gecko-dev/build/moz.configure/toolchain.configure

# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
# vim: set filetype=python:
# This Source Code Form is subject to the terms of the Mozilla Public
# License, v. 2.0. If a copy of the MPL was not distributed with this
# file, You can obtain one at http://mozilla.org/MPL/2.0/.

# yasm detection
# ==============================================================
yasm = check_prog('YASM', ['yasm'], allow_missing=True)

@depends_if(yasm)
@checking('yasm version')
def yasm_version(yasm):
    version = check_cmd_output(
        yasm, '--version',
        onerror=lambda: die('Failed to get yasm version.')
    ).splitlines()[0].split()[1]
    return Version(version)

# Until we move all the yasm consumers out of old-configure.
# bug 1257904
add_old_configure_assignment('_YASM_MAJOR_VERSION',
                             delayed_getattr(yasm_version, 'major'))
add_old_configure_assignment('_YASM_MINOR_VERSION',
                             delayed_getattr(yasm_version, 'minor'))

@depends(yasm, target)
def yasm_asflags(yasm, target):
    if yasm:
        asflags = {
            ('OSX', 'x86'): '-f macho32',
            ('OSX', 'x86_64'): '-f macho64',
            ('WINNT', 'x86'): '-f win32',
            ('WINNT', 'x86_64'): '-f x64',
        }.get((target.os, target.cpu), None)
        if asflags is None:
            # We're assuming every x86 platform we support that's
            # not Windows or Mac is ELF.
            if target.cpu == 'x86':
                asflags = '-f elf32'
            elif target.cpu == 'x86_64':
                asflags = '-f elf64'
        if asflags:
            asflags += ' -rnasm -pnasm'
        return asflags

set_config('YASM_ASFLAGS', yasm_asflags)

@depends(yasm_asflags)
def have_yasm(value):
    if value:
        return True

set_config('HAVE_YASM', have_yasm)
# Until the YASM variable is not necessary in old-configure.
add_old_configure_assignment('YASM', have_yasm)


# Android NDK
# ==============================================================

@depends('--disable-compile-environment', build_project, gonkdir, '--help')
def android_ndk_include(compile_env, build_project, gonkdir, _):
    if compile_env and (gonkdir or build_project in ('mobile/android', 'js')):
        return 'android-ndk.configure'

include(android_ndk_include)


# MacOS deployment target version
# ==============================================================
# This needs to happen before any compilation test is done.

option('--enable-macos-target', env='MACOSX_DEPLOYMENT_TARGET', nargs=1,
       default='10.7', help='Set the minimum MacOS version needed at runtime')

@depends('--enable-macos-target', target)
@imports(_from='os', _import='environ')
def macos_target(value, target):
    if value and target.os == 'OSX':
        # Ensure every compiler process we spawn uses this value.
        environ['MACOSX_DEPLOYMENT_TARGET'] = value[0]
        return value[0]
    if value and value.origin != 'default':
        die('--enable-macos-target cannot be used when targeting %s',
            target.os)


set_config('MACOSX_DEPLOYMENT_TARGET', macos_target)
add_old_configure_assignment('MACOSX_DEPLOYMENT_TARGET', macos_target)


# Compiler wrappers
# ==============================================================
# Normally, we'd use js_option and automatically have those variables
# propagated to js/src, but things are complicated by possible additional
# wrappers in CC/CXX, and by other subconfigures that do not handle those
# options and do need CC/CXX altered.
option('--with-compiler-wrapper', env='COMPILER_WRAPPER', nargs=1,
       help='Enable compiling with wrappers such as distcc and ccache')

option('--with-ccache', env='CCACHE', nargs='?',
       help='Enable compiling with ccache')

@depends_if('--with-ccache')
def ccache(value):
    if len(value):
        return value
    # If --with-ccache was given without an explicit value, we default to
    # 'ccache'.
    return 'ccache'

ccache = check_prog('CCACHE', progs=(), input=ccache)

