virtualx-engine/SConstruct

#!/usr/bin/env python

EnsureSConsVersion(3, 0, 0)
EnsurePythonVersion(3, 5)

# System
import glob
import os
import pickle
import sys

# Local
import methods
import gles_builders
from platform_methods import run_in_subprocess

# Scan possible build platforms

platform_list = []  # list of platforms
platform_opts = {}  # options for each platform
platform_flags = {}  # flags for each platform

active_platforms = []
active_platform_ids = []
platform_exporters = []
platform_apis = []

for x in sorted(glob.glob("platform/*")):
    if (not os.path.isdir(x) or not os.path.exists(x + "/detect.py")):
        continue
    tmppath = "./" + x

    sys.path.insert(0, tmppath)
    import detect

    if (os.path.exists(x + "/export/export.cpp")):
        platform_exporters.append(x[9:])
    if (os.path.exists(x + "/api/api.cpp")):
        platform_apis.append(x[9:])
    if (detect.is_active()):
        active_platforms.append(detect.get_name())
        active_platform_ids.append(x)
    if (detect.can_build()):
        x = x.replace("platform/", "")  # rest of world
        x = x.replace("platform\\", "")  # win32
        platform_list += [x]
        platform_opts[x] = detect.get_opts()
        platform_flags[x] = detect.get_flags()
    sys.path.remove(tmppath)
    sys.modules.pop('detect')

module_list = methods.detect_modules()

methods.save_active_platforms(active_platforms, active_platform_ids)

custom_tools = ['default']

platform_arg = ARGUMENTS.get("platform", ARGUMENTS.get("p", False))

if os.name == "nt" and (platform_arg == "android" or ARGUMENTS.get("use_mingw", False)):
    custom_tools = ['mingw']
elif platform_arg == 'javascript':
    # Use generic POSIX build toolchain for Emscripten.
    custom_tools = ['cc', 'c++', 'ar', 'link', 'textfile', 'zip']

env_base = Environment(tools=custom_tools)
if 'TERM' in os.environ:
    env_base['ENV']['TERM'] = os.environ['TERM']
env_base.AppendENVPath('PATH', os.getenv('PATH'))
env_base.AppendENVPath('PKG_CONFIG_PATH', os.getenv('PKG_CONFIG_PATH'))
env_base.disabled_modules = []
env_base.use_ptrcall = False
env_base.module_version_string = ""
env_base.msvc = False

env_base.__class__.disable_module = methods.disable_module

env_base.__class__.add_module_version_string = methods.add_module_version_string

env_base.__class__.add_source_files = methods.add_source_files
env_base.__class__.use_windows_spawn_fix = methods.use_windows_spawn_fix

env_base.__class__.add_shared_library = methods.add_shared_library
env_base.__class__.add_library = methods.add_library
env_base.__class__.add_program = methods.add_program
env_base.__class__.CommandNoCache = methods.CommandNoCache
env_base.__class__.disable_warnings = methods.disable_warnings

env_base["x86_libtheora_opt_gcc"] = False
env_base["x86_libtheora_opt_vc"] = False

# avoid issues when building with different versions of python out of the same directory
env_base.SConsignFile(".sconsign{0}.dblite".format(pickle.HIGHEST_PROTOCOL))

# Build options

customs = ['custom.py']

profile = ARGUMENTS.get("profile", False)
if profile:
    if os.path.isfile(profile):
        customs.append(profile)
    elif os.path.isfile(profile + ".py"):
        customs.append(profile + ".py")

opts = Variables(customs, ARGUMENTS)

# Target build options
opts.Add('arch', "Platform-dependent architecture (arm/arm64/x86/x64/mips/...)", '')
opts.Add(EnumVariable('bits', "Target platform bits", 'default', ('default', '32', '64')))
opts.Add('p', "Platform (alias for 'platform')", '')
opts.Add('platform', "Target platform (%s)" % ('|'.join(platform_list), ), '')
opts.Add(EnumVariable('target', "Compilation target", 'debug', ('debug', 'release_debug', 'release')))
opts.Add(EnumVariable('optimize', "Optimization type", 'speed', ('speed', 'size')))

opts.Add(BoolVariable('tools', "Build the tools (a.k.a. the Godot editor)", True))
opts.Add(BoolVariable('use_lto', 'Use link-time optimization', False))
opts.Add(BoolVariable('use_precise_math_checks', 'Math checks use very precise epsilon (useful to debug the engine)', False))

