From 1d2f07ed4ce028a7c1f9b18f5d959f30213545ca Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 10 Oct 2022 15:06:53 +0100
Subject: [PATCH] libstdc++: Revert addition of constraints to
 make_signed/make_unsigned

Constraining the primary template makes it unusable in uninstantiated
contexts.

libstdc++-v3/ChangeLog:

	* include/std/type_traits (make_signed, make_unsigned): Remove
	constraints on primary template.
	* testsuite/20_util/make_signed/requirements/typedefs_neg.cc:
	Undo changes to expected error in C++20 mode.
	* testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc:
	Likewise.
	* testsuite/24_iterators/range_access/range_access_cpp20_neg.cc:
	Likewise.
	* testsuite/20_util/make_signed/requirements/uninstantiated.cc:
	New test.
	* testsuite/20_util/make_unsigned/requirements/uninstantiated.cc:
	New test.
---
 libstdc++-v3/include/std/type_traits                      | 6 ------
 .../20_util/make_signed/requirements/typedefs_neg.cc      | 3 +--
 .../20_util/make_signed/requirements/uninstantiated.cc    | 8 ++++++++
 .../20_util/make_unsigned/requirements/typedefs_neg.cc    | 3 +--
 .../20_util/make_unsigned/requirements/uninstantiated.cc  | 8 ++++++++
 .../24_iterators/range_access/range_access_cpp20_neg.cc   | 3 +--
 6 files changed, 19 insertions(+), 12 deletions(-)
 create mode 100644 libstdc++-v3/testsuite/20_util/make_signed/requirements/uninstantiated.cc
 create mode 100644 libstdc++-v3/testsuite/20_util/make_unsigned/requirements/uninstantiated.cc

diff --git a/libstdc++-v3/include/std/type_traits b/libstdc++-v3/include/std/type_traits
index 6108b98aa6a6..1d7c3b04a0ea 100644
--- a/libstdc++-v3/include/std/type_traits
+++ b/libstdc++-v3/include/std/type_traits
@@ -1802,9 +1802,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Primary template.
   /// make_unsigned
   template<typename _Tp>
-#if __cpp_concepts
-    requires is_integral<_Tp>::value || __is_enum(_Tp)
-#endif
     struct make_unsigned
     { typedef typename __make_unsigned_selector<_Tp>::__type type; };
 
@@ -1937,9 +1934,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   // Primary template.
   /// make_signed
   template<typename _Tp>
-#if __cpp_concepts
-    requires is_integral<_Tp>::value || __is_enum(_Tp)
-#endif
     struct make_signed
     { typedef typename __make_signed_selector<_Tp>::__type type; };
 
diff --git a/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc b/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
index 88b8ae887ef4..451eeb8c92db 100644
--- a/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/make_signed/requirements/typedefs_neg.cc
@@ -43,5 +43,4 @@ void test01()
   using T8 = make_signed<float>::type; // { dg-error "here" }
 }
 
-// { dg-error "invalid use of incomplete type" "" { target c++17_down } 0 }
-// { dg-error "constraint failure" "" { target c++20 } 0 }
+// { dg-error "invalid use of incomplete type" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/20_util/make_signed/requirements/uninstantiated.cc b/libstdc++-v3/testsuite/20_util/make_signed/requirements/uninstantiated.cc
new file mode 100644
index 000000000000..3facf0c595ad
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/make_signed/requirements/uninstantiated.cc
@@ -0,0 +1,8 @@
+// { dg-do compile { target c++11 } }
+#include <type_traits>
+
+// Check that we can name invalid specializations, just don't instantiate them.
+
+using X = std::make_signed<float>;
+using Y = std::make_signed<bool>;
+using Z = std::make_signed<void>;
diff --git a/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc b/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
index 50f15e7037c4..49d520936a3f 100644
--- a/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
+++ b/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/typedefs_neg.cc
@@ -43,5 +43,4 @@ void test01()
   using T8 = make_unsigned<float>::type; // { dg-error "here" }
 }
 
-// { dg-error "invalid use of incomplete type" "" { target c++17_down } 0 }
-// { dg-error "constraint failure" "" { target c++20 } 0 }
+// { dg-error "invalid use of incomplete type" "" { target *-*-* } 0 }
diff --git a/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/uninstantiated.cc b/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/uninstantiated.cc
new file mode 100644
index 000000000000..9b8609673790
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/make_unsigned/requirements/uninstantiated.cc
@@ -0,0 +1,8 @@
+// { dg-do compile { target c++11 } }
+#include <type_traits>
+
+// Check that we can name invalid specializations, just don't instantiate them.
+
+using X = std::make_unsigned<float>;
+using Y = std::make_unsigned<bool>;
+using Z = std::make_unsigned<void>;
diff --git a/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc b/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
index 26c8ae0ee1e7..c0825a585871 100644
--- a/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
+++ b/libstdc++-v3/testsuite/24_iterators/range_access/range_access_cpp20_neg.cc
@@ -46,5 +46,4 @@ test03()
   C c;
   std::ssize(c);  // { dg-error "no matching function" }
 }
-// { dg-error "incomplete type .*make_signed.*S" "" { target c++17_down } 0 }
-// { dg-error "constraint failure" "" { target c++20 } 0 }
+// { dg-error "incomplete type .*make_signed.*S" "" { target *-*-* } 0 }
-- 
2.47.2