@depends_if(ccache)
def using_ccache(ccache):
    return True

set_config('MOZ_USING_CCACHE', using_ccache)

@depends('--with-compiler-wrapper', ccache)
@imports(_from='mozbuild.shellutil', _import='split', _as='shell_split')
def compiler_wrapper(wrapper, ccache):
    if wrapper:
        raw_wrapper = wrapper[0]
        wrapper = shell_split(raw_wrapper)
        wrapper_program = find_program(wrapper[0])
        if not wrapper_program:
            die('Cannot find `%s` from the given compiler wrapper `%s`',
                wrapper[0], raw_wrapper)
        wrapper[0] = wrapper_program

    if ccache:
        if wrapper:
            return tuple([ccache] + wrapper)
        else:
            return (ccache,)
    elif wrapper:
        return tuple(wrapper)

add_old_configure_assignment('COMPILER_WRAPPER', compiler_wrapper)

@depends_if(compiler_wrapper)
def using_compiler_wrapper(compiler_wrapper):
    return True

set_config('MOZ_USING_COMPILER_WRAPPER', using_compiler_wrapper)


# Cross-compilation related things.
# ==============================================================
js_option('--with-toolchain-prefix', env='TOOLCHAIN_PREFIX', nargs=1,
          help='Prefix for the target toolchain')

@depends('--with-toolchain-prefix', target, host, cross_compiling)
def toolchain_prefix(value, target, host, cross_compiling):
    if value:
        return value[0]
    # Special case x86-64 <-> x86 cross compiling until we have the right tests
    # in moz.configure land.
    if cross_compiling and not all(i.cpu in ('x86_64', 'x86')
                                   for i in (target, host)):
        return '%s-' % target.toolchain

set_config('TOOLCHAIN_PREFIX', toolchain_prefix)
add_old_configure_assignment('TOOLCHAIN_PREFIX', toolchain_prefix)


# Compilers
# ==============================================================
@imports('os')
@imports('subprocess')
@imports(_from='mozbuild.configure.util', _import='LineIO')
@imports(_from='tempfile', _import='mkstemp')
def try_preprocess(compiler, language, source):
    suffix = {
        'C': '.c',
        'C++': '.cpp',
    }[language]

    fd, path = mkstemp(prefix='conftest.', suffix=suffix)
    try:
        source = source.encode('ascii', 'replace')

        log.debug('Creating `%s` with content:', path)
        with LineIO(lambda l: log.debug('| %s', l)) as out:
            out.write(source)

        os.write(fd, source)
        os.close(fd)
        cmd = compiler + ['-E', path]
        return check_cmd_output(*cmd)
    finally:
        os.remove(path)


@imports(_from='mozbuild.configure.constants', _import='CompilerType')
@imports(_from='mozbuild.configure.constants',
         _import='CPU_preprocessor_checks')
@imports(_from='mozbuild.configure.constants',
         _import='kernel_preprocessor_checks')
@imports(_from='textwrap', _import='dedent')
def get_compiler_info(compiler, language):
    '''Returns information about the given `compiler` (command line in the
    form of a list or tuple), in the given `language`.

    The returned information includes:
    - the compiler type (msvc, clang-cl, clang or gcc)
    - the compiler version
    - the compiler supported language
    - the compiler supported language version
    '''
    # Note: MSVC doesn't expose __STDC_VERSION__. It does expose __STDC__,
    # but only when given the -Za option, which disables compiler
    # extensions.
    # Note: We'd normally do a version check for clang, but versions of clang
    # in Xcode have a completely different versioning scheme despite exposing
    # the version with the same defines.
    # So instead, we make things such that the version is missing when the
    # clang used is below the minimum supported version (currently clang 3.6).
    # We then only include the version information when the C++ compiler
    # matches the feature check, so that an unsupported version of clang would
    # have no version number.
    check = dedent('''\
        #if defined(_MSC_VER)
        #if defined(__clang__)
        %COMPILER clang-cl
        %VERSION _MSC_FULL_VER
        #else
        %COMPILER msvc
        %VERSION _MSC_FULL_VER
        #endif
        #elif defined(__clang__)
        %COMPILER clang
        #  if !__cplusplus || __has_feature(cxx_alignof)
        %VERSION __clang_major__.__clang_minor__.__clang_patchlevel__
        #  endif
        #elif defined(__GNUC__)
        %COMPILER gcc
        %VERSION __GNUC__.__GNUC_MINOR__.__GNUC_PATCHLEVEL__
        #endif

