tools/licenses.py - chromium/src - Git at Google

 #!/usr/bin/env python
 # Copyright (c) 2012 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.

 """Utility for checking and processing licensing information in third_party
 directories.

 Usage: licenses.py <command>

 Commands:
   scan     scan third_party directories, verifying that we have licensing info
   credits  generate about:credits on stdout

 (You can also import this as a module.)
 """
 from __future__ import print_function

 import argparse
 import codecs
 import json
 import os
 import shutil
 import re
 import subprocess
 import sys
 import tempfile

 if sys.version_info.major == 2:
   import cgi as html
 else:
   import html

 # TODO(agrieve): Move build_utils.WriteDepFile into a non-android directory.
 _REPOSITORY_ROOT = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
 sys.path.insert(0, os.path.join(_REPOSITORY_ROOT, 'build/android/gyp'))
 from util import build_utils


 # Paths from the root of the tree to directories to skip.
 PRUNE_PATHS = set([
     # Placeholder directory only, not third-party code.
     os.path.join('third_party','adobe'),

     # Will remove it once converted private sdk using cipd.
     os.path.join('third_party','android_tools_internal'),

     # Build files only, not third-party code.
     os.path.join('third_party','widevine'),

     # Only binaries, used during development.
     os.path.join('third_party','valgrind'),

     # Used for development and test, not in the shipping product.
     os.path.join('build','secondary'),
     os.path.join('third_party','bison'),
     os.path.join('third_party','blanketjs'),
     os.path.join('third_party','chromite'),
     os.path.join('third_party','cygwin'),
     os.path.join('third_party','gles2_conform'),
     os.path.join('third_party','gnu_binutils'),
     os.path.join('third_party','gold'),
     os.path.join('third_party','gperf'),
     os.path.join('third_party','lighttpd'),
     os.path.join('third_party','llvm'),
     os.path.join('third_party','llvm-build'),
     os.path.join('third_party','mingw-w64'),
     os.path.join('third_party','nacl_sdk_binaries'),
     os.path.join('third_party','pefile'),
     os.path.join('third_party','perl'),
     os.path.join('third_party','psyco_win32'),
     os.path.join('third_party','pyelftools'),
     os.path.join('third_party','pylib'),
     os.path.join('third_party','pywebsocket'),
     os.path.join('third_party','syzygy'),

     # Chromium code.
     os.path.join('tools', 'swarming_client'),

     # Stuff pulled in from chrome-internal for official builds/tools.
     os.path.join('third_party', 'clear_cache'),
     os.path.join('third_party', 'gnu'),
     os.path.join('third_party', 'googlemac'),
     os.path.join('third_party', 'pcre'),
     os.path.join('third_party', 'psutils'),
     os.path.join('third_party', 'sawbuck'),
     # See crbug.com/350472
     os.path.join('chrome', 'browser', 'resources', 'chromeos', 'quickoffice'),
     # Chrome for Android proprietary code.
     os.path.join('clank'),

     # Redistribution does not require attribution in documentation.
     os.path.join('third_party','directxsdk'),

     # For testing only, presents on some bots.
     os.path.join('isolate_deps_dir'),

     # Mock test data.
     os.path.join('tools', 'binary_size', 'libsupersize', 'testdata'),

     # Overrides some WebRTC files, same license. Skip this one.
     os.path.join('third_party', 'webrtc_overrides'),
 ])

 # Directories we don't scan through.
 VCS_METADATA_DIRS = ('.svn', '.git')
 PRUNE_DIRS = VCS_METADATA_DIRS + ('layout_tests', )  # lots of subdirs

 # A third_party directory can define this file, containing a list of
 # subdirectories to process in addition to itself. Intended for directories
 # that contain multiple others as transitive dependencies.
 ADDITIONAL_PATHS_FILENAME = 'additional_readme_paths.json'

