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# Copyright 2019 The Dawn Authors
# 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
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# See the License for the specific language governing permissions and
# limitations under the License.
# Template to help invoking code generators based on
# Internal use only, this should only be called from templates implementing
# generator-specific actions.
# Variables:
# script: Path to generator script.
# args: List of extra command-line arguments passed to the generator.
# outputs: List of expected outputs, generation will fail if there is a
# mistmatch.
# deps: additional deps for the code generation targets.
# generator_lib_dir: directory where is located.
# custom_gen_dir: Optional custom target gen dir. Defaults to $target_gen_dir
# but allows output files to not depend on the location of the
# that generates them.
# template_dir: Optional template root directory. Defaults to
# "${generator_lib_dir}/templates".
# jinja2_path: Optional Jinja2 installation path.
# allowed_output_dirs: Optional list of directories that are the only
# directories in which files of `outputs` are allowed to be (and not
# in children directories). Generation will fail if an output isn't
# in a directory in the list.
# root_dir: Optional root source dir for Python dependencies
# computation. Defaults to "${generator_lib_dir}/..". Any dependency
# outside of this directory is considered a system file and will be
# omitted.
template("generator_lib_action") {
_generator_args = []
if (defined(invoker.args)) {
_generator_args += invoker.args
"generator_lib_dir must be defined before calling this action!")
_template_dir = "${invoker.generator_lib_dir}/templates"
if (defined(invoker.template_dir)) {
_template_dir = invoker.template_dir
_generator_args += [
if (defined(invoker.root_dir)) {
_generator_args += [
rebase_path(_root_dir, root_build_dir),
if (defined(invoker.jinja2_path)) {
_generator_args += [
# Chooses either the default gen_dir or the custom one required by the
# invoker. This allows moving the definition of code generators in different
# files without changing the location of generated file. Without
# this generated headers could cause issues when old headers aren't removed.
_gen_dir = target_gen_dir
if (defined(invoker.custom_gen_dir)) {
_gen_dir = invoker.custom_gen_dir
# For build parallelism GN wants to know the exact inputs and outputs of
# action targets like we use for our code generator. We avoid asking the
# generator about its inputs by using the "depfile" feature of GN/Ninja.
# A ninja limitation is that the depfile is a subset of Makefile that can
# contain a single target, so we output a single "JSON-tarball" instead.
_json_tarball = "${_gen_dir}/${target_name}.json_tarball"
_json_tarball_target = "${target_name}__json_tarball"
_json_tarball_depfile = "${_json_tarball}.d"
_generator_args += [
rebase_path(_json_tarball, root_build_dir),
rebase_path(_json_tarball_depfile, root_build_dir),
# After the JSON tarball is created we need an action target to extract it
# with a list of its outputs. The invoker provided a list of expected
# outputs. To make sure the list is in sync between the generator and the
# build files, we write it to a file and ask the generator to assert it is
# correct.
_expected_outputs_file = "${_gen_dir}/${target_name}.expected_outputs"
write_file(_expected_outputs_file, invoker.outputs)
_generator_args += [
rebase_path(_expected_outputs_file, root_build_dir),
# Check that all of the outputs are in a directory that's allowed. This is
# useful to keep the list of directories in sink with other parts of the
# build.
if (defined(invoker.allowed_output_dirs)) {
_allowed_output_dirs_file = "${_gen_dir}/${target_name}.allowed_output_dirs"
write_file(_allowed_output_dirs_file, invoker.allowed_output_dirs)
_generator_args += [
rebase_path(_allowed_output_dirs_file, root_build_dir),
# The code generator invocation that will write the JSON tarball, check the
# outputs are what's expected and write a depfile for Ninja.
action(_json_tarball_target) {
script = invoker.script
outputs = [ _json_tarball ]
depfile = _json_tarball_depfile
args = _generator_args
if (defined(invoker.deps)) {
deps = invoker.deps
# Extract the JSON tarball into the gen_dir
action(target_name) {
script = "${invoker.generator_lib_dir}/"
args = [
rebase_path(_json_tarball, root_build_dir),
rebase_path(_gen_dir, root_build_dir),
deps = [ ":${_json_tarball_target}" ]
inputs = [ _json_tarball ]
# The expected output list is relative to the gen_dir but action
# target outputs are from the root dir so we need to rebase them.
outputs = []
foreach(source, invoker.outputs) {
outputs += [ "${_gen_dir}/${source}" ]