        #if __cplusplus
        %cplusplus __cplusplus
        #elif __STDC_VERSION__
        %STDC_VERSION __STDC_VERSION__
        #elif __STDC__
        %STDC_VERSION 198900L
        #endif
    ''')

    # While we're doing some preprocessing, we might as well do some more
    # preprocessor-based tests at the same time, to check the toolchain
    # matches what we want.
    for name, preprocessor_checks in (
        ('CPU', CPU_preprocessor_checks),
        ('KERNEL', kernel_preprocessor_checks),
    ):
        for n, (value, condition) in enumerate(preprocessor_checks.iteritems()):
            check += dedent('''\
                #%(if)s %(condition)s
                %%%(name)s %(value)s
            ''' % {
                'if': 'elif' if n else 'if',
                'condition': condition,
                'name': name,
                'value': value,
            })
        check += '#endif\n'

    result = try_preprocess(compiler, language, check)

    if not result:
        raise FatalCheckError(
            'Unknown compiler or compiler not supported.')

    data = {}
    for line in result.splitlines():
        if line.startswith('%'):
            k, _, v = line.partition(' ')
            k = k.lstrip('%')
            data[k] = v.replace(' ', '')
            log.debug('%s = %s', k, data[k])

    try:
        type = CompilerType(data['COMPILER'])
    except:
        raise FatalCheckError(
            'Unknown compiler or compiler not supported.')

    cplusplus = int(data.get('cplusplus', '0L').rstrip('L'))
    stdc_version = int(data.get('STDC_VERSION', '0L').rstrip('L'))

    version = data.get('VERSION')
    if version and type in ('msvc', 'clang-cl'):
        msc_ver = version
        version = msc_ver[0:2]
        if len(msc_ver) > 2:
            version += '.' + msc_ver[2:4]
        if len(msc_ver) > 4:
            version += '.' + msc_ver[4:]

    if version:
        version = Version(version)

    return namespace(
        type=type,
        version=version,
        cpu=data.get('CPU'),
        kernel=data.get('KERNEL'),
        language='C++' if cplusplus else 'C',
        language_version=cplusplus if cplusplus else stdc_version,
    )


@imports(_from='mozbuild.shellutil', _import='quote')
def check_compiler(compiler, language, target):
    info = get_compiler_info(compiler, language)

    flags = []

    def append_flag(flag):
        if flag not in flags:
            if info.type == 'clang-cl':
                flags.append('-Xclang')
            flags.append(flag)

    # Check language standards
    # --------------------------------------------------------------------
    if language != info.language:
        raise FatalCheckError(
            '`%s` is not a %s compiler.' % (quote(*compiler), language))

    # Note: We do a strict version check because there sometimes are backwards
    # incompatible changes in the standard, and not all code that compiles as
    # C99 compiles as e.g. C11 (as of writing, this is true of libnestegg, for
    # example)
    if info.language == 'C' and info.language_version != 199901:
        if info.type in ('clang-cl', 'clang', 'gcc'):
            append_flag('-std=gnu99')

    # Note: MSVC, while supporting C++11, still reports 199711L for __cplusplus.
    # Note: this is a strict version check because we used to always add
    # -std=gnu++11.
    if info.language == 'C++' and info.language_version != 201103:
        if info.type in ('clang-cl', 'clang', 'gcc'):
            append_flag('-std=gnu++11')

