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NAME

       gitworkflows - An overview of recommended workflows with git

SYNOPSIS

       git *

DESCRIPTION

       This document attempts to write down and motivate some of the workflow
       elements used for git.git itself. Many ideas apply in general, though
       the full workflow is rarely required for smaller projects with fewer
       people involved.

       We formulate a set of rules for quick reference, while the prose tries
       to motivate each of them. Do not always take them literally; you should
       value good reasons for your actions higher than manpages such as this
       one.

SEPARATE CHANGES

       As a general rule, you should try to split your changes into small
       logical steps, and commit each of them. They should be consistent,
       working independently of any later commits, pass the test suite, etc.
       This makes the review process much easier, and the history much more
       useful for later inspection and analysis, for example with git-blame(1)
       and git-bisect(1).

       To achieve this, try to split your work into small steps from the very
       beginning. It is always easier to squash a few commits together than to
       split one big commit into several. Don't be afraid of making too small
       or imperfect steps along the way. You can always go back later and edit
       the commits with git rebase --interactive before you publish them. You
       can use git stash save --keep-index to run the test suite independent
       of other uncommitted changes; see the EXAMPLES section of git-stash(1).

MANAGING BRANCHES

       There are two main tools that can be used to include changes from one
       branch on another: git-merge(1) and git-cherry-pick(1).

       Merges have many advantages, so we try to solve as many problems as
       possible with merges alone. Cherry-picking is still occasionally
       useful; see "Merging upwards" below for an example.

       Most importantly, merging works at the branch level, while
       cherry-picking works at the commit level. This means that a merge can
       carry over the changes from 1, 10, or 1000 commits with equal ease,
       which in turn means the workflow scales much better to a large number
       of contributors (and contributions). Merges are also easier to
       understand because a merge commit is a "promise" that all changes from
       all its parents are now included.

       There is a tradeoff of course: merges require a more careful branch
       management. The following subsections discuss the important points.

   Graduation
       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:

       o    maint tracks the commits that should go into the next "maintenance
           release", i.e., update of the last released stable version;

       o    master tracks the commits that should go into the next release;

       o    next is intended as a testing branch for topics being tested for
           stability for master.

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

       o    pu (proposed updates) is an integration branch for things that are
           not quite ready for inclusion yet (see "Integration Branches"
           below).

       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.

   Merging upwards
       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:

       Example 1. Merge upwards

       Always commit your fixes to the oldest supported branch that require
       them. Then (periodically) merge the integration branches upwards into
       each other.

       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.

   Topic branches
       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:

       Example 2. Topic branches

       Make a side branch for every topic (feature, bugfix, ...). Fork it off
       at the oldest integration branch that you will eventually want to merge
       it into.

       Many things can then be done very naturally:

       o   To get the feature/bugfix into an integration branch, simply merge
           it. If the topic has evolved further in the meantime, merge again.
           (Note that you do not necessarily have to merge it to the oldest
           integration branch first. For example, you can first merge a bugfix
           to next, give it some testing time, and merge to maint when you
           know it is stable.)

       o   If you find you need new features from the branch other to continue
           working on your topic, merge other to topic. (However, do not do
           this "just habitually", see below.)

       o   If you find you forked off the wrong branch and want to move it
           "back in time", use git-rebase(1).

       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:

       Example 3. Merge to downstream only at well-defined points

       Do not merge to downstream except with a good reason: upstream API
       changes affect your branch; your branch no longer merges to upstream
       cleanly; etc.

       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.

   Throw-away integration
       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.

       Example 4. Throw-away integration branches

       To test the interaction of several topics, merge them into a throw-away
       branch. You must never base any work on such a 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.

   Branch management for a release
       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:

       Example 5. Verify master is a superset of maint

       git log master..maint

       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:

       Example 6. Release tagging

       git tag -s -m "GIT X.Y.Z" vX.Y.Z master

       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.

   Maintenance branch management after a feature release
       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).

       Example 7. Copy maint

       git branch maint-X.Y.(Z-1) maint

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

       Example 8. Update maint to new release

       o    git checkout maint

       o    git merge --ff-only master

       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.

   Branch management for next and pu after a feature release
       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:

       Example 9. Rewind and rebuild next

       o    git checkout next

       o    git reset --hard master

       o    git merge ai/topic_in_next1

       o    git merge ai/topic_in_next2

       o   ...

       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.

DISTRIBUTED WORKFLOWS

       After the last section, you should know how to manage topics. In
       general, you will not be the only person working on the project, so you
       will have to share your work.

       Roughly speaking, there are two important workflows: merge and patch.
       The important difference is that the merge workflow can propagate full
       history, including merges, while patches cannot. Both workflows can be
       used in parallel: in git.git, only subsystem maintainers use the merge
       workflow, while everyone else sends patches.

       Note that the maintainer(s) may impose restrictions, such as
       "Signed-off-by" requirements, that all commits/patches submitted for
       inclusion must adhere to. Consult your project's documentation for more
       information.

   Merge workflow
       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:

       o    git-push(1) copies your branches to a remote repository, usually
           to one that can be read by all involved parties;

       o    git-fetch(1) that copies remote branches to your repository; and

       o    git-pull(1) that does fetch and merge in one go.

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

       Getting changes out is easy:

       Example 10. Push/pull: Publishing branches/topics

       git push <remote> <branch> and tell everyone where they can fetch from.

       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:

       Example 11. Push/pull: Staying up to date

       Use git fetch <remote> or git remote update to stay up to date.

       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

           Please pull from
               <url> <branch>

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

       Example 12. Push/pull: Merging remote topics

       git pull <url> <branch>

       Occasionally, the maintainer may get merge conflicts when he tries to
       pull changes from downstream. In this case, he 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.

   Patch workflow
       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).

       Example 13. format-patch/am: Publishing branches/topics

       o    git format-patch -M upstream..topic to turn them into preformatted
           patch files

       o    git send-email --to=<recipient> <patches>

       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):

       Example 14. format-patch/am: Keeping topics up to date

       git pull --rebase <url> <branch>

       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:

       Example 15. format-patch/am: Importing patches

       git am < patch

       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.

SEE ALSO

       gittutorial(7), git-push(1), git-pull(1), git-merge(1), git-rebase(1),
       git-format-patch(1), git-send-email(1), git-am(1)

GIT

       Part of the git(1) suite.