[libcxx] limit debug mode tests on platforms without fork

[ldionne]

Summary

Add a has-fork feature flag and only enable debug-mode tests on systems with fork() support.

[EricWF]

These tests turn on debug mode themselves - they don't need to be limited the configurations where the user turns it on.

I don't want the debug tests to be their "own configuration". They should be run in all configurations (except testing the Apple system libc++)

[mclow.lists]

In D61348#1485462, @EricWF wrote:

These tests turn on debug mode themselves - they don't need to be limited the configurations where the user turns it on.

These tests need to be fixed so that they DTRT when the user specifies -debug_level=X (where X is 0/1) as a LIT param as well.

[bcain]

In D61348#1486014, @mclow.lists wrote:

In D61348#1485462, @EricWF wrote:

These tests turn on debug mode themselves - they don't need to be limited the configurations where the user turns it on.

These tests need to be fixed so that they DTRT when the user specifies -debug_level=X (where X is 0/1) as a LIT param as well.

Ok but does that mean that the REQUIRES only belongs on a subset of the tests? Ones with MODULES_DEFINES: _LIBCPP_DEBUG=1 maybe?

I got here (to this change) indirectly. One of our hexagon targets doesn't support waitpid() so we see compilation failures on the tests that include debug_mode_helper.h. When I read this comment regarding system lib I think I misunderstood and assumed that these tests only are necessary for some library configurations.

I can follow-through on this change if you and Eric agree on what it should be. But maybe I will work on a feature test for waitpid (LIBCXX_HAVE_WAITPID?) instead (or in addition) and somehow gate these tests that way.

[mclow.lists]

In D61348#1486107, @bcain wrote:

I can follow-through on this change if you and Eric agree on what it should be.

We're talking about that ;-)

[bcain]

Changed debug-mode feature to be deactivated when the LIBCXX_TEST_HAVE_FORK option is disabled. This hopefully sidesteps the debate triggered by the previous revision.

Added REQUIRES: debug-mode to libcxx/input.output/filesystems/class.path/path.itr/iterator_db.pass.cpp, this was unintentionally omitted before.

[bcain]

In D61348#1486428, @bcain wrote:

Changed debug-mode feature to be deactivated when the LIBCXX_TEST_HAVE_FORK option is disabled. This hopefully sidesteps the debate triggered by the previous revision.

I think this change makes sense and avoids the controversy. But I suppose the 'debug-mode' feature label might be misleading. Maybe it be better if I just changed it to 'has-fork'?

[bcain]

Changed to use 'has-fork' feature instead of 'debug-mode'.

[bcain]

Previous patch was missing update to config.py.

[ldionne]

Is this still relevant? We now have a way of disabling all debug mode tests by using --param enable_debug_tests=False. If not, let's drop this to clean up the review queue.

[ldionne]

[Github PR transition cleanup]

We also use has-unix-headers now as a proxy to this. Closing since it's inactive and I don't think it is directly relevant anymore.

libcxx/CMakeLists.txt

option(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY
      This option may only be set to ON when LIBCXX_ENABLE_THREADS=ON" OFF)
 
 # Misc options ----------------------------------------------------------------
 # FIXME: Turn -pedantic back ON. It is currently off because it warns
 # about #include_next which is used everywhere.
 option(LIBCXX_ENABLE_PEDANTIC "Compile with pedantic enabled." OFF)
 option(LIBCXX_ENABLE_WERROR "Fail and stop if a warning is triggered." OFF)
 option(LIBCXX_DISABLE_MACRO_CONFLICT_WARNINGS "Disable #warnings about conflicting macros." OFF)
+option(LIBCXX_TEST_HAVE_FORK "Target system has fork()/wait() support available for test suite." ON)
+config_define_if(LIBCXX_TEST_HAVE_FORK _LIBCPP_TEST_HAVE_FORK)
 
 option(LIBCXX_GENERATE_COVERAGE "Enable generating code coverage." OFF)
 set(LIBCXX_COVERAGE_LIBRARY "" CACHE STRING
     "The Profile-rt library used to build with code coverage")
 
 # Don't allow a user to accidentally overwrite the system libc++ installation on Darwin.
 # If the user specifies -DCMAKE_INSTALL_PREFIX=/usr the install rules for libc++
 # will not be generated and a warning will be issued.

libcxx/test/CMakeLists.txt

 pythonize_bool(LIBCXX_GENERATE_COVERAGE)
 pythonize_bool(LIBCXXABI_ENABLE_SHARED)
 pythonize_bool(LIBCXXABI_USE_LLVM_UNWINDER)
 pythonize_bool(LIBCXX_USE_COMPILER_RT)
 pythonize_bool(LIBCXX_HAS_ATOMIC_LIB)
 pythonize_bool(LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB)
 pythonize_bool(LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY)
 pythonize_bool(LIBCXX_DEBUG_BUILD)
+pythonize_bool(LIBCXX_TEST_HAVE_FORK)
 
 # By default, for non-standalone builds, libcxx and libcxxabi share a library
 # directory.
 if (NOT LIBCXX_CXX_ABI_LIBRARY_PATH)
   set(LIBCXX_CXX_ABI_LIBRARY_PATH "${LIBCXX_LIBRARY_DIR}" CACHE PATH
       "The path to libc++abi library.")
 endif()
 

libcxx/test/libcxx/containers/sequences/array/array.zero/db_back.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test array<T, 0>::front() raises a debug error.
 