 # A list of paths that contain license information but that would otherwise
 # not be included.  Possible reasons include:
 #   - Third party directories in //clank which are considered to be Google-owned
 #   - Directories that are directly checked out from upstream, and thus
 #     don't have a README.chromium
 #   - Directories that contain example code, or build tooling.
 #   - Nested third_party code inside other third_party libraries.
 ADDITIONAL_PATHS = (
     os.path.join('chrome', 'common', 'extensions', 'docs', 'examples'),
     os.path.join('chrome', 'test', 'chromeos', 'autotest'),
     os.path.join('chrome', 'test', 'data'),
     os.path.join('clank', 'third_party', 'elements'),
     os.path.join('native_client'),
     os.path.join('testing', 'gmock'),
     os.path.join('testing', 'gtest'),
     os.path.join('third_party', 'boringssl', 'src', 'third_party', 'fiat'),
     os.path.join('tools', 'gyp'),
     os.path.join('tools', 'page_cycler', 'acid3'),
     os.path.join('url', 'third_party', 'mozilla'),
     os.path.join('v8'),
     # Fake directories to include the strongtalk and fdlibm licenses.
     os.path.join('v8', 'strongtalk'),
     os.path.join('v8', 'fdlibm'),
 )


 # Directories where we check out directly from upstream, and therefore
 # can't provide a README.chromium.  Please prefer a README.chromium
 # wherever possible.
 SPECIAL_CASES = {
     os.path.join('native_client'): {
         "Name": "native client",
         "URL": "http://code.google.com/p/nativeclient",
         "License": "BSD",
     },
     os.path.join('testing', 'gmock'): {
         "Name": "gmock",
         "URL": "http://code.google.com/p/googlemock",
         "License": "BSD",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('testing', 'gtest'): {
         "Name": "gtest",
         "URL": "http://code.google.com/p/googletest",
         "License": "BSD",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'angle'): {
         "Name": "Almost Native Graphics Layer Engine",
         "URL": "http://code.google.com/p/angleproject/",
         "License": "BSD",
     },
     os.path.join('third_party', 'angle', 'third_party', 'vulkan-headers'): {
         "Name": "Vulkan-Headers",
         "URL": "https://github.com/KhronosGroup/Vulkan-Headers",
         "License": "Apache 2.0",
         "License File": "src/LICENSE.txt",
     },
     os.path.join('third_party', 'cros_system_api'): {
         "Name": "Chromium OS system API",
         "URL": "http://www.chromium.org/chromium-os",
         "License": "BSD",
         # Absolute path here is resolved as relative to the source root.
         "License File": "/LICENSE.chromium_os",
     },
     os.path.join('third_party', 'devtools-frontend'): {
         # TODO(crbug.com/1151057): Remove this special case when issue is fixed.
         "Name": "Devtools-Frontend",
         "URL": "https://chromium.googlesource.com/devtools/devtools-frontend",
         "License": "BSD",
         "License File": "src/LICENSE",
     },
     os.path.join('third_party', 'lss'): {
         "Name": "linux-syscall-support",
         "URL": "http://code.google.com/p/linux-syscall-support/",
         "License": "BSD",
         "License File": "/LICENSE",
     },
     os.path.join('third_party', 'openscreen', 'src', 'third_party', 'abseil'): {
         "Name": "abseil",
         "URL": "https://github.com/abseil/abseil-cpp/",
         "License": "Apache 2.0",
         "License File": "/third_party/abseil-cpp/LICENSE",
     },
     os.path.join('third_party', 'openscreen', 'src', 'third_party',
                  'boringssl'):
     {
         "Name": "BoringSSL",
         "URL": "https://boringssl.googlesource.com/boringssl/",
         "License": "BSDish",
         "License File": "/third_party/boringssl/src/LICENSE",
     },
     os.path.join('third_party', 'openscreen', 'src', 'third_party', 'jsoncpp'):
     {
         "Name": "jsoncpp",
         "URL": "https://github.com/open-source-parsers/jsoncpp",
         "License": "MIT",
         "License File": "/third_party/jsoncpp/LICENSE",
     },
     os.path.join('third_party', 'openscreen', 'src', 'third_party', 'mozilla'):
     {
         "Name": "mozilla",
         "URL": "https://github.com/mozilla",
         "License": "MPL 1.1/GPL 2.0/LGPL 2.1",
         "License File": "LICENSE.txt",
     },
     os.path.join('third_party', 'pdfium'): {
