#===----------------------------------------------------------------------===##
#
# 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
#
#===----------------------------------------------------------------------===##

import locale
import os
import platform
import pkgutil
import pipes
import re
import shlex
import shutil
import sys

from libcxx.compiler import CXXCompiler
from libcxx.test.target_info import make_target_info
from libcxx.test.executor import *
from libcxx.test.tracing import *
import libcxx.util

def loadSiteConfig(lit_config, config, param_name, env_name):
    # We haven't loaded the site specific configuration (the user is
    # probably trying to run on a test file directly, and either the site
    # configuration hasn't been created by the build system, or we are in an
    # out-of-tree build situation).
    site_cfg = lit_config.params.get(param_name,
                                     os.environ.get(env_name))
    if not site_cfg:
        lit_config.warning('No site specific configuration file found!'
                           ' Running the tests in the default configuration.')
    elif not os.path.isfile(site_cfg):
        lit_config.fatal(
            "Specified site configuration file does not exist: '%s'" %
            site_cfg)
    else:
        lit_config.note('using site specific configuration at %s' % site_cfg)
        ld_fn = lit_config.load_config

        # Null out the load_config function so that lit.site.cfg doesn't
        # recursively load a config even if it tries.
        # TODO: This is one hell of a hack. Fix it.
        def prevent_reload_fn(*args, **kwargs):
            pass
        lit_config.load_config = prevent_reload_fn
        ld_fn(config, site_cfg)
        lit_config.load_config = ld_fn

# Extract the value of a numeric macro such as __cplusplus or a feature-test
# macro.
def intMacroValue(token):
    return int(token.rstrip('LlUu'))

class Configuration(object):
    # pylint: disable=redefined-outer-name
    def __init__(self, lit_config, config):
        self.lit_config = lit_config
        self.config = config
        self.is_windows = platform.system() == 'Windows'
        self.cxx = None
        self.cxx_is_clang_cl = None
        self.cxx_stdlib_under_test = None
        self.project_obj_root = None
        self.libcxx_src_root = None
        self.libcxx_obj_root = None
        self.cxx_library_root = None
        self.cxx_runtime_root = None
        self.abi_library_root = None
        self.link_shared = self.get_lit_bool('enable_shared', default=True)
        self.debug_build = self.get_lit_bool('debug_build',   default=False)
        self.exec_env = dict(os.environ)
        self.use_target = False
        self.use_system_cxx_lib = False
        self.use_clang_verify = False
        self.long_tests = None
        self.execute_external = False

    def get_lit_conf(self, name, default=None):
        val = self.lit_config.params.get(name, None)
        if val is None:
            val = getattr(self.config, name, None)
            if val is None:
                val = default
        return val

    def get_lit_bool(self, name, default=None, env_var=None):
        def check_value(value, var_name):
            if value is None:
                return default
            if isinstance(value, bool):
                return value
            if not isinstance(value, str):
                raise TypeError('expected bool or string')
            if value.lower() in ('1', 'true'):
                return True
            if value.lower() in ('', '0', 'false'):
                return False
            self.lit_config.fatal(
                "parameter '{}' should be true or false".format(var_name))

        conf_val = self.get_lit_conf(name)
        if env_var is not None and env_var in os.environ and \
                os.environ[env_var] is not None:
            val = os.environ[env_var]
            if conf_val is not None:
                self.lit_config.warning(
                    'Environment variable %s=%s is overriding explicit '
                    '--param=%s=%s' % (env_var, val, name, conf_val))
            return check_value(val, env_var)
        return check_value(conf_val, name)

    def get_modules_enabled(self):
        return self.get_lit_bool('enable_modules',
                                default=False,
                                env_var='LIBCXX_ENABLE_MODULES')

    def make_static_lib_name(self, name):
        """Return the full filename for the specified library name"""
        if self.is_windows:
            assert name == 'c++'  # Only allow libc++ to use this function for now.
            return 'lib' + name + '.lib'
        else:
            return 'lib' + name + '.a'

    def configure(self):
        self.configure_executor()
        self.configure_use_system_cxx_lib()
        self.configure_target_info()
        self.configure_cxx()
        self.configure_triple()
        self.configure_deployment()
        self.configure_src_root()
        self.configure_obj_root()
        self.configure_cxx_stdlib_under_test()
        self.configure_cxx_library_root()
        self.configure_use_clang_verify()
        self.configure_use_thread_safety()
        self.configure_execute_external()
        self.configure_ccache()
        self.configure_compile_flags()
        self.configure_filesystem_compile_flags()
        self.configure_link_flags()
        self.configure_env()
        self.configure_color_diagnostics()
        self.configure_debug_mode()
        self.configure_warnings()
        self.configure_sanitizer()
        self.configure_coverage()
        self.configure_modules()
        self.configure_coroutines()
        self.configure_substitutions()
        self.configure_features()

    def print_config_info(self):
        # Print the final compile and link flags.
        self.lit_config.note('Using compiler: %s' % self.cxx.path)
        self.lit_config.note('Using flags: %s' % self.cxx.flags)
        if self.cxx.use_modules:
            self.lit_config.note('Using modules flags: %s' %
                                 self.cxx.modules_flags)
        self.lit_config.note('Using compile flags: %s'
                             % self.cxx.compile_flags)
        if len(self.cxx.warning_flags):
            self.lit_config.note('Using warnings: %s' % self.cxx.warning_flags)
        self.lit_config.note('Using link flags: %s' % self.cxx.link_flags)
        # Print as list to prevent "set([...])" from being printed.
        self.lit_config.note('Using available_features: %s' %
                             list(self.config.available_features))
        show_env_vars = {}
        for k,v in self.exec_env.items():
            if k not in os.environ or os.environ[k] != v:
                show_env_vars[k] = v
        self.lit_config.note('Adding environment variables: %r' % show_env_vars)
        sys.stderr.flush()  # Force flushing to avoid broken output on Windows

    def get_test_format(self):
        from libcxx.test.format import LibcxxTestFormat
        return LibcxxTestFormat(
            self.cxx,
            self.use_clang_verify,
            self.execute_external,
            self.executor,
            exec_env=self.exec_env)

