tools/gen_android_bp - third_party/perfetto - Git at Google

 #!/usr/bin/env python
 # Copyright (C) 2017 The Android Open Source Project
 #
 # Licensed under the Apache License, Version 2.0 (the "License");
 # you may not use this file except in compliance with the License.
 # You may obtain a copy of the License at
 #
 #      http://www.apache.org/licenses/LICENSE-2.0
 #
 # Unless required by applicable law or agreed to in writing, software
 # distributed under the License is distributed on an "AS IS" BASIS,
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.

 # This tool translates a collection of BUILD.gn files into a mostly equivalent
 # Android.bp file for the Android Soong build system. The input to the tool is a
 # JSON description of the GN build definition generated with the following
 # command:
 #
 #   gn desc out --format=json --all-toolchains "//*" > desc.json
 #
 # The tool is then given a list of GN labels for which to generate Android.bp
 # build rules. The dependencies for the GN labels are squashed to the generated
 # Android.bp target, except for actions which get their own genrule. Some
 # libraries are also mapped to their Android equivalents -- see |builtin_deps|.

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

 # Default targets to translate to the blueprint file.
 default_targets = ['//:perfetto_tests']

 # Arguments for the GN output directory.
 gn_args = 'target_os="android" target_cpu="arm" is_debug=false'

 # All module names are prefixed with this string to avoid collisions.
 module_prefix = 'perfetto_'

 # Shared libraries which are directly translated to Android system equivalents.
 library_whitelist = [
     'android',
     'log',
 ]

 # Name of the module which settings such as compiler flags for all other
 # modules.
 defaults_module = module_prefix + 'defaults'

 # Location of the project in the Android source tree.
 tree_path = 'external/perfetto'


 def enable_gmock(module):
     module.static_libs.append('libgmock')


 def enable_gtest(module):
     assert module.type == 'cc_test'


 def enable_protobuf_full(module):
     module.shared_libs.append('libprotobuf-cpp-full')


 def enable_protobuf_lite(module):
     module.shared_libs.append('libprotobuf-cpp-lite')


 def enable_protoc_lib(module):
     module.shared_libs.append('libprotoc')


 def enable_libunwind(module):
     module.shared_libs.append('libunwind')


 # Android equivalents for third-party libraries that the upstream project
 # depends on.
 builtin_deps = {
     '//buildtools:gmock': enable_gmock,
     '//buildtools:gtest': enable_gtest,
     '//buildtools:gtest_main': enable_gtest,
     '//buildtools:libunwind': enable_libunwind,
     '//buildtools:protobuf_full': enable_protobuf_full,
     '//buildtools:protobuf_lite': enable_protobuf_lite,
     '//buildtools:protoc_lib': enable_protoc_lib,
 }

 # ----------------------------------------------------------------------------
 # End of configuration.
 # ----------------------------------------------------------------------------


 class Error(Exception):
     pass


 class ThrowingArgumentParser(argparse.ArgumentParser):
     def __init__(self, context):
         super(ThrowingArgumentParser, self).__init__()
         self.context = context

     def error(self, message):
         raise Error('%s: %s' % (self.context, message))


 class Module(object):
     """A single module (e.g., cc_binary, cc_test) in a blueprint."""

     def __init__(self, mod_type, name):
         self.type = mod_type
         self.name = name
         self.srcs = []
         self.comment = None
         self.shared_libs = []
         self.static_libs = []
         self.tools = []
         self.cmd = None
         self.out = []
         self.export_include_dirs = []
         self.generated_headers = []
         self.defaults = []
         self.cflags = []
         self.local_include_dirs = []

     def to_string(self, output):
         if self.comment:
             output.append('// %s' % self.comment)
         output.append('%s {' % self.type)
         self._output_field(output, 'name')
         self._output_field(output, 'srcs')
         self._output_field(output, 'shared_libs')
         self._output_field(output, 'static_libs')
         self._output_field(output, 'tools')
         self._output_field(output, 'cmd', sort=False)
         self._output_field(output, 'out')
         self._output_field(output, 'export_include_dirs')
         self._output_field(output, 'generated_headers')
         self._output_field(output, 'defaults')
         self._output_field(output, 'cflags')
         self._output_field(output, 'local_include_dirs')
         output.append('}')
         output.append('')

     def _output_field(self, output, name, sort=True):
         value = getattr(self, name)
         if not value:
             return
         if isinstance(value, list):
             output.append('  %s: [' % name)
             for item in sorted(value) if sort else value:
                 output.append('    "%s",' % item)
             output.append('  ],')
         else:
             output.append('  %s: "%s",' % (name, value))


 class Blueprint(object):
     """In-memory representation of an Android.bp file."""