    # We force clang-cl to emulate Visual C++ 2013 Update 3 with fallback to
    # cl.exe.
    if info.type == 'clang-cl' and info.version != '18.00.30723':
        # Those flags are direct clang-cl flags that don't need -Xclang, add
        # them directly.
        flags.append('-fms-compatibility-version=18.00.30723')
        flags.append('-fallback')

    # Check compiler target
    # --------------------------------------------------------------------
    if not info.cpu or info.cpu != target.cpu:
        if info.type == 'clang':
            append_flag('--target=%s' % target.toolchain)
        elif info.type == 'gcc':
            same_arch_different_bits = (
                ('x86', 'x86_64'),
                ('ppc', 'ppc64'),
                ('sparc', 'sparc64'),
            )
            if (target.cpu, info.cpu) in same_arch_different_bits:
                append_flag('-m32')
            elif (info.cpu, target.cpu) in same_arch_different_bits:
                append_flag('-m64')

    if not info.kernel or info.kernel != target.kernel:
        if info.type == 'clang':
            append_flag('--target=%s' % target.toolchain)

    return namespace(
        type=info.type,
        version=info.version,
        target_cpu=info.cpu,
        target_kernel=info.kernel,
        flags=flags,
    )


@template
def default_c_compilers(host_or_target):
    '''Template defining the set of default C compilers for the host and
    target platforms.
    `host_or_target` is either `host` or `target` (the @depends functions
    from init.configure.
    '''
    assert host_or_target in (host, target)

    @depends(host_or_target, host, toolchain_prefix)
    def default_c_compilers(host_or_target, host, toolchain_prefix):
        if host_or_target.kernel == 'WINNT':
            return ('cl', 'clang-cl', 'gcc', 'clang')
        if host_or_target.kernel == 'Darwin':
            return ('clang',)
        if host_or_target != host:  # cross compilation
            return ('%sgcc' % toolchain_prefix, 'gcc', 'clang')
        return ('gcc', 'clang')

    return default_c_compilers


@template
def default_cxx_compilers(c_compiler):
    '''Template defining the set of default C++ compilers for the host and
    target platforms.
    `c_compiler` is the @depends function returning a Compiler instance for
    the desired platform.

    Because the build system expects the C and C++ compilers to be from the
    same compiler suite, we derive the default C++ compilers from the C
    compiler that was found if none was provided.
    '''

    @depends(c_compiler)
    def default_cxx_compilers(c_compiler):
        dir = os.path.dirname(c_compiler.compiler)
        file = os.path.basename(c_compiler.compiler)

        if c_compiler.type == 'gcc':
            return (os.path.join(dir, file.replace('gcc', 'g++')),)

        if c_compiler.type == 'clang':
            return (os.path.join(dir, file.replace('clang', 'clang++')),)

        return (c_compiler.compiler,)

    return default_cxx_compilers


@template
def compiler(language, host_or_target, c_compiler=None, other_compiler=None,
             other_c_compiler=None):
    '''Template handling the generic base checks for the compiler for the
    given `language` on the given platform (`host_or_target`).
    `host_or_target` is either `host` or `target` (the @depends functions
    from init.configure.
    When the language is 'C++', `c_compiler` is the result of the `compiler`
    template for the language 'C' for the same `host_or_target`.
    When `host_or_target` is `host`, `other_compiler` is the result of the
    `compiler` template for the same `language` for `target`.
    When `host_or_target` is `host` and the language is 'C++',
    `other_c_compiler` is the result of the `compiler` template for the
    language 'C' for `target`.
    '''
    assert host_or_target in (host, target)
    assert language in ('C', 'C++')
    assert language == 'C' or c_compiler
    assert host_or_target == target or other_compiler
    assert language == 'C' or host_or_target == target or other_c_compiler

    host_or_target_str = {
        host: 'host',
        target: 'target',
    }[host_or_target]

    var = {
        ('C', target): 'CC',
        ('C++', target): 'CXX',
        ('C', host): 'HOST_CC',
        ('C++', host): 'HOST_CXX',
    }[language, host_or_target]

    default_compilers = {
        'C': lambda: default_c_compilers(host_or_target),
        'C++': lambda: default_cxx_compilers(c_compiler),
    }[language]()

    what='the %s %s compiler' % (host_or_target_str, language),

    option(env=var, nargs=1, help='Path to %s' % what)