         "Name": "PDFium",
         "URL": "http://code.google.com/p/pdfium/",
         "License": "BSD",
     },
     os.path.join('third_party', 'ppapi'): {
         "Name": "ppapi",
         "URL": "http://code.google.com/p/ppapi/",
     },
     os.path.join('third_party', 'scons-2.0.1'): {
         "Name": "scons-2.0.1",
         "URL": "http://www.scons.org",
         "License": "MIT",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'catapult'): {
         "Name": "catapult",
         "URL": "https://github.com/catapult-project/catapult",
         "License": "BSD",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'crashpad', 'crashpad', 'third_party', 'lss'): {
         "Name": "linux-syscall-support",
         "URL": "https://chromium.googlesource.com/linux-syscall-support/",
         "License": "BSD",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'crashpad', 'crashpad', 'third_party',
                  'mini_chromium'):
     {
         "Name": "mini_chromium",
         "URL": "https://chromium.googlesource.com/chromium/mini_chromium/",
         "License": "BSD",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'crashpad', 'crashpad', 'third_party', 'xnu'): {
         "Name": "xnu",
         "URL": "https://opensource.apple.com/source/xnu/",
         "License": "Apple Public Source License 2.0",
         "License File": "APPLE_LICENSE",
     },
     os.path.join('third_party', 'crashpad', 'crashpad', 'third_party', 'zlib'):
     {
         "Name": "zlib",
         "URL": "https://zlib.net/",
         "License": "zlib",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'v8-i18n'): {
         "Name": "Internationalization Library for v8",
         "URL": "http://code.google.com/p/v8-i18n/",
         "License": "Apache 2.0",
     },
     os.path.join('third_party', 'blink'): {
         # about:credits doesn't show "Blink" but "WebKit".
         # Blink is a fork of WebKit, and Chromium project has maintained it
         # since the fork.  about:credits needs to mention the code before
         # the fork.
         "Name": "WebKit",
         "URL": "http://webkit.org/",
         "License": "BSD and LGPL v2 and LGPL v2.1",
         # Absolute path here is resolved as relative to the source root.
         "License File": "/third_party/blink/LICENSE_FOR_ABOUT_CREDITS",
     },
     os.path.join('third_party', 'webpagereplay'): {
         "Name": "webpagereplay",
         "URL": "http://code.google.com/p/web-page-replay",
         "License": "Apache 2.0",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('tools', 'gyp'): {
         "Name": "gyp",
         "URL": "http://code.google.com/p/gyp",
         "License": "BSD",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('v8'): {
         "Name": "V8 JavaScript Engine",
         "URL": "http://code.google.com/p/v8",
         "License": "BSD",
     },
     os.path.join('v8', 'strongtalk'): {
         "Name": "Strongtalk",
         "URL": "http://www.strongtalk.org/",
         "License": "BSD",
         # Absolute path here is resolved as relative to the source root.
         "License File": "/v8/LICENSE.strongtalk",
     },
     os.path.join('v8', 'fdlibm'): {
         "Name": "fdlibm",
         "URL": "http://www.netlib.org/fdlibm/",
         "License": "Freely Distributable",
         # Absolute path here is resolved as relative to the source root.
         "License File": "/v8/LICENSE.fdlibm",
         "License Android Compatible": "yes",
     },
     os.path.join('third_party', 'khronos_glcts'): {
         # These sources are not shipped, are not public, and it isn't
         # clear why they're tripping the license check.
         "Name": "khronos_glcts",
         "URL": "http://no-public-url",
         "License": "Khronos",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('tools', 'telemetry', 'third_party', 'gsutil'): {
         "Name": "gsutil",
         "URL": "https://cloud.google.com/storage/docs/gsutil",
         "License": "Apache 2.0",
         "License File": "NOT_SHIPPED",
     },
     os.path.join('third_party', 'swiftshader'): {
         "Name": "SwiftShader",
         "URL": "https://swiftshader.googlesource.com/SwiftShader",
         "License": "Apache 2.0 and compatible licenses",
         "License Android Compatible": "yes",
         "License File": "/third_party/swiftshader/LICENSE.txt",
     },
 }

