[libc++] Use -I instead of -isystem to include headers in the test suite

[philnik]

Summary

Using -isystem marks the headers as system headers, which means that we
don't actually get all the warnings that we'd normally get if we included
the headers as user headers.

The goal of the test suite is normally to mirror as closely as possible
how users would use the library. Technically, this change goes against
that philosophy, since users should be using -isystem (if they ever
need to specify the libc++ path explicitly, which should be a rare
occurence). However, I believe fishing out additional warnings from
the headers provides more value, hence this change. Ideally, we'd be
able to still use -isystem, but instruct Clang to still emit warnings
from the libc++ headers (e.g. we could tell Clang to emit warnings in
any file inside <...>/usr/include/c++/v1).

[jloser]

Ideally, we'd be able to still use -isystem, but instruct Clang to still emit warnings from the libc++ headers (e.g. we could tell Clang to emit warnings in any file inside <...>/usr/include/c++/v1).

I think that this can be done with --no-system-header-prefix=path/to/usr/include/c++/v1 FWIW. Note that while Clang supports this, GCC does not for example.

In any case, I like the ideas for this patch; I'm fine with your current solution.

[ldionne]

In D118616#3284245, @jloser wrote:

Ideally, we'd be able to still use -isystem, but instruct Clang to still emit warnings from the libc++ headers (e.g. we could tell Clang to emit warnings in any file inside <...>/usr/include/c++/v1).

I think that this can be done with --no-system-header-prefix=path/to/usr/include/c++/v1 FWIW. Note that while Clang supports this, GCC does not for example.

In any case, I like the ideas for this patch; I'm fine with your current solution.

Thanks a lot for the information, I wasn't aware of that option at all. This is quite nice.

However, I just had a look into using that option and it looks like it doesn't help us at all. Indeed, the documentation says:

The –system-header-prefix= and –no-system-header-prefix= command-line arguments can be used to override whether subsets of an include path are treated as system headers. When the name in a #include directive is found within a header search path and starts with a system prefix, the header is treated as a system header.

Since we always include libc++ headers without any prefix in the #include <...> directive, this doesn't help. I would have imagined that doing something like --no-system-header-prefix=<...>/include/c++/v1 would do the trick, but trying it out confirms that it would only work if we included libc++ headers from the test suite as #include <include/c++/v1/chrono> for example.

[ldionne]

This is the alternative patch I tried, and it didn't work as one would expect:

commit 09058c0c732ea895def9f3e08b08672b2d5f1bc9
Author: Louis Dionne <[e-mail]>
Date:   Mon Jan 31 11:14:07 2022 -0500

    [libc++] Don't treat libc++ headers as system headers in the test suite
    
    This makes it possible to fish out warnings from our headers inside the
    test suite without having to use `-I` instead of `-isystem` to include
    those headers. This patch should pretty much negate the need for
    _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER, which was only used to enable
    these warnings in the test suite and when building the library.
    
    Differential Revision: https://reviews.llvm.org/D118616

diff --git a/libcxx/utils/libcxx/test/features.py b/libcxx/utils/libcxx/test/features.py
index 429e2d82c97b..2c5837075f4a 100644
--- a/libcxx/utils/libcxx/test/features.py
+++ b/libcxx/utils/libcxx/test/features.py
@@ -42,6 +42,8 @@ DEFAULT_FEATURES = [
                                                                  sys.platform.lower().strip() == 'darwin'), # TODO: this doesn't handle cross-compiling to Apple platforms.
   Feature(name='objective-c++',                 when=lambda cfg: hasCompileFlag(cfg, '-xobjective-c++ -fobjc-arc')),
   Feature(name='verify-support',                when=lambda cfg: hasCompileFlag(cfg, '-Xclang -verify-ignore-unexpected')),
+  Feature(name='warnings-in-system-headers',    when=lambda cfg: hasCompileFlag(cfg, '--no-system-header-prefix=%{include}'),
+                                                actions=[AddCompileFlag('--no-system-header-prefix=%{include}')]),
 
   Feature(name='non-lockfree-atomics',
           when=lambda cfg: sourceBuilds(cfg, """
@@ -89,8 +91,7 @@ DEFAULT_FEATURES = [
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}'.format(**compilerMacros(cfg)),                        when=_isAppleClang),
   Feature(name=lambda cfg: 'apple-clang-{__clang_major__}.{__clang_minor__}.{__clang_patchlevel__}'.format(**compilerMacros(cfg)), when=_isAppleClang),
 
-  Feature(name='clang',                                                                                                            when=_isClang,
-          actions=[AddCompileFlag('-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER')]),
+  Feature(name='clang',                                                                                                            when=_isClang),
   Feature(name=lambda cfg: 'clang-{__clang_major__}'.format(**compilerMacros(cfg)),                                                when=_isClang),
   Feature(name=lambda cfg: 'clang-{__clang_major__}.{__clang_minor__}'.format(**compilerMacros(cfg)),                              when=_isClang),
   Feature(name=lambda cfg: 'clang-{__clang_major__}.{__clang_minor__}.{__clang_patchlevel__}'.format(**compilerMacros(cfg)),       when=_isClang),

[ldionne]

Workaround failure on AIX

[ldionne]

Try to fix the failure differently.

