): Adjust as per P2609R3.
	(indirectly_unary_invocable): Likewise.
	(indirectly_regular_unary_invocable): Likewise.
	(indirect_unary_predicate): Likewise.
	(indirect_binary_predicate): Likewise.
	(indirect_equivalence_relation): Likewise.
	(indirect_strict_weak_order): Likewise.
	(__detail::__projected::__type): Define member aliases
	__projected_Iter and __projected_Proj providing the
	template arguments of the current specialization.
	* include/bits/version.def (ranges): Update value.
	* include/bits/version.h: Regenerate.
	* testsuite/24_iterators/indirect_callable/p2609r3.cc: New test.
	* testsuite/std/ranges/version_c++23.cc: Update expected value
	of __cpp_lib_ranges macro.

Reviewed-by: Jonathan Wakely <jwakely@redhat.com>

5 files changed, 77 insertions, 19 deletions

diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index ce0b8a1..9306b7b 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -552,9 +552,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     concept indirectly_readable
       = __detail::__indirectly_readable_impl<remove_cvref_t<_In>>;
 
+  namespace __detail
+  {
+    template<typename _Tp>
+      struct __indirect_value
+      { using type = iter_value_t<_Tp>&; };
+
+    // __indirect_value<projected<_Iter, _Proj>> is defined later.
+  } // namespace __detail
+
+  template<typename _Tp>
+    using __indirect_value_t = typename __detail::__indirect_value<_Tp>::type;
+
   template<indirectly_readable _Tp>
     using iter_common_reference_t
-      = common_reference_t<iter_reference_t<_Tp>, iter_value_t<_Tp>&>;
+      = common_reference_t<iter_reference_t<_Tp>, __indirect_value_t<_Tp>>;
 
   /// Requirements for writing a value into an iterator's referenced object.
   template<typename _Out, typename _Tp>
@@ -710,24 +722,24 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
   template<typename _Fn, typename _Iter>
     concept indirectly_unary_invocable = indirectly_readable<_Iter>
-      && copy_constructible<_Fn> && invocable<_Fn&, iter_value_t<_Iter>&>
+      && copy_constructible<_Fn> && invocable<_Fn&, __indirect_value_t<_Iter>>
       && invocable<_Fn&, iter_reference_t<_Iter>>
       && invocable<_Fn&, iter_common_reference_t<_Iter>>
-      && common_reference_with<invoke_result_t<_Fn&, iter_value_t<_Iter>&>,
+      && common_reference_with<invoke_result_t<_Fn&, __indirect_value_t<_Iter>>,
 			       invoke_result_t<_Fn&, iter_reference_t<_Iter>>>;
 
   template<typename _Fn, typename _Iter>
     concept indirectly_regular_unary_invocable = indirectly_readable<_Iter>
       && copy_constructible<_Fn>
-      && regular_invocable<_Fn&, iter_value_t<_Iter>&>
+      && regular_invocable<_Fn&, __indirect_value_t<_Iter>>
       && regular_invocable<_Fn&, iter_reference_t<_Iter>>
       && regular_invocable<_Fn&, iter_common_reference_t<_Iter>>
-      && common_reference_with<invoke_result_t<_Fn&, iter_value_t<_Iter>&>,
+      && common_reference_with<invoke_result_t<_Fn&, __indirect_value_t<_Iter>>,
 			       invoke_result_t<_Fn&, iter_reference_t<_Iter>>>;
 
   template<typename _Fn, typename _Iter>
     concept indirect_unary_predicate = indirectly_readable<_Iter>
-      && copy_constructible<_Fn> && predicate<_Fn&, iter_value_t<_Iter>&>
+      && copy_constructible<_Fn> && predicate<_Fn&, __indirect_value_t<_Iter>>
       && predicate<_Fn&, iter_reference_t<_Iter>>
       && predicate<_Fn&, iter_common_reference_t<_Iter>>;
 
@@ -735,9 +747,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     concept indirect_binary_predicate
       = indirectly_readable<_I1> && indirectly_readable<_I2>
       && copy_constructible<_Fn>
-      && predicate<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
-      && predicate<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
-      && predicate<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
+      && predicate<_Fn&, __indirect_value_t<_I1>, __indirect_value_t<_I2>>
+      && predicate<_Fn&, __indirect_value_t<_I1>, iter_reference_t<_I2>>
+      && predicate<_Fn&, iter_reference_t<_I1>, __indirect_value_t<_I2>>
       && predicate<_Fn&, iter_reference_t<_I1>, iter_reference_t<_I2>>
       && predicate<_Fn&, iter_common_reference_t<_I1>,
 		   iter_common_reference_t<_I2>>;
@@ -746,9 +758,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     concept indirect_equivalence_relation
       = indirectly_readable<_I1> && indirectly_readable<_I2>
       && copy_constructible<_Fn>
-      && equivalence_relation<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
-      && equivalence_relation<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
-      && equivalence_relation<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
+      && equivalence_relation<_Fn&, __indirect_value_t<_I1>, __indirect_value_t<_I2>>
+      && equivalence_relation<_Fn&, __indirect_value_t<_I1>, iter_reference_t<_I2>>
+      && equivalence_relation<_Fn&, iter_reference_t<_I1>, __indirect_value_t<_I2>>
       && equivalence_relation<_Fn&, iter_reference_t<_I1>,
 			      iter_reference_t<_I2>>
       && equivalence_relation<_Fn&, iter_common_reference_t<_I1>,
@@ -758,9 +770,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
     concept indirect_strict_weak_order
       = indirectly_readable<_I1> && indirectly_readable<_I2>
       && copy_constructible<_Fn>
-      && strict_weak_order<_Fn&, iter_value_t<_I1>&, iter_value_t<_I2>&>
-      && strict_weak_order<_Fn&, iter_value_t<_I1>&, iter_reference_t<_I2>>
-      && strict_weak_order<_Fn&, iter_reference_t<_I1>, iter_value_t<_I2>&>
+      && strict_weak_order<_Fn&, __indirect_value_t<_I1>, __indirect_value_t<_I2>>
+      && strict_weak_order<_Fn&, __indirect_value_t<_I1>, iter_reference_t<_I2>>
+      && strict_weak_order<_Fn&, iter_reference_t<_I1>, __indirect_value_t<_I2>>
       && strict_weak_order<_Fn&, iter_reference_t<_I1>, iter_reference_t<_I2>>
       && strict_weak_order<_Fn&, iter_common_reference_t<_I1>,
 			   iter_common_reference_t<_I2>>;
@@ -779,6 +791,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	{
 	  using value_type = remove_cvref_t<indirect_result_t<_Proj&, _Iter>>;
 	  indirect_result_t<_Proj&, _Iter> operator*() const; // not defined
+
+	  // These are used to identify and obtain the template arguments of a
+	  // specialization of the 'projected' alias template below.
+	  using __projected_Iter = _Iter;
+	  using __projected_Proj = _Proj;
 	};
       };
 