 # Special value for 'License File' field used to indicate that the license file
 # should not be used in about:credits.
 NOT_SHIPPED = "NOT_SHIPPED"

 # Paths for libraries that we have checked are not shipped on iOS. These are
 # left out of the licenses file primarily because we don't want to cause a
 # firedrill due to someone thinking that Chrome for iOS is using LGPL code
 # when it isn't.
 # This is a temporary hack; the real solution is crbug.com/178215
 KNOWN_NON_IOS_LIBRARIES = set([
     os.path.join('base', 'third_party', 'symbolize'),
     os.path.join('base', 'third_party', 'xdg_mime'),
     os.path.join('base', 'third_party', 'xdg_user_dirs'),
     os.path.join('buildtools', 'third_party', 'libc++'),
     os.path.join('buildtools', 'third_party', 'libc++abi'),
     os.path.join('chrome', 'installer', 'mac', 'third_party', 'bsdiff'),
     os.path.join('chrome', 'installer', 'mac', 'third_party', 'xz'),
     os.path.join('chrome', 'test', 'data', 'third_party', 'kraken'),
     os.path.join('chrome', 'test', 'data', 'third_party', 'spaceport'),
     os.path.join('chrome', 'third_party', 'mozilla_security_manager'),
     os.path.join('third_party', 'angle'),
     os.path.join('third_party', 'apple_apsl'),
     os.path.join('third_party', 'apple_sample_code'),
     os.path.join('third_party', 'ashmem'),
     os.path.join('third_party', 'blink'),
     os.path.join('third_party', 'bspatch'),
     os.path.join('third_party', 'cld'),
     os.path.join('third_party', 'flot'),
     os.path.join('third_party', 'gtk+'),
     os.path.join('third_party', 'iaccessible2'),
     os.path.join('third_party', 'iccjpeg'),
     os.path.join('third_party', 'isimpledom'),
     os.path.join('third_party', 'jsoncpp'),
     os.path.join('third_party', 'khronos'),
     os.path.join('third_party', 'libXNVCtrl'),
     os.path.join('third_party', 'libevent'),
     os.path.join('third_party', 'libjpeg'),
     os.path.join('third_party', 'libusb'),
     os.path.join('third_party', 'libxslt'),
     os.path.join('third_party', 'lss'),
     os.path.join('third_party', 'lzma_sdk'),
     os.path.join('third_party', 'mesa'),
     os.path.join('third_party', 'motemplate'),
     os.path.join('third_party', 'mozc'),
     os.path.join('third_party', 'mozilla'),
     os.path.join('third_party', 'npapi'),
     os.path.join('third_party', 'ots'),
     os.path.join('third_party', 'perfetto'),
     os.path.join('third_party', 'ppapi'),
     os.path.join('third_party', 'qcms'),
     os.path.join('third_party', 're2'),
     os.path.join('third_party', 'safe_browsing'),
     os.path.join('third_party', 'smhasher'),
     os.path.join('third_party', 'sudden_motion_sensor'),
     os.path.join('third_party', 'swiftshader'),
     os.path.join('third_party', 'swig'),
     os.path.join('third_party', 'talloc'),
     os.path.join('third_party', 'tcmalloc'),
     os.path.join('third_party', 'usb_ids'),
     os.path.join('third_party', 'v8-i18n'),
     os.path.join('third_party', 'wtl'),
     os.path.join('third_party', 'yasm'),
     os.path.join('v8', 'strongtalk'),
 ])


 class LicenseError(Exception):
   """We raise this exception when a directory's licensing info isn't
     fully filled out."""
   pass


