# Homebrew/brew Maintainer Guide

This document describes a few components of the `Homebrew/brew` repository that are useful for maintainers to be aware of, but don't necessarily need to appear in documentation for most users and contributors.

## Reviewing PRs

Using `gh pr checkout NUMBER` is a super easy way to check out a PR branch using the GitHub CLI.

When reviewing a PR, use "comment", "approve", or "request changes" when submitting based on the following guidelines:

- Comment: if the PR isn't quite ready to be merged
- Approve: if you feel that the PR is in a good state to be merged, even if there are non-blocking changes you'd like to be made
- Request changes: if you feel strongly that the PR is likely to cause a problem for users or have another reason to oppose the PR.

## Merging PRs

Merging is done using the standard "Merge" button in the `Homebrew/brew` repository to preserve history and GPG commit signing. The "Squash and Merge" and "Rebase and Merge" buttons are disabled.

PRs must meet the following conditions to be merged:

- Have at least one maintainer approval.
- Have passing CI (continuous integration). This is a _mandatory_ step. PRs with failing CI should _never_ be merged. See the [CI](#ci) section below for more information about `Homebrew/brew` CI.

If possible, PRs should also have GPG-signed commits (see the private `ops` repository for instructions on setting this up).

### Automatic approvals

To ensure that non-urgent PRs have the opportunity to be seen and reviewed by any other maintainers who wish to take a look, all PRs require an approval before they can be merged.

## CI

Every PR in `Homebrew/brew` runs a series of CI tests to try to prevent bugs from being introduced. **A PR _must_ have passing CI before it can be merged.**

There are many checks that run on every PR. The following is a quick list of the various checks and what they represent:

- `Vendor Gems / vendor-gems`: This is skipped except for dependabot PRs. It updates the RBI files to match any new/changed dependencies. See [Type Checking With Sorbet](Typechecking.md) for more information about RBI files and typechecking.
- `Codecov / codecov/patch` and `codecov/project`: These show the Codecov report for the PR. See the [`brew tests` and Codecov](#brew-tests-and-codecov) section below for more info about Codecov.
- `CI / vendored gems`: This checks whether there was a change to the vendored gems on Linux that needs to be committed to the PR branch.
- `CI / test default formula (Linux)`: This runs `brew test-bot` on Linux to ensure it still works as expected.
- `CI / syntax`: This is run first to check whether the PR passes `brew style` and `brew typecheck`. If this job fails the following jobs will not run.
- `CI / tap syntax`: This runs `brew style` and `brew audit` on all official taps (note that although this runs on Linux, it does check all cask repositories).
- `CI / docker`: This builds and deploys a new Homebrew Docker image to GitHub Packages and Docker Hub.
- `CI / test everything (macOS)`: This runs several checks on macOS including `brew tests`, `brew update-tests`, `brew test-bot --only-formulae --test-default-formula`, `brew readall` and `brew doctor`.
- `CI / tests (generic OS)` and `CI / tests (Linux)`: These run `brew tests` with various options on Linux.
- `Documentation CI / linting` and `rubydoc`: These check the prose and formatting of the written documentation, and verify the [rubydoc API documentation](https://rubydoc.brew.sh) can be built without issue.

_Note that this list is non-exhaustive and can change over time._

### `brew tests` and Codecov

A coverage report is generated by Codecov for every PR, and its results are shown as CI jobs. These reports are publicly viewable on [Homebrew/brew's Codecov page](https://app.codecov.io/gh/Homebrew/brew). Additionally, annotations will appear in the PR's "Files changed" tab where lines of code have been added that aren't being hit by `brew tests`. If the Codecov job fails, that's a sign that some more tests should be added to test the functionality being added in the PR.

Codecov should be used as a guide to indicate when more tests are probably needed, but it's unrealistic for every line of code to have a test associated with it, especially when testing would require a slow integration test. For this reason, it's okay to merge PRs that fail the Codecov check if necessary, but this should be avoided if possible.

### `brew tests` and BuildPulse

BuildPulse monitors CI jobs for every push to `Homebrew/brew` to detect flaky tests and track them over time. The reports are available to Homebrew maintainers on [buildpulse.io](https://app.buildpulse.io/@Homebrew) and daily summaries are published to [`#buildpulse-health`](https://machomebrew.slack.com/archives/C0268BSJBJ8) in Slack.

BuildPulse can be used as a guide to identify which flaky tests are causing the most disruption to the CI suite. To make the biggest improvements to the reliability of the build, we can focus on the most disruptive flaky tests first (i.e. the tests causing the most intermittent failures).

To help find the root cause for a particular flaky test, buildpulse.io provides links to the most recent CI job and commit where the test failed and then passed with no change to the underlying code. You may want to check out the code at that commit to attempt to reproduce the failure locally. You can also see the list of recent failures on [buildpulse.io](https://app.buildpulse.io/@Homebrew) to determine if the test always fails the same way.

## Manpages and Shell Completions

Homebrew's manpages and shell completions are generated automatically by the `brew generate-man-completions` command. Contributors are welcome to run this command and commit the changes in a PR, but they don't have to. If they don't, a follow-up PR to make the necessary changes will be opened automatically by [@BrewTestBot](https://github.com/BrewTestBot) once the original PR is merged. These follow-up PRs can be merged immediately if the changes seem correct.

An update can be requested manually by triggering the workflow from the [Update sponsors, maintainers, manpage and completions](https://github.com/Homebrew/brew/actions/workflows/sponsors-maintainers-man-completions.yml) section under the "Actions" tab. Click on the "Run workflow" dropdown and then the "Run workflow" button. A PR will be opened shortly if there are any changes.
