The gitworkflows(7) illustrated

The gitworkflows(7)
illustrated
by K. Tateishi
(@ktateish)

What’s gitworkflows?
A set of workflows used in the Git project itself.
Details are described in the online manual
gitworkflows(7) shipped with Git.

Why gitworkflows?
● You can push -f for integration branches
● You can merge topic branches casually
● You can keep master stable with clear
history
● Scalable to a large number of developers
You know you can freely modify your commits
and topic branches with Git. You can do it for
integration branches with gitworkflows.

In these slides
I’ll show you how gitworkflows* work with
simple commit graphs.
It helps you to understand gitworkflows even
though they are little complicated.
Here we go.
* Maybe slightly different from actual workflows used by git.git, because these slides are based on my
interpretation of the gitworkflows(7).

There is an initial commit.
Let’s start from here.

master
This is the ‘master’ branch

This is the ‘master’ branch

Say you need three topics (A, B, C) for the first release.
A
B
C

And they’ve done.
Integrate to master?

No. ‘master’ can’t be reset after topics once merged
(and pushed to public repositories).
Use a ‘throw-away’ integration branch instead.

‘pu’ is the name of the throw-away integration branch.
Stands for ‘Proposed Update’
pu

‘pu’ should be branched from the tip of the most advanced
non-throw-away branch.
‘master’ would be fine at this time.
(You may use git branch pu master)

Merge topic A…
(checkout pu and merge topic-A. You can use --
no-ff merge like below if you want)
merge

Merge topic A, B and C into ‘pu’.
merge

Then, let’s do tests especially about interactions among the
merged topics/features. (They can’t be tested on each
branch)

BTW you can push ‘pu’ to public repositories if needed.
(push origin pu)
e.g. a CI server is watching a public repository for running
automated tests and you want to push for it.

You may find some bugs/lacks of functionalities on ‘pu’
with integrated state of the three topics.

One of them was introduced on topic A
So fix it on that topic.
commit

Others should be added/fixed on each branch.
commit

And merge them into ‘pu’?
No.
‘pu’ is a throw-away integration branch.

So reset ‘pu’ to ‘master’
(checkout pu and reset --hard master)
reset

So reset ‘pu’ to ‘master’ so that throw away the old ‘pu’.

And then, re-do merges...
merge

Now you’ve got new ‘pu’ that cleanly merged three
topics.

Note that all developers involved including you can’t work
on ‘pu’. All topics have to be forked off from ‘master’

Without reset, resulting branch / commit graph would be little
more complicated, even though they have identical trees.
trees of these two commits
are identical
- with reset
- without reset

OK. Let’s push new ‘pu’ to public repositories and test it.

You have to do push -f origin pu or push origin
+pu if you’ve pushed old ‘pu’ before, because new ‘pu’ isn’t
direct descendant of the old ‘pu’ on origin.

After test, you found that two features from topic A, B were
good and stable but one from topic C wasn’t.

You decide to merge topic A and B into ‘master’ because
they are stable enough.

Merge topic A…
(checkout master and merge topic-A)
merge

Merge topic A and B into ‘master’.
merge

# Now topic A, B are not important any more for these slides.
# So gray out them.

At the same time, a bug on topic C was spotted and fixed.
Let’s rebuild ‘pu’.
commit

‘pu’ should be reset to ‘master’ again.
reset

Resetting ‘pu’ also means that throwing away the old
‘pu’.

Merge topic C, then push ‘master’ and ‘pu’.
Again, you have to use forced push for ‘pu’, so you may say:
git push origin master +pu
(prefix ‘+’ for the branch name means forced push.)
merge

You want more time to stabilize topic C.
So you decide to make the first release with two features
already merged into ‘master’.

For making release, tag an annotated tag ( ) at ‘master’
tag

v1.0.0
The release tag name is ‘v1.0.0’
Then push it.
(tag -a ‘v1.0.0’ master and push origin v1.
0.0)
tag

You received new topics created after release. They
would be branched from ‘master’.
new topics

Some new topics would be good but some are possibly
not good (i.e. break something).

So new topics should be merged into ‘pu’ first.
merge

Merge another topic into ‘pu’ and push it.
merge

You find two of three active topic branches look good
after tests. But you are unsure for...
Good
Good

Unsure for: - Stability of the implementation
- Excellence of the design
- Requirement of the feature
etc.

It means that keeping them in ‘pu’ is tiring because they
won’t be changed for a while, but merging them into
‘master’ can’t be done because they may be changed or
possibly deleted.

In other words, you need an integration branch for
stabilizing, testing or previews for those topics.

‘next’ is the integration branch for such use. It’s like a
hybrid of throw-away and non throw-away. You can
reset ‘next’ with an announcement for developers, but
don’t do it so frequently.
next
tag

‘next’ will be branched from ‘master’.
(branch next master)

Merge the remaining old active topic, C…
(checkout next and merge topic-C)
merge

And merge new one, say topic D.
merge

Here, ‘pu’ always should be branched from the most
advanced non-throw-away integration branch.

So let’s rebuild ‘pu’ on ‘next’ at this time.
(checkout pu and reset --hard next)
reset

Merge the remaining new topic, say topic E.
merge

Then, push ‘next’ and ‘pu’
(push origin next +pu)

Note that you and developers involved cannot work on
‘next’ because it sometimes get reset. So all feature
branches should be forked off from ‘master’

What are the differences between ‘next’ and ‘pu’?

‘pu’ is easily disposable but ‘next’ isn’t.