# Components
opts.Add(BoolVariable('deprecated', "Enable deprecated features", True))
opts.Add(BoolVariable('minizip', "Enable ZIP archive support using minizip", True))
opts.Add(BoolVariable('xaudio2', "Enable the XAudio2 audio driver", False))

# Advanced options
opts.Add(BoolVariable('verbose', "Enable verbose output for the compilation", False))
opts.Add(BoolVariable('progress', "Show a progress indicator during compilation", True))
opts.Add(EnumVariable('warnings', "Set the level of warnings emitted during compilation", 'all', ('extra', 'all', 'moderate', 'no')))
opts.Add(BoolVariable('werror', "Treat compiler warnings as errors. Depends on the level of warnings set with 'warnings'", False))
opts.Add(BoolVariable('dev', "If yes, alias for verbose=yes warnings=extra werror=yes", False))
opts.Add('extra_suffix', "Custom extra suffix added to the base filename of all generated binary files", '')
opts.Add(BoolVariable('vsproj', "Generate a Visual Studio solution", False))
opts.Add(EnumVariable('macports_clang', "Build using Clang from MacPorts", 'no', ('no', '5.0', 'devel')))
opts.Add(BoolVariable('disable_3d', "Disable 3D nodes for a smaller executable", False))
opts.Add(BoolVariable('disable_advanced_gui', "Disable advanced GUI nodes and behaviors", False))
opts.Add(BoolVariable('no_editor_splash', "Don't use the custom splash screen for the editor", False))
opts.Add('system_certs_path', "Use this path as SSL certificates default for editor (for package maintainers)", '')

# Thirdparty libraries
#opts.Add(BoolVariable('builtin_assimp', "Use the built-in Assimp library", True))
opts.Add(BoolVariable('builtin_bullet', "Use the built-in Bullet library", True))
opts.Add(BoolVariable('builtin_certs', "Bundle default SSL certificates to be used if you don't specify an override in the project settings", True))
opts.Add(BoolVariable('builtin_enet', "Use the built-in ENet library", True))
opts.Add(BoolVariable('builtin_freetype', "Use the built-in FreeType library", True))
opts.Add(BoolVariable('builtin_glslang', "Use the built-in glslang library", True))
opts.Add(BoolVariable('builtin_libogg', "Use the built-in libogg library", True))
opts.Add(BoolVariable('builtin_libpng', "Use the built-in libpng library", True))
opts.Add(BoolVariable('builtin_libtheora', "Use the built-in libtheora library", True))
opts.Add(BoolVariable('builtin_libvorbis', "Use the built-in libvorbis library", True))
opts.Add(BoolVariable('builtin_libvpx', "Use the built-in libvpx library", True))
opts.Add(BoolVariable('builtin_libwebp', "Use the built-in libwebp library", True))
opts.Add(BoolVariable('builtin_wslay', "Use the built-in wslay library", True))
opts.Add(BoolVariable('builtin_mbedtls', "Use the built-in mbedTLS library", True))
opts.Add(BoolVariable('builtin_miniupnpc', "Use the built-in miniupnpc library", True))
opts.Add(BoolVariable('builtin_opus', "Use the built-in Opus library", True))
opts.Add(BoolVariable('builtin_pcre2', "Use the built-in PCRE2 library", True))
opts.Add(BoolVariable('builtin_pcre2_with_jit', "Use JIT compiler for the built-in PCRE2 library", True))
opts.Add(BoolVariable('builtin_recast', "Use the built-in Recast library", True))
opts.Add(BoolVariable('builtin_rvo2', "Use the built-in RVO2 library", True))
opts.Add(BoolVariable('builtin_squish', "Use the built-in squish library", True))
opts.Add(BoolVariable('builtin_vulkan', "Use the built-in Vulkan loader library and headers", True))
opts.Add(BoolVariable('builtin_xatlas', "Use the built-in xatlas library", True))
opts.Add(BoolVariable('builtin_zlib', "Use the built-in zlib library", True))
opts.Add(BoolVariable('builtin_zstd', "Use the built-in Zstd library", True))

# Compilation environment setup
opts.Add("CXX", "C++ compiler")
opts.Add("CC", "C compiler")
opts.Add("LINK", "Linker")
opts.Add("CCFLAGS", "Custom flags for both the C and C++ compilers")
opts.Add("CFLAGS", "Custom flags for the C compiler")
opts.Add("CXXFLAGS", "Custom flags for the C++ compiler")
opts.Add("LINKFLAGS", "Custom flags for the linker")

