Homebrew/homebrew-core Maintainer Guide

Quick merge checklist

A detailed checklist can be found below. This is all that really matters:

Checking dependencies is important, because they will probably stick around forever. Nobody really checks if they are necessary or not.

Depend on as little stuff as possible. Disable X11 functionality if possible. For example, we build Wireshark, but not the heavy GUI.

Homebrew is about Unix software. Stuff that builds to an .app should be in Homebrew Cask instead.

Merging, rebasing, cherry-picking

For most PRs that make formula modifications, you can simply approve the PR and an automatic merge (with bottles) will be performed by @BrewTestBot. See BrewTestBot for Maintainers for more information.

Certain PRs may not be merged automatically by @BrewTestBot, even after they’ve been approved. This includes PRs with the new formula, automerge-skip, and linux-only labels. To trigger a merge for these PRs, run brew pr-publish.

PRs modifying formulae that don’t need bottles or making changes that don’t require new bottles to be pulled should use GitHub’s squash & merge or rebase & merge workflows.

Otherwise, you should use brew pr-pull (or rebase/cherry-pick contributions).

Don’t rebase until you finally push. Once master is pushed, you can’t rebase: you’re a maintainer now!

Cherry-picking changes the date of the commit, which kind of sucks.

Don’t merge unclean branches. So if someone is still learning git and their branch is filled with nonsensical merges, then rebase and squash the commits. Our main branch history should be useful to other people, not confusing.

Only one maintainer is necessary to approve and merge the addition of a new or updated formula which passes CI. However, if the formula addition or update proves controversial the maintainer who adds it will be expected to answer requests and fix problems that arise with it in future.

How to merge without bottles

Here are guidelines about when to use squash & merge versus rebase & merge. These options should only be used with PRs where bottles are not affected.

  PR modifies a single formula PR modifies multiple formulae
Commits look good rebase & merge or squash & merge rebase & merge
Commits need work squash & merge manually merge using the command line

Naming

The name is the strictest item, because avoiding a later name change is desirable.

Choose a name that’s the most common name for the project. For example, we initially chose objective-caml but we should have chosen ocaml. Choose what people say to each other when talking about the project.

Formulae that are also packaged by other package managers (e.g. Debian, Ubuntu) should be named consistently (subject to minor differences due to Homebrew formula naming conventions).

Add other names as aliases using symlinks within Aliases in the tap root. Ensure the name referenced on the homepage is one of these, as it may be different and have underscores and hyphens and so on.

We now accept versioned formulae as long as they meet the requirements.

Testing

We need to at least check that it builds. Use BrewTestBot for this.

Verify the formula works if possible. If you can’t tell (e.g. if it’s a library) trust the original contributor; it worked for them, so chances are it is fine. If you aren’t an expert in the tool in question, you can’t really gauge if the formula installed the program correctly. At some point an expert will come along, cry blue murder that it doesn’t work, and fix it. This is how open source works. Ideally, request a test do block to test that functionality is consistently available.

If the formula uses a repository, then the url parameter should have a tag or revision. urls have versions and are stable (not yet implemented!).

Don’t merge any formula updates with failing brew tests. If a test do block is failing it needs to be fixed. This may involve replacing more involved tests with those that are more reliable. This is fine: false positives are better than false negatives as we don’t want to teach maintainers to merge red PRs. If the test failure is believed to be due to a bug in Homebrew/brew or the CI system, that bug must be fixed, or worked around in the formula to yield a passing test, before the PR can be merged.

Duplicates

We now accept stuff that comes with macOS as long as it uses keg_only :provided_by_macos to be keg-only by default.

Removing formulae

Formulae that:

should not be removed from Homebrew. The exception to this rule are versioned formulae for which there are higher standards of usage and a maximum number of versions for a given formula.

For more information about deprecating, disabling and removing formulae, see the Deprecating, Disabling and Removing Formulae page.

Detailed merge checklist

The following checklist is intended to help maintainers decide on whether to merge, request changes or close a PR. It also brings more transparency for contributors in addition to the Acceptable Formulae requirements.