 def AbsolutePath(path, filename, root):
   """Convert a path in README.chromium to be absolute based on the source
     root."""
   if filename.startswith('/'):
     # Absolute-looking paths are relative to the source root
     # (which is the directory we're run from).
     absolute_path = os.path.join(root, filename[1:])
   else:
     absolute_path = os.path.join(root, path, filename)
   if os.path.exists(absolute_path):
     return absolute_path
   return None


 def ParseDir(path, root, require_license_file=True, optional_keys=None):
   """Examine a third_party/foo component and extract its metadata."""
   # Parse metadata fields out of README.chromium.
   # We examine "LICENSE" for the license file by default.
   metadata = {
       "License File": "LICENSE",  # Relative path to license text.
       "Name": None,  # Short name (for header on about:credits).
       "URL": None,  # Project home page.
       "License": None,  # Software license.
   }

   if optional_keys is None:
     optional_keys = []

   if path in SPECIAL_CASES:
     metadata.update(SPECIAL_CASES[path])
   else:
     # Try to find README.chromium.
     readme_path = os.path.join(root, path, 'README.chromium')
     if not os.path.exists(readme_path):
       raise LicenseError("missing README.chromium or licenses.py "
                          "SPECIAL_CASES entry in %s\n" % path)

     for line in open(readme_path):
       line = line.strip()
       if not line:
         break
       for key in list(metadata.keys()) + optional_keys:
         field = key + ": "
         if line.startswith(field):
           metadata[key] = line[len(field):]

   # Check that all expected metadata is present.
   errors = []
   for key, value in metadata.items():
     if not value:
       errors.append("couldn't find '" + key + "' line "
                     "in README.chromium or licences.py "
                     "SPECIAL_CASES")

   # Special-case modules that aren't in the shipping product, so don't need
   # their license in about:credits.
   if metadata["License File"] != NOT_SHIPPED:
     # Check that the license file exists.
     for filename in (metadata["License File"], "COPYING"):
       license_path = AbsolutePath(path, filename, root)
       if license_path is not None:
         break

     if require_license_file and not license_path:
       errors.append("License file not found. "
                     "Either add a file named LICENSE, "
                     "import upstream's COPYING if available, "
                     "or add a 'License File:' line to "
                     "README.chromium with the appropriate path.")
     metadata["License File"] = license_path

   if errors:
     raise LicenseError("Errors in %s:\n %s\n" % (path, ";\n ".join(errors)))
   return metadata


 def ContainsFiles(path, root):
   """Determines whether any files exist in a directory or in any of its
     subdirectories."""
   for _, dirs, files in os.walk(os.path.join(root, path)):
     if files:
       return True
     for vcs_metadata in VCS_METADATA_DIRS:
       if vcs_metadata in dirs:
         dirs.remove(vcs_metadata)
   return False


 def FilterDirsWithFiles(dirs_list, root):
   # If a directory contains no files, assume it's a DEPS directory for a
   # project not used by our current configuration and skip it.
   return [x for x in dirs_list if ContainsFiles(x, root)]


 def ProcessAdditionalReadmePathsJson(root, dirname, third_party_dirs):
   """For a given directory, process the additional readme paths, and add to
     third_party_dirs."""
   additional_paths_file = os.path.join(root, dirname, ADDITIONAL_PATHS_FILENAME)
   if os.path.exists(additional_paths_file):
     with open(additional_paths_file) as paths_file:
       extra_paths = json.load(paths_file)
       third_party_dirs.update([os.path.join(dirname, p) for p in extra_paths])


 def FindThirdPartyDirs(prune_paths, root):
   """Find all third_party directories underneath the source root."""
   third_party_dirs = set()
   for path, dirs, files in os.walk(root):
     path = path[len(root) + 1:]  # Pretty up the path.