# add platform specific options

for k in platform_opts.keys():
    opt_list = platform_opts[k]
    for o in opt_list:
        opts.Add(o)

for x in module_list:
    module_enabled = True
    tmppath = "./modules/" + x
    sys.path.insert(0, tmppath)
    import config
    enabled_attr = getattr(config, "is_enabled", None)
    if (callable(enabled_attr) and not config.is_enabled()):
        module_enabled = False
    sys.path.remove(tmppath)
    sys.modules.pop('config')
    opts.Add(BoolVariable('module_' + x + '_enabled', "Enable module '%s'" % (x, ), module_enabled))

opts.Update(env_base)  # update environment
Help(opts.GenerateHelpText(env_base))  # generate help

# add default include paths

env_base.Prepend(CPPPATH=['#'])

# configure ENV for platform
env_base.platform_exporters = platform_exporters
env_base.platform_apis = platform_apis

if (env_base["use_precise_math_checks"]):
    env_base.Append(CPPDEFINES=['PRECISE_MATH_CHECKS'])

if (env_base['target'] == 'debug'):
    env_base.Append(CPPDEFINES=['DEBUG_MEMORY_ALLOC','DISABLE_FORCED_INLINE'])

    # The two options below speed up incremental builds, but reduce the certainty that all files
    # will properly be rebuilt. As such, we only enable them for debug (dev) builds, not release.

    # To decide whether to rebuild a file, use the MD5 sum only if the timestamp has changed.
    # http://scons.org/doc/production/HTML/scons-user/ch06.html#idm139837621851792
    env_base.Decider('MD5-timestamp')
    # Use cached implicit dependencies by default. Can be overridden by specifying `--implicit-deps-changed` in the command line.
    # http://scons.org/doc/production/HTML/scons-user/ch06s04.html
    env_base.SetOption('implicit_cache', 1)

if (env_base['no_editor_splash']):
    env_base.Append(CPPDEFINES=['NO_EDITOR_SPLASH'])

if not env_base['deprecated']:
    env_base.Append(CPPDEFINES=['DISABLE_DEPRECATED'])

env_base.platforms = {}

selected_platform = ""

if env_base['platform'] != "":
    selected_platform = env_base['platform']
elif env_base['p'] != "":
    selected_platform = env_base['p']
    env_base["platform"] = selected_platform
else:
    # Missing `platform` argument, try to detect platform automatically
    if sys.platform.startswith('linux'):
        selected_platform = 'x11'
    elif sys.platform == 'darwin':
        selected_platform = 'osx'
    elif sys.platform == 'win32':
        selected_platform = 'windows'
    else:
        print("Could not detect platform automatically. Supported platforms:")
        for x in platform_list:
            print("\t" + x)
        print("\nPlease run SCons again and select a valid platform: platform=<string>")

    if selected_platform != "":
        print("Automatically detected platform: " + selected_platform)
        env_base["platform"] = selected_platform

if selected_platform in platform_list:
    tmppath = "./platform/" + selected_platform
    sys.path.insert(0, tmppath)
    import detect
    if "create" in dir(detect):
        env = detect.create(env_base)
    else:
        env = env_base.Clone()

    if env['dev']:
        env['verbose'] = True
        env['warnings'] = "extra"
        env['werror'] = True

    if env['vsproj']:
        env.vs_incs = []
        env.vs_srcs = []

        def AddToVSProject(sources):
            for x in sources:
                if type(x) == type(""):
                    fname = env.File(x).path
                else:
                    fname = env.File(x)[0].path
                pieces = fname.split(".")
                if len(pieces) > 0:
                    basename = pieces[0]
                    basename = basename.replace('\\\\', '/')
                    if os.path.isfile(basename + ".h"):
                        env.vs_incs = env.vs_incs + [basename + ".h"]
                    elif os.path.isfile(basename + ".hpp"):
                        env.vs_incs = env.vs_incs + [basename + ".hpp"]
                    if os.path.isfile(basename + ".c"):
                        env.vs_srcs = env.vs_srcs + [basename + ".c"]
                    elif os.path.isfile(basename + ".cpp"):
                        env.vs_srcs = env.vs_srcs + [basename + ".cpp"]
        env.AddToVSProject = AddToVSProject

    env.extra_suffix = ""

    if env["extra_suffix"] != '':
        env.extra_suffix += '.' + env["extra_suffix"]