[philnik]

Commandeering to fix clang-tidy, and Louis is not available at the moment.

[philnik]

• Also fix clang-tidy in this patch

[philnik]

• Fix modules build

[philnik]

• Fix CI

[philnik]

• Hopefully fix Windows CI

[philnik]

• Next try to fix Windows

[philnik]

• And another try

[philnik]

• Maybe this works

[mstorsjo]

libcxx/include/__config_site.in

39

For the cases where this was needed, the safest fix would be to make sure to include libcxx headers before standard c headers. Or alternatively we could maybe consider if _LIBCPP_EXTRA_SITE_DEFINES should add an #undef before each define.

[EricWF]

Wait... How long have we been using -isystem in the test suite. That suppresses all warnings in the headers along that path.

[• Quuxplusone]

LGTM mod comments, but I consider this to be @ldionne's jurisdiction, and it certainly doesn't seem super urgent, so I think we should just wait for him to take a look.

Can you explain in the commit message how this relates to clang-tidy? Even looking at https://reviews.llvm.org/D118616?vs=404892&id=409993#toc I don't really understand your comment "Also fix clang-tidy in this patch."

libcxx/include/__config

60–62

Then personally I'd prefer to pass -Wno-macro-redefined in those specific tests. We shouldn't do anything in <__config> that is beneficial only for certain tests in the test suite; we should do it here iff we think it'll benefit real users. Do we want real users to be able to do, like, -D_LIBCPP_ABI_ALTERNATE_STRING_LAYOUT=1? If so, then lines 95-96 are good but the comment on line 94 should talk about that, not about tests in the test suite.

libcxx/include/__iterator/iterator_traits.h

201

Please file a bug for this (I assume a clang-tidy bug, right?) and link it from here and/or in the commit message.

libcxx/include/__ranges/reverse_view.h

113–129 ↗

(On Diff #410084)

These changes LGTM but should be committed separately from whatever else is going on here.
You can just say "Reviewed as part of D118616". Or I'll do it myself if I get around to it tomorrow morning. :)

libcxx/include/ext/__hash

20–23

Here and below, this shouldn't be necessary. Remember the economist's $100 bill: if this were needed, why wouldn't we be doing it everywhere? (E.g., in <string>.) It seems likely that there's some master list of "libc++ headers" somewhere and that <ext/__hash> and <ext/hash_map> are accidentally missing from that list.

libcxx/test/std/containers/sequences/array/size_and_alignment.pass.cpp

16

I might think this also needs to be guarded by && defined(__clang__), but I suppose we never test any non-Clang compilers on AIX. Okay.

[philnik]

In D118616#3333754, @Quuxplusone wrote:

LGTM mod comments, but I consider this to be @ldionne's jurisdiction, and it certainly doesn't seem super urgent, so I think we should just wait for him to take a look.

Can you explain in the commit message how this relates to clang-tidy? Even looking at https://reviews.llvm.org/D118616?vs=404892&id=409993#toc I don't really understand your comment "Also fix clang-tidy in this patch."

Louis opened this PR before I landed the clang-tidy PR and this happens to be the fix for clang-tidy ignoring the headers. With the "Also fix clang-tidy in this patch" I meant that I'm fixing the warnings that clang-tidy produced after rebasing. I'm not sure what to add to the commit message. It's exactly the same problem, only that it's not clang producing the warnings, but clang-tidy.

libcxx/include/__config_site.in

39

I don't think the first option makes sense. That would mean that it makes a difference in which order the headers are included, which I'm not a fan of. The second one is an option, but I didn't have any luck with it yet.

libcxx/include/__iterator/iterator_traits.h

201

clang-tidy is kind-of right. __i - __i is a redundant expression, and I had to look at it a few times before I got why it's correct in this case. Where else would subtracting something from itself make sense?

libcxx/include/ext/__hash

20–23

I thought the <ext/*> headers weren't in module.modulemap, because they were deprecated. It's also possible they are not in there by accident.

[Mordante]

I didn't look at the patch closely.

libcxx/include/__iterator/iterator_traits.h

201

I agree with Arthur, this seems like a bug. clang-tidy uses the AST so it knows the code is in a requires clause.

I have a strong preference to at least mention the bug here, that makes validating whether it's fixed in the future easier. I don't object to adding it to the commit message.

[ldionne]

Thanks for commandeering. Can you also change the testing configurations in libcxxabi/test/configs/?

libcxx/include/__config

60–62

+1 here, we should just add those suppressions in the tests that need them

[philnik]

• Address comments

[ldionne]

libcxx/include/ext/__hash

20–23

I don't understand why this diff is necessary in this patch. What happens if you remove it? What fails?

[philnik]

libcxx/include/ext/__hash

20–23

Because we replace -isystem with -I. All warnings in headers are now part of the tests, so there must not be any warnings because of -Werror. So basically, the modules build would fail.