    def configure_executor(self):
        exec_str = self.get_lit_conf('executor', "None")
        te = eval(exec_str)
        if te:
            self.lit_config.note("Using executor: %r" % exec_str)
            if self.lit_config.useValgrind:
                # We have no way of knowing where in the chain the
                # ValgrindExecutor is supposed to go. It is likely
                # that the user wants it at the end, but we have no
                # way of getting at that easily.
                selt.lit_config.fatal("Cannot infer how to create a Valgrind "
                                      " executor.")
        else:
            te = LocalExecutor()
            if self.lit_config.useValgrind:
                te = ValgrindExecutor(self.lit_config.valgrindArgs, te)
        self.executor = te

    def configure_target_info(self):
        self.target_info = make_target_info(self)

    def configure_cxx(self):
        # Gather various compiler parameters.
        cxx = self.get_lit_conf('cxx_under_test')
        self.cxx_is_clang_cl = cxx is not None and \
                               os.path.basename(cxx) == 'clang-cl.exe'
        # If no specific cxx_under_test was given, attempt to infer it as
        # clang++.
        if cxx is None or self.cxx_is_clang_cl:
            search_paths = self.config.environment['PATH']
            if cxx is not None and os.path.isabs(cxx):
                search_paths = os.path.dirname(cxx)
            clangxx = libcxx.util.which('clang++', search_paths)
            if clangxx:
                cxx = clangxx
                self.lit_config.note(
                    "inferred cxx_under_test as: %r" % cxx)
            elif self.cxx_is_clang_cl:
                self.lit_config.fatal('Failed to find clang++ substitution for'
                                      ' clang-cl')
        if not cxx:
            self.lit_config.fatal('must specify user parameter cxx_under_test '
                                  '(e.g., --param=cxx_under_test=clang++)')
        self.cxx = CXXCompiler(cxx) if not self.cxx_is_clang_cl else \
                   self._configure_clang_cl(cxx)
        cxx_type = self.cxx.type
        if cxx_type is not None:
            assert self.cxx.version is not None
            maj_v, min_v, _ = self.cxx.version
            self.config.available_features.add(cxx_type)
            self.config.available_features.add('%s-%s' % (cxx_type, maj_v))
            self.config.available_features.add('%s-%s.%s' % (
                cxx_type, maj_v, min_v))
        self.cxx.compile_env = dict(os.environ)
        # 'CCACHE_CPP2' prevents ccache from stripping comments while
        # preprocessing. This is required to prevent stripping of '-verify'
        # comments.
        self.cxx.compile_env['CCACHE_CPP2'] = '1'

    def _configure_clang_cl(self, clang_path):
        def _split_env_var(var):
            return [p.strip() for p in os.environ.get(var, '').split(';') if p.strip()]

        def _prefixed_env_list(var, prefix):
            from itertools import chain
            return list(chain.from_iterable((prefix, path) for path in _split_env_var(var)))

        assert self.cxx_is_clang_cl
        flags = []
        compile_flags = _prefixed_env_list('INCLUDE', '-isystem')
        link_flags = _prefixed_env_list('LIB', '-L')
        for path in _split_env_var('LIB'):
            self.add_path(self.exec_env, path)
        return CXXCompiler(clang_path, flags=flags,
                           compile_flags=compile_flags,
                           link_flags=link_flags)

    def _dump_macros_verbose(self, *args, **kwargs):
        macros_or_error = self.cxx.dumpMacros(*args, **kwargs)
        if isinstance(macros_or_error, tuple):
            cmd, out, err, rc = macros_or_error
            report = libcxx.util.makeReport(cmd, out, err, rc)
            report += "Compiler failed unexpectedly when dumping macros!"
            self.lit_config.fatal(report)
            return None
        assert isinstance(macros_or_error, dict)
        return macros_or_error

    def configure_src_root(self):
        self.libcxx_src_root = self.get_lit_conf(
            'libcxx_src_root', os.path.dirname(self.config.test_source_root))

    def configure_obj_root(self):
        self.project_obj_root = self.get_lit_conf('project_obj_root')
        self.libcxx_obj_root = self.get_lit_conf('libcxx_obj_root')
        if not self.libcxx_obj_root and self.project_obj_root is not None:
            possible_roots = [
                os.path.join(self.project_obj_root, 'libcxx'),
                os.path.join(self.project_obj_root, 'projects', 'libcxx'),
                os.path.join(self.project_obj_root, 'runtimes', 'libcxx'),
            ]
            for possible_root in possible_roots:
                if os.path.isdir(possible_root):
                    self.libcxx_obj_root = possible_root
                    break
            else:
                self.libcxx_obj_root = self.project_obj_root

    def configure_cxx_library_root(self):
        self.cxx_library_root = self.get_lit_conf('cxx_library_root',
                                                  self.libcxx_obj_root)
        self.cxx_runtime_root = self.get_lit_conf('cxx_runtime_root',
                                                   self.cxx_library_root)

    def configure_use_system_cxx_lib(self):
        # This test suite supports testing against either the system library or
        # the locally built one; the former mode is useful for testing ABI
        # compatibility between the current headers and a shipping dynamic
        # library.
        # Default to testing against the locally built libc++ library.
        self.use_system_cxx_lib = self.get_lit_conf('use_system_cxx_lib')
        if self.use_system_cxx_lib == 'true':
            self.use_system_cxx_lib = True
        elif self.use_system_cxx_lib == 'false':
            self.use_system_cxx_lib = False
        elif self.use_system_cxx_lib:
            assert os.path.isdir(self.use_system_cxx_lib), "the specified use_system_cxx_lib parameter (%s) is not a valid directory" % self.use_system_cxx_lib
            self.use_system_cxx_lib = os.path.abspath(self.use_system_cxx_lib)
        self.lit_config.note(
            "inferred use_system_cxx_lib as: %r" % self.use_system_cxx_lib)

    def configure_cxx_stdlib_under_test(self):
        self.cxx_stdlib_under_test = self.get_lit_conf(
            'cxx_stdlib_under_test', 'libc++')
        if self.cxx_stdlib_under_test not in \
                ['libc++', 'libstdc++', 'msvc', 'cxx_default']:
            self.lit_config.fatal(
                'unsupported value for "cxx_stdlib_under_test": %s'
                % self.cxx_stdlib_under_test)
        self.config.available_features.add(self.cxx_stdlib_under_test)
        if self.cxx_stdlib_under_test == 'libstdc++':
            self.config.available_features.add('libstdc++')
            # Manually enable the experimental and filesystem tests for libstdc++
            # if the options aren't present.
            # FIXME this is a hack.
            if self.get_lit_conf('enable_experimental') is None:
                self.config.enable_experimental = 'true'