     def __init__(self):
         self.modules = {}

     def add_module(self, module):
         """Adds a new module to the blueprint, replacing any existing module
         with the same name.

         Args:
             module: Module instance.
         """
         self.modules[module.name] = module

     def to_string(self, output):
         for m in self.modules.itervalues():
             m.to_string(output)


 def label_to_path(label):
     """Turn a GN output label (e.g., //some_dir/file.cc) into a path."""
     assert label.startswith('//')
     return label[2:]


 def label_to_module_name(label):
     """Turn a GN label (e.g., //:perfetto_tests) into a module name."""
     label = re.sub(r'^//:?', '', label)
     module = re.sub(r'[^a-zA-Z0-9_]', '_', label)
     if not module.startswith(module_prefix):
         return module_prefix + module
     return module


 def label_without_toolchain(label):
     """Strips the toolchain from a GN label.

     Return a GN label (e.g //buildtools:protobuf(//gn/standalone/toolchain:
     gcc_like_host) without the parenthesised toolchain part.
     """
     return label.split('(')[0]


 def is_supported_source_file(name):
     """Returns True if |name| can appear in a 'srcs' list."""
     return os.path.splitext(name)[1] in ['.c', '.cc', '.proto']


 def is_generated_by_action(desc, label):
     """Checks if a label is generated by an action.

     Returns True if a GN output label |label| is an output for any action,
     i.e., the file is generated dynamically.
     """
     for target in desc.itervalues():
         if target['type'] == 'action' and label in target['outputs']:
             return True
     return False


 def apply_module_dependency(blueprint, desc, module, dep_name):
     """Recursively collect dependencies for a given module.

     Walk the transitive dependencies for a GN target and apply them to a given
     module. This effectively flattens the dependency tree so that |module|
     directly contains all the sources, libraries, etc. in the corresponding GN
     dependency tree.

     Args:
         blueprint: Blueprint instance which is being generated.
         desc: JSON GN description.
         module: Module to which dependencies should be added.
         dep_name: GN target of the dependency.
     """
     # Don't try to inject library/source dependencies into genrules because they
     # are not compiled in the traditional sense.
     if module.type == 'cc_genrule':
         return

     # If the dependency refers to a library which we can replace with an Android
     # equivalent, stop recursing and patch the dependency in.
     if label_without_toolchain(dep_name) in builtin_deps:
         builtin_deps[label_without_toolchain(dep_name)](module)
         return

     # Similarly some shared libraries are directly mapped to Android
     # equivalents.
     target = desc[dep_name]
     for lib in target.get('libs', []):
         android_lib = 'lib' + lib
         if lib in library_whitelist and not android_lib in module.shared_libs:
             module.shared_libs.append(android_lib)

     type = target['type']
     if type == 'action':
         create_modules_from_target(blueprint, desc, dep_name)
         # Depend both on the generated sources and headers -- see
         # make_genrules_for_action.
         module.srcs.append(':' + label_to_module_name(dep_name))
         module.generated_headers.append(
             label_to_module_name(dep_name) + '_headers')
     elif type in ['group', 'source_set', 'executable'] and 'sources' in target:
         # Ignore source files that are generated by actions since they will be
         # implicitly added by the genrule dependencies.
         module.srcs.extend(
             label_to_path(src) for src in target['sources']
             if is_supported_source_file(src)
             and not is_generated_by_action(desc, src))


 def make_genrules_for_action(blueprint, desc, target_name):
     """Generate genrules for a GN action.

     GN actions are used to dynamically generate files during the build. The
     Soong equivalent is a genrule. This function turns a specific kind of
     genrule which turns .proto files into source and header files into a pair
     equivalent cc_genrules.