    # Environment flags
    CCFLAGS = env.get('CCFLAGS', '')
    env['CCFLAGS'] = ''
    env.Append(CCFLAGS=str(CCFLAGS).split())

    CFLAGS = env.get('CFLAGS', '')
    env['CFLAGS'] = ''
    env.Append(CFLAGS=str(CFLAGS).split())

    CXXFLAGS = env.get('CXXFLAGS', '')
    env['CXXFLAGS'] = ''
    env.Append(CXXFLAGS=str(CXXFLAGS).split())

    LINKFLAGS = env.get('LINKFLAGS', '')
    env['LINKFLAGS'] = ''
    env.Append(LINKFLAGS=str(LINKFLAGS).split())

    # Platform specific flags
    flag_list = platform_flags[selected_platform]
    for f in flag_list:
        if not (f[0] in ARGUMENTS):  # allow command line to override platform flags
            env[f[0]] = f[1]

    # Must happen after the flags definition, so that they can be used by platform detect
    detect.configure(env)

    # Set our C and C++ standard requirements.
    # C++17 is required as we need guaranteed copy elision as per GH-36436.
    # Prepending to make it possible to override.
    # This needs to come after `configure`, otherwise we don't have env.msvc.
    if not env.msvc:
        # Specifying GNU extensions support explicitly, which are supported by
        # both GCC and Clang. Both currently default to gnu11 and gnu++14.
        env.Prepend(CFLAGS=['-std=gnu11'])
        env.Prepend(CXXFLAGS=['-std=gnu++17'])
    else:
        # MSVC doesn't have clear C standard support, /std only covers C++.
        # We apply it to CCFLAGS (both C and C++ code) in case it impacts C features.
        env.Prepend(CCFLAGS=['/std:c++17'])

    # Enforce our minimal compiler version requirements
    cc_version = methods.get_compiler_version(env) or [-1, -1]
    cc_version_major = cc_version[0]
    cc_version_minor = cc_version[1]

    if methods.using_gcc(env):
        # GCC 8 before 8.4 has a regression in the support of guaranteed copy elision
        # which causes a build failure: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=86521
        if cc_version_major == 8 and cc_version_minor < 4:
            print("Detected GCC 8 version < 8.4, which is not supported due to a "
                  "regression in its C++17 guaranteed copy elision support. Use a "
                  "newer GCC version, or Clang 6 or later by passing \"use_llvm=yes\" "
                  "to the SCons command line.")
            sys.exit(255)
        elif cc_version_major < 7:
            print("Detected GCC version older than 7, which does not fully support "
                  "C++17. Supported versions are GCC 7, 9 and later. Use a newer GCC "
                  "version, or Clang 6 or later by passing \"use_llvm=yes\" to the "
                  "SCons command line.")
            sys.exit(255)
    elif methods.using_clang(env):
        # Apple LLVM versions differ from upstream LLVM version \o/, compare
        # in https://en.wikipedia.org/wiki/Xcode#Toolchain_versions
        if env["platform"] == "osx" or env["platform"] == "iphone":
            vanilla = methods.is_vanilla_clang(env)
            if vanilla and cc_version_major < 6:
                print("Detected Clang version older than 6, which does not fully support "
                      "C++17. Supported versions are Clang 6 and later.")
                sys.exit(255)
            elif not vanilla and cc_version_major < 10:
                print("Detected Apple Clang version older than 10, which does not fully "
                      "support C++17. Supported versions are Apple Clang 10 and later.")
                sys.exit(255)
        elif cc_version_major < 6:
            print("Detected Clang version older than 6, which does not fully support "
                  "C++17. Supported versions are Clang 6 and later.")
            sys.exit(255)