    def configure_use_clang_verify(self):
        '''If set, run clang with -verify on failing tests.'''
        self.use_clang_verify = self.get_lit_bool('use_clang_verify')
        if self.use_clang_verify is None:
            # NOTE: We do not test for the -verify flag directly because
            #   -verify will always exit with non-zero on an empty file.
            self.use_clang_verify = self.cxx.isVerifySupported()
            self.lit_config.note(
                "inferred use_clang_verify as: %r" % self.use_clang_verify)
        if self.use_clang_verify:
                self.config.available_features.add('verify-support')

    def configure_use_thread_safety(self):
        '''If set, run clang with -verify on failing tests.'''
        has_thread_safety = self.cxx.hasCompileFlag('-Werror=thread-safety')
        if has_thread_safety:
            self.cxx.compile_flags += ['-Werror=thread-safety']
            self.config.available_features.add('thread-safety')
            self.lit_config.note("enabling thread-safety annotations")

    def configure_execute_external(self):
        # Choose between lit's internal shell pipeline runner and a real shell.
        # If LIT_USE_INTERNAL_SHELL is in the environment, we use that as the
        # default value. Otherwise we ask the target_info.
        use_lit_shell_default = os.environ.get('LIT_USE_INTERNAL_SHELL')
        if use_lit_shell_default is not None:
            use_lit_shell_default = use_lit_shell_default != '0'
        else:
            use_lit_shell_default = self.target_info.use_lit_shell_default()
        # Check for the command line parameter using the default value if it is
        # not present.
        use_lit_shell = self.get_lit_bool('use_lit_shell',
                                          use_lit_shell_default)
        self.execute_external = not use_lit_shell

    def configure_ccache(self):
        use_ccache_default = os.environ.get('LIBCXX_USE_CCACHE') is not None
        use_ccache = self.get_lit_bool('use_ccache', use_ccache_default)
        if use_ccache:
            self.cxx.use_ccache = True
            self.lit_config.note('enabling ccache')

    def add_deployment_feature(self, feature):
        (arch, name, version) = self.config.deployment
        self.config.available_features.add('%s=%s-%s' % (feature, arch, name))
        self.config.available_features.add('%s=%s' % (feature, name))
        self.config.available_features.add('%s=%s%s' % (feature, name, version))

    def configure_features(self):
        additional_features = self.get_lit_conf('additional_features')
        if additional_features:
            for f in additional_features.split(','):
                self.config.available_features.add(f.strip())
        self.target_info.add_locale_features(self.config.available_features)

        target_platform = self.target_info.platform()

        # Write an "available feature" that combines the triple when
        # use_system_cxx_lib is enabled. This is so that we can easily write
        # XFAIL markers for tests that are known to fail with versions of
        # libc++ as were shipped with a particular triple.
        if self.use_system_cxx_lib:
            self.config.available_features.add('with_system_cxx_lib')
            self.config.available_features.add(
                'with_system_cxx_lib=%s' % self.config.target_triple)

            # Add subcomponents individually.
            target_components = self.config.target_triple.split('-')
            for component in target_components:
                self.config.available_features.add(
                    'with_system_cxx_lib=%s' % component)

            # Add available features for more generic versions of the target
            # triple attached to  with_system_cxx_lib.
            if self.use_deployment:
                self.add_deployment_feature('with_system_cxx_lib')

        # Configure the availability feature. Availability is only enabled
        # with libc++, because other standard libraries do not provide
        # availability markup.
        if self.use_deployment and self.cxx_stdlib_under_test == 'libc++':
            self.config.available_features.add('availability')
            self.add_deployment_feature('availability')

        if platform.system() == 'Darwin':
            self.config.available_features.add('apple-darwin')

        # Insert the platform name into the available features as a lower case.
        self.config.available_features.add(target_platform)

        # Simulator testing can take a really long time for some of these tests
        # so add a feature check so we can REQUIRES: long_tests in them
        self.long_tests = self.get_lit_bool('long_tests')
        if self.long_tests is None:
            # Default to running long tests.
            self.long_tests = True
            self.lit_config.note(
                "inferred long_tests as: %r" % self.long_tests)

        if self.long_tests:
            self.config.available_features.add('long_tests')

        if not self.get_lit_bool('enable_filesystem', default=True):
            self.config.available_features.add('c++filesystem-disabled')
            self.config.available_features.add('dylib-has-no-filesystem')


        # Run a compile test for the -fsized-deallocation flag. This is needed
        # in test/std/language.support/support.dynamic/new.delete
        if self.cxx.hasCompileFlag('-fsized-deallocation'):
            self.config.available_features.add('-fsized-deallocation')

        if self.cxx.hasCompileFlag('-faligned-allocation'):
            self.config.available_features.add('-faligned-allocation')
        else:
            # FIXME remove this once more than just clang-4.0 support
            # C++17 aligned allocation.
            self.config.available_features.add('no-aligned-allocation')

        if self.cxx.hasCompileFlag('-fdelayed-template-parsing'):
            self.config.available_features.add('fdelayed-template-parsing')

        if self.get_lit_bool('has_libatomic', False):
            self.config.available_features.add('libatomic')

        macros = self._dump_macros_verbose()
        if '__cpp_if_constexpr' not in macros:
            self.config.available_features.add('libcpp-no-if-constexpr')

        if '__cpp_structured_bindings' not in macros:
            self.config.available_features.add('libcpp-no-structured-bindings')

        if '__cpp_deduction_guides' not in macros or \
                intMacroValue(macros['__cpp_deduction_guides']) < 201611:
            self.config.available_features.add('libcpp-no-deduction-guides')

        if self.is_windows:
            self.config.available_features.add('windows')
            if self.cxx_stdlib_under_test == 'libc++':
                # LIBCXX-WINDOWS-FIXME is the feature name used to XFAIL the
                # initial Windows failures until they can be properly diagnosed
                # and fixed. This allows easier detection of new test failures
                # and regressions. Note: New failures should not be suppressed
                # using this feature. (Also see llvm.org/PR32730)
                self.config.available_features.add('LIBCXX-WINDOWS-FIXME')

        # Attempt to detect the glibc version by querying for __GLIBC__
        # in 'features.h'.
        macros = self.cxx.dumpMacros(flags=['-include', 'features.h'])
        if isinstance(macros, dict) and '__GLIBC__' in macros:
            maj_v, min_v = (macros['__GLIBC__'], macros['__GLIBC_MINOR__'])
            self.config.available_features.add('glibc')
            self.config.available_features.add('glibc-%s' % maj_v)
            self.config.available_features.add('glibc-%s.%s' % (maj_v, min_v))