     Args:
         blueprint: Blueprint instance which is being generated.
         desc: JSON GN description.
         target_name: GN target for genrule generation.

     Returns:
         A (source_genrule, header_genrule) module tuple.
     """
     target = desc[target_name]

     # We only support genrules which call protoc (with or without a plugin) to
     # turn .proto files into header and source files.
     args = target['args']
     if not args[0].endswith('/protoc'):
         raise Error('Unsupported action in target %s: %s' % (target_name,
                                                              target['args']))

     # We create two genrules for each action: one for the protobuf headers and
     # another for the sources. This is because the module that depends on the
     # generated files needs to declare two different types of dependencies --
     # source files in 'srcs' and headers in 'generated_headers' -- and it's not
     # valid to generate .h files from a source dependency and vice versa.
     source_module = Module('cc_genrule', label_to_module_name(target_name))
     source_module.srcs.extend(label_to_path(src) for src in target['sources'])
     source_module.tools = ['aprotoc']

     header_module = Module('cc_genrule',
                            label_to_module_name(target_name) + '_headers')
     header_module.srcs = source_module.srcs[:]
     header_module.tools = source_module.tools[:]
     header_module.export_include_dirs = ['.']

     # TODO(skyostil): Is there a way to avoid hardcoding the tree path here?
     # TODO(skyostil): Find a way to avoid creating the directory.
     cmd = [
         'mkdir -p $(genDir)/%s &&' % tree_path, '$(location aprotoc)',
         '--cpp_out=$(genDir)/%s' % tree_path,
         '--proto_path=%s' % tree_path
     ]
     namespaces = ['pb']

     parser = ThrowingArgumentParser('Action in target %s (%s)' %
                                     (target_name, ' '.join(target['args'])))
     parser.add_argument('--proto_path')
     parser.add_argument('--cpp_out')
     parser.add_argument('--plugin')
     parser.add_argument('--plugin_out')
     parser.add_argument('protos', nargs=argparse.REMAINDER)

     args = parser.parse_args(args[1:])
     if args.plugin:
         _, plugin = os.path.split(args.plugin)
         # TODO(skyostil): Can we detect this some other way?
         if plugin == 'ipc_plugin':
             namespaces.append('ipc')
         elif plugin == 'protoc_plugin':
             namespaces = ['pbzero']
         for dep in target['deps']:
             if desc[dep]['type'] != 'executable':
                 continue
             _, executable = os.path.split(desc[dep]['outputs'][0])
             if executable == plugin:
                 cmd += [
                     '--plugin=protoc-gen-plugin=$(location %s)' %
                     label_to_module_name(dep)
                 ]
                 source_module.tools.append(label_to_module_name(dep))
                 # Also make sure the module for the tool is generated.
                 create_modules_from_target(blueprint, desc, dep)
                 break
         else:
             raise Error('Unrecognized protoc plugin in target %s: %s' %
                         (target_name, args[i]))
     if args.plugin_out:
         plugin_args = args.plugin_out.split(':')[0]
         cmd += ['--plugin_out=%s:$(genDir)/%s' % (plugin_args, tree_path)]

     cmd += ['$(in)']
     source_module.cmd = ' '.join(cmd)
     header_module.cmd = source_module.cmd
     header_module.tools = source_module.tools[:]

     for ns in namespaces:
         source_module.out += [
             '%s/%s' % (tree_path, src.replace('.proto', '.%s.cc' % ns))
             for src in source_module.srcs
         ]
         header_module.out += [
             '%s/%s' % (tree_path, src.replace('.proto', '.%s.h' % ns))
             for src in header_module.srcs
         ]
     return source_module, header_module


 def create_modules_from_target(blueprint, desc, target_name):
     """Generate module(s) for a given GN target.

     Given a GN target name, generate one or more corresponding modules into a
     blueprint.

