Project Builder#

pw_build: Integrations for Bazel, GN, and CMake

The pw_build Python module contains a light-weight build command execution library used for projects that require running multiple commands to perform a build. For example: running cmake alongside gn.

Get started

How to write your own build script.


Reference details about the pw_build Python API.

pw build CLI

Command line interface usage.

Get Started#

The quickest way to get started with Project Builder is to create a build script based on existing examples.

Example Build Scripts#

Examples of Project Builder based pw build commands:


At a high level:

  • A single BuildRecipe contains many BuildCommands which are run sequentially.

  • Multiple BuildRecipes can be created and passed into the ProjectBuilder class which provides logging and terminal output options.

  • A ProjectBuilder instance is then passed to the run_builds function which allows specifying the number of parallel workers (the number of recipes which are executed in parallel).

flowchart TB subgraph BuildRecipeA ["<strong>BuildRecipe</strong>: ninja"] buildCommandA1["<strong>BuildCommand</strong><br> gn gen out"] buildCommandA2["<strong>BuildCommand</strong><br> ninja -C out default"] buildCommandA1-->buildCommandA2 end subgraph BuildRecipeB ["<strong>BuildRecipe</strong>: bazel"] buildCommandB1["<strong>BuildCommand</strong><br> bazel build //...:all"] buildCommandB2["<strong>BuildCommand</strong><br> bazel test //...:all"] buildCommandB1-->buildCommandB2 end ProjectBuilder["<strong>ProjectBuilder</strong>(build_recipes=...)"] BuildRecipeA-->ProjectBuilder BuildRecipeB-->ProjectBuilder run_builds["<strong>run_builds</strong>(project_builder=..., workers=1)"] ProjectBuilder-->run_builds


class pw_build.build_recipe.BuildCommand(build_dir: ~pathlib.Path | None = None, build_system_command: str | None = None, build_system_extra_args: list[str] = <factory>, targets: list[str] = <factory>, command: list[str] = <factory>, run_if: ~typing.Callable[[~pathlib.Path], bool] = <function BuildCommand.<lambda>>)#

Store details of a single build step.

Example usage:

from pw_build.build_recipe import BuildCommand, BuildRecipe

def should_gen_gn(out: Path):
    return not (out / '').is_file()

cmd1 = BuildCommand(build_dir='out',
                    command=['gn', 'gen', '{build_dir}'],

cmd2 = BuildCommand(build_dir='out',
                    build_system_extra_args=['-k', '0'],
  • build_dir – Output directory for this build command. This can be omitted if the BuildCommand is included in the steps of a BuildRecipe.

  • build_system_command – This command should end with ninja, make, or bazel.

  • build_system_extra_args – A list of extra arguments passed to the build_system_command. If running bazel test include test as an extra arg here.

  • targets – Optional list of targets to build in the build_dir.

  • command – List of strings to run as a command. These are passed to Any instances of the '{build_dir}' string literal will be replaced at run time with the out directory.

  • run_if – A callable function to run before executing this BuildCommand. The callable takes one Path arg for the build_dir. If the callable returns true this command is executed. All BuildCommands are run by default.

BuildCommand Run Filters#

pw_build.build_recipe.should_gn_gen(out: Path) bool#

Returns True if the gn gen command should be run.

Returns True if or files are missing from the build directory.

pw_build.build_recipe.should_gn_gen_with_args(gn_arg_dict: Mapping[str, bool | str | list | tuple]) Callable#

Returns a callable which writes an file prior to checks.


gn_arg_dict – Dictionary of key value pairs to use as gn args.


Callable which takes a single Path argument and returns a bool for True if the gn gen command should be run.

The returned function will:

  1. Always re-write the file.

  2. Return True if or files are missing.

pw_build.build_recipe.should_regenerate_cmake(cmake_generate_command: list[str]) Callable[[Path], bool]#

Return a callable to determine if cmake should be regenerated.


cmake_generate_command – Full list of args to run cmake.

The returned function will return True signaling CMake should be re-run if:

  1. The provided CMake command does not match an existing args in the cmake_cfg_command.txt file in the build dir.

  2. is missing or cmake_cfg_command.txt is missing.

