As a given feature goes from experimental to stable, it also "graduates" between the corresponding branches of the software. git.git uses the following integration branches:

There is a fourth official branch that is used slightly differently:

Each of the four branches is usually a direct descendant of the one above it.

Conceptually, the feature enters at an unstable branch (usually next or pu), and "graduates" to master for the next release once it is considered stable enough.

The "downwards graduation" discussed above cannot be done by actually merging downwards, however, since that would merge all changes on the unstable branch into the stable one. Hence the following:

This gives a very controlled flow of fixes. If you notice that you have applied a fix to e.g. master that is also required in maint, you will need to cherry-pick it (using git-cherry-pick[1]) downwards. This will happen a few times and is nothing to worry about unless you do it very frequently.

Any nontrivial feature will require several patches to implement, and may get extra bugfixes or improvements during its lifetime.

Committing everything directly on the integration branches leads to many problems: Bad commits cannot be undone, so they must be reverted one by one, which creates confusing histories and further error potential when you forget to revert part of a group of changes. Working in parallel mixes up the changes, creating further confusion.

Use of "topic branches" solves these problems. The name is pretty self explanatory, with a caveat that comes from the "merge upwards" rule above:

Many things can then be done very naturally:

Note that the last point clashes with the other two: a topic that has been merged elsewhere should not be rebased. See the section on RECOVERING FROM UPSTREAM REBASE in git-rebase[1].

We should point out that "habitually" (regularly for no real reason) merging an integration branch into your topics — and by extension, merging anything upstream into anything downstream on a regular basis — is frowned upon:

Otherwise, the topic that was merged to suddenly contains more than a single (well-separated) change. The many resulting small merges will greatly clutter up history. Anyone who later investigates the history of a file will have to find out whether that merge affected the topic in development. An upstream might even inadvertently be merged into a "more stable" branch. And so on.

If you followed the last paragraph, you will now have many small topic branches, and occasionally wonder how they interact. Perhaps the result of merging them does not even work? But on the other hand, we want to avoid merging them anywhere "stable" because such merges cannot easily be undone.

The solution, of course, is to make a merge that we can undo: merge into a throw-away branch.

If you make it (very) clear that this branch is going to be deleted right after the testing, you can even publish this branch, for example to give the testers a chance to work with it, or other developers a chance to see if their in-progress work will be compatible. git.git has such an official throw-away integration branch called pu.

Assuming you are using the merge approach discussed above, when you are releasing your project you will need to do some additional branch management work.

A feature release is created from the master branch, since master tracks the commits that should go into the next feature release.

The master branch is supposed to be a superset of maint. If this condition does not hold, then maint contains some commits that are not included on master. The fixes represented by those commits will therefore not be included in your feature release.

To verify that master is indeed a superset of maint, use git log:

This command should not list any commits. Otherwise, check out master and merge maint into it.

Now you can proceed with the creation of the feature release. Apply a tag to the tip of master indicating the release version:

You need to push the new tag to a public Git server (see "DISTRIBUTED WORKFLOWS" below). This makes the tag available to others tracking your project. The push could also trigger a post-update hook to perform release-related items such as building release tarballs and preformatted documentation pages.

Similarly, for a maintenance release, maint is tracking the commits to be released. Therefore, in the steps above simply tag and push maint rather than master.

After a feature release, you need to manage your maintenance branches.

First, if you wish to continue to release maintenance fixes for the feature release made before the recent one, then you must create another branch to track commits for that previous release.

To do this, the current maintenance branch is copied to another branch named with the previous release version number (e.g. maint-X.Y.(Z-1) where X.Y.Z is the current release).

The maint branch should now be fast-forwarded to the newly released code so that maintenance fixes can be tracked for the current release:

If the merge fails because it is not a fast-forward, then it is possible some fixes on maint were missed in the feature release. This will not happen if the content of the branches was verified as described in the previous section.

After a feature release, the integration branch next may optionally be rewound and rebuilt from the tip of master using the surviving topics on next:

The advantage of doing this is that the history of next will be clean. For example, some topics merged into next may have initially looked promising, but were later found to be undesirable or premature. In such a case, the topic is reverted out of next but the fact remains in the history that it was once merged and reverted. By recreating next, you give another incarnation of such topics a clean slate to retry, and a feature release is a good point in history to do so.

If you do this, then you should make a public announcement indicating that next was rewound and rebuilt.

The same rewind and rebuild process may be followed for pu. A public announcement is not necessary since pu is a throw-away branch, as described above.

The merge workflow works by copying branches between upstream and downstream. Upstream can merge contributions into the official history; downstream base their work on the official history.

There are three main tools that can be used for this:

Note the last point. Do not use git pull unless you actually want to merge the remote branch.

Getting changes out is easy:

You will still have to tell people by other means, such as mail. (Git provides the git-request-pull[1] to send preformatted pull requests to upstream maintainers to simplify this task.)

If you just want to get the newest copies of the integration branches, staying up to date is easy too:

Then simply fork your topic branches from the stable remotes as explained earlier.

If you are a maintainer and would like to merge other people’s topic branches to the integration branches, they will typically send a request to do so by mail. Such a request looks like

In that case, git pull can do the fetch and merge in one go, as follows.

Occasionally, the maintainer may get merge conflicts when they try to pull changes from downstream. In this case, they can ask downstream to do the merge and resolve the conflicts themselves (perhaps they will know better how to resolve them). It is one of the rare cases where downstream should merge from upstream.

If you are a contributor that sends changes upstream in the form of emails, you should use topic branches as usual (see above). Then use git-format-patch[1] to generate the corresponding emails (highly recommended over manually formatting them because it makes the maintainer’s life easier).

See the git-format-patch[1] and git-send-email[1] manpages for further usage notes.

If the maintainer tells you that your patch no longer applies to the current upstream, you will have to rebase your topic (you cannot use a merge because you cannot format-patch merges):

You can then fix the conflicts during the rebase. Presumably you have not published your topic other than by mail, so rebasing it is not a problem.

If you receive such a patch series (as maintainer, or perhaps as a reader of the mailing list it was sent to), save the mails to files, create a new topic branch and use git am to import the commits:

One feature worth pointing out is the three-way merge, which can help if you get conflicts: git am -3 will use index information contained in patches to figure out the merge base. See git-am[1] for other options.