     Args:
         blueprint: Blueprint instance which is being generated.
         desc: JSON GN description.
         target_name: GN target for module generation.
     """
     target = desc[target_name]
     if target['type'] == 'executable':
         if 'host' in target['toolchain']:
             module_type = 'cc_binary_host'
         elif target.get('testonly'):
             module_type = 'cc_test'
         else:
             module_type = 'cc_binary'
         modules = [Module(module_type, label_to_module_name(target_name))]
     elif target['type'] == 'action':
         modules = make_genrules_for_action(blueprint, desc, target_name)
     else:
         raise Error('Unknown target type: %s' % target['type'])

     for module in modules:
         module.comment = 'GN target: %s' % target_name
         if module.type != 'cc_genrule':
             module.defaults = [defaults_module]

         apply_module_dependency(blueprint, desc, module, target_name)
         for dep in resolve_dependencies(desc, target_name):
             apply_module_dependency(blueprint, desc, module, dep)

         blueprint.add_module(module)


 def resolve_dependencies(desc, target_name):
     """Return the transitive set of dependent-on targets for a GN target.

     Args:
         blueprint: Blueprint instance which is being generated.
         desc: JSON GN description.

     Returns:
         A set of transitive dependencies in the form of GN targets.
     """

     if label_without_toolchain(target_name) in builtin_deps:
         return set()
     target = desc[target_name]
     resolved_deps = set()
     for dep in target.get('deps', []):
         resolved_deps.add(dep)
         # Ignore the transitive dependencies of actions because they are
         # explicitly converted to genrules.
         if desc[dep]['type'] == 'action':
             continue
         resolved_deps.update(resolve_dependencies(desc, dep))
     return resolved_deps


 def create_blueprint_for_targets(desc, targets):
     """Generate a blueprint for a list of GN targets."""
     blueprint = Blueprint()

     # Default settings used by all modules.
     defaults = Module('cc_defaults', defaults_module)
     defaults.local_include_dirs = ['include']
     defaults.cflags = [
         '-Wno-error=return-type',
         '-Wno-sign-compare',
         '-Wno-sign-promo',
         '-Wno-unused-parameter',
     ]

     blueprint.add_module(defaults)
     for target in targets:
         create_modules_from_target(blueprint, desc, target)
     return blueprint


 def repo_root():
     """Returns an absolute path to the repository root."""

     return os.path.join(
         os.path.realpath(os.path.dirname(__file__)), os.path.pardir)


 def create_build_description():
     """Creates the JSON build description by running GN."""

     out = os.path.join(repo_root(), 'out', 'tmp.gen_android_bp')
     try:
         try:
             os.makedirs(out)
         except OSError as e:
             if e.errno != errno.EEXIST:
                 raise
         subprocess.check_output(
             ['gn', 'gen', out, '--args=%s' % gn_args], cwd=repo_root())
         desc = subprocess.check_output(
             ['gn', 'desc', out, '--format=json', '--all-toolchains', '//*'],
             cwd=repo_root())
         return json.loads(desc)
     finally:
         shutil.rmtree(out)


 def main():
     parser = argparse.ArgumentParser(
         description='Generate Android.bp from a GN description.')
     parser.add_argument(
         '--desc',
         help=
         'GN description (e.g., gn desc out --format=json --all-toolchains "//*"'
     )
     parser.add_argument(
         '--output',
         help='Blueprint file to create',
         default=os.path.join(repo_root(), 'Android.bp'),
     )
     parser.add_argument(
         'targets',
         nargs=argparse.REMAINDER,
         help='Targets to include in the blueprint (e.g., "//:perfetto_tests")')
     args = parser.parse_args()

     if args.desc:
         with open(args.desc) as f:
             desc = json.load(f)
     else:
         desc = create_build_description()

     blueprint = create_blueprint_for_targets(desc, args.targets
                                              or default_targets)
     output = [
         """// Copyright (C) 2017 The Android Open Source Project
 //
 // Licensed under the Apache License, Version 2.0 (the "License");
 // you may not use this file except in compliance with the License.
 // You may obtain a copy of the License at
 //
 //      http://www.apache.org/licenses/LICENSE-2.0
 //
 // Unless required by applicable law or agreed to in writing, software
 // distributed under the License is distributed on an "AS IS" BASIS,
 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 // See the License for the specific language governing permissions and
 // limitations under the License.
 //
 // This file is automatically generated by %s. Do not edit.
 """ % (__file__)
     ]
     blueprint.to_string(output)
     with open(args.output, 'w') as f:
         f.write('\n'.join(output))


 if __name__ == '__main__':
     sys.exit(main())
	#!/usr/bin/env python
	# Copyright (C) 2017 The Android Open Source Project
	#
	# Licensed under the Apache License, Version 2.0 (the "License");
	# you may not use this file except in compliance with the License.
	# You may obtain a copy of the License at
	#
	# http://www.apache.org/licenses/LICENSE-2.0
	#
	# Unless required by applicable law or agreed to in writing, software
	# distributed under the License is distributed on an "AS IS" BASIS,
	# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	# See the License for the specific language governing permissions and
	# limitations under the License.