When the function is run it will create the build directory if needed and write the cmake_generate_command args to the cmake_cfg_command.txt file.


class pw_build.build_recipe.BuildRecipe(
build_dir: ~pathlib.Path,
steps: list[pw_build.build_recipe.BuildCommand] = <factory>,
title: str | None = None,
enabled: bool = True,
auto_create_build_dir: bool = True,

Dataclass to store a list of BuildCommands.

Example usage:

from pw_build.build_recipe import BuildCommand, BuildRecipe

def should_gen_gn(out: Path) -> bool:
    return not (out / '').is_file()

recipe = BuildRecipe(
    title='Vanilla Ninja Build',
        BuildCommand(command=['gn', 'gen', '{build_dir}'],
                     build_system_extra_args=['-k', '0'],
  • build_dir – Output directory for this BuildRecipe. On init this out dir is set for all included steps.

  • steps – List of BuildCommands to run.

  • title – Custom title. The build_dir is used if this is ommited.

  • auto_create_build_dir – Auto create the build directory and all necessary parent directories before running any build commands.


class pw_build.project_builder.ProjectBuilder(build_recipes: ~typing.Sequence[~pw_build.build_recipe.BuildRecipe], jobs: int | None = None, banners: bool = True, keep_going: bool = False, abort_callback: ~typing.Callable = <function _exit>, execute_command: ~typing.Callable[[list, dict, ~pw_build.build_recipe.BuildRecipe, ~logging.Logger, ~typing.Callable | None], bool] = <function execute_command_no_logging>, charset: ~pw_build.project_builder.ProjectBuilderCharset = ProjectBuilderCharset(slug_ok='OK  ', slug_fail='FAIL', slug_building='... '), colors: bool = True, separate_build_file_logging: bool = False, send_recipe_logs_to_root: bool = False, root_logger: ~logging.Logger = <Logger pw_build (WARNING)>, root_logfile: ~pathlib.Path | None = None, log_level: int = 20, allow_progress_bars: bool = True, use_verbatim_error_log_formatting: bool = False, log_build_steps: bool = False)#

Pigweed Project Builder

Controls how build recipes are executed and logged.

Example usage:

import logging
from pathlib import Path

from pw_build.build_recipe import BuildCommand, BuildRecipe
from pw_build.project_builder import ProjectBuilder

def should_gen_gn(out: Path) -> bool:
    return not (out / '').is_file()

recipe = BuildRecipe(
    title='Vanilla Ninja Build',
        BuildCommand(command=['gn', 'gen', '{build_dir}'],
                     build_system_extra_args=['-k', '0'],

project_builder = ProjectBuilder(
    build_recipes=[recipe1, ...]
  • build_recipes – List of build recipes.

  • jobs – The number of jobs bazel, make, and ninja should use by passing -j to each.

  • keep_going – If True keep going flags are passed to bazel and ninja with the -k option.

  • banners – Print the project banner at the start of each build.

  • allow_progress_bars – If False progress bar output will be disabled.

  • log_build_steps – If True all build step lines will be logged to the screen and logfiles. Default: False.

  • colors – Print ANSI colors to stdout and logfiles

  • log_level – Optional log_level, defaults to logging.INFO.

  • root_logfile – Optional root logfile.

  • separate_build_file_logging – If True separate logfiles will be created per build recipe. The location of each file depends on if a root_logfile is provided. If a root logfile is used each build recipe logfile will be created in the same location. If no root_logfile is specified the per build log files are placed in each build dir as log.txt

  • send_recipe_logs_to_root – If True will send all build recipie output to the root logger. This only makes sense to use if the builds are run in serial.

  • use_verbatim_error_log_formatting – Use a blank log format when printing errors from sub builds to the root logger.

pw_build.project_builder.run_builds(project_builder: ProjectBuilder, workers: int = 1) int#

Execute all build recipe steps.

  • project_builder – A ProjectBuilder instance

  • workers – The number of build recipes that should be run in parallel. Defaults to 1 or no parallel execution.


1 for a failed build, 0 for success.

