We’d love to accept your patches and contributions to Pigweed. There are just a few small guidelines you need to follow.

Before participating in our community, please take a moment to review our Code of Conduct. We expect everyone who interacts with the project to respect these guidelines.

Get started#

See Get started With upstream Pigweed development.

Pigweed contribution overview#


If you have any trouble with this flow, reach out in our chat room or on the mailing list for help.

One-time contributor setup#

  1. Sign the Contributor License Agreement.

  2. Verify that your Git user email (git config is either Google Account email or an Alternate email for the Google account used to sign the CLA (Manage Google account → Personal Info → email).

  3. Obtain a login cookie from Gerrit’s new-password page.

  4. Install the Build System Support to automatically add a Change-Id: ... line to your commit.

  5. Install the Pigweed presubmit check hook with pw presubmit --install. Remember to Activate your Pigweed environment first!

Presubmission process#

Before making or sending major changes or SEEDs, please reach out in our chat room or on the mailing list first to ensure the changes make sense for upstream. We generally go through a design phase before making large changes. See 0001: The SEED Process for a description of this process; but please discuss with us before writing a full SEED. Let us know of any priorities, timelines, requirements, and limitations ahead of time.

For minor changes that don’t fit the SEED process, follow the Small changes guidance and the Change submission process.


Skipping communicating with us before doing large amounts of work risks accepting your contribution. Communication is key!

Change submission process#


A change is a single git commit, and is also known as Change List or CL for short.


Follow Small changes for a smooth submission process

  1. Go through the Presubmission process and review this document’s guidance.

  2. Ensure all files include the correct copyright and license headers.

  3. Include any necessary changes to the documentation.

  4. Run pw_presubmit to detect style or compilation issues before uploading.

  5. Upload the change with git push origin HEAD:refs/for/main.

  6. Add as a reviewer. This will automatically choose an appropriate person to review the change.

  7. Address any reviewer feedback by amending the commit (git commit --amend).

  8. Submit change to CI builders to merge. If you are not part of Pigweed’s core team, you can ask the reviewer to add the +2 CQ vote, which will trigger a rebase and submit once the builders pass.

Contributor License Agreement#

Contributions to this project must be accompanied by a Contributor License Agreement. You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to <> to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you’ve already submitted one (even if it was for a different project), you probably don’t need to do it again.

Contribution Standards#

Contributions, i.e. CLs, are expected to be complete solutions, accompanied by documentation and unit tests when merited, e.g. new code, bug fixes, or code that changes some behavior. This also means that code changes must be tested. Tests will avoid or minimize any negative impact to Pigweed users, while documentation will help others learn about the new changes.

We understand that you may have different priorities or not know the best way to complete your contribution. In that case, reach out via our chat room or on the mailing list for help or File a bug requesting fixes describing how this may be blocking you. Otherwise you risk working on a CL that does not match our vision and could be rejected. To keep our focus, we cannot adopt incomplete CLs.

Build System Support#

Pigweed users are split across a number of build systems including:

In order to ensure parity between different build systems, contributions must include support for at least Bazel (BUILD.bazel), GN ( and CMake (CMakeLists.txt).

We understand that most people don’t have experience with all of the build systems Pigweed supports, and that this requirement is a burden on contributors. We find most people are able to follow the patterns in existing build files to add support for their changes; but not always. We’re happy to help with build questions on Discord for that reason. Don’t be shy if you need help!

Gerrit Commit Hook#

Gerrit requires all changes to have a Change-Id tag at the bottom of each commit message. You should set this up to be done automatically using the instructions below.

The commands below assume that your current working directory is the root of your Pigweed repository.


f=`git rev-parse --git-dir`/hooks/commit-msg ; mkdir -p $(dirname $f) ; curl -Lo $f ; chmod +x $f


git rev-parse --git-dir > gitrepopath.txt & set /p "g="< gitrepopath.txt & del gitrepopath.txt & call set "f=%g%/hooks" & call mkdir "%f%" & call curl -Lo "%f%/commit-msg"

Commit Message#

See the commit message section of the style guide for how commit messages should look.


Most changes to Pigweed should have an associated documentation change.


To build the documentation, follow the getting started guide so you can build Pigweed. Then:

  1. Change to your checkout directory and . if necessary

  2. Run pw watch -C out to build the code, run tests, and build docs

  3. Wait for the build to finish (see a PASS)

  4. Navigate to <CHECKOUT>/out/docs/gen/docs/html/index.html

  5. Edit the relevant .rst file. Save when ready

  6. Refresh your browser after the build completes

Alternately, you can use the local webserver in watch; this works better for some pages that have external resources: pw watch --serve-docs then navigate to http://localhost:8000 in your browser.

Submission checklist#

All Pigweed changes must either:

  1. Include updates to documentation, or

  2. Include No-Docs-Update-Reason: <reason> in a Gerrit comment on the CL. For example:

    • No-Docs-Update-Reason: formatting tweaks

    • No-Docs-Update-Reason: internal cleanups

    • No-Docs-Update-Reason: bugfix

It’s acceptable to only document new changes in an otherwise underdocumented module, but it’s not acceptable to not document new changes because the module doesn’t have any other documentation.

Code Reviews#

See Code Reviews for information about the code review process.

Experimental Repository and Where to Land Code#

Pigweed’s has an Experimental Repository which differs from our main repository in a couple key ways:

  • Code is not expected to become production grade.

  • Code review standards are relaxed to allow experimentation.

  • In general the value of the code in the repository is the knowledge gained from the experiment, not the code itself.

Good uses of the repo include:

  • Experimenting with using an API (ex. C++20 coroutines) with no plans to turn it into production code.