    # Handle the compiler given by the user through one of the CC/CXX/HOST_CC/
    # HOST_CXX variables.
    @depends_if(var)
    @imports(_from='itertools', _import='takewhile')
    @imports(_from='mozbuild.shellutil', _import='split', _as='shell_split')
    def provided_compiler(cmd):
        # Historically, the compiler variables have contained more than the
        # path to the compiler itself. So for backwards compatibility, try to
        # find what is what in there, assuming the first dash-prefixed item is
        # a compiler option, the item before that is the compiler, and anything
        # before that is a compiler wrapper.
        cmd = shell_split(cmd[0])

        without_flags = list(takewhile(lambda x: not x.startswith('-'), cmd))

        return namespace(
            wrapper=without_flags[:-1],
            compiler=without_flags[-1],
            flags=cmd[len(without_flags):],
        )

    # Derive the host compiler from the corresponding target compiler when no
    # explicit compiler was given and we're not cross compiling. For the C++
    # compiler, though, prefer to derive from the host C compiler when it
    # doesn't match the target C compiler.
    # As a special case, since clang supports all kinds of targets in the same
    # executable, when cross compiling with clang, default to the same compiler
    # as the target compiler, resetting flags.
    if host_or_target == host:
        args = (c_compiler, other_c_compiler) if other_c_compiler else ()

        @depends(provided_compiler, other_compiler, cross_compiling, *args)
        def provided_compiler(value, other_compiler, cross_compiling, *args):
            if value:
                return value
            c_compiler, other_c_compiler = args if args else (None, None)
            if not cross_compiling and c_compiler == other_c_compiler:
                return other_compiler
            if cross_compiling and other_compiler.type == 'clang':
                return namespace(**{
                    k: [] if k == 'flags' else v
                    for k, v in other_compiler.__dict__.iteritems()
                })

    # Normally, we'd use `var` instead of `_var`, but the interaction with
    # old-configure complicates things, and for now, we a) can't take the plain
    # result from check_prog as CC/CXX/HOST_CC/HOST_CXX and b) have to let
    # old-configure AC_SUBST it (because it's autoconf doing it, not us)
    compiler = check_prog('_%s' % var, what=what, progs=default_compilers,
                          input=delayed_getattr(provided_compiler, 'compiler'))

    @depends(compiler, provided_compiler, compiler_wrapper, host_or_target)
    @checking('whether %s can be used' % what, lambda x: bool(x))
    @imports(_from='mozbuild.shellutil', _import='quote')
    def valid_compiler(compiler, provided_compiler, compiler_wrapper,
                       host_or_target):
        wrapper = list(compiler_wrapper or ())
        if provided_compiler:
            provided_wrapper = list(provided_compiler.wrapper)
            # When doing a subconfigure, the compiler is set by old-configure
            # and it contains the wrappers from --with-compiler-wrapper and
            # --with-ccache.
            if provided_wrapper[:len(wrapper)] == wrapper:
                provided_wrapper = provided_wrapper[len(wrapper):]
            wrapper.extend(provided_wrapper)
            flags = provided_compiler.flags
        else:
            flags = []

        # Ideally, we'd always use the absolute path, but unfortunately, on
        # Windows, the compiler is very often in a directory containing spaces.
        # Unfortunately, due to the way autoconf does its compiler tests with
        # eval, that doesn't work out. So in that case, check that the
        # compiler can still be found in $PATH, and use the file name instead
        # of the full path.
        if quote(compiler) != compiler:
            full_path = os.path.abspath(compiler)
            compiler = os.path.basename(compiler)
            found_compiler = find_program(compiler)
            if not found_compiler:
                die('%s is not in your $PATH'
                    % quote(os.path.dirname(full_path)))
            if os.path.normcase(find_program(compiler)) != os.path.normcase(
                    full_path):
                die('Found `%s` before `%s` in your $PATH. '
                    'Please reorder your $PATH.',
                    quote(os.path.dirname(found_compiler)),
                    quote(os.path.dirname(full_path)))

        info = check_compiler(wrapper + [compiler] + flags, language,
                              host_or_target)