    # Configure compiler warnings
    if env.msvc:
        # Truncations, narrowing conversions, signed/unsigned comparisons...
        disable_nonessential_warnings = ['/wd4267', '/wd4244', '/wd4305', '/wd4018', '/wd4800']
        if (env["warnings"] == 'extra'):
            env.Append(CCFLAGS=['/Wall']) # Implies /W4
        elif (env["warnings"] == 'all'):
            env.Append(CCFLAGS=['/W3'] + disable_nonessential_warnings)
        elif (env["warnings"] == 'moderate'):
            env.Append(CCFLAGS=['/W2'] + disable_nonessential_warnings)
        else: # 'no'
            env.Append(CCFLAGS=['/w'])
        # Set exception handling model to avoid warnings caused by Windows system headers.
        env.Append(CCFLAGS=['/EHsc'])
        if (env["werror"]):
            env.Append(CCFLAGS=['/WX'])
        # Force to use Unicode encoding
        env.Append(MSVC_FLAGS=['/utf8'])
    else: # Rest of the world
        shadow_local_warning = []
        all_plus_warnings = ['-Wwrite-strings']

        if methods.using_gcc(env):
            if cc_version_major >= 7:
                shadow_local_warning = ['-Wshadow-local']

        if (env["warnings"] == 'extra'):
            env.Append(CCFLAGS=['-Wall', '-Wextra', '-Wno-unused-parameter']
                + all_plus_warnings + shadow_local_warning)
            env.Append(CXXFLAGS=['-Wctor-dtor-privacy', '-Wnon-virtual-dtor'])
            if methods.using_gcc(env):
                env.Append(CCFLAGS=['-Walloc-zero',
                    '-Wduplicated-branches', '-Wduplicated-cond',
                    '-Wstringop-overflow=4', '-Wlogical-op'])
                # -Wnoexcept was removed temporarily due to GH-36325.
                env.Append(CXXFLAGS=['-Wplacement-new=1'])
                if cc_version_major >= 9:
                    env.Append(CCFLAGS=['-Wattribute-alias=2'])
            if methods.using_clang(env):
                env.Append(CCFLAGS=['-Wimplicit-fallthrough'])
        elif (env["warnings"] == 'all'):
            env.Append(CCFLAGS=['-Wall'] + shadow_local_warning)
        elif (env["warnings"] == 'moderate'):
            env.Append(CCFLAGS=['-Wall', '-Wno-unused']  + shadow_local_warning)
        else: # 'no'
            env.Append(CCFLAGS=['-w'])
        if (env["werror"]):
            env.Append(CCFLAGS=['-Werror'])
            # FIXME: Temporary workaround after the Vulkan merge, remove once warnings are fixed.
            if methods.using_gcc(env):
                env.Append(CXXFLAGS=['-Wno-error=cpp'])
            else:
                env.Append(CXXFLAGS=['-Wno-error=#warnings'])
        else: # always enable those errors
            env.Append(CCFLAGS=['-Werror=return-type'])

    if (hasattr(detect, 'get_program_suffix')):
        suffix = "." + detect.get_program_suffix()
    else:
        suffix = "." + selected_platform

    if (env["target"] == "release"):
        if env["tools"]:
            print("Tools can only be built with targets 'debug' and 'release_debug'.")
            sys.exit(255)
        suffix += ".opt"
        env.Append(CPPDEFINES=['NDEBUG'])

    elif (env["target"] == "release_debug"):
        if env["tools"]:
            suffix += ".opt.tools"
        else:
            suffix += ".opt.debug"
    else:
        if env["tools"]:
            suffix += ".tools"
        else:
            suffix += ".debug"

    if env["arch"] != "":
        suffix += "." + env["arch"]
    elif (env["bits"] == "32"):
        suffix += ".32"
    elif (env["bits"] == "64"):
        suffix += ".64"

    suffix += env.extra_suffix

    sys.path.remove(tmppath)
    sys.modules.pop('detect')

    env.module_list = []
    env.module_icons_paths = []
    env.doc_class_path = {}

    for x in sorted(module_list):
        if not env['module_' + x + '_enabled']:
            continue
        tmppath = "./modules/" + x
        sys.path.insert(0, tmppath)
        env.current_module = x
        import config
        if config.can_build(env, selected_platform):
            config.configure(env)
            env.module_list.append(x)