     # .gitignore ignores /out*/, so do the same here.
     if path in prune_paths or path.startswith('out'):
       dirs[:] = []
       continue

     # Prune out directories we want to skip.
     # (Note that we loop over PRUNE_DIRS so we're not iterating over a
     # list that we're simultaneously mutating.)
     for skip in PRUNE_DIRS:
       if skip in dirs:
         dirs.remove(skip)

     if os.path.basename(path) == 'third_party':
       # Add all subdirectories that are not marked for skipping.
       for dir in dirs:
         dirpath = os.path.join(path, dir)
         if dirpath not in prune_paths:
           third_party_dirs.add(dirpath)

         ProcessAdditionalReadmePathsJson(root, dirpath, third_party_dirs)

       # Don't recurse into any subdirs from here.
       dirs[:] = []
       continue

     # Don't recurse into paths in ADDITIONAL_PATHS, like we do with regular
     # third_party/foo paths.
     if path in ADDITIONAL_PATHS:
       dirs[:] = []

   for dir in ADDITIONAL_PATHS:
     if dir not in prune_paths:
       third_party_dirs.add(dir)
       ProcessAdditionalReadmePathsJson(root, dir, third_party_dirs)

   return third_party_dirs


 def FindThirdPartyDirsWithFiles(root):
   third_party_dirs = FindThirdPartyDirs(PRUNE_PATHS, root)
   return FilterDirsWithFiles(third_party_dirs, root)


 # Many builders do not contain 'gn' in their PATH, so use the GN binary from
 # //buildtools.
 def _GnBinary():
   exe = 'gn'
   if sys.platform.startswith('linux'):
     subdir = 'linux64'
   elif sys.platform == 'darwin':
     subdir = 'mac'
   elif sys.platform == 'win32':
     subdir, exe = 'win', 'gn.exe'
   else:
     raise RuntimeError("Unsupported platform '%s'." % sys.platform)

   return os.path.join(_REPOSITORY_ROOT, 'buildtools', subdir, exe)


 def GetThirdPartyDepsFromGNDepsOutput(gn_deps, target_os):
   """Returns third_party/foo directories given the output of "gn desc deps".

     Note that it always returns the direct sub-directory of third_party
     where README.chromium and LICENSE files are, so that it can be passed to
     ParseDir(). e.g.:
         third_party/cld_3/src/src/BUILD.gn -> third_party/cld_3

     It returns relative paths from _REPOSITORY_ROOT, not absolute paths.
     """
   third_party_deps = set()
   for absolute_build_dep in gn_deps.split():
     relative_build_dep = os.path.relpath(absolute_build_dep, _REPOSITORY_ROOT)
     m = re.search(
         r'^((.+[/\\])?third_party[/\\][^/\\]+[/\\])(.+[/\\])?BUILD\.gn$',
         relative_build_dep)
     if not m:
       continue
     third_party_path = m.group(1)
     if any(third_party_path.startswith(p + os.sep) for p in PRUNE_PATHS):
       continue
     if (target_os == 'ios' and any(
         third_party_path.startswith(p + os.sep)
         for p in KNOWN_NON_IOS_LIBRARIES)):
       # Skip over files that are known not to be used on iOS.
       continue
     third_party_deps.add(third_party_path[:-1])
   return third_party_deps


 def FindThirdPartyDeps(gn_out_dir, gn_target, target_os):
   if not gn_out_dir:
     raise RuntimeError("--gn-out-dir is required if --gn-target is used.")

   # Generate gn project in temp directory and use it to find dependencies.
   # Current gn directory cannot be used when we run this script in a gn action
   # rule, because gn doesn't allow recursive invocations due to potential side
   # effects.
   tmp_dir = None
   try:
     tmp_dir = tempfile.mkdtemp(dir=gn_out_dir)
     shutil.copy(os.path.join(gn_out_dir, "args.gn"), tmp_dir)
     subprocess.check_output([_GnBinary(), "gen", tmp_dir])
     gn_deps = subprocess.check_output([
         _GnBinary(), "desc", tmp_dir, gn_target, "deps", "--as=buildfile",
         "--all"
     ])
     if isinstance(gn_deps, bytes):
       gn_deps = gn_deps.decode("utf-8")
   finally:
     if tmp_dir and os.path.exists(tmp_dir):
       shutil.rmtree(tmp_dir)