        # Check that the additional flags we got are enough to not require any
        # more flags.
        if info.flags:
            flags += info.flags
            info = check_compiler(wrapper + [compiler] + flags, language,
                                  host_or_target)

        if not info.target_cpu or info.target_cpu != host_or_target.cpu:
            raise FatalCheckError(
                '%s %s compiler target CPU (%s) does not match --%s CPU (%s)'
                % (host_or_target_str.capitalize(), language,
                   info.target_cpu or 'unknown', host_or_target_str,
                   host_or_target.raw_cpu))

        if not info.target_kernel or (info.target_kernel !=
                                      host_or_target.kernel):
            raise FatalCheckError(
                '%s %s compiler target kernel (%s) does not match --%s kernel (%s)'
                % (host_or_target_str.capitalize(), language,
                   info.target_kernel or 'unknown', host_or_target_str,
                   host_or_target.kernel))

        if info.flags:
            raise FatalCheckError(
                'Unknown compiler or compiler not supported.')

        # Compiler version checks
        # ===================================================
        # Check the compiler version here instead of in `compiler_version` so
        # that the `checking` message doesn't pretend the compiler can be used
        # to then bail out one line later.
        if info.type == 'gcc' and info.version < '4.8.0':
            raise FatalCheckError(
                'Only GCC 4.8 or newer is supported (found version %s).'
                % info.version)

        # If you want to bump the version check here search for
        # __cpp_static_assert above, and see the associated comment.
        if info.type == 'clang' and not info.version:
            raise FatalCheckError(
                'Only clang/llvm 3.6 or newer is supported.')

        if info.type == 'msvc':
            if info.version < '19.00.23918':
                raise FatalCheckError(
                    'This version (%s) of the MSVC compiler is not '
                    'supported.\n'
                    'You must install Visual C++ 2015 Update 2 or newer in '
                    'order to build.\n'
                    'See https://developer.mozilla.org/en/'
                    'Windows_Build_Prerequisites' % info.version)

        return namespace(
            wrapper=wrapper,
            compiler=compiler,
            flags=flags,
            type=info.type,
            version=info.version,
        )

    @depends(valid_compiler)
    @checking('%s version' % what)
    def compiler_version(compiler):
        return compiler.version

    if language == 'C++':
        @depends(valid_compiler, c_compiler)
        def valid_compiler(compiler, c_compiler):
            if compiler.type != c_compiler.type:
                die('The %s C compiler is %s, while the %s C++ compiler is '
                    '%s. Need to use the same compiler suite.',
                    host_or_target_str, c_compiler.type,
                    host_or_target_str, compiler.type)

            if compiler.version != c_compiler.version:
                die('The %s C compiler is version %s, while the %s C++ '
                    'compiler is version %s. Need to use the same compiler '
                    'version.',
                    host_or_target_str, c_compiler.version,
                    host_or_target_str, compiler.version)
            return compiler

    # Set CC/CXX/HOST_CC/HOST_CXX for old-configure, which needs the wrapper
    # and the flags that were part of the user input for those variables to
    # be provided.
    add_old_configure_assignment(var, depends_if(valid_compiler)(
        lambda x: list(x.wrapper) + [x.compiler] + list(x.flags)))