        # Support Objective-C++ only on MacOS and if the compiler supports it.
        if self.target_info.platform() == "darwin" and \
           self.target_info.is_host_macosx() and \
           self.cxx.hasCompileFlag(["-x", "objective-c++", "-fobjc-arc"]):
            self.config.available_features.add("objective-c++")

    def configure_compile_flags(self):
        self.configure_default_compile_flags()
        # Configure extra flags
        compile_flags_str = self.get_lit_conf('compile_flags', '')
        self.cxx.compile_flags += shlex.split(compile_flags_str)
        if self.is_windows:
            # FIXME: Can we remove this?
            self.cxx.compile_flags += ['-D_CRT_SECURE_NO_WARNINGS']
            # Required so that tests using min/max don't fail on Windows,
            # and so that those tests don't have to be changed to tolerate
            # this insanity.
            self.cxx.compile_flags += ['-DNOMINMAX']
        additional_flags = self.get_lit_conf('test_compiler_flags')
        if additional_flags:
            self.cxx.compile_flags += shlex.split(additional_flags)

    def configure_default_compile_flags(self):
        # Try and get the std version from the command line. Fall back to
        # default given in lit.site.cfg is not present. If default is not
        # present then force c++11.
        std = self.get_lit_conf('std')
        if not std:
            # Choose the newest possible language dialect if none is given.
            possible_stds = ['c++2a', 'c++17', 'c++1z', 'c++14', 'c++11',
                             'c++03']
            if self.cxx.type == 'gcc':
                maj_v, _, _ = self.cxx.version
                maj_v = int(maj_v)
                if maj_v < 7:
                    possible_stds.remove('c++1z')
                # FIXME: How many C++14 tests actually fail under GCC 5 and 6?
                # Should we XFAIL them individually instead?
                if maj_v <= 6:
                    possible_stds.remove('c++14')
            for s in possible_stds:
                if self.cxx.hasCompileFlag('-std=%s' % s):
                    std = s
                    self.lit_config.note(
                        'inferred language dialect as: %s' % std)
                    break
            if not std:
                self.lit_config.fatal(
                    'Failed to infer a supported language dialect from one of %r'
                    % possible_stds)
        self.cxx.compile_flags += ['-std={0}'.format(std)]
        std_feature = std.replace('gnu++', 'c++')
        std_feature = std.replace('1z', '17')
        self.config.available_features.add(std_feature)
        # Configure include paths
        self.configure_compile_flags_header_includes()
        self.target_info.add_cxx_compile_flags(self.cxx.compile_flags)
        # Configure feature flags.
        self.configure_compile_flags_exceptions()
        self.configure_compile_flags_rtti()
        self.configure_compile_flags_abi_version()
        enable_32bit = self.get_lit_bool('enable_32bit', False)
        if enable_32bit:
            self.cxx.flags += ['-m32']
        # Use verbose output for better errors
        self.cxx.flags += ['-v']
        sysroot = self.get_lit_conf('sysroot')
        if sysroot:
            self.cxx.flags += ['--sysroot=' + sysroot]
        gcc_toolchain = self.get_lit_conf('gcc_toolchain')
        if gcc_toolchain:
            self.cxx.flags += ['--gcc-toolchain=' + gcc_toolchain]
        # NOTE: the _DEBUG definition must preceed the triple check because for
        # the Windows build of libc++, the forced inclusion of a header requires
        # that _DEBUG is defined.  Incorrect ordering will result in -target
        # being elided.
        if self.is_windows and self.debug_build:
            self.cxx.compile_flags += ['-D_DEBUG']
        if self.use_target:
            if not self.cxx.addFlagIfSupported(
                    ['--target=' + self.config.target_triple]):
                self.lit_config.warning('use_target is true but --target is '\
                        'not supported by the compiler')
        if self.use_deployment:
            arch, name, version = self.config.deployment
            self.cxx.flags += ['-arch', arch]
            self.cxx.flags += ['-m' + name + '-version-min=' + version]

        # Add includes for support headers used in the tests.
        support_path = os.path.join(self.libcxx_src_root, 'test/support')
        self.cxx.compile_flags += ['-I' + support_path]

        # Add includes for the PSTL headers
        pstl_root = self.get_lit_conf('pstl_root')
        if pstl_root is not None:
            self.cxx.compile_flags += ['-I' + os.path.join(pstl_root, 'include')]
            self.cxx.compile_flags += ['-I' + os.path.join(pstl_root, 'test')]
            self.config.available_features.add('parallel-algorithms')

        # FIXME(EricWF): variant_size.pass.cpp requires a slightly larger
        # template depth with older Clang versions.
        self.cxx.addFlagIfSupported('-ftemplate-depth=270')

    def configure_compile_flags_header_includes(self):
        support_path = os.path.join(self.libcxx_src_root, 'test', 'support')
        self.configure_config_site_header()
        if self.cxx_stdlib_under_test != 'libstdc++' and \
           not self.is_windows:
            self.cxx.compile_flags += [
                '-include', os.path.join(support_path, 'nasty_macros.hpp')]
        if self.cxx_stdlib_under_test == 'msvc':
            self.cxx.compile_flags += [
                '-include', os.path.join(support_path,
                                         'msvc_stdlib_force_include.hpp')]
            pass
        if self.is_windows and self.debug_build and \
                self.cxx_stdlib_under_test != 'msvc':
            self.cxx.compile_flags += [
                '-include', os.path.join(support_path,
                                         'set_windows_crt_report_mode.h')
            ]
        cxx_headers = self.get_lit_conf('cxx_headers')
        if cxx_headers == '' or (cxx_headers is None
                                 and self.cxx_stdlib_under_test != 'libc++'):
            self.lit_config.note('using the system cxx headers')
            return
        self.cxx.compile_flags += ['-nostdinc++']
        if cxx_headers is None:
            cxx_headers = os.path.join(self.libcxx_src_root, 'include')
        if not os.path.isdir(cxx_headers):
            self.lit_config.fatal("cxx_headers='%s' is not a directory."
                                  % cxx_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_config_site_header(self):
        # Check for a possible __config_site in the build directory. We
        # use this if it exists.
        if self.libcxx_obj_root is None:
            return
        config_site_header = os.path.join(self.libcxx_obj_root, '__config_site')
        if not os.path.isfile(config_site_header):
            return
        contained_macros = self.parse_config_site_and_add_features(
            config_site_header)
        self.lit_config.note('Using __config_site header %s with macros: %r'
            % (config_site_header, contained_macros))
        # FIXME: This must come after the call to
        # 'parse_config_site_and_add_features(...)' in order for it to work.
        self.cxx.compile_flags += ['-include', config_site_header]