[• Quuxplusone]

libcxx/include/__locale

24–26

I don't think you should touch the order of these two lines (because I'm paranoid). But if your goal is to alphabetize the includes in this file, then you should also touch lines 31-32 at the same time.

libcxx/include/__ranges/reverse_view.h

113–129 ↗

(On Diff #410084)

I finally remembered this comment, and landed these six lines in 6d751c410d6f5400c2c26d47e5033679fbd736d6. Please rebase. :)

[EricWF]

libcxx/include/ext/__hash

20–23

But there's a #pragma system_header?

[• Quuxplusone]

libcxx/include/ext/__hash

20–23

I thought the <ext/*> headers weren't in module.modulemap, because they were deprecated. It's also possible they are not in there by accident.

I hypothesize that they're missing only by accident. I've posted D120758, and I'd be interested to see if you can eliminate these diffs by rebasing on it (or just adopting its diffs into this PR; I'll be happy to abandon it).

[philnik]

• Rebased
• Address comments
• Exclude ext/ from modules build

Adding the things in ext/ to the modulemap doesn't work, because it would ignore __DEPRECATED.

[• Quuxplusone]

libcxx/include/ext/__hash

13

I notice this is not guarded correctly by _LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER. We should fix that, but probably fix it after the dust has settled on all these reviews.

libcxx/utils/libcxx/test/params.py

80

I think this macro should have the word TEST in it somewhere.

However, since you use it only for the generated header tests, IMHO it would be quite reasonable to just rip out the ext/ headers from those generated tests specifically (i.e. adopt a small portion of D120831's changes), and then you don't need the macro at all, right?

[ldionne]

This LGTM if CI is passing, however I would much rather rip out the ext/ headers from tests and avoid introducing the _LIBCXX_MODULES_BUILD macro.

FWIW, this is going to interact with D120684 almost certainly. The second one to land his patch is probably going to have additional work to do. If CI passes on your patch, I don't mind you shipping it as-is, and then tackling the removal of _LIBCXX_MODULES_BUILD separately, just for the sake of making progress on this (and allowing me to start fixing any remaining issues with my patch).

[philnik]

• Disable some warnings in bad_engine tests

[philnik]

• Disable warnings in trivial_abi tests

libcxx/.clang-tidy

 InheritParentConfig: true
-Checks: '-readability-identifier-naming,-llvm-header-guard,-misc-unconventional-assign-operator,-llvm-else-after-return'
+Checks: '-readability-identifier-naming,-llvm-header-guard,-misc-unconventional-assign-operator,-llvm-else-after-return,-llvm-qualified-auto'

libcxx/include/__config

 #  define _LIBCPP_OBJECT_FORMAT_COFF  1
 #elif defined(__wasm__)
 #  define _LIBCPP_OBJECT_FORMAT_WASM  1
 #else
    // ... add new file formats here ...
 #endif
 
 #if _LIBCPP_ABI_VERSION >= 2
 // Change short string representation so that string data starts at offset 0,
 // improving its alignment in some cases.
 #  define _LIBCPP_ABI_ALTERNATE_STRING_LAYOUT
 // Fix deque iterator type in order to support incomplete types.
 #  define _LIBCPP_ABI_INCOMPLETE_TYPES_IN_DEQUE
 // Fix undefined behavior in how std::list stores its linked nodes.
 #  define _LIBCPP_ABI_LIST_REMOVE_NODE_POINTER_UB
 // Fix undefined behavior in  how __tree stores its end and parent nodes.
 #  define _LIBCPP_ABI_TREE_REMOVE_NODE_POINTER_UB
 // Fix undefined behavior in how __hash_table stores its pointer types.
 #  define _LIBCPP_ABI_FIX_UNORDERED_NODE_POINTER_UB

 #else
 #  define _LIBCPP_DIAGNOSTIC_PUSH
 #  define _LIBCPP_DIAGNOSTIC_POP
 #  define _LIBCPP_CLANG_DIAGNOSTIC_IGNORED(str)
 #  define _LIBCPP_GCC_DIAGNOSTIC_IGNORED(str)
 #endif
 
 #if defined(_AIX) && !defined(_LIBCPP_COMPILER_GCC)
-#define _LIBCPP_PACKED_BYTE_FOR_AIX _Pragma("pack(1)")
-#define _LIBCPP_PACKED_BYTE_FOR_AIX_END _Pragma("pack(pop)")
+#  define _LIBCPP_PACKED_BYTE_FOR_AIX _Pragma("pack(1)")
+#  define _LIBCPP_PACKED_BYTE_FOR_AIX_END _Pragma("pack(pop)")
 #else
-#define _LIBCPP_PACKED_BYTE_FOR_AIX      /* empty */
-#define _LIBCPP_PACKED_BYTE_FOR_AIX_END  /* empty */
+#  define _LIBCPP_PACKED_BYTE_FOR_AIX      /* empty */
+#  define _LIBCPP_PACKED_BYTE_FOR_AIX_END  /* empty */
 #endif
 