Common build failures and how to handle them

Test errors

“undefined reference to …”

This error might pop up when parameters passed to gcc are in the wrong order.

An example from libmagic formula:

==> brew test libmagic --verbose
Testing libmagic
==> /usr/bin/gcc -I/home/linuxbrew/.linuxbrew/Cellar/libmagic/5.38/include -L/home/linuxbrew/.linuxbrew/Cellar/libmagic/5.38/lib -lmagic test.c -o test
/tmp/ccNeDVRt.o: In function `main':
test.c:(.text+0x15): undefined reference to `magic_open'
test.c:(.text+0x4a): undefined reference to `magic_load'
test.c:(.text+0x81): undefined reference to `magic_file'
collect2: error: ld returned 1 exit status

Solution:

if OS.mac?
  system ENV.cc, "-I#{include}", "-L#{lib}", "-lmagic", "test.c", "-o", "test"
else
  system ENV.cc, "test.c", "-I#{include}", "-L#{lib}", "-lmagic", "-o", "test"
end

For an explanation of why this happens, read the Ubuntu 11.04 Toolchain documentation.

Staging Branches

Summary

Some formulae (e.g. Python, OpenSSL, ICU, Boost) have a large number of dependents. This makes updating these formulae (or their dependents) difficult because the standard procedure involves updating a large number of formulae in a single pull request. An alternative procedure that can significantly simplify this process is to use a staging branch.

The idea of using a staging branch is to merge updates and publish bottles for the affected formula to a non-default branch. This allows work to be done incrementally in smaller PRs, instead of in one giant PR that touches many formulae. When the staging branch is ready, it can be merged to the master/default branch.

Before making use of a staging branch, there is one important disadvantage to consider: once you have merged bottle updates to the staging branch, it is very difficult to take them back. This typically involves deleting uploaded bottles, which will occasionally require an owner of the Homebrew GitHub organisation to delete uploaded bottles one at a time.

How to use a staging branch

Here is a rough outline of how to use a staging branch:

  1. Create the staging branch in Homebrew/homebrew-core. The name of the staging branch must start with the name of the root formula, followed by a -, and end in -staging. You can omit the @ and anything that follows for versioned formulae (e.g. icu4c-staging, openssl-migration-staging, python@3.12-staging). It might be helpful to look at the code that parses the branch names to check whether a PR targets a staging branch.

  2. Open an issue in homebrew-core inviting contributors to help. Be sure to include instructions for how to do so, and a checklist of formulae that need to be updated. See Homebrew/homebrew-core#134251 for an example.

  3. Open a draft PR that merges the staging branch into the master branch. This allows you to keep track of the work done so far. You may wish to apply the no long build conflict label to this PR to avoid conflicting changes from being merged to the master branch.

  4. Open PRs targeting the staging branch that update the affected formulae. Each PR should touch as few formulae as possible. The typical PR that targets the staging branch will update only one formula at a time. Staging branch PRs can be merged using the same process as PRs that target the master branch. Ideally, these PRs should be opened in topological order according to the dependency graph, but we don’t currently have good tooling for generating a topological sort. (Help wanted.)

  5. Label PRs that target the staging branch with the staging-branch-pr label for ease of tracking and review. (TODO: Add some automation for this to homebrew-core.)

  6. Monitor the draft PR you created in step 3 above for merge conflicts. If you encounter a merge conflict, you must resolve those conflicts in a staging branch PR that merges the master branch into the staging branch.

  7. When the staging branch is ready to be merged into master, mark the draft PR as ready for review and merge it into the master branch. Your PR may spend a long time in the merge queue waiting for the bottle fetch tests to run.

For examples of uses of the staging branch, see homebrew-core PRs labelled openssl-3-migration-staging, Homebrew/homebrew-core#134260, or Homebrew/homebrew-core#133611.

Finally: while the use of a staging branch worked extremely well in the two instances it was used (see PRs linked in the previous paragraph), the procedure outlined above is not perfect. Suggestions for improvement are much appreciated.

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