    # Set CC_TYPE/CC_VERSION/HOST_CC_TYPE/HOST_CC_VERSION to allow
    # old-configure to do some of its still existing checks.
    if language == 'C':
        add_old_configure_assignment(
            '%s_TYPE' % var, delayed_getattr(valid_compiler, 'type'))
        add_old_configure_assignment(
            '%s_VERSION' % var, delayed_getattr(valid_compiler, 'version'))

    return valid_compiler


c_compiler = compiler('C', target)
cxx_compiler = compiler('C++', target, c_compiler=c_compiler)
host_c_compiler = compiler('C', host, other_compiler=c_compiler)
host_cxx_compiler = compiler('C++', host, c_compiler=host_c_compiler,
                             other_compiler=cxx_compiler,
                             other_c_compiler=c_compiler)

@depends(c_compiler)
def default_debug_flags(compiler_info):
    # Debug info is ON by default.
    if compiler_info.type == 'msvc':
        return '-Zi'
    return '-g'

option(env='MOZ_DEBUG_FLAGS',
       nargs=1,
       help='Debug compiler flags')

imply_option('--enable-debug-symbols',
             depends_if('--enable-debug')(lambda v: v))

js_option('--enable-debug-symbols',
          nargs='?',
          default=True,
          help='Enable debug symbols using the given compiler flags')

set_config('MOZ_DEBUG_SYMBOLS',
           depends_if('--enable-debug-symbols')(lambda _: True))

@depends('MOZ_DEBUG_FLAGS', '--enable-debug-symbols', default_debug_flags)
def debug_flags(env_debug_flags, enable_debug_flags, default_debug_flags):
    # If MOZ_DEBUG_FLAGS is set, and --enable-debug-symbols is set to a value,
    # --enable-debug-symbols takes precedence. Note, the value of
    # --enable-debug-symbols may be implied by --enable-debug.
    if len(enable_debug_flags):
        return enable_debug_flags[0]
    if env_debug_flags:
        return env_debug_flags[0]
    return default_debug_flags

set_config('MOZ_DEBUG_FLAGS', debug_flags)
add_old_configure_assignment('MOZ_DEBUG_FLAGS', debug_flags)

# Some standard library headers (notably bionic on Android) declare standard
# functions (e.g. getchar()) and also #define macros for those standard
# functions.  libc++ deals with this by doing something like the following
# (explanatory comments added):
#
#   #ifdef FUNC
#   // Capture the definition of FUNC.
#   inline _LIBCPP_INLINE_VISIBILITY int __libcpp_FUNC(...) { return FUNC(...); }
#   #undef FUNC
#   // Use a real inline definition.
#   inline _LIBCPP_INLINE_VISIBILITY int FUNC(...) { return _libcpp_FUNC(...); }
#   #endif
#
# _LIBCPP_INLINE_VISIBILITY is typically defined as:
#
#   __attribute__((__visibility__("hidden"), __always_inline__))
#
# Unfortunately, this interacts badly with our system header wrappers, as the:
#
#   #pragma GCC visibility push(default)
#
# that they do prior to including the actual system header is treated by the
# compiler as an explicit declaration of visibility on every function declared
# in the header.  Therefore, when the libc++ code above is encountered, it is
# as though the compiler has effectively seen:
#
#   int FUNC(...) __attribute__((__visibility__("default")));
#   int FUNC(...) __attribute__((__visibility__("hidden")));
#
# and the compiler complains about the mismatched visibility declarations.
#
# However, libc++ will only define _LIBCPP_INLINE_VISIBILITY if there is no
# existing definition.  We can therefore define it to the empty string (since
# we are properly managing visibility ourselves) and avoid this whole mess.
# Note that we don't need to do this with gcc, as libc++ detects gcc and
# effectively does the same thing we are doing here.
@depends(c_compiler, target)
def libcxx_inline_visibility(c_compiler, target):
    if c_compiler.type == 'clang' and target.os == 'Android':
        return ''

set_define('_LIBCPP_INLINE_VISIBILITY', libcxx_inline_visibility)
set_define('_LIBCPP_INLINE_VISIBILITY_EXCEPT_GCC49', libcxx_inline_visibility)

include('rust.configure')