 #endif // __cplusplus
 
 #endif // _LIBCPP_CONFIG

libcxx/include/__config_site.in

 #cmakedefine _LIBCPP_HAS_NO_FILESYSTEM_LIBRARY
 #cmakedefine _LIBCPP_HAS_PARALLEL_ALGORITHMS
 #cmakedefine _LIBCPP_HAS_NO_RANDOM_DEVICE
 #cmakedefine _LIBCPP_HAS_NO_LOCALIZATION
 #cmakedefine _LIBCPP_HAS_NO_WIDE_CHARACTERS
 #cmakedefine _LIBCPP_HAS_NO_INCOMPLETE_FORMAT
 #cmakedefine _LIBCPP_HAS_NO_INCOMPLETE_RANGES
 
+// __USE_MINGW_ANSI_STDIO gets redefined on MinGW
+#ifdef __clang__
+#  pragma clang diagnostic push
+#  pragma clang diagnostic ignored "-Wmacro-redefined"
+#endif
+
 @_LIBCPP_ABI_DEFINES@
 @_LIBCPP_EXTRA_SITE_DEFINES@
 
+#ifdef __clang__
+#  pragma clang diagnostic pop
+#endif
+
 #endif // _LIBCPP_CONFIG_SITE

libcxx/include/__iterator/iterator_traits.h

concept __cpp17_random_access_iterator =
   __cpp17_bidirectional_iterator<_Ip> &&
   totally_ordered<_Ip> &&
   requires(_Ip __i, typename incrementable_traits<_Ip>::difference_type __n) {
     { __i += __n } -> same_as<_Ip&>;
     { __i -= __n } -> same_as<_Ip&>;
     { __i +  __n } -> same_as<_Ip>;
     { __n +  __i } -> same_as<_Ip>;
     { __i -  __n } -> same_as<_Ip>;
-    { __i -  __i } -> same_as<decltype(__n)>;
+    { __i -  __i } -> same_as<decltype(__n)>; // NOLINT(misc-redundant-expression) ; This is llvm.org/PR54114
     {  __i[__n]  } -> convertible_to<iter_reference_t<_Ip>>;
   };
 } // namespace __iterator_traits_detail
 
 template<class _Ip>
 concept __has_member_reference = requires { typename _Ip::reference; };
 
 template<class _Ip>

libcxx/include/__locale

 #include <cstdint>
 #include <locale.h>
 #include <memory>
 #include <mutex>
 #include <string>
 #include <utility>
 
 #if defined(_LIBCPP_MSVCRT_LIKE)
-# include <cstring>
 # include <__support/win32/locale_win32.h>
+# include <cstring>
 #elif defined(_AIX) || defined(__MVS__)
 # include <__support/ibm/xlocale.h>
 #elif defined(__ANDROID__)
 # include <__support/android/locale_bionic.h>
 #elif defined(__sun__)
-# include <xlocale.h>
 # include <__support/solaris/xlocale.h>
+# include <xlocale.h>
 #elif defined(_NEWLIB_VERSION)
 # include <__support/newlib/xlocale.h>
 #elif defined(__OpenBSD__)
 # include <__support/openbsd/xlocale.h>
 #elif (defined(__APPLE__)      || defined(__FreeBSD__) \
     || defined(__EMSCRIPTEN__) || defined(__IBMCPP__))
 # include <xlocale.h>
 #elif defined(__Fuchsia__)

libcxx/include/ext/__hash

 // -*- 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
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP_EXT_HASH
 #define _LIBCPP_EXT_HASH
 
 #  pragma GCC system_header
 
+#include <__config>
 #include <__string>
 #include <cstring>
 #include <string>
 
 namespace __gnu_cxx {
 
 template <typename _Tp> struct _LIBCPP_TEMPLATE_VIS hash { };
 
 template <> struct _LIBCPP_TEMPLATE_VIS hash<const char*>
  : public std::unary_function<const char*, size_t>
 {
     _LIBCPP_INLINE_VISIBILITY
     size_t operator()(const char *__c) const _NOEXCEPT
     {
         return std::__do_string_hash(__c, __c + strlen(__c));
     }

libcxx/test/configs/apple-libc++-shared.cfg.in

 # Testing configuration for Apple's system libc++.
 #
 # This configuration differs from a normal LLVM shared library configuration in
 # that we must use DYLD_LIBRARY_PATH to run the tests against the just-built library,
 # since Apple's libc++ has an absolute install_name.
 #
 # We also don't use a per-target include directory layout, so we have only one
 # include directory for the libc++ headers.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{install}/include/c++/v1 -I %{libcxx}/test/support'
+    '-nostdinc++ -I %{install}/include/c++/v1 -I %{libcxx}/test/support'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{install}/lib -lc++'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env DYLD_LIBRARY_PATH=%{install}/lib -- '
 ))
 