            # Get doc classes paths (if present)
            try:
                doc_classes = config.get_doc_classes()
                doc_path = config.get_doc_path()
                for c in doc_classes:
                    env.doc_class_path[c] = "modules/" + x + "/" + doc_path
            except:
                pass
            # Get icon paths (if present)
            try:
                icons_path = config.get_icons_path()
                env.module_icons_paths.append("modules/" + x + "/" + icons_path)
            except:
                # Default path for module icons
                env.module_icons_paths.append("modules/" + x + "/" + "icons")

        sys.path.remove(tmppath)
        sys.modules.pop('config')

    methods.update_version(env.module_version_string)

    env["PROGSUFFIX"] = suffix + env.module_version_string + env["PROGSUFFIX"]
    env["OBJSUFFIX"] = suffix + env["OBJSUFFIX"]
    # (SH)LIBSUFFIX will be used for our own built libraries
    # LIBSUFFIXES contains LIBSUFFIX and SHLIBSUFFIX by default,
    # so we need to append the default suffixes to keep the ability
    # to link against thirdparty libraries (.a, .so, .lib, etc.).
    if os.name == "nt":
        # On Windows, only static libraries and import libraries can be
        # statically linked - both using .lib extension
        env["LIBSUFFIXES"] += [env["LIBSUFFIX"]]
    else:
        env["LIBSUFFIXES"] += [env["LIBSUFFIX"], env["SHLIBSUFFIX"]]
    env["LIBSUFFIX"] = suffix + env["LIBSUFFIX"]
    env["SHLIBSUFFIX"] = suffix + env["SHLIBSUFFIX"]

    if (env.use_ptrcall):
        env.Append(CPPDEFINES=['PTRCALL_ENABLED'])
    if env['tools']:
        env.Append(CPPDEFINES=['TOOLS_ENABLED'])
    if env['disable_3d']:
        if env['tools']:
            print("Build option 'disable_3d=yes' cannot be used with 'tools=yes' (editor), only with 'tools=no' (export template).")
            sys.exit(255)
        else:
            env.Append(CPPDEFINES=['_3D_DISABLED'])
    if env['disable_advanced_gui']:
        if env['tools']:
            print("Build option 'disable_advanced_gui=yes' cannot be used with 'tools=yes' (editor), only with 'tools=no' (export template).")
            sys.exit(255)
        else:
            env.Append(CPPDEFINES=['ADVANCED_GUI_DISABLED'])
    if env['minizip']:
        env.Append(CPPDEFINES=['MINIZIP_ENABLED'])

    editor_module_list = ['regex']
    for x in editor_module_list:
        if not env['module_' + x + '_enabled']:
            if env['tools']:
                print("Build option 'module_" + x + "_enabled=no' cannot be used with 'tools=yes' (editor), only with 'tools=no' (export template).")
                sys.exit(255)

    if not env['verbose']:
        methods.no_verbose(sys, env)

    if (not env["platform"] == "server"):
        env.Append(BUILDERS = { 'GLES2_GLSL' : env.Builder(action=run_in_subprocess(gles_builders.build_gles2_headers), suffix='glsl.gen.h', src_suffix='.glsl')})
        env.Append(BUILDERS = { 'RD_GLSL' : env.Builder(action=run_in_subprocess(gles_builders.build_rd_headers), suffix='glsl.gen.h', src_suffix='.glsl')})

    scons_cache_path = os.environ.get("SCONS_CACHE")
    if scons_cache_path != None:
        CacheDir(scons_cache_path)
        print("Scons cache enabled... (path: '" + scons_cache_path + "')")

    Export('env')

    # build subdirs, the build order is dependent on link order.

    SConscript("core/SCsub")
    SConscript("servers/SCsub")
    SConscript("scene/SCsub")
    SConscript("editor/SCsub")
    SConscript("drivers/SCsub")

    SConscript("platform/SCsub")
    SConscript("modules/SCsub")
    SConscript("main/SCsub")

    SConscript("platform/" + selected_platform + "/SCsub")  # build selected platform

    # Microsoft Visual Studio Project Generation
    if env['vsproj']:
        env['CPPPATH'] = [Dir(path) for path in env['CPPPATH']]
        methods.generate_vs_project(env, GetOption("num_jobs"))
        methods.generate_cpp_hint_file("cpp.hint")

    # Check for the existence of headers
    conf = Configure(env)
    if ("check_c_headers" in env):
        for header in env["check_c_headers"]:
            if (conf.CheckCHeader(header[0])):
                env.AppendUnique(CPPDEFINES=[header[1]])

elif selected_platform != "":
    if selected_platform == "list":
        print("The following platforms are available:\n")
    else:
        print('Invalid target platform "' + selected_platform + '".')
        print("The following platforms were detected:\n")

    for x in platform_list:
        print("\t" + x)

    print("\nPlease run SCons again and select a valid platform: platform=<string>")

    if selected_platform == "list":
        # Exit early to suppress the rest of the built-in SCons messages
        sys.exit(0)
    else:
        sys.exit(255)