  • One-off test programs to gather data.

We would like to avoid large pieces of code being developed in the experimental repository then imported into the Pigweed repository. If large amounts of code end up needing to migrate from experimental to main, then it must be landed incrementally as a series of reviewable patches, typically no larger than 500 lines each. This creates a large code review burden that often results in poorer reviews. Therefore, if the eventual location of the code will be the main Pigweed repository, it is strongly encouraged that the code be developed in the main repository under an experimental flag.


The current organization of the experimental repository does not reflect this policy. This will be re-organized once we have concrete recommendations on its organization.

Community Guidelines#

This project follows Google’s Open Source Community Guidelines and the Code of Conduct.

Presubmit Checks and Continuous Integration#

All Pigweed change lists (CLs) must adhere to Pigweed’s style guide and pass a suite of automated builds, tests, and style checks to be merged upstream. Much of this checking is done using Pigweed’s pw_presubmit module by automated builders. These builders run before each Pigweed CL is submitted and in our continuous integration infrastructure (see Pigweed’s build console).

Running Presubmit Checks#

To run automated presubmit checks on a pending CL, click the CQ DRY RUN button in the Gerrit UI. The results appear in the Tryjobs section, below the source listing. Jobs that passed are green; jobs that failed are red.

If all checks pass, you will see a Dry run: This CL passed the CQ dry run. comment on your change. If any checks fail, you will see a Dry run: Failed builds: message. All failures must be addressed before submitting.

In addition to the publicly visible presubmit checks, Pigweed runs internal presubmit checks that are only visible within Google. If any these checks fail, external developers will see a Dry run: Failed builds: comment on the CL, even if all visible checks passed. Reach out to the Pigweed team for help addressing these issues.

Project Presubmit Checks#

In addition to Pigweed’s presubmit checks, some projects that use Pigweed run their presubmit checks in Pigweed’s infrastructure. This supports a development flow where projects automatically update their Pigweed submodule if their tests pass. If a project cannot build against Pigweed’s tip-of-tree, it will stay on a fixed Pigweed revision until the issues are fixed. See the examples repo for an example of this.

Pigweed does its best to keep builds passing for dependent projects. In some circumstances, the Pigweed maintainers may choose to merge changes that break dependent projects. This will only be done if

  • a feature or fix is needed urgently in Pigweed or for a different project, and

  • the project broken by the change does not imminently need Pigweed updates.

The downstream project will continue to build against their last working revision of Pigweed until the incompatibilities are fixed.

In these situations, Pigweed’s commit queue submission process will fail for all changes. If a change passes all presubmit checks except for known failures, the Pigweed team may permit manual submission of the CL. Contact the Pigweed team for submission approval.

Code coverage in Gerrit#

Unit test coverage data for C++ is computed by the coverage builder and displayed in Gerrit.

Code coverage display in Gerrit
  1. When will coverage data be visible on my CL? The coverage builder needs to finish running (about 6 minutes), and then the data needs to be ingested by the coverage pipeline (ran every 30 minutes).

  2. What tests is this based on? Only the C++ unit tests of the modules ran as part of the GN build. (There’s no coverage data for Python or Rust yet.)

  3. Can I generate a coverage report locally? Yes. Running pw presubmit --step coverage will generate a HTML report at out/presubmit/coverage/host_clang_coverage/obj/coverage_report/html/index.html.

  4. I’d love to have this in my Pigweed-based project! See Generate code coverage reports: pw_coverage_report for GN and Code Coverage for Bazel.

Running local presubmits#

To speed up the review process, consider adding pw_presubmit as a git push hook using the following command:


$ pw presubmit --install

This will be effectively the same as running the following command before every git push:

$ pw presubmit
pw presubmit demo

If you ever need to bypass the presubmit hook (due to it being broken, for example) you may push using this command:

$ git push origin HEAD:refs/for/main --no-verify

Presubmit and branch management#

When creating new feature branches, make sure to specify the upstream branch to track, e.g.

$ git checkout -b myfeature origin/main

When tracking an upstream branch, pw presubmit will only run checks on the modified files, rather than the entire repository.

Presubmit flags#

pw presubmit can accept a number of flags

-b commit, --base commit

Git revision against which to diff for changed files. Default is the tracking branch of the current branch. Set commit to “HEAD” to check files added or modified but not yet commited. Cannot be used with –full.


Run presubmit on all files, not just changed files. Cannot be used with –base.

-e regular_expression, --exclude regular_expression

Exclude paths matching any of these regular expressions, which are interpreted relative to each Git repository’s root.

-k, --keep-going

Continue instead of aborting when errors occur.

--output-directory OUTPUT_DIRECTORY

Output directory (default: <repo root>/out/presubmit)

--package-root PACKAGE_ROOT

Package root directory (default: <output directory>/packages)

--clear, --clean

Delete the presubmit output directory and exit.

-p, --program PROGRAM

Which presubmit program to run

--step STEP

Provide explicit steps instead of running a predefined program.


Install the presubmit as a Git pre-push hook and exit.

Updating Python dependencies in the virtualenv_setup directory#

If you update any of the requirements or constraints files in //pw_env_setup/py/pw_env_setup/virtualenv_setup, you must run this command to ensure that all of the hashes are updated:

pw presubmit --step update_upstream_python_constraints --full

For Python packages that have native extensions, the command needs to be run 3 times: once on Linux, once on macOS, and once on Windows. Please run it on the OSes that are available to you; a core Pigweed teammate will run it on the rest. See the warning about caching Python packages for multiple platforms in Downloading Packages.