libcxx/test/configs/ibm-libc++-shared.cfg.in

 # This testing configuration handles running the test suite against libc++ on
 # AIX using a shared library.
 #
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}', ''))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -D__LIBC_NO_CPP_MATH_OVERLOADS__ -isystem %{install}/include/c++/v1 -I %{libcxx}/test/support'
+    '-nostdinc++ -D__LIBC_NO_CPP_MATH_OVERLOADS__ -I %{install}/include/c++/v1 -I %{libcxx}/test/support'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{install}/lib -lc++ -lc++abi -latomic -Wl,-bbigtoc'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env LIBPATH=%{install}/lib -- '
 ))
 

libcxx/test/configs/llvm-libc++-mingw.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using either a DLL or a static library, with MinGW/Clang on Windows.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}', ''))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{lib} -lc++'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env PATH=%{lib} -- '
 ))
 

libcxx/test/configs/llvm-libc++-shared-clangcl.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a DLL, with Clang-cl on Windows.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib -L %{lib} -lc++ -lmsvcrt -lmsvcprt -loldnames'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env PATH=%{lib} -- '
 ))
 

libcxx/test/configs/llvm-libc++-shared-gcc.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a shared library, with GCC. This is done differently from Clang because
 # GCC does not support the -nostdlib++ command-line flag.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}', ''))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support'
 ))
 config.substitutions.append(('%{link_flags}',
     '-L %{lib} -Wl,-rpath,%{lib} -nodefaultlibs -lc++ -lm -lgcc_s -lgcc -lpthread -lc -lgcc_s -lgcc -latomic'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T -- '
 ))
 

libcxx/test/configs/llvm-libc++-shared.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a shared library.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{lib} -Wl,-rpath,%{lib} -lc++ -pthread'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T -- '
 ))
 

libcxx/test/configs/llvm-libc++-static-clangcl.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a static library, with Clang-cl on Windows.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}', '--driver-mode=g++'))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support -D_CRT_SECURE_NO_WARNINGS -D_CRT_NONSTDC_NO_WARNINGS -D_CRT_STDIO_ISO_WIDE_SPECIFIERS -DNOMINMAX'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib -L %{lib} -llibc++ -lmsvcrt -lmsvcprt -loldnames'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env PATH=%{lib} -- '
 ))
 

libcxx/test/configs/llvm-libc++-static.cfg.in

 # This testing configuration handles running the test suite against LLVM's libc++
 # using a static library.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{include} -isystem %{target-include} -I %{libcxx}/test/support'
+    '-nostdinc++ -I %{include} -I %{target-include} -I %{libcxx}/test/support'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{lib} -lc++ -lc++abi -pthread'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T -- '
 ))
 

libcxx/test/libcxx/clang_tidy.sh.cpp

 #    include <experimental/type_traits>
 #    include <experimental/unordered_map>
 #    include <experimental/unordered_set>
 #    include <experimental/utility>
 #    include <experimental/vector>
 #endif // __cplusplus >= 201103L
 
 // extended headers
-#include <ext/hash_map>
-#include <ext/hash_set>
+#ifndef _LIBCXX_MODULES_BUILD
+#    include <ext/hash_map>
+#    include <ext/hash_set>
+#endif
 
 // clang-format on
 
 ////////////////////////////////////////////////////////////////////////////////
 // END-GENERATED-HEADERS
 ////////////////////////////////////////////////////////////////////////////////

libcxx/test/libcxx/containers/gnu_cxx/hash_map.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: modules-build
+
 // Prevent <ext/hash_map> from generating deprecated warnings for this test.
 #if defined(__DEPRECATED)
 #   undef __DEPRECATED
 #endif
 
 #include <ext/hash_map>
 #include <cassert>
 

libcxx/test/libcxx/containers/gnu_cxx/hash_map_name_lookup.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: modules-build
+
 // Poison the std:: names we might use inside __gnu_cxx to ensure they're
 // properly qualified.
 struct allocator;
 struct pair;
 struct equal_to;
 struct unique_ptr;
 
 // Prevent <ext/hash_map> from generating deprecated warnings for this test.

libcxx/test/libcxx/containers/gnu_cxx/hash_set.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: modules-build
+
 // Prevent <ext/hash_set> from generating deprecated warnings for this test.
 #if defined(__DEPRECATED)
 #   undef __DEPRECATED
 #endif
 
 #include <ext/hash_set>
 #include <cassert>
 

libcxx/test/libcxx/containers/gnu_cxx/hash_set_name_lookup.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: modules-build
+
 // Poison the std:: names we might use inside __gnu_cxx to ensure they're
 // properly qualified.
 struct allocator;
 struct pair;
 struct equal_to;
 struct unique_ptr;
 
 // Prevent <ext/hash_set> from generating deprecated warnings for this test.

libcxx/test/libcxx/containers/sequences/deque/incomplete.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
 //
 //===----------------------------------------------------------------------===//
 
 // <deque>
 
 // deque()
 // deque::iterator()
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_INCOMPLETE_TYPES_IN_DEQUE
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_INCOMPLETE_TYPES_IN_DEQUE
 