# The following only makes sense when the env is defined, and assumes it is
if 'env' in locals():
    screen = sys.stdout
    # Progress reporting is not available in non-TTY environments since it
    # messes with the output (for example, when writing to a file)
    show_progress = (env['progress'] and sys.stdout.isatty())
    node_count = 0
    node_count_max = 0
    node_count_interval = 1
    node_count_fname = str(env.Dir('#')) + '/.scons_node_count'

    import time, math

    class cache_progress:
        # The default is 1 GB cache and 12 hours half life
        def __init__(self, path = None, limit = 1073741824, half_life = 43200):
            self.path = path
            self.limit = limit
            self.exponent_scale = math.log(2) / half_life
            if env['verbose'] and path != None:
                screen.write('Current cache limit is ' + self.convert_size(limit) + ' (used: ' + self.convert_size(self.get_size(path)) + ')\n')
            self.delete(self.file_list())

        def __call__(self, node, *args, **kw):
            global node_count, node_count_max, node_count_interval, node_count_fname, show_progress
            if show_progress:
                # Print the progress percentage
                node_count += node_count_interval
                if (node_count_max > 0 and node_count <= node_count_max):
                    screen.write('\r[%3d%%] ' % (node_count * 100 / node_count_max))
                    screen.flush()
                elif (node_count_max > 0 and node_count > node_count_max):
                    screen.write('\r[100%] ')
                    screen.flush()
                else:
                    screen.write('\r[Initial build] ')
                    screen.flush()

        def delete(self, files):
            if len(files) == 0:
                return
            if env['verbose']:
                # Utter something
                screen.write('\rPurging %d %s from cache...\n' % (len(files), len(files) > 1 and 'files' or 'file'))
            [os.remove(f) for f in files]

        def file_list(self):
            if self.path is None:
                # Nothing to do
                return []
            # Gather a list of (filename, (size, atime)) within the
            # cache directory
            file_stat = [(x, os.stat(x)[6:8]) for x in glob.glob(os.path.join(self.path, '*', '*'))]
            if file_stat == []:
                # Nothing to do
                return []
            # Weight the cache files by size (assumed to be roughly
            # proportional to the recompilation time) times an exponential
            # decay since the ctime, and return a list with the entries
            # (filename, size, weight).
            current_time = time.time()
            file_stat = [(x[0], x[1][0], (current_time - x[1][1])) for x in file_stat]
            # Sort by the most recently accessed files (most sensible to keep) first
            file_stat.sort(key=lambda x: x[2])
            # Search for the first entry where the storage limit is
            # reached
            sum, mark = 0, None
            for i,x in enumerate(file_stat):
                sum += x[1]
                if sum > self.limit:
                    mark = i
                    break
            if mark is None:
                return []
            else:
                return [x[0] for x in file_stat[mark:]]

        def convert_size(self, size_bytes):
            if size_bytes == 0:
                return "0 bytes"
            size_name = ("bytes", "KB", "MB", "GB", "TB", "PB", "EB", "ZB", "YB")
            i = int(math.floor(math.log(size_bytes, 1024)))
            p = math.pow(1024, i)
            s = round(size_bytes / p, 2)
            return "%s %s" % (int(s) if i == 0 else s, size_name[i])

        def get_size(self, start_path = '.'):
            total_size = 0
            for dirpath, dirnames, filenames in os.walk(start_path):
                for f in filenames:
                    fp = os.path.join(dirpath, f)
                    total_size += os.path.getsize(fp)
            return total_size

    def progress_finish(target, source, env):
        global node_count, progressor
        with open(node_count_fname, 'w') as f:
            f.write('%d\n' % node_count)
        progressor.delete(progressor.file_list())

    try:
        with open(node_count_fname) as f:
            node_count_max = int(f.readline())
    except:
        pass

    cache_directory = os.environ.get("SCONS_CACHE")
    # Simple cache pruning, attached to SCons' progress callback. Trim the
    # cache directory to a size not larger than cache_limit.
    cache_limit = float(os.getenv("SCONS_CACHE_LIMIT", 1024)) * 1024 * 1024
    progressor = cache_progress(cache_directory, cache_limit)
    Progress(progressor, interval = node_count_interval)

    progress_finish_command = Command('progress_finish', [], progress_finish)
    AlwaysBuild(progress_finish_command)