From c50b8d550d20e42e88b70f0a6e0f6798e30ddcb2 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Fri, 9 May 2025 17:50:52 +0100
Subject: [PATCH] libstdc++: Restore std::scoped_lock for non-gthreads targets
 [PR120198]
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This was a regression introduced with using version.def to define
feature test macros (r14-3248-g083b7f2833d71d). std::scoped_lock doesn't
need to depend on gthreads and so can be defined unconditionally, even
for freestanding.

libstdc++-v3/ChangeLog:

	PR libstdc++/120198
	* include/bits/version.def (scoped_lock): Do not depend on
	gthreads or hosted.
	* include/bits/version.h: Regenerate.
	* include/std/mutex (scoped_lock): Update comment.
	* testsuite/30_threads/scoped_lock/requirements/typedefs.cc:
	Remove dg-require-gthreads and use custom lockable type instead
	of std::mutex. Check that typedef is only present for a single
	template argument.

Reviewed-by: Tomasz Kamiński <tkaminsk@redhat.com>
(cherry picked from commit bdd2753f5f021a15a6c4ef02565356985fea1300)
---
 libstdc++-v3/include/bits/version.def         |  2 --
 libstdc++-v3/include/bits/version.h           |  2 +-
 libstdc++-v3/include/std/mutex                |  2 +-
 .../scoped_lock/requirements/typedefs.cc      | 28 ++++++++++++++++---
 4 files changed, 26 insertions(+), 8 deletions(-)

diff --git a/libstdc++-v3/include/bits/version.def b/libstdc++-v3/include/bits/version.def
index 91c144cc4f0a..49c0a0a9fc06 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -668,8 +668,6 @@ ftms = {
   values = {
     v = 201703;
     cxxmin = 17;
-    hosted = yes;
-    gthread = yes;
   };
 };
 
diff --git a/libstdc++-v3/include/bits/version.h b/libstdc++-v3/include/bits/version.h
index 82901af2ad62..5c6d8a9f8afc 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -739,7 +739,7 @@
 #undef __glibcxx_want_parallel_algorithm
 
 #if !defined(__cpp_lib_scoped_lock)
-# if (__cplusplus >= 201703L) && defined(_GLIBCXX_HAS_GTHREADS) && _GLIBCXX_HOSTED
+# if (__cplusplus >= 201703L)
 #  define __glibcxx_scoped_lock 201703L
 #  if defined(__glibcxx_want_all) || defined(__glibcxx_want_scoped_lock)
 #   define __cpp_lib_scoped_lock 201703L
diff --git a/libstdc++-v3/include/std/mutex b/libstdc++-v3/include/std/mutex
index 8dd9b23191fd..e4b14c017201 100644
--- a/libstdc++-v3/include/std/mutex
+++ b/libstdc++-v3/include/std/mutex
@@ -731,7 +731,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
 	}
     }
 
-#ifdef __cpp_lib_scoped_lock // C++ >= 17 && hosted && gthread
+#ifdef __cpp_lib_scoped_lock // C++ >= 17
   /** @brief A scoped lock type for multiple lockable objects.
    *
    * A scoped_lock controls mutex ownership within a scope, releasing
diff --git a/libstdc++-v3/testsuite/30_threads/scoped_lock/requirements/typedefs.cc b/libstdc++-v3/testsuite/30_threads/scoped_lock/requirements/typedefs.cc
index 5ee9104b17d4..335b8e791471 100644
--- a/libstdc++-v3/testsuite/30_threads/scoped_lock/requirements/typedefs.cc
+++ b/libstdc++-v3/testsuite/30_threads/scoped_lock/requirements/typedefs.cc
@@ -1,5 +1,4 @@
 // { dg-do compile { target c++17 } }
-// { dg-require-gthreads "" }
 // { dg-add-options no_pch }
 
 // Copyright (C) 2017-2024 Free Software Foundation, Inc.
@@ -29,9 +28,30 @@
 # error "Feature-test macro for scoped_lock has wrong value"
 #endif
 
+struct BasicLockable
+{
+  BasicLockable() = default;
+  ~BasicLockable() = default;
+  void lock() { }
+  void unlock() { }
+};
+
 void test01()
 {
-  // Check for required typedefs
-  typedef std::scoped_lock<std::mutex> test_type;
-  typedef test_type::mutex_type mutex_type;
+  // Check for required typedef.
+  using test_type = std::scoped_lock<BasicLockable>;
+  static_assert(std::is_same_v<test_type::mutex_type, BasicLockable>);
+}
+
+template<typename T, typename = void>
+constexpr bool has_mutex_type = false;
+
+template<typename T>
+constexpr bool has_mutex_type<T, std::void_t<typename T::mutex_type>> = true;
+
+void test02()
+{
+  // Check that typedef is absent as required.
+  using test_type = std::scoped_lock<BasicLockable, BasicLockable>;
+  static_assert(!has_mutex_type<test_type>);
 }
-- 
2.47.2