	# This tool translates a collection of BUILD.gn files into a mostly equivalent
	# Android.bp file for the Android Soong build system. The input to the tool is a
	# JSON description of the GN build definition generated with the following
	# command:
	#
	# gn desc out --format=json --all-toolchains "//*" > desc.json
	#
	# The tool is then given a list of GN labels for which to generate Android.bp
	# build rules. The dependencies for the GN labels are squashed to the generated
	# Android.bp target, except for actions which get their own genrule. Some
	# libraries are also mapped to their Android equivalents -- see \|builtin_deps\|.

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

	# Default targets to translate to the blueprint file.
	default_targets = ['//:perfetto_tests']

	# Arguments for the GN output directory.
	gn_args = 'target_os="android" target_cpu="arm" is_debug=false'

	# All module names are prefixed with this string to avoid collisions.
	module_prefix = 'perfetto_'

	# Shared libraries which are directly translated to Android system equivalents.
	library_whitelist = [
	'android',
	'log',
	]

	# Name of the module which settings such as compiler flags for all other
	# modules.
	defaults_module = module_prefix + 'defaults'

	# Location of the project in the Android source tree.
	tree_path = 'external/perfetto'


	def enable_gmock(module):
	module.static_libs.append('libgmock')


	def enable_gtest(module):
	assert module.type == 'cc_test'


	def enable_protobuf_full(module):
	module.shared_libs.append('libprotobuf-cpp-full')


	def enable_protobuf_lite(module):
	module.shared_libs.append('libprotobuf-cpp-lite')


	def enable_protoc_lib(module):
	module.shared_libs.append('libprotoc')


	def enable_libunwind(module):
	module.shared_libs.append('libunwind')


	# Android equivalents for third-party libraries that the upstream project
	# depends on.
	builtin_deps = {
	'//buildtools:gmock': enable_gmock,
	'//buildtools:gtest': enable_gtest,
	'//buildtools:gtest_main': enable_gtest,
	'//buildtools:libunwind': enable_libunwind,
	'//buildtools:protobuf_full': enable_protobuf_full,
	'//buildtools:protobuf_lite': enable_protobuf_lite,
	'//buildtools:protoc_lib': enable_protoc_lib,
	}

	# ----------------------------------------------------------------------------
	# End of configuration.
	# ----------------------------------------------------------------------------


	class Error(Exception):
	pass


	class ThrowingArgumentParser(argparse.ArgumentParser):
	def __init__(self, context):
	super(ThrowingArgumentParser, self).__init__()
	self.context = context

	def error(self, message):
	raise Error('%s: %s' % (self.context, message))


	class Module(object):
	"""A single module (e.g., cc_binary, cc_test) in a blueprint."""

	def __init__(self, mod_type, name):
	self.type = mod_type
	self.name = name
	self.srcs = []
	self.comment = None
	self.shared_libs = []
	self.static_libs = []
	self.tools = []
	self.cmd = None
	self.out = []
	self.export_include_dirs = []
	self.generated_headers = []
	self.defaults = []
	self.cflags = []
	self.local_include_dirs = []

	def to_string(self, output):
	if self.comment:
	output.append('// %s' % self.comment)
	output.append('%s {' % self.type)
	self._output_field(output, 'name')
	self._output_field(output, 'srcs')
	self._output_field(output, 'shared_libs')
	self._output_field(output, 'static_libs')
	self._output_field(output, 'tools')
	self._output_field(output, 'cmd', sort=False)
	self._output_field(output, 'out')
	self._output_field(output, 'export_include_dirs')
	self._output_field(output, 'generated_headers')
	self._output_field(output, 'defaults')
	self._output_field(output, 'cflags')
	self._output_field(output, 'local_include_dirs')
	output.append('}')
	output.append('')

	def _output_field(self, output, name, sort=True):
	value = getattr(self, name)
	if not value:
	return
	if isinstance(value, list):
	output.append(' %s: [' % name)
	for item in sorted(value) if sort else value:
	output.append(' "%s",' % item)
	output.append(' ],')
	else:
	output.append(' %s: "%s",' % (name, value))


	class Blueprint(object):
	"""In-memory representation of an Android.bp file."""