   return GetThirdPartyDepsFromGNDepsOutput(gn_deps, target_os)


 def ScanThirdPartyDirs(root=None):
   """Scan a list of directories and report on any problems we find."""
   if root is None:
     root = os.getcwd()
   third_party_dirs = FindThirdPartyDirsWithFiles(root)

   errors = []
   for path in sorted(third_party_dirs):
     try:
       metadata = ParseDir(path, root)
     except LicenseError as e:
       errors.append((path, e.args[0]))
       continue

   for path, error in sorted(errors):
     print(path + ": " + error)

   return len(errors) == 0


 def GenerateCredits(
         file_template_file, entry_template_file, output_file, target_os,
         gn_out_dir, gn_target, depfile=None):
   """Generate about:credits."""

   def EvaluateTemplate(template, env, escape=True):
     """Expand a template with variables like {{foo}} using a
         dictionary of expansions."""
     for key, val in env.items():
       if escape:
         val = html.escape(val)
       template = template.replace('{{%s}}' % key, val)
     return template

   def MetadataToTemplateEntry(metadata, entry_template):
     env = {
         'name': metadata['Name'],
         'url': metadata['URL'],
         'license': open(metadata['License File']).read(),
     }
     return {
         'name': metadata['Name'],
         'content': EvaluateTemplate(entry_template, env),
         'license_file': metadata['License File'],
     }

   if gn_target:
     third_party_dirs = FindThirdPartyDeps(gn_out_dir, gn_target, target_os)

     # Sanity-check to raise a build error if invalid gn_... settings are
     # somehow passed to this script.
     if not third_party_dirs:
       raise RuntimeError("No deps found.")
   else:
     third_party_dirs = FindThirdPartyDirs(PRUNE_PATHS, _REPOSITORY_ROOT)

   if not file_template_file:
     file_template_file = os.path.join(_REPOSITORY_ROOT, 'components',
                                       'about_ui', 'resources',
                                       'about_credits.tmpl')
   if not entry_template_file:
     entry_template_file = os.path.join(_REPOSITORY_ROOT, 'components',
                                        'about_ui', 'resources',
                                        'about_credits_entry.tmpl')

   entry_template = open(entry_template_file).read()
   entries = []
   # Start from Chromium's LICENSE file
   chromium_license_metadata = {
       'Name': 'The Chromium Project',
       'URL': 'http://www.chromium.org',
       'License File': os.path.join(_REPOSITORY_ROOT, 'LICENSE')
   }
   entries.append(
       MetadataToTemplateEntry(chromium_license_metadata, entry_template))

   entries_by_name = {}
   for path in third_party_dirs:
     try:
       metadata = ParseDir(path, _REPOSITORY_ROOT)
     except LicenseError:
       # TODO(phajdan.jr): Convert to fatal error (http://crbug.com/39240).
       continue
     if metadata['License File'] == NOT_SHIPPED:
       continue
     if target_os == 'ios' and not gn_target:
       # Skip over files that are known not to be used on iOS. But
       # skipping is unnecessary if GN was used to query the actual
       # dependencies.
       # TODO(lambroslambrou): Remove this step once the iOS build is
       # updated to provide --gn-target to this script.
       if path in KNOWN_NON_IOS_LIBRARIES:
         continue

     new_entry = MetadataToTemplateEntry(metadata, entry_template)
     # Skip entries that we've already seen (it exists in multiple directories).
     prev_entry = entries_by_name.setdefault(new_entry['name'], new_entry)
     if prev_entry is not new_entry and (
         prev_entry['content'] == new_entry['content']):
       continue

     entries.append(new_entry)

   entries.sort(key=lambda entry: (entry['name'].lower(), entry['content']))
   for entry_id, entry in enumerate(entries):
     entry['content'] = entry['content'].replace('{{id}}', str(entry_id))