 #include <deque>
 #include <cassert>
 
 #include "test_macros.h"
 
 struct A {
   std::deque<A> d;

libcxx/test/libcxx/double_include.sh.cpp

 #    include <experimental/type_traits>
 #    include <experimental/unordered_map>
 #    include <experimental/unordered_set>
 #    include <experimental/utility>
 #    include <experimental/vector>
 #endif // __cplusplus >= 201103L
 
 // extended headers
-#include <ext/hash_map>
-#include <ext/hash_set>
+#ifndef _LIBCXX_MODULES_BUILD
+#    include <ext/hash_map>
+#    include <ext/hash_set>
+#endif
 
 // clang-format on
 
 ////////////////////////////////////////////////////////////////////////////////
 // END-GENERATED-HEADERS
 ////////////////////////////////////////////////////////////////////////////////
 
 #if defined(WITH_MAIN)
 int main(int, char**) { return 0; }
 #endif

libcxx/test/libcxx/extensions/hash/specializations.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: modules-build
+
 // NOTE: Undefined __DEPRECATED to prevent this test from failing with -Werror
 #undef __DEPRECATED
 #include <assert.h>
 #include <ext/hash_map>
 #include <string>
 
 #include "test_macros.h"
 

libcxx/test/libcxx/memory/trivial_abi/shared_ptr_arg.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
 //
 //===----------------------------------------------------------------------===//
 
 // <memory>
 
 // Test shared_ptr<T> with trivial_abi as parameter type.
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI
 
 // XFAIL: gcc
 // UNSUPPORTED: c++03
 
 #include <memory>
 #include <cassert>
 
 __attribute__((noinline)) void call_something() { asm volatile(""); }

libcxx/test/libcxx/memory/trivial_abi/unique_ptr_arg.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
 //
 //===----------------------------------------------------------------------===//
 
 // <memory>
 
 // Test unique_ptr<T> with trivial_abi as parameter type.
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
 
 // XFAIL: gcc
 
 #include <memory>
 #include <cassert>
 
 __attribute__((noinline)) void call_something() { asm volatile(""); }
 

libcxx/test/libcxx/memory/trivial_abi/unique_ptr_array.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
 //
 //===----------------------------------------------------------------------===//
 
 // <memory>
 
 // Test unique_ptr<T[]> with trivial_abi as parameter type.
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
 
 // XFAIL: gcc
 // UNSUPPORTED: c++03
 
 #include <memory>
 #include <cassert>
 
 __attribute__((noinline)) void call_something() { asm volatile(""); }

libcxx/test/libcxx/memory/trivial_abi/unique_ptr_destruction_order.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
 //
 //===----------------------------------------------------------------------===//
 
 // <memory>
 
 // Test arguments destruction order involving unique_ptr<T> with trivial_abi.
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
 
 // XFAIL: gcc
 
 #include <memory>
 #include <cassert>
 
 __attribute__((noinline)) void call_something() { asm volatile(""); }
 

libcxx/test/libcxx/memory/trivial_abi/unique_ptr_ret.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
 //
 //===----------------------------------------------------------------------===//
 
 // <memory>
 
 // Test unique_ptr<T> with trivial_abi as return-type.
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_ENABLE_UNIQUE_PTR_TRIVIAL_ABI
 
 // XFAIL: gcc
 
 #include <memory>
 #include <cassert>
 
 __attribute__((noinline)) void call_something() { asm volatile(""); }
 

libcxx/test/libcxx/memory/trivial_abi/weak_ptr_ret.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
 //
 //===----------------------------------------------------------------------===//
 
 // <memory>
 
 // Test weak_ptr<T> with trivial_abi as return-type.
 
-// ADDITIONAL_COMPILE_FLAGS: -D_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI
+// ADDITIONAL_COMPILE_FLAGS: -Wno-macro-redefined -D_LIBCPP_ABI_ENABLE_SHARED_PTR_TRIVIAL_ABI
 
 // XFAIL: gcc
 
 #include <memory>
 #include <cassert>
 
 __attribute__((noinline)) void call_something() { asm volatile(""); }
 

libcxx/test/libcxx/min_max_macros.compile.pass.cpp

 TEST_MACROS();
 #    include <experimental/utility>
 TEST_MACROS();
 #    include <experimental/vector>
 TEST_MACROS();
 #endif // __cplusplus >= 201103L
 
 // extended headers
-#include <ext/hash_map>
+#ifndef _LIBCXX_MODULES_BUILD
+#    include <ext/hash_map>
 TEST_MACROS();
-#include <ext/hash_set>
+#    include <ext/hash_set>
 TEST_MACROS();
+#endif
 
 // clang-format on
 
 ////////////////////////////////////////////////////////////////////////////////
 // END-GENERATED-HEADERS
 ////////////////////////////////////////////////////////////////////////////////

libcxx/test/libcxx/nasty_macros.compile.pass.cpp

 #    include <experimental/type_traits>
 #    include <experimental/unordered_map>
 #    include <experimental/unordered_set>
 #    include <experimental/utility>
 #    include <experimental/vector>
 #endif // __cplusplus >= 201103L
 