	def __init__(self):
	self.modules = {}

	def add_module(self, module):
	"""Adds a new module to the blueprint, replacing any existing module
	with the same name.

	Args:
	module: Module instance.
	"""
	self.modules[module.name] = module

	def to_string(self, output):
	for m in self.modules.itervalues():
	m.to_string(output)


	def label_to_path(label):
	"""Turn a GN output label (e.g., //some_dir/file.cc) into a path."""
	assert label.startswith('//')
	return label[2:]


	def label_to_module_name(label):
	"""Turn a GN label (e.g., //:perfetto_tests) into a module name."""
	label = re.sub(r'^//:?', '', label)
	module = re.sub(r'[^a-zA-Z0-9_]', '_', label)
	if not module.startswith(module_prefix):
	return module_prefix + module
	return module


	def label_without_toolchain(label):
	"""Strips the toolchain from a GN label.

	Return a GN label (e.g //buildtools:protobuf(//gn/standalone/toolchain:
	gcc_like_host) without the parenthesised toolchain part.
	"""
	return label.split('(')[0]


	def is_supported_source_file(name):
	"""Returns True if \|name\| can appear in a 'srcs' list."""
	return os.path.splitext(name)[1] in ['.c', '.cc', '.proto']


	def is_generated_by_action(desc, label):
	"""Checks if a label is generated by an action.

	Returns True if a GN output label \|label\| is an output for any action,
	i.e., the file is generated dynamically.
	"""
	for target in desc.itervalues():
	if target['type'] == 'action' and label in target['outputs']:
	return True
	return False


	def apply_module_dependency(blueprint, desc, module, dep_name):
	"""Recursively collect dependencies for a given module.

	Walk the transitive dependencies for a GN target and apply them to a given
	module. This effectively flattens the dependency tree so that \|module\|
	directly contains all the sources, libraries, etc. in the corresponding GN
	dependency tree.

	Args:
	blueprint: Blueprint instance which is being generated.
	desc: JSON GN description.
	module: Module to which dependencies should be added.
	dep_name: GN target of the dependency.
	"""
	# Don't try to inject library/source dependencies into genrules because they
	# are not compiled in the traditional sense.
	if module.type == 'cc_genrule':
	return

	# If the dependency refers to a library which we can replace with an Android
	# equivalent, stop recursing and patch the dependency in.
	if label_without_toolchain(dep_name) in builtin_deps:
	builtin_deps[label_without_toolchain(dep_name)](module)
	return

	# Similarly some shared libraries are directly mapped to Android
	# equivalents.
	target = desc[dep_name]
	for lib in target.get('libs', []):
	android_lib = 'lib' + lib
	if lib in library_whitelist and not android_lib in module.shared_libs:
	module.shared_libs.append(android_lib)

	type = target['type']
	if type == 'action':
	create_modules_from_target(blueprint, desc, dep_name)
	# Depend both on the generated sources and headers -- see
	# make_genrules_for_action.
	module.srcs.append(':' + label_to_module_name(dep_name))
	module.generated_headers.append(
	label_to_module_name(dep_name) + '_headers')
	elif type in ['group', 'source_set', 'executable'] and 'sources' in target:
	# Ignore source files that are generated by actions since they will be
	# implicitly added by the genrule dependencies.
	module.srcs.extend(
	label_to_path(src) for src in target['sources']
	if is_supported_source_file(src)
	and not is_generated_by_action(desc, src))


	def make_genrules_for_action(blueprint, desc, target_name):
	"""Generate genrules for a GN action.

	GN actions are used to dynamically generate files during the build. The
	Soong equivalent is a genrule. This function turns a specific kind of
	genrule which turns .proto files into source and header files into a pair
	equivalent cc_genrules.

