From: Jonathan Wakely <jwakely@redhat.com>
Date: Thu, 21 Oct 2021 00:19:45 +0000 (+0100)
Subject: libstdc++: Remove constraints from std::optional monadic ops [PR102863]
X-Git-Tag: basepoints/gcc-13~3727
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=0fac85a24f40ef6098b756e8e8655205f4bfbf3e;p=thirdparty%2Fgcc.git

libstdc++: Remove constraints from std::optional monadic ops [PR102863]

The constraints on transform and and_then can cause errors when checking
satisfaction. The constraints that were present in R6 of the paper were
moved for he final F8 revision, and so should have been included in the
implementation.

libstdc++-v3/ChangeLog:

	PR libstdc++/102863
	* include/std/optional (optional::and_then, optional::transform):
	Remove requires-clause.
	* testsuite/20_util/optional/monadic/and_then.cc: Check
	overload resolution doesn't cause errors.
	* testsuite/20_util/optional/monadic/transform.cc: Likewise.
---

diff --git a/libstdc++-v3/include/std/optional b/libstdc++-v3/include/std/optional
index eac91d3c160c..783d7ca1b64b 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1048,7 +1048,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
       // [optional.monadic]
 
-      template<typename _Fn> requires invocable<_Fn, _Tp&>
+      template<typename _Fn>
 	constexpr auto
 	and_then(_Fn&& __f) &
 	{
@@ -1060,7 +1060,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return _Up();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, const _Tp&>
+      template<typename _Fn>
 	constexpr auto
 	and_then(_Fn&& __f) const &
 	{
@@ -1072,7 +1072,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return _Up();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, _Tp>
+      template<typename _Fn>
 	constexpr auto
 	and_then(_Fn&& __f) &&
 	{
@@ -1084,7 +1084,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return _Up();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, const _Tp>
+      template<typename _Fn>
 	constexpr auto
 	and_then(_Fn&& __f) const &&
 	{
@@ -1096,7 +1096,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return _Up();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, _Tp&>
+      template<typename _Fn>
 	constexpr auto
 	transform(_Fn&& __f) &
 	{
@@ -1107,7 +1107,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return optional<_Up>();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, const _Tp&>
+      template<typename _Fn>
 	constexpr auto
 	transform(_Fn&& __f) const &
 	{
@@ -1118,7 +1118,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return optional<_Up>();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, _Tp>
+      template<typename _Fn>
 	constexpr auto
 	transform(_Fn&& __f) &&
 	{
@@ -1129,7 +1129,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	    return optional<_Up>();
 	}
 
-      template<typename _Fn> requires invocable<_Fn, const _Tp>
+      template<typename _Fn>
 	constexpr auto
 	transform(_Fn&& __f) const &&
 	{
diff --git a/libstdc++-v3/testsuite/20_util/optional/monadic/and_then.cc b/libstdc++-v3/testsuite/20_util/optional/monadic/and_then.cc
index 02dcafe6c580..f69ab952643f 100644
--- a/libstdc++-v3/testsuite/20_util/optional/monadic/and_then.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/monadic/and_then.cc
@@ -113,8 +113,20 @@ test_forwarding()
 
 static_assert( test_forwarding() );
 
+void f(int&) { }
+
+void
+test_unconstrained()
+{
+  // PR libstc++/102863 - Optional monadic ops should not be constrained
+  std::optional<int> x;
+  auto answer = x.and_then([](auto& y) { f(y); return std::optional<int>{42}; });
+  VERIFY( !answer );
+}
+
 int main()
 {
   test_and_then();
   test_forwarding();
+  test_unconstrained();
 }
diff --git a/libstdc++-v3/testsuite/20_util/optional/monadic/transform.cc b/libstdc++-v3/testsuite/20_util/optional/monadic/transform.cc
index 13977b8ba8d4..356c94de6d09 100644
--- a/libstdc++-v3/testsuite/20_util/optional/monadic/transform.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/monadic/transform.cc
@@ -132,9 +132,21 @@ test_copy_elision()
 
 static_assert( test_copy_elision() );
 
+void f(int&) { }
+
+void
+test_unconstrained()
+{
+  // PR libstc++/102863 - Optional monadic ops should not be constrained
+  std::optional<int> x;
+  auto answer = x.transform([](auto& y) { f(y); return 42; });
+  VERIFY( !answer );
+}
+
 int main()
 {
   test_transform();
   test_forwarding();
   test_copy_elision();
+  test_unconstrained();
 }