 // extended headers
-#include <ext/hash_map>
-#include <ext/hash_set>
+#ifndef _LIBCXX_MODULES_BUILD
+#    include <ext/hash_map>
+#    include <ext/hash_set>
+#endif
 
 // clang-format on
 
 ////////////////////////////////////////////////////////////////////////////////
 // END-GENERATED-HEADERS
 ////////////////////////////////////////////////////////////////////////////////

libcxx/test/libcxx/no_assert_include.compile.pass.cpp

 #    include <experimental/type_traits>
 #    include <experimental/unordered_map>
 #    include <experimental/unordered_set>
 #    include <experimental/utility>
 #    include <experimental/vector>
 #endif // __cplusplus >= 201103L
 
 // extended headers
-#include <ext/hash_map>
-#include <ext/hash_set>
+#ifndef _LIBCXX_MODULES_BUILD
+#    include <ext/hash_map>
+#    include <ext/hash_set>
+#endif
 
 // clang-format on
 
 ////////////////////////////////////////////////////////////////////////////////
 // END-GENERATED-HEADERS
 ////////////////////////////////////////////////////////////////////////////////
 
 #ifdef assert
 #error "Do not include cassert or assert.h in standard header files"
 #endif

libcxx/test/libcxx/numerics/rand/rand.dis/rand.dist.bern/rand.dist.bern.geo/bad_engine.verify.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++03
+// ADDITIONAL_COMPILE_FLAGS: -Wno-sign-compare -Wno-shift-count-negative
 
 // <random>
 
 #include <random>
 
 template<class Int>
 struct G {
   using result_type = Int;

libcxx/test/libcxx/numerics/rand/rand.dis/rand.dist.bern/rand.dist.bern.negbin/bad_engine.verify.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++03
+// ADDITIONAL_COMPILE_FLAGS: -Wno-shift-count-negative
 
 // <random>
 
 #include <random>
 
 template<class Int>
 struct G {
   using result_type = Int;

libcxx/test/libcxx/numerics/rand/rand.dis/rand.dist.norm/rand.dist.norm.f/bad_engine.verify.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++03
+// ADDITIONAL_COMPILE_FLAGS: -Wno-sign-compare
 
 // <random>
 
 #include <random>
 
 template<class Int>
 struct G {
   using result_type = Int;

libcxx/test/libcxx/numerics/rand/rand.dis/rand.dist.pois/rand.dist.pois.poisson/bad_engine.verify.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++03
+// ADDITIONAL_COMPILE_FLAGS: -Wno-shift-count-negative
 
 // <random>
 
 #include <random>
 
 template<class Int>
 struct G {
   using result_type = Int;

libcxx/test/libcxx/numerics/rand/rand.dis/rand.dist.uni/rand.dist.uni.int/bad_engine.verify.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++03
+// ADDITIONAL_COMPILE_FLAGS: -Wno-sign-compare
 
 // <random>
 
 #include <random>
 
 template<class Int>
 struct G {
   using result_type = Int;

libcxx/test/std/containers/sequences/array/size_and_alignment.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
 //
 //===----------------------------------------------------------------------===//
 
 // <array>
 
 // template <class T, size_t N >
 // struct array
 
 // Test the size and alignment matches that of an array of a given type.
 
+// Ignore error about requesting a large alignment not being ABI compatible with older AIX systems.
+#if defined(_AIX)
+# pragma clang diagnostic ignored "-Waix-compat"
+#endif
+
 #include <array>
 #include <iterator>
 #include <type_traits>
 #include <cstddef>
 
 #include "test_macros.h"
 
-
 template <class T, size_t Size>
 struct MyArray {
   T elems[Size];
 };
 
 template <class T, size_t Size>
 void test() {
   typedef T CArrayT[Size == 0 ? 1 : Size];

libcxx/utils/generate_header_tests.py

 {top_level_headers}
 
 // experimental headers
 #if __cplusplus >= 201103L
 {experimental_headers}
 #endif // __cplusplus >= 201103L
 
 // extended headers
+#ifndef _LIBCXX_MODULES_BUILD
 {extended_headers}
+#endif
 """
 
 
 def should_keep_header(p, exclusions=None):
     if os.path.isdir(p):
         return False
 
     if exclusions:
def produce_top_level_headers(post_include=None, exclusions=None):
     return produce_headers([include_path], 0, post_include=post_include, exclusions=exclusions)
 
 
 def produce_experimental_headers(post_include=None, exclusions=None):
     return produce_headers([include_path, 'experimental'], 1, post_include=post_include, exclusions=exclusions)
 
 
 def produce_extended_headers(post_include=None, exclusions=None):
-    return produce_headers([include_path, 'ext'], 0, post_include=post_include, exclusions=exclusions)
+    return produce_headers([include_path, 'ext'], 1, post_include=post_include, exclusions=exclusions)
 
 
 def replace_generated_headers(test_path, test_str):
     with open(test_path, 'r') as f:
         content = f.read()
 