	Args:
	blueprint: Blueprint instance which is being generated.
	desc: JSON GN description.
	target_name: GN target for genrule generation.

	Returns:
	A (source_genrule, header_genrule) module tuple.
	"""
	target = desc[target_name]

	# We only support genrules which call protoc (with or without a plugin) to
	# turn .proto files into header and source files.
	args = target['args']
	if not args[0].endswith('/protoc'):
	raise Error('Unsupported action in target %s: %s' % (target_name,
	target['args']))

	# We create two genrules for each action: one for the protobuf headers and
	# another for the sources. This is because the module that depends on the
	# generated files needs to declare two different types of dependencies --
	# source files in 'srcs' and headers in 'generated_headers' -- and it's not
	# valid to generate .h files from a source dependency and vice versa.
	source_module = Module('cc_genrule', label_to_module_name(target_name))
	source_module.srcs.extend(label_to_path(src) for src in target['sources'])
	source_module.tools = ['aprotoc']

	header_module = Module('cc_genrule',
	label_to_module_name(target_name) + '_headers')
	header_module.srcs = source_module.srcs[:]
	header_module.tools = source_module.tools[:]
	header_module.export_include_dirs = ['.']

	# TODO(skyostil): Is there a way to avoid hardcoding the tree path here?
	# TODO(skyostil): Find a way to avoid creating the directory.
	cmd = [
	'mkdir -p $(genDir)/%s &&' % tree_path, '$(location aprotoc)',
	'--cpp_out=$(genDir)/%s' % tree_path,
	'--proto_path=%s' % tree_path
	]
	namespaces = ['pb']

	parser = ThrowingArgumentParser('Action in target %s (%s)' %
	(target_name, ' '.join(target['args'])))
	parser.add_argument('--proto_path')
	parser.add_argument('--cpp_out')
	parser.add_argument('--plugin')
	parser.add_argument('--plugin_out')
	parser.add_argument('protos', nargs=argparse.REMAINDER)

	args = parser.parse_args(args[1:])
	if args.plugin:
	_, plugin = os.path.split(args.plugin)
	# TODO(skyostil): Can we detect this some other way?
	if plugin == 'ipc_plugin':
	namespaces.append('ipc')
	elif plugin == 'protoc_plugin':
	namespaces = ['pbzero']
	for dep in target['deps']:
	if desc[dep]['type'] != 'executable':
	continue
	_, executable = os.path.split(desc[dep]['outputs'][0])
	if executable == plugin:
	cmd += [
	'--plugin=protoc-gen-plugin=$(location %s)' %
	label_to_module_name(dep)
	]
	source_module.tools.append(label_to_module_name(dep))
	# Also make sure the module for the tool is generated.
	create_modules_from_target(blueprint, desc, dep)
	break
	else:
	raise Error('Unrecognized protoc plugin in target %s: %s' %
	(target_name, args[i]))
	if args.plugin_out:
	plugin_args = args.plugin_out.split(':')[0]
	cmd += ['--plugin_out=%s:$(genDir)/%s' % (plugin_args, tree_path)]

	cmd += ['$(in)']
	source_module.cmd = ' '.join(cmd)
	header_module.cmd = source_module.cmd
	header_module.tools = source_module.tools[:]

	for ns in namespaces:
	source_module.out += [
	'%s/%s' % (tree_path, src.replace('.proto', '.%s.cc' % ns))
	for src in source_module.srcs
	]
	header_module.out += [
	'%s/%s' % (tree_path, src.replace('.proto', '.%s.h' % ns))
	for src in header_module.srcs
	]
	return source_module, header_module


	def create_modules_from_target(blueprint, desc, target_name):
	"""Generate module(s) for a given GN target.

	Given a GN target name, generate one or more corresponding modules into a
	blueprint.