 #define _LIBCPP_DEBUG 1
 #include <array>
 #include "debug_mode_helper.h"
 

libcxx/test/libcxx/containers/sequences/array/array.zero/db_front.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test array<T, 0>::front() raises a debug error.
 
 #define _LIBCPP_DEBUG 1
 #include <array>
 #include "debug_mode_helper.h"
 

libcxx/test/libcxx/containers/sequences/array/array.zero/db_indexing.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test array<T, 0>::operator[] raises a debug error.
 
 #define _LIBCPP_DEBUG 1
 #include <array>
 #include "debug_mode_helper.h"
 

libcxx/test/libcxx/containers/sequences/list/list.cons/db_copy.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // <list>
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // list(list&& c);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))
 
 #include <list>

libcxx/test/libcxx/containers/sequences/list/list.cons/db_move.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // list(list&& c);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(1))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/emplace_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // template <class... Args> void emplace(const_iterator p, Args&&... args);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call erase(const_iterator position) with end()
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_db2.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call erase(const_iterator position) with iterator from another container
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call erase(const_iterator first, const_iterator last); with first iterator from another container
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db2.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call erase(const_iterator first, const_iterator last); with second iterator from another container
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db3.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call erase(const_iterator first, const_iterator last); with both iterators from another container
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/erase_iter_iter_db4.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call erase(const_iterator first, const_iterator last); with a bad range
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_iter_iter_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // template <InputIterator Iter>
 //   iterator insert(const_iterator position, Iter first, Iter last);
 
 

libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_rvalue_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // iterator insert(const_iterator position, value_type&& x);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_size_value_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // iterator insert(const_iterator position, size_type n, const value_type& x);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/insert_iter_value_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // iterator insert(const_iterator position, const value_type& x);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.modifiers/pop_back_db1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // void pop_back();
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // void splice(const_iterator position, list& x);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // void splice(const_iterator position, list<T,Allocator>& x, iterator i);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/containers/sequences/list/list.ops/db_splice_pos_list_iter_iter.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // void splice(const_iterator position, list& x, iterator first, iterator last);
 
 #define _LIBCPP_DEBUG 1
 #define _LIBCPP_ASSERT(x, m) ((x) ? (void)0 : std::exit(0))

libcxx/test/libcxx/debug/containers/db_associative_container_tests.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03, c++11, c++14
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
 
 #define _LIBCPP_DEBUG 1
 
 #include <map>
 #include <set>

libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.multithread.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03, c++11, c++14
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-has-no-threads
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test multihtreaded container debugging
 
 #define _LIBCPP_DEBUG 1
 
 #include <cassert>
 #include <cstddef>

libcxx/test/libcxx/debug/containers/db_sequence_container_iterators.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03, c++11, c++14
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
 
 #define _LIBCPP_DEBUG 1
 
 #include <forward_list>
 #include <list>

libcxx/test/libcxx/debug/containers/db_string.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03, c++11, c++14
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
 
 #define _LIBCPP_DEBUG 1
 #include <string>
 #include <vector>
 

libcxx/test/libcxx/debug/containers/db_unord_container_tests.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03, c++11, c++14
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-no-if-constexpr
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // test container debugging
 
 #define _LIBCPP_DEBUG 1
 #include <unordered_map>
 #include <unordered_set>
 #include <utility>

libcxx/test/libcxx/debug/debug_abort.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // Test that the default debug handler aborts the program.
 