    def parse_config_site_and_add_features(self, header):
        """ parse_config_site_and_add_features - Deduce and add the test
            features that that are implied by the #define's in the __config_site
            header. Return a dictionary containing the macros found in the
            '__config_site' header.
        """
        # Parse the macro contents of __config_site by dumping the macros
        # using 'c++ -dM -E' and filtering the predefines.
        predefines = self._dump_macros_verbose()
        macros = self._dump_macros_verbose(header)
        feature_macros_keys = set(macros.keys()) - set(predefines.keys())
        feature_macros = {}
        for k in feature_macros_keys:
            feature_macros[k] = macros[k]
        # We expect the header guard to be one of the definitions
        assert '_LIBCPP_CONFIG_SITE' in feature_macros
        del feature_macros['_LIBCPP_CONFIG_SITE']
        # The __config_site header should be non-empty. Otherwise it should
        # have never been emitted by CMake.
        assert len(feature_macros) > 0
        # FIXME: This is a hack that should be fixed using module maps (or something)
        # If modules are enabled then we have to lift all of the definitions
        # in __config_site onto the command line.
        modules_enabled = self.get_modules_enabled()
        self.cxx.compile_flags += ['-Wno-macro-redefined']
        # Transform each macro name into the feature name used in the tests.
        # Ex. _LIBCPP_HAS_NO_THREADS -> libcpp-has-no-threads
        for m in feature_macros:
            if modules_enabled:
                define = '-D%s' % m
                if feature_macros[m]:
                    define += '=%s' % (feature_macros[m])
                self.cxx.compile_flags += [define]
            if m == '_LIBCPP_DISABLE_VISIBILITY_ANNOTATIONS' or \
               m == '_LIBCPP_HIDE_FROM_ABI_PER_TU_BY_DEFAULT':
                continue
            if m == '_LIBCPP_ABI_VERSION':
                self.config.available_features.add('libcpp-abi-version-v%s'
                    % feature_macros[m])
                continue
            if m == '_LIBCPP_NO_VCRUNTIME':
                self.config.available_features.add('libcpp-no-vcruntime')
                continue
            assert m.startswith('_LIBCPP_HAS_') or m.startswith('_LIBCPP_ABI_')
            m = m.lower()[1:].replace('_', '-')
            self.config.available_features.add(m)
        return feature_macros


    def configure_compile_flags_exceptions(self):
        enable_exceptions = self.get_lit_bool('enable_exceptions', True)
        if not enable_exceptions:
            self.config.available_features.add('libcpp-no-exceptions')
            self.cxx.compile_flags += ['-fno-exceptions']

    def configure_compile_flags_rtti(self):
        enable_rtti = self.get_lit_bool('enable_rtti', True)
        if not enable_rtti:
            self.config.available_features.add('libcpp-no-rtti')
            self.cxx.compile_flags += ['-fno-rtti', '-D_LIBCPP_NO_RTTI']

    def configure_compile_flags_abi_version(self):
        abi_version = self.get_lit_conf('abi_version', '').strip()
        abi_unstable = self.get_lit_bool('abi_unstable')
        # Only add the ABI version when it is non-default.
        # FIXME(EricWF): Get the ABI version from the "__config_site".
        if abi_version and abi_version != '1':
          self.cxx.compile_flags += ['-D_LIBCPP_ABI_VERSION=' + abi_version]
        if abi_unstable:
          self.config.available_features.add('libcpp-abi-unstable')
          self.cxx.compile_flags += ['-D_LIBCPP_ABI_UNSTABLE']

    def configure_filesystem_compile_flags(self):
        static_env = os.path.join(self.libcxx_src_root, 'test', 'std',
                                  'input.output', 'filesystems', 'Inputs', 'static_test_env')
        static_env = os.path.realpath(static_env)
        assert os.path.isdir(static_env)
        self.cxx.compile_flags += ['-DLIBCXX_FILESYSTEM_STATIC_TEST_ROOT="%s"' % static_env]

        dynamic_env = os.path.join(self.config.test_exec_root,
                                   'filesystem', 'Output', 'dynamic_env')
        dynamic_env = os.path.realpath(dynamic_env)
        if not os.path.isdir(dynamic_env):
            os.makedirs(dynamic_env)
        self.cxx.compile_flags += ['-DLIBCXX_FILESYSTEM_DYNAMIC_TEST_ROOT="%s"' % dynamic_env]
        self.exec_env['LIBCXX_FILESYSTEM_DYNAMIC_TEST_ROOT'] = ("%s" % dynamic_env)

        dynamic_helper = os.path.join(self.libcxx_src_root, 'test', 'support',
                                      'filesystem_dynamic_test_helper.py')
        assert os.path.isfile(dynamic_helper)

        self.cxx.compile_flags += ['-DLIBCXX_FILESYSTEM_DYNAMIC_TEST_HELPER="%s %s"'
                                   % (sys.executable, dynamic_helper)]


    def configure_link_flags(self):
        # Configure library path
        self.configure_link_flags_cxx_library_path()
        self.configure_link_flags_abi_library_path()

        # Configure libraries
        if self.cxx_stdlib_under_test == 'libc++':
            self.cxx.link_flags += ['-nodefaultlibs']
            # FIXME: Handle MSVCRT as part of the ABI library handling.
            if self.is_windows:
                self.cxx.link_flags += ['-nostdlib']
            self.configure_link_flags_cxx_library()
            self.configure_link_flags_abi_library()
            self.configure_extra_library_flags()
        elif self.cxx_stdlib_under_test == 'libstdc++':
            self.config.available_features.add('c++experimental')
            self.cxx.link_flags += ['-lstdc++fs', '-lm', '-pthread']
        elif self.cxx_stdlib_under_test == 'msvc':
            # FIXME: Correctly setup debug/release flags here.
            pass
        elif self.cxx_stdlib_under_test == 'cxx_default':
            self.cxx.link_flags += ['-pthread']
        else:
            self.lit_config.fatal('invalid stdlib under test')

        link_flags_str = self.get_lit_conf('link_flags', '')
        self.cxx.link_flags += shlex.split(link_flags_str)

