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Contributing to Notmuch

This is your friendly guide to contributing to Notmuch. In a nutshell, the Notmuch project maintains fairly high standards for code, review, tests, and documentation. It may seem a bit intimidating at first, and you may find it difficult to get your first contributions accepted, but once you get the hang of it, it'll be fun. This page should help you get there. DON'T PANIC.

The headlines below act as a checklist. Not all of them apply in all situations. Use your best judgment, and the Notmuch community will help out as needed.

  1. Contributing to Notmuch
    1. Obtain the Notmuch source code
    2. Make your changes
    3. Pay attention to the Notmuch coding style
    4. Split your commits in logical chunks
    5. Write meaningful commit messages
    6. Update the test suite
    7. Update the documentation
    8. Update NEWS
    9. Update command-line completion
    10. Subscribe to the Notmuch mailing list
    11. Send your patches to the mailing list
    12. Write a cover letter
    13. Tag your patches in nmbug
    14. Address review comments, participate in discussion
    15. Send another round addressing review comments
    16. Review other people's work
    17. Report bugs
    18. Update the Notmuch website
    19. Join the Notmuch IRC channel

Obtain the Notmuch source code

The Notmuch source code is maintained in git. Get the source code using:

    git clone git://notmuchmail.org/git/notmuch

This guide assumes a working knowledge of git. There are plenty of resources available on git, such as Pro Git and the git man pages. Please refer to them as necessary.

Make your changes

The changes you submit should almost always be based on the current Notmuch git master. There are plenty of ways to work in git, and this is not your git guide, but a typical workflow might start with:

    git fetch origin
    git checkout -b my-local-branch origin/master
    # make changes
    git add ...
    git commit

If you're planning big changes, it may be advisable to not polish the patch series according to all the details described below at first. Instead, it may save everyone's time to introduce the idea using draft or work-in-progress patches, and get the design right from the beginning. Add a cover letter explaining what you want to achieve. You may prefix the subjects of such patches with "RFC" or "DRAFT" if you like.

Pay attention to the Notmuch coding style

The Notmuch code base follows a fairly uniform coding style. See the existing code around your changes, and read devel/STYLE in the Notmuch source. It's not difficult to get it right, and may save you an extra review round.

Split your commits in logical chunks

Each commit should contain one logical change only. The code should build and the tests should pass after each commit. Changes to lib, cli, emacs, tests, man pages, or news are usually best kept separate. Also separate cleanups from functional changes. See the Notmuch source history (git log) for examples.

For in-depth discussion on the subject, see Software Release Practice HOWTO by Eric S. Raymond.

Write meaningful commit messages

Quoting Carl, "The single line summary is good about saying what the commit does, but I always want to see at least one sentence about the why as well."

See also Pro Git on commit guidelines, including commit messages.

It is customary to prefix the subject line with "lib:", "cli:", "emacs:", etc. depending on which part of Notmuch the commit is changing. See git log for examples.

Wrap the lines to about 72 characters.

If you want to share notes that shall not become part of the commit message when applied to the upstream Notmuch repository, add the notes at the end, after a line containing "---".

Update the test suite

Notmuch has a test suite with fairly good coverage. At the very least, make test must pass after your changes. Therefore you must amend the tests if you make functional changes that have existing test coverage. Preferably, you should add new tests for any new functionality, and it helps in getting your changes accepted.

If you're fixing a bug, it is recommended to add a "known broken" test highlighting the issue in a first patch, and then fix the bug (and remove the known broken mark on the test) in the next patch in the series. This makes it easy to confirm your changes actually fix the issue. Some people use this approach also for adding new features.

See test/README in the Notmuch source for further information.

Update the documentation

If you modify or add new features to the Notmuch command-line tools, you should update the manual pages under the doc directory of the Notmuch source.

If you modify or add new features to the Notmuch Emacs UI, you should update the Emacs documentation.

Update NEWS

If you make user visible changes, you should add an entry to the NEWS file.

Update command-line completion

If you modify or add new features to the Notmuch command-line tools, it would be a nice bonus if you also updated the Notmuch command-line completion scripts under the completion directory of the Notmuch source. Not required, but nice to have, and definitely can be done afterwards.

Subscribe to the Notmuch mailing list

While strictly not required, it is advisable to subscribe to the Notmuch mailing list before submitting patches.

Send your patches to the mailing list

Changes to Notmuch are contributed as emailed patches. Once you have your changes ready in your local repository, you need to send them to the Notmuch mailing list. The simplest way is to use git send-email to send the patches directly from your repository:

    git send-email --to notmuch@notmuchmail.org origin/master

An alternative is to do this in two steps; first generating patch files (using git format-patch), and then sending the patch files to the mailing list (using git send-email or a mail client):

    git format-patch origin/master
    git send-email --to notmuch@notmuchmail.org *.patch

Either way, using git send-email to actually send the patches is recommended. It may be distributed separately from git, typically in a package named git-email.

Write a cover letter

If you are submitting a non-trivial set of patches, or if there's any extra information you want to share that is not really part of the commit messages, it is advisable to write a cover letter to give an overview of your work. See the Notmuch mailing list archives for examples. Use the --cover-letter option of git format-patch, or --compose option of git send-email.

Tag your patches in nmbug

When you're developing an email tool, all the problems start looking like email. This applies to patch and bug tracking as well. The Notmuch project uses nmbug for tracking. The Notmuch developers will tag your patches too, making them show up in the nmbug status page, but requesting access and tagging your patches yourself will be helpful in the long run.

Address review comments, participate in discussion

Each change to Notmuch must be peer reviewed before it is accepted, usually by one or two developers, depending on the impact of the changes. You are expected to follow up on the review comments you receive, either by discussing the comments and the code, or modifying your patches. Again, see the Notmuch mailing list archives for examples.

Send another round addressing review comments

If your patches need to be changed based on review (they usually do), you need to make the changes and re-submit. git rebase -i is your friend in updating your series. Also note that the upstream master may have changed; be sure to rebase your updated changes on top of the current master.

Once you have the updated series ready, send it to the mailing list again. It will be helpful for others to use the -vN option of git format-patch or git send-email to add a version number of the patch series to the subject (replacing vN with v2, v3, etc.) Use a cover letter (or, in the case of a single patch, the notes after a "---" at the end of the commit message) to summarize the main changes since the previous version of the patch series. Also include the message-id reference of the previous version.

Using the --in-reply-to option of git format-patch or git send-email to send the patch series as a reply to the earlier version is generally discouraged, particularly for large series, but there are no hard rules. Usually the message-id reference to the previous version is sufficient and preferred.

Tag the old patches obsolete in nmbug if you have access.

Review other people's work

You scratch my back and I'll scratch yours. It will be easier to get people to review your patches if you review theirs.

Report bugs

Send bug reports to the Notmuch mailing list. Preferably prefix the subject line with "BUG:" or similar. Tag the message as a bug in nmbug.

Even better, send a patch adding a "known broken" test to the test suite highlighting the issue.

Update the Notmuch website

Update the Notmuch website, especially if you've landed a commit that changes or obsoletes information on the site. It's a wiki; see the instructions on how to edit the wiki.

Join the Notmuch IRC channel

Patch review happens on the Notmuch mailing list, but there is plenty of discussion going on in the freenode #notmuch IRC channel. See freenode.net/irc_servers.shtml for information how to get there.