	Args:
	blueprint: Blueprint instance which is being generated.
	desc: JSON GN description.
	target_name: GN target for module generation.
	"""
	target = desc[target_name]
	if target['type'] == 'executable':
	if 'host' in target['toolchain']:
	module_type = 'cc_binary_host'
	elif target.get('testonly'):
	module_type = 'cc_test'
	else:
	module_type = 'cc_binary'
	modules = [Module(module_type, label_to_module_name(target_name))]
	elif target['type'] == 'action':
	modules = make_genrules_for_action(blueprint, desc, target_name)
	else:
	raise Error('Unknown target type: %s' % target['type'])

	for module in modules:
	module.comment = 'GN target: %s' % target_name
	if module.type != 'cc_genrule':
	module.defaults = [defaults_module]

	apply_module_dependency(blueprint, desc, module, target_name)
	for dep in resolve_dependencies(desc, target_name):
	apply_module_dependency(blueprint, desc, module, dep)

	blueprint.add_module(module)


	def resolve_dependencies(desc, target_name):
	"""Return the transitive set of dependent-on targets for a GN target.

	Args:
	blueprint: Blueprint instance which is being generated.
	desc: JSON GN description.

	Returns:
	A set of transitive dependencies in the form of GN targets.
	"""

	if label_without_toolchain(target_name) in builtin_deps:
	return set()
	target = desc[target_name]
	resolved_deps = set()
	for dep in target.get('deps', []):
	resolved_deps.add(dep)
	# Ignore the transitive dependencies of actions because they are
	# explicitly converted to genrules.
	if desc[dep]['type'] == 'action':
	continue
	resolved_deps.update(resolve_dependencies(desc, dep))
	return resolved_deps


	def create_blueprint_for_targets(desc, targets):
	"""Generate a blueprint for a list of GN targets."""
	blueprint = Blueprint()

	# Default settings used by all modules.
	defaults = Module('cc_defaults', defaults_module)
	defaults.local_include_dirs = ['include']
	defaults.cflags = [
	'-Wno-error=return-type',
	'-Wno-sign-compare',
	'-Wno-sign-promo',
	'-Wno-unused-parameter',
	]

	blueprint.add_module(defaults)
	for target in targets:
	create_modules_from_target(blueprint, desc, target)
	return blueprint


	def repo_root():
	"""Returns an absolute path to the repository root."""

	return os.path.join(
	os.path.realpath(os.path.dirname(__file__)), os.path.pardir)


	def create_build_description():
	"""Creates the JSON build description by running GN."""

	out = os.path.join(repo_root(), 'out', 'tmp.gen_android_bp')
	try:
	try:
	os.makedirs(out)
	except OSError as e:
	if e.errno != errno.EEXIST:
	raise
	subprocess.check_output(
	['gn', 'gen', out, '--args=%s' % gn_args], cwd=repo_root())
	desc = subprocess.check_output(
	['gn', 'desc', out, '--format=json', '--all-toolchains', '//*'],
	cwd=repo_root())
	return json.loads(desc)
	finally:
	shutil.rmtree(out)


	def main():
	parser = argparse.ArgumentParser(
	description='Generate Android.bp from a GN description.')
	parser.add_argument(
	'--desc',
	help=
	'GN description (e.g., gn desc out --format=json --all-toolchains "//*"'
	)
	parser.add_argument(
	'--output',
	help='Blueprint file to create',
	default=os.path.join(repo_root(), 'Android.bp'),
	)
	parser.add_argument(
	'targets',
	nargs=argparse.REMAINDER,
	help='Targets to include in the blueprint (e.g., "//:perfetto_tests")')
	args = parser.parse_args()

	if args.desc:
	with open(args.desc) as f:
	desc = json.load(f)
	else:
	desc = create_build_description()

	blueprint = create_blueprint_for_targets(desc, args.targets
	or default_targets)
	output = [
	"""// Copyright (C) 2017 The Android Open Source Project
	//
	// Licensed under the Apache License, Version 2.0 (the "License");
	// you may not use this file except in compliance with the License.
	// You may obtain a copy of the License at
	//
	// http://www.apache.org/licenses/LICENSE-2.0
	//
	// Unless required by applicable law or agreed to in writing, software
	// distributed under the License is distributed on an "AS IS" BASIS,
	// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	// See the License for the specific language governing permissions and
	// limitations under the License.
	//
	// This file is automatically generated by %s. Do not edit.
	""" % (__file__)
	]
	blueprint.to_string(output)
	with open(args.output, 'w') as f:
	f.write('\n'.join(output))


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