    def configure_link_flags_cxx_library_path(self):
        if not self.use_system_cxx_lib:
            if self.cxx_library_root:
                self.cxx.link_flags += ['-L' + self.cxx_library_root]
                if self.is_windows and self.link_shared:
                    self.add_path(self.cxx.compile_env, self.cxx_library_root)
            if self.cxx_runtime_root:
                if not self.is_windows:
                    self.cxx.link_flags += ['-Wl,-rpath,' +
                                            self.cxx_runtime_root]
                elif self.is_windows and self.link_shared:
                    self.add_path(self.exec_env, self.cxx_runtime_root)
        elif os.path.isdir(str(self.use_system_cxx_lib)):
            self.cxx.link_flags += ['-L' + self.use_system_cxx_lib]
            if not self.is_windows:
                self.cxx.link_flags += ['-Wl,-rpath,' +
                                        self.use_system_cxx_lib]
            if self.is_windows and self.link_shared:
                self.add_path(self.cxx.compile_env, self.use_system_cxx_lib)
        additional_flags = self.get_lit_conf('test_linker_flags')
        if additional_flags:
            self.cxx.link_flags += shlex.split(additional_flags)

    def configure_link_flags_abi_library_path(self):
        # Configure ABI library paths.
        self.abi_library_root = self.get_lit_conf('abi_library_path')
        if self.abi_library_root:
            self.cxx.link_flags += ['-L' + self.abi_library_root]
            if not self.is_windows:
                self.cxx.link_flags += ['-Wl,-rpath,' + self.abi_library_root]
            else:
                self.add_path(self.exec_env, self.abi_library_root)

    def configure_link_flags_cxx_library(self):
        libcxx_experimental = self.get_lit_bool('enable_experimental', default=False)
        if libcxx_experimental:
            self.config.available_features.add('c++experimental')
            self.cxx.link_flags += ['-lc++experimental']
        if self.link_shared:
            self.cxx.link_flags += ['-lc++']
        else:
            cxx_library_root = self.get_lit_conf('cxx_library_root')
            if cxx_library_root:
                libname = self.make_static_lib_name('c++')
                abs_path = os.path.join(cxx_library_root, libname)
                assert os.path.exists(abs_path) and \
                       "static libc++ library does not exist"
                self.cxx.link_flags += [abs_path]
            else:
                self.cxx.link_flags += ['-lc++']

    def configure_link_flags_abi_library(self):
        cxx_abi = self.get_lit_conf('cxx_abi', 'libcxxabi')
        if cxx_abi == 'libstdc++':
            self.cxx.link_flags += ['-lstdc++']
        elif cxx_abi == 'libsupc++':
            self.cxx.link_flags += ['-lsupc++']
        elif cxx_abi == 'libcxxabi':
            # If the C++ library requires explicitly linking to libc++abi, or
            # if we're testing libc++abi itself (the test configs are shared),
            # then link it.
            testing_libcxxabi = self.get_lit_conf('name', '') == 'libc++abi'
            if self.target_info.allow_cxxabi_link() or testing_libcxxabi:
                libcxxabi_shared = self.get_lit_bool('libcxxabi_shared', default=True)
                if libcxxabi_shared:
                    self.cxx.link_flags += ['-lc++abi']
                else:
                    cxxabi_library_root = self.get_lit_conf('abi_library_path')
                    if cxxabi_library_root:
                        libname = self.make_static_lib_name('c++abi')
                        abs_path = os.path.join(cxxabi_library_root, libname)
                        self.cxx.link_flags += [abs_path]
                    else:
                        self.cxx.link_flags += ['-lc++abi']
        elif cxx_abi == 'libcxxrt':
            self.cxx.link_flags += ['-lcxxrt']
        elif cxx_abi == 'vcruntime':
            debug_suffix = 'd' if self.debug_build else ''
            self.cxx.link_flags += ['-l%s%s' % (lib, debug_suffix) for lib in
                                    ['vcruntime', 'ucrt', 'msvcrt']]
        elif cxx_abi == 'none' or cxx_abi == 'default':
            if self.is_windows:
                debug_suffix = 'd' if self.debug_build else ''
                self.cxx.link_flags += ['-lmsvcrt%s' % debug_suffix]
        else:
            self.lit_config.fatal(
                'C++ ABI setting %s unsupported for tests' % cxx_abi)

    def configure_extra_library_flags(self):
        if self.get_lit_bool('cxx_ext_threads', default=False):
            self.cxx.link_flags += ['-lc++external_threads']
        self.target_info.add_cxx_link_flags(self.cxx.link_flags)

    def configure_color_diagnostics(self):
        use_color = self.get_lit_conf('color_diagnostics')
        if use_color is None:
            use_color = os.environ.get('LIBCXX_COLOR_DIAGNOSTICS')
        if use_color is None:
            return
        if use_color != '':
            self.lit_config.fatal('Invalid value for color_diagnostics "%s".'
                                  % use_color)
        color_flag = '-fdiagnostics-color=always'
        # Check if the compiler supports the color diagnostics flag. Issue a
        # warning if it does not since color diagnostics have been requested.
        if not self.cxx.hasCompileFlag(color_flag):
            self.lit_config.warning(
                'color diagnostics have been requested but are not supported '
                'by the compiler')
        else:
            self.cxx.flags += [color_flag]

    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)
        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',
                                            default_enable_warnings)
        self.cxx.useWarnings(enable_warnings)
        self.cxx.warning_flags += [
            '-D_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER',
            '-Wall', '-Wextra', '-Werror'
        ]
        if self.cxx.hasWarningFlag('-Wuser-defined-warnings'):
            self.cxx.warning_flags += ['-Wuser-defined-warnings']
            self.config.available_features.add('diagnose-if-support')
        self.cxx.addWarningFlagIfSupported('-Wshadow')
        self.cxx.addWarningFlagIfSupported('-Wno-unused-command-line-argument')
        self.cxx.addWarningFlagIfSupported('-Wno-attributes')
        self.cxx.addWarningFlagIfSupported('-Wno-pessimizing-move')
        self.cxx.addWarningFlagIfSupported('-Wno-c++11-extensions')
        self.cxx.addWarningFlagIfSupported('-Wno-user-defined-literals')
        self.cxx.addWarningFlagIfSupported('-Wno-noexcept-type')
        self.cxx.addWarningFlagIfSupported('-Wno-aligned-allocation-unavailable')
        # These warnings should be enabled in order to support the MSVC
        # team using the test suite; They enable the warnings below and
        # expect the test suite to be clean.
        self.cxx.addWarningFlagIfSupported('-Wsign-compare')
        self.cxx.addWarningFlagIfSupported('-Wunused-variable')
        self.cxx.addWarningFlagIfSupported('-Wunused-parameter')
        self.cxx.addWarningFlagIfSupported('-Wunreachable-code')
        std = self.get_lit_conf('std', None)
        if std in ['c++98', 'c++03']:
            # The '#define static_assert' provided by libc++ in C++03 mode
            # causes an unused local typedef whenever it is used.
            self.cxx.addWarningFlagIfSupported('-Wno-unused-local-typedef')