     preamble = begin_pattern + '\n// clang-format off\n\n' + warning_note
     postamble = '\n// clang-format on\n\n' + end_pattern

libcxx/utils/libcxx/test/config.py

def configure_compile_flags_header_includes(self):
         if not os.path.isdir(cxx_headers):
             self.lit_config.fatal("cxx_headers='{}' is not a directory.".format(cxx_headers))
         (path, version) = os.path.split(cxx_headers)
         (path, cxx) = os.path.split(path)
         triple = self.get_lit_conf('target_triple', None)
         if triple is not None:
             cxx_target_headers = os.path.join(path, triple, cxx, version)
             if os.path.isdir(cxx_target_headers):
-                self.cxx.compile_flags += ['-isystem', cxx_target_headers]
-        self.cxx.compile_flags += ['-isystem', cxx_headers]
+                self.cxx.compile_flags += ['-I', cxx_target_headers]
+        self.cxx.compile_flags += ['-I', cxx_headers]
         if self.libcxx_obj_root is not None:
             cxxabi_headers = os.path.join(self.libcxx_obj_root, 'include',
                                           'c++build')
             if os.path.isdir(cxxabi_headers):
                 self.cxx.compile_flags += ['-I' + cxxabi_headers]
 
     def configure_link_flags(self):
         # Configure library path

libcxx/utils/libcxx/test/params.py

Parameter(name='std', choices=_allStandards, type=str,
             ]),
 
   Parameter(name='enable_modules', choices=[True, False], type=bool, default=False,
             help="Whether to build the test suite with Clang modules enabled.",
             actions=lambda modules: [
               AddFeature('modules-build'),
               AddCompileFlag('-fmodules'),
               AddCompileFlag('-fcxx-modules'), # AppleClang disregards -fmodules entirely when compiling C++. This enables modules for C++.
+              AddCompileFlag('-D_LIBCXX_MODULES_BUILD') # Needed to exclude headers that are not supported in a modules build
             ] if modules else []),
 
   Parameter(name='enable_exceptions', choices=[True, False], type=bool, default=True,
             help="Whether to enable exceptions when compiling the test suite.",
             actions=lambda exceptions: [] if exceptions else [
               AddFeature('no-exceptions'),
               AddCompileFlag('-fno-exceptions')
             ]),

libcxxabi/test/configs/apple-libc++abi-backdeployment.cfg.in

libcxx.test.dsl.Parameter(name='unwind_runtime_root', type=str,
         the tests.
         """),
 ]
 
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{install}/include/c++/v1 -DLIBCXXABI_NO_TIMER -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
+    '-nostdinc++ -I %{install}/include/c++/v1 -DLIBCXXABI_NO_TIMER -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
     '-I %{libcxx}/test/support -I %{libcxx}/src'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{install}/lib -lc++ -lc++abi'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env DYLD_LIBRARY_PATH="%{cxx-runtime-root}:%{abi-runtime-root}:%{unwind-runtime-root}" -- '
 ))
 
 libcxx.test.newconfig.configure(
     libcxx.test.params.DEFAULT_PARAMETERS + BACKDEPLOYMENT_PARAMETERS,
     libcxx.test.features.DEFAULT_FEATURES,
     config,
     lit_config
 )

libcxxabi/test/configs/apple-libc++abi-shared.cfg.in

 # Testing configuration for Apple's system libc++abi.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}',
     '-isysroot {}'.format('@CMAKE_OSX_SYSROOT@') if '@CMAKE_OSX_SYSROOT@' else ''
 ))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{install}/include/c++/v1 -DLIBCXXABI_NO_TIMER -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
+    '-nostdinc++ -I %{install}/include/c++/v1 -DLIBCXXABI_NO_TIMER -D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
     '-I %{libcxx}/test/support -I %{libcxx}/src'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{install}/lib -lc++ -lc++abi'
 ))
 config.substitutions.append(('%{exec}',
     '%{executor} --execdir %T --env DYLD_LIBRARY_PATH=%{install}/lib -- '
 ))

libcxxabi/test/configs/ibm-libc++abi-shared.cfg.in

 # Testing configuration for libc++abi on AIX.
 
 lit_config.load_config(config, '@CMAKE_CURRENT_BINARY_DIR@/cmake-bridge.cfg')
 
 config.substitutions.append(('%{flags}',''))
 config.substitutions.append(('%{compile_flags}',
-    '-nostdinc++ -isystem %{install}/include/c++/v1 ' + 
+    '-nostdinc++ -I %{install}/include/c++/v1 ' +
     '-D__LIBC_NO_CPP_MATH_OVERLOADS__ -DLIBCXXABI_NO_TIMER ' +
     '-D_LIBCPP_ENABLE_CXX17_REMOVED_UNEXPECTED_FUNCTIONS ' +
     '-I %{libcxx}/test/support -I %{libcxx}/src'
 ))
 config.substitutions.append(('%{link_flags}',
     '-nostdlib++ -L %{install}/lib -lc++ -lc++abi -Wl,-bbigtoc'
 ))
 config.substitutions.append(('%{exec}',