GITWORKFLOWS(7) Git Manual GITWORKFLOWS(7)
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.
Git 1.8.3.1 07/30/2024 GITWORKFLOWS(7)
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