    def configure_sanitizer(self):
        san = self.get_lit_conf('use_sanitizer', '').strip()
        if san:
            self.target_info.add_sanitizer_features(san, self.config.available_features)
            # Search for llvm-symbolizer along the compiler path first
            # and then along the PATH env variable.
            symbolizer_search_paths = os.environ.get('PATH', '')
            cxx_path = libcxx.util.which(self.cxx.path)
            if cxx_path is not None:
                symbolizer_search_paths = (
                    os.path.dirname(cxx_path) +
                    os.pathsep + symbolizer_search_paths)
            llvm_symbolizer = libcxx.util.which('llvm-symbolizer',
                                                symbolizer_search_paths)

            def add_ubsan():
                self.cxx.flags += ['-fsanitize=undefined',
                                   '-fno-sanitize=float-divide-by-zero',
                                   '-fno-sanitize-recover=all']
                self.exec_env['UBSAN_OPTIONS'] = 'print_stacktrace=1'
                self.config.available_features.add('ubsan')

            # Setup the sanitizer compile flags
            self.cxx.flags += ['-g', '-fno-omit-frame-pointer']
            if san == 'Address' or san == 'Address;Undefined' or san == 'Undefined;Address':
                self.cxx.flags += ['-fsanitize=address']
                if llvm_symbolizer is not None:
                    self.exec_env['ASAN_SYMBOLIZER_PATH'] = llvm_symbolizer
                # FIXME: Turn ODR violation back on after PR28391 is resolved
                # https://bugs.llvm.org/show_bug.cgi?id=28391
                self.exec_env['ASAN_OPTIONS'] = 'detect_odr_violation=0'
                self.config.available_features.add('asan')
                self.config.available_features.add('sanitizer-new-delete')
                self.cxx.compile_flags += ['-O1']
                if san == 'Address;Undefined' or san == 'Undefined;Address':
                    add_ubsan()
            elif san == 'Memory' or san == 'MemoryWithOrigins':
                self.cxx.flags += ['-fsanitize=memory']
                if san == 'MemoryWithOrigins':
                    self.cxx.compile_flags += [
                        '-fsanitize-memory-track-origins']
                if llvm_symbolizer is not None:
                    self.exec_env['MSAN_SYMBOLIZER_PATH'] = llvm_symbolizer
                self.config.available_features.add('msan')
                self.config.available_features.add('sanitizer-new-delete')
                self.cxx.compile_flags += ['-O1']
            elif san == 'Undefined':
                add_ubsan()
                self.cxx.compile_flags += ['-O2']
            elif san == 'Thread':
                self.cxx.flags += ['-fsanitize=thread']
                self.config.available_features.add('tsan')
                self.config.available_features.add('sanitizer-new-delete')
            else:
                self.lit_config.fatal('unsupported value for '
                                      'use_sanitizer: {0}'.format(san))
            san_lib = self.get_lit_conf('sanitizer_library')
            if san_lib:
                self.cxx.link_flags += [
                    san_lib, '-Wl,-rpath,%s' % os.path.dirname(san_lib)]

    def configure_coverage(self):
        self.generate_coverage = self.get_lit_bool('generate_coverage', False)
        if self.generate_coverage:
            self.cxx.flags += ['-g', '--coverage']
            self.cxx.compile_flags += ['-O0']

    def configure_coroutines(self):
        if self.cxx.hasCompileFlag('-fcoroutines-ts'):
            macros = self._dump_macros_verbose(flags=['-fcoroutines-ts'])
            if '__cpp_coroutines' not in macros:
                self.lit_config.warning('-fcoroutines-ts is supported but '
                    '__cpp_coroutines is not defined')
            # Consider coroutines supported only when the feature test macro
            # reflects a recent value.
            if intMacroValue(macros['__cpp_coroutines']) >= 201703:
                self.config.available_features.add('fcoroutines-ts')

    def configure_modules(self):
        modules_flags = ['-fmodules']
        if platform.system() != 'Darwin':
            modules_flags += ['-Xclang', '-fmodules-local-submodule-visibility']
        supports_modules = self.cxx.hasCompileFlag(modules_flags)
        enable_modules = self.get_modules_enabled()
        if enable_modules and not supports_modules:
            self.lit_config.fatal(
                '-fmodules is enabled but not supported by the compiler')
        if not supports_modules:
            return
        self.config.available_features.add('modules-support')
        module_cache = os.path.join(self.config.test_exec_root,
                                   'modules.cache')
        module_cache = os.path.realpath(module_cache)
        if os.path.isdir(module_cache):
            shutil.rmtree(module_cache)
        os.makedirs(module_cache)
        self.cxx.modules_flags = modules_flags + \
            ['-fmodules-cache-path=' + module_cache]
        if enable_modules:
            self.config.available_features.add('-fmodules')
            self.cxx.useModules()