 #define _LIBCPP_DEBUG 0
 
 #include <csignal>
 #include <cstdlib>

libcxx/test/libcxx/debug/debug_helper_test.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
 #define _LIBCPP_DEBUG 1
 
 #include <__debug>
 #include "debug_mode_helper.h"

libcxx/test/libcxx/debug/debug_register.pass.cpp

 // -*- C++ -*-
 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 #define _LIBCPP_DEBUG 1
 
 #include <cstdlib>
 #include <string>
 #include <type_traits>
 #include <__debug>

libcxx/test/libcxx/input.output/filesystems/class.path/path.itr/iterator_db.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
 // <filesystem>
 
 // class path
 
 #define _LIBCPP_DEBUG 0
 #include "filesystem_include.hpp"

libcxx/test/libcxx/iterators/advance.debug1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call advance(non-bidi iterator, -1)

libcxx/test/libcxx/iterators/next.debug1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 
 // Call next(non-bidi iterator, -1)

libcxx/test/libcxx/iterators/prev.debug1.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // MODULES_DEFINES: _LIBCPP_DEBUG=1
 // UNSUPPORTED: with_system_cxx_lib
 // UNSUPPORTED: c++98, c++03
 // UNSUPPORTED: windows
 // UNSUPPORTED: with_system_cxx_lib
 
 // <list>
 

libcxx/test/libcxx/thread/futures/futures.promise/set_exception.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-has-no-threads
 // UNSUPPORTED: c++98, c++03
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <future>
 
 // class promise<R>
 
 // void set_exception(exception_ptr p);
 // Test that a null exception_ptr is diagnosed.

libcxx/test/libcxx/thread/futures/futures.promise/set_exception_at_thread_exit.pass.cpp

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 // UNSUPPORTED: windows
 // UNSUPPORTED: libcpp-has-no-threads
 // UNSUPPORTED: c++98, c++03
 
 // MODULES_DEFINES: _LIBCPP_DEBUG=0
 
-// Can't test the system lib because this test enables debug mode
+// REQUIRES: has-fork
 // UNSUPPORTED: with_system_cxx_lib
 
 // <future>
 
 // class promise<R>
 
 // void set_exception_on_thread_exit(exception_ptr p);
 // Test that a null exception_ptr is diagnosed.

libcxx/test/lit.site.cfg.in

 config.target_triple            = "@TARGET_TRIPLE@"
 config.use_target               = bool("@LIBCXX_TARGET_TRIPLE@")
 config.sysroot                  = "@LIBCXX_SYSROOT@"
 config.gcc_toolchain            = "@LIBCXX_GCC_TOOLCHAIN@"
 config.generate_coverage        = @LIBCXX_GENERATE_COVERAGE@
 config.target_info              = "@LIBCXX_TARGET_INFO@"
 config.test_linker_flags        = "@LIBCXX_TEST_LINKER_FLAGS@"
 config.test_compiler_flags      = "@LIBCXX_TEST_COMPILER_FLAGS@"
+config.test_has_fork            = "@LIBCXX_TEST_HAVE_FORK@"
 
 config.executor                 = "@LIBCXX_EXECUTOR@"
 config.llvm_unwinder            = @LIBCXXABI_USE_LLVM_UNWINDER@
 config.builtins_library         = "@LIBCXX_BUILTINS_LIBRARY@"
 config.has_libatomic            = @LIBCXX_HAS_ATOMIC_LIB@
 config.use_libatomic            = @LIBCXX_HAVE_CXX_ATOMICS_WITH_LIB@
 config.debug_build              = @LIBCXX_DEBUG_BUILD@
 config.libcxxabi_shared         = @LIBCXXABI_ENABLE_SHARED@
 config.cxx_ext_threads          = @LIBCXX_BUILD_EXTERNAL_THREAD_LIBRARY@
 
 # Let the main config do the real work.
 config.loaded_site_config = True
 lit_config.load_config(config, "@LIBCXX_SOURCE_DIR@/test/lit.cfg")

libcxx/test/support/debug_mode_helper.h

 #error _LIBCPP_DEBUG must be defined before including this header
 #endif
 
 #include <ciso646>
 #ifndef _LIBCPP_VERSION
 #error "This header may only be used for libc++ tests"
 #endif
 
+#ifndef _LIBCPP_TEST_HAVE_FORK
+#error "This header may only be used on systems that support fork() and wait()"
+#endif
+
 #include <__debug>
 #include <utility>
 #include <cstddef>
 #include <cstdlib>
 #include <cassert>
 #include <string_view>
 #include <sstream>
 #include <iostream>

libcxx/utils/libcxx/test/config.py

class Configuration(object):
 
     def configure_debug_mode(self):
         debug_level = self.get_lit_conf('debug_level', None)
         if not debug_level:
             return
         if debug_level not in ['0', '1']:
             self.lit_config.fatal('Invalid value for debug_level "%s".'
                                   % debug_level)
+        if self.config.test_has_fork:
+            self.config.available_features.add('has-fork')
         self.cxx.compile_flags += ['-D_LIBCPP_DEBUG=%s' % debug_level]
 
     def configure_warnings(self):
         # Turn on warnings by default for Clang based compilers when C++ >= 11
         default_enable_warnings = self.cxx.type in ['clang', 'apple-clang'] \
             and len(self.config.available_features.intersection(
                 ['c++11', 'c++14', 'c++17', 'c++2a'])) != 0
         enable_warnings = self.get_lit_bool('enable_warnings',