   entries_contents = '\n'.join([entry['content'] for entry in entries])
   file_template = open(file_template_file).read()
   template_contents = "<!-- Generated by licenses.py; do not edit. -->"
   template_contents += EvaluateTemplate(
       file_template, {'entries': entries_contents}, escape=False)

   if output_file:
     changed = True
     try:
       old_output = open(output_file, 'r').read()
       if old_output == template_contents:
         changed = False
     except:
       pass
     if changed:
       with open(output_file, 'w') as output:
         output.write(template_contents)
   else:
     print(template_contents)

   if depfile:
     assert output_file
     # Add in build.ninja so that the target will be considered dirty whenever
     # gn gen is run. Otherwise, it will fail to notice new files being added.
     # This is still no perfect, as it will fail if no build files are changed,
     # but a new README.chromium / LICENSE is added. This shouldn't happen in
     # practice however.
     license_file_list = (entry['license_file'] for entry in entries)
     license_file_list = (os.path.relpath(p) for p in license_file_list)
     license_file_list = sorted(set(license_file_list))
     build_utils.WriteDepfile(depfile, output_file,
                              license_file_list + ['build.ninja'])

   return True


 def _ReadFile(path):
   """Reads a file from disk.
     Args:
       path: The path of the file to read, relative to the root of the
       repository.
     Returns:
       The contents of the file as a string.
     """
   with codecs.open(os.path.join(_REPOSITORY_ROOT, path), 'r', 'utf-8') as f:
     return f.read()


 def GenerateLicenseFile(output_file, gn_out_dir, gn_target, target_os):
   """Generate a plain-text LICENSE file which can be used when you ship a part
     of Chromium code (specified by gn_target) as a stand-alone library
     (e.g., //ios/web_view).

     The LICENSE file contains licenses of both Chromium and third-party
     libraries which gn_target depends on. """

   third_party_dirs = FindThirdPartyDeps(gn_out_dir, gn_target, target_os)

   # Start with Chromium's LICENSE file.
   content = [_ReadFile('LICENSE')]

   # Add necessary third_party.
   for directory in sorted(third_party_dirs):
     metadata = ParseDir(directory, _REPOSITORY_ROOT, require_license_file=True)
     license_file = metadata['License File']
     if license_file and license_file != NOT_SHIPPED:
       content.append('-' * 20)
       content.append(directory.split(os.sep)[-1])
       content.append('-' * 20)
       content.append(_ReadFile(license_file))

   content_text = '\n'.join(content)

   if output_file:
     with codecs.open(output_file, 'w', 'utf-8') as output:
       output.write(content_text)
   else:
     print(content_text)


 def main():
   parser = argparse.ArgumentParser()
   parser.add_argument(
       '--file-template', help='Template HTML to use for the license page.')
   parser.add_argument(
       '--entry-template', help='Template HTML to use for each license.')
   parser.add_argument('--target-os', help='OS that this build is targeting.')
   parser.add_argument(
       '--gn-out-dir', help='GN output directory for scanning dependencies.')
   parser.add_argument('--gn-target', help='GN target to scan for dependencies.')
   parser.add_argument(
       'command', choices=['help', 'scan', 'credits', 'license_file'])
   parser.add_argument('output_file', nargs='?')
   build_utils.AddDepfileOption(parser)
   args = parser.parse_args()

   if args.command == 'scan':
     if not ScanThirdPartyDirs():
       return 1
   elif args.command == 'credits':
     if not GenerateCredits(args.file_template, args.entry_template,
                            args.output_file, args.target_os, args.gn_out_dir,
                            args.gn_target, args.depfile):
       return 1
   elif args.command == 'license_file':
     try:
       GenerateLicenseFile(args.output_file, args.gn_out_dir, args.gn_target,
                           args.target_os)
     except LicenseError as e:
       print("Failed to parse README.chromium: {}".format(e))
       return 1
   else:
     print(__doc__)
     return 1


 if __name__ == '__main__':
   sys.exit(main())