Upstream pw build Command-Line Interface Usage#

This is the command line interface provided by the pw build command ( in upstream Pigweed.


usage: pw build [-h] [-C directory [target ...]]
                [--build-system-command directory command]
                [--run-command RUN_COMMAND] [-j JOBS] [-k] [--parallel]
                [--parallel-workers PARALLEL_WORKERS] [--logfile LOGFILE]
                [--separate-logfiles] [--debug-logging]
                [--banners | --no-banners] [--colors | --no-colors]
                [--patterns PATTERNS]
                [--ignore-patterns IGNORE_PATTERNS_STRING]
                [--exclude-list EXCLUDE_LIST [EXCLUDE_LIST ...]]
                [--restart | --no-restart] [--serve-docs]
                [--serve-docs-port SERVE_DOCS_PORT]
                [--serve-docs-path SERVE_DOCS_PATH] [-f] [-r RECIPE] [-s STEP]
                [-l] [--all] [--progress-bars | --no-progress-bars]
                [--log-build-steps | --no-log-build-steps] [-w] [-b BASE]
                [--tab-complete-option [TAB_COMPLETE_OPTION]]
                [--tab-complete-format {bash,fish,zsh}]
                [--tab-complete-recipe [TAB_COMPLETE_RECIPE]]
                [--tab-complete-presubmit-step [TAB_COMPLETE_PRESUBMIT_STEP]]
                [target ...]

Named Arguments#

-r, --recipe

Run a build recipe. Include an asterix to match more than one name. For example: –recipe ‘gn_*’

Default: []

-s, --step

Run presubmit step. Include an asterix to match more than one step name. For example: –step ‘*_format’

Default: []

-l, --list

List all known build recipes and presubmit steps.

Default: False


Run all known build recipes.

Default: False

--progress-bars, --no-progress-bars

Show progress bars in the terminal. (default: True)

Default: True

--log-build-steps, --no-log-build-steps

Show ninja build step log lines in output.

-w, --watch

Use pw_watch to monitor changes.

Default: False

-b, --base

Git revision to diff for changed files. This is used for presubmit steps.


Print tab completions for the supplied option text.


Possible choices: bash, fish, zsh

Output format for tab completion results.

Default: “bash”


Print tab completions for the supplied recipe name.


Print tab completions for the supplied presubmit name.

Build Directory and Command Options#

-C, --build-directory

Specify a build directory and optionally targets to build. pw watch -C out target1 target2 is equivalent to ‘ninja -C out taret1 target2’. The ‘out’ directory will be used if no others are provided.

Default: []


Default build targets. For example if the build directory is ‘out’ then, ‘ninja -C out taret1 target2’ will be run. To specify one or more directories, use the -C / --build-directory option.

Default: []


Build system command for . Default: ninja

Default: []


Additional commands to run. These are run before any -C arguments and may be repeated. For example: –run-command ‘bazel build //pw_cli/…’ –run-command ‘bazel test //pw_cli/…’ -C out python.lint python.test

Default: []

Build Execution Options#

-j, --jobs

Specify the number of cores to use for each build system. This is passed to ninja, bazel and make as “-j”

-k, --keep-going

Keep building past the first failure. This is equivalent to running “ninja -k 0” or “bazel build -k”.

Default: False


Run all builds in parallel.

Default: False


How many builds may run at the same time when –parallel is enabled. Default: 0 meaning run all in parallel.

Default: 0

Log File Options#


Global build output log file.


Create separate log files per build directory.

Default: False


Enable Python build execution tool debug logging.

Default: False

Display Output Options#

--banners, --no-banners

Show pass/fail banners. (default: True)

Default: True

--colors, --no-colors

Force color output from ninja. (default: True)

Default: True

Watch Options#


Comma delimited list of globs to watch to trigger recompile.

Default: “.bazel,.bzl,*.bloaty,*.c,*.cc,*.css,*.cpp,*.cmake,CMakeLists.txt,*.dts,*.dtsi,*.emb,*.gn,*.gni,*.go,*.h,*.hpp,*.html,*.js,*.ld,*.md,*.options,*.proto,*.py,*.rs,*.rst,*.s,*.S,*.toml,*.ts”


Comma delimited list of globs to ignore events from.


Directories to ignore during pw watch. This option may be repeated. Directories are passed as separate arguments.

Default: []

--restart, --no-restart

Whether to restart ongoing builds if files change. (default: True)

Default: True


Start a webserver for docs on localhost. The port for this webserver can be set with the –serve-docs-port option. Defaults to

Default: False


Set the port for the docs webserver. Default: 8000.

Default: 8000


Set the path for the docs to serve. Default: docs/gen/docs in the build directory.

Default: docs/gen/docs

-f, --fullscreen

Use a fullscreen interface.

Default: False