    def configure_substitutions(self):
        sub = self.config.substitutions
        cxx_path = pipes.quote(self.cxx.path)
        # Configure compiler substitutions
        sub.append(('%cxx', cxx_path))
        sub.append(('%libcxx_src_root', self.libcxx_src_root))
        # Configure flags substitutions
        flags_str = ' '.join([pipes.quote(f) for f in self.cxx.flags])
        compile_flags_str = ' '.join([pipes.quote(f) for f in self.cxx.compile_flags])
        link_flags_str = ' '.join([pipes.quote(f) for f in self.cxx.link_flags])
        all_flags = '%s %s %s' % (flags_str, compile_flags_str, link_flags_str)
        sub.append(('%flags', flags_str))
        sub.append(('%compile_flags', compile_flags_str))
        sub.append(('%link_flags', link_flags_str))
        sub.append(('%all_flags', all_flags))
        if self.cxx.isVerifySupported():
            verify_str = ' ' + ' '.join(self.cxx.verify_flags) + ' '
            sub.append(('%verify', verify_str))
        # Add compile and link shortcuts
        compile_str = (cxx_path + ' -o %t.o %s -c ' + flags_str
                       + ' ' + compile_flags_str)
        link_str = (cxx_path + ' -o %t.exe %t.o ' + flags_str + ' '
                    + link_flags_str)
        assert type(link_str) is str
        build_str = cxx_path + ' -o %t.exe %s ' + all_flags
        if self.cxx.use_modules:
            sub.append(('%compile_module', compile_str))
            sub.append(('%build_module', build_str))
        elif self.cxx.modules_flags is not None:
            modules_str = ' '.join(self.cxx.modules_flags) + ' '
            sub.append(('%compile_module', compile_str + ' ' + modules_str))
            sub.append(('%build_module', build_str + ' ' + modules_str))
        sub.append(('%compile', compile_str))
        sub.append(('%link', link_str))
        sub.append(('%build', build_str))
        # Configure exec prefix substitutions.
        # Configure run env substitution.
        sub.append(('%run', '%t.exe'))
        # Configure not program substitutions
        not_py = os.path.join(self.libcxx_src_root, 'utils', 'not.py')
        not_str = '%s %s ' % (pipes.quote(sys.executable), pipes.quote(not_py))
        sub.append(('not ', not_str))

    def can_use_deployment(self):
        # Check if the host is on an Apple platform using clang.
        if not self.target_info.platform() == "darwin":
            return False
        if not self.target_info.is_host_macosx():
            return False
        if not self.cxx.type.endswith('clang'):
            return False
        return True

    def configure_triple(self):
        # Get or infer the target triple.
        target_triple = self.get_lit_conf('target_triple')
        self.use_target = self.get_lit_bool('use_target', False)
        if self.use_target and target_triple:
            self.lit_config.warning('use_target is true but no triple is specified')

        # Use deployment if possible.
        self.use_deployment = not self.use_target and self.can_use_deployment()
        if self.use_deployment:
            return

        # Save the triple (and warn on Apple platforms).
        self.config.target_triple = target_triple
        if self.use_target and 'apple' in target_triple:
            self.lit_config.warning('consider using arch and platform instead'
                                    ' of target_triple on Apple platforms')

        # If no target triple was given, try to infer it from the compiler
        # under test.
        if not self.config.target_triple:
            target_triple = self.cxx.getTriple()
            # Drop sub-major version components from the triple, because the
            # current XFAIL handling expects exact matches for feature checks.
            # Example: x86_64-apple-darwin14.0.0 -> x86_64-apple-darwin14
            # The 5th group handles triples greater than 3 parts
            # (ex x86_64-pc-linux-gnu).
            target_triple = re.sub(r'([^-]+)-([^-]+)-([^.]+)([^-]*)(.*)',
                                   r'\1-\2-\3\5', target_triple)
            # linux-gnu is needed in the triple to properly identify linuxes
            # that use GLIBC. Handle redhat and opensuse triples as special
            # cases and append the missing `-gnu` portion.
            if (target_triple.endswith('redhat-linux') or
                target_triple.endswith('suse-linux')):
                target_triple += '-gnu'
            self.config.target_triple = target_triple
            self.lit_config.note(
                "inferred target_triple as: %r" % self.config.target_triple)

    def configure_deployment(self):
        assert not self.use_deployment is None
        assert not self.use_target is None
        if not self.use_deployment:
            # Warn about ignored parameters.
            if self.get_lit_conf('arch'):
                self.lit_config.warning('ignoring arch, using target_triple')
            if self.get_lit_conf('platform'):
                self.lit_config.warning('ignoring platform, using target_triple')
            return

        assert not self.use_target
        assert self.target_info.is_host_macosx()

        # Always specify deployment explicitly on Apple platforms, since
        # otherwise a platform is picked up from the SDK.  If the SDK version
        # doesn't match the system version, tests that use the system library
        # may fail spuriously.
        arch = self.get_lit_conf('arch')
        if not arch:
            arch = self.cxx.getTriple().split('-', 1)[0]
            self.lit_config.note("inferred arch as: %r" % arch)

        inferred_platform, name, version = self.target_info.get_platform()
        if inferred_platform:
            self.lit_config.note("inferred platform as: %r" % (name + version))
        self.config.deployment = (arch, name, version)

        # Set the target triple for use by lit.
        self.config.target_triple = arch + '-apple-' + name + version
        self.lit_config.note(
            "computed target_triple as: %r" % self.config.target_triple)

        # If we're testing a system libc++ as opposed to the upstream LLVM one,
        # take the version of the system libc++ into account to compute which
        # features are enabled/disabled. Otherwise, disable availability markup,
        # which is not relevant for non-shipped flavors of libc++.
        if self.use_system_cxx_lib:
            # Dylib support for shared_mutex was added in macosx10.12.
            if name == 'macosx' and version in ('10.%s' % v for v in range(7, 12)):
                self.config.available_features.add('dylib-has-no-shared_mutex')
                self.lit_config.note("shared_mutex is not supported by the deployment target")
            # Throwing bad_optional_access, bad_variant_access and bad_any_cast is
            # supported starting in macosx10.14.
            if name == 'macosx' and version in ('10.%s' % v for v in range(7, 14)):
                self.config.available_features.add('dylib-has-no-bad_optional_access')
                self.lit_config.note("throwing bad_optional_access is not supported by the deployment target")

                self.config.available_features.add('dylib-has-no-bad_variant_access')
                self.lit_config.note("throwing bad_variant_access is not supported by the deployment target")

                self.config.available_features.add('dylib-has-no-bad_any_cast')
                self.lit_config.note("throwing bad_any_cast is not supported by the deployment target")
            # Filesystem is support on Apple platforms starting with macosx10.15.
            if name == 'macosx' and version in ('10.%s' % v for v in range(7, 15)):
                self.config.available_features.add('dylib-has-no-filesystem')
                self.lit_config.note("the deployment target does not support <filesystem>")
        else:
            self.cxx.flags += ['-D_LIBCPP_DISABLE_AVAILABILITY']

    def configure_env(self):
        self.target_info.configure_env(self.exec_env)

    def add_path(self, dest_env, new_path):
        if 'PATH' not in dest_env:
            dest_env['PATH'] = new_path
        else:
            split_char = ';' if self.is_windows else ':'
            dest_env['PATH'] = '%s%s%s' % (new_path, split_char,
                                           dest_env['PATH'])