@@ -790,6 +807,9 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	  using value_type = remove_cvref_t<indirect_result_t<_Proj&, _Iter>>;
 	  using difference_type = iter_difference_t<_Iter>;
 	  indirect_result_t<_Proj&, _Iter> operator*() const; // not defined
+
+	  using __projected_Iter = _Iter;
+	  using __projected_Proj = _Proj;
 	};
       };
   } // namespace __detail
@@ -799,6 +819,17 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	   indirectly_regular_unary_invocable<_Iter> _Proj>
     using projected = typename __detail::__projected<_Iter, _Proj>::__type;
 
+  // Matches specializations of the 'projected' alias template.
+  template<typename _Tp>
+    requires same_as<_Tp, projected<typename _Tp::__projected_Iter,
+				    typename _Tp::__projected_Proj>>
+    struct __detail::__indirect_value<_Tp>
+    {
+      using _Iter = typename _Tp::__projected_Iter;
+      using _Proj = typename _Tp::__projected_Proj;
+      using type = invoke_result_t<_Proj&, __indirect_value_t<_Iter>>;
+    };
+
   // [alg.req], common algorithm requirements
 
   /// [alg.req.ind.move], concept `indirectly_movable`
diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 6791c6f..ea82c6f 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1072,7 +1072,7 @@ ftms = {
 ftms = {
   name = ranges;
   values = {
-    v = 202211;
+    v = 202302;
     cxxmin = 23;
     extra_cond = "__glibcxx_concepts";
   };
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index 0b78cb9..981f0b7 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -1205,9 +1205,9 @@
 
 #if !defined(__cpp_lib_ranges)
 # if (__cplusplus >= 202100L) && (__glibcxx_concepts)
-#  define __glibcxx_ranges 202211L
+#  define __glibcxx_ranges 202302L
 #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_ranges)
-#   define __cpp_lib_ranges 202211L
+#   define __cpp_lib_ranges 202302L
 #  endif
 # elif (__cplusplus >= 202002L) && (__glibcxx_concepts)
 #  define __glibcxx_ranges 202110L
diff --git a/libstdc++-v3/testsuite/24_iterators/indirect_callable/p2609r3.cc b/libstdc++-v3/testsuite/24_iterators/indirect_callable/p2609r3.cc
new file mode 100644
index 0000000..fe7839d
--- /dev/null
+++ b/libstdc++-v3/testsuite/24_iterators/indirect_callable/p2609r3.cc
@@ -0,0 +1,27 @@
+// Verify the P2609R3 "Relaxing Ranges Just A Smidge" changes.
+// { dg-do compile { target c++20 } }
+
+#include <iterator>
+#include <algorithm>
+#include <memory>
+#include <ranges>
+
+int
+main()
+{
+  auto v = std::views::iota(0, 5);
+  auto proj = [](int v) { return std::make_unique<int>(v); };
+  using it = std::projected<std::ranges::iterator_t<decltype(v)>, decltype(proj)>;
+
+  auto f = [](auto) { return false; };
+  static_assert(std::indirectly_unary_invocable<decltype(f), it>);
+  static_assert(std::indirectly_regular_unary_invocable<decltype(f), it>);
+  static_assert(std::indirect_unary_predicate<decltype(f), it>);
+
+  auto g = [](auto, auto) { return false; };
+  static_assert(std::indirect_binary_predicate<decltype(g), it, it>);
+  static_assert(std::indirect_equivalence_relation<decltype(g), it, it>);
+  static_assert(std::indirect_strict_weak_order<decltype(g), it, it>);
+
+  std::ranges::for_each(v, f, proj);
+}
diff --git a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
index d475d3d..0187115 100644
--- a/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
+++ b/libstdc++-v3/testsuite/std/ranges/version_c++23.cc
@@ -4,7 +4,7 @@
 #include <version>
 
 #if __STDC_HOSTED__
-# if __cpp_lib_ranges != 202211L
+# if __cpp_lib_ranges != 202302L
 #  error "Feature-test macro __cpp_lib_ranges has wrong value in <version>"
 # endif
 #endif