For example, if a topic merged only to ‘pu’ have a bug and
fixed on it ...
commit

Then, simply reset ‘pu’ to ‘next’...
(checkout pu and reset --hard next)
reset

And merge new tip of that topic.
(i.e. rewind and reconstruct ‘pu’)
merge

On the other hand, if a topic kept in ‘next’ have another
commit...
commit

‘next’ can’t be reset, so just merge new tip of that topic
on current ‘next’...

And rebuild ‘pu’ on new ‘next’
reset and
merge

Note that you can merge the new branch head of topic D
into ‘pu’ first if needed.
(e.g. it has too large impact to merge into ‘next’)
merge into ‘pu’ first
(+ push and test)
if it looks good,
then merge into ‘next’
reconstruct ‘pu’.
this is identical graph
shown in previous page

Here is another situation.
You got new topic (say F).

You found a topic kept in ‘pu’, topic E, was totally broken
and the topic developer can’t fix it right away. When it
happened, just reconstruct ‘pu’ ignoring broken
branches.
Broken

And merge again only good branches.
merge

If the broken branch was rebased with fixes after a
while...
rebased
rebased
topic

Merge the rebased new branch into ‘pu’
rebased merge

If you find a branch kept in ‘next’, e.g. topic C, is broken
and it can’t be fixed for a while...
Broken

You should revert the whole branch
(revert -m 1 <merge commit>)
revert
revert commit
reverted
merge

Of course you should rebuild ‘pu’ and push them.
reset and
merge

After a while, when the topic C was fixed all bugs rebasing
it...
rebased

Merge it into ‘next’...
merge

And rebuild ‘pu’, then push ‘next’ and ‘pu’.
reset and
merge

Again, note that ‘next’ shouldn’t be reset easily like ‘pu’.
When you want to redo something on ‘next’, just revert or re-
merge instead.

But ‘next’ can be reset with announcements for involved
developers when it get awfully dirty with a number of revert
and duplicate merges.

And you’ll also have chances to reset ‘next’ after feature
release. It will be shown later.
Let’s keep developing for the second release for now.

When you think topics merged into ‘next’ are stable / having
good design / etc. you can merge them into ‘master’
Good enough to be
merged into ‘master’

Repeat ‘pu’ -> ‘next’ -> ‘master’ cycle until enough features
required for the next feature release are merged into
‘master’
new topic

‘master’
merge

‘master’
good enough
for master

‘master’
good enough
for next

‘master’
merge
reset and
merge

These merges in ‘pu’ -> ‘next’ -> ‘master’ order,
downstream-ward propagation of features, are called
‘graduate’.

Unfortunately sometimes even topics merged into ‘master’
have bugs.
Fix them on their topics? No.
a bug found

Once a topic merged into ‘master’, it will be regarded as
‘master’ itself. So fix branches should be created on
‘master’ for bugs of ‘master’.
fix-branch for the bug

Merge it into (‘pu’ and) ‘next’ first.
merge
reset and merge

Then merge it into ‘master’ if it looks good.
merge

Note that you can merge the fix branch into ‘master’ directly
when the commits in fix branch are trivial.

Note that you can merge the fix branch into ‘master’ directly
when the commits in fix branch are trivial.
merge

But after that, don’t forget to merge ‘master’ into ‘next’ for
the fix will be included in ‘next’
(‘next’ must have the bug because it has all topics merged
into ‘master’)
merge
reset and merge

There is another situation for fixing bugs.
If the release v1.0.0 have a bug, how should we address it?
a bug found

Fix it on ‘master’ and let v1.0.0 users upgrade to ‘master’?
But some v1.0.0 users don’t want to use new features
merged into ‘master’.

So you want a new integration branch only for bug fixing.
‘maint’ is such a branch. It will be branched from the latest
feature release, i.e. v1.0.0.
maint
create branch

The fix branch have to be branched from ‘maint’.
Don’t branch from ‘master’ or any upstream.

If you branch the fix branch for ‘maint’ from ‘master’...
*WRONG*
*WRONG*

When the fix branch merged into ‘maint’, additional topics
are also merged into ‘maint’. Those downwards merging will
break ‘maint’ branch.
*WRONG*
merge
*WRONG*
unintentionally
merged commits

You can handle this case by cherry-pick the commit into
‘maint’, but you should take care where you fork off from.
cherry-pick
workaround

So the fix branch should be forked off from ‘maint’.
As a general rule, fork off topics from the oldest integration
branch which the topics will be finally merged into.

Basically merge the fix branch for ‘maint’ into ‘next’ (or ‘pu’)
first as usual because ‘maint’ never get reset.
merge
reset and merge

Then merge it into ‘maint’ when it looks good on ‘next’.
merge

Of course you can merge fix branches directly into ‘maint’
when they are trivial.
merge

Sometimes you should merge ‘maint’ into ‘master’, and
merge ‘master’ into ‘next’ for propagation of the fixes.
Periodic upward merges are good habits.

merge

reset and merge

When some fixes accumulated in ‘maint’, publish a fix-
release.

Tag v1.0.1 on ‘maint’ for the fix-release and push it.
v1.
0.1
tag

Well, after a while you want to make a new feature-release.
And you want have a code-freeze period for this release.

To freeze your code, just stop merging feature topics and
only merge fix-topics, including ‘maint’, into ‘master’.
merge fix branches only
while frozen

fix
fix
feature

fix
feature
fix

fix
feature
merging maint is ok
fix

fix
feature
merging fix branches
are also ok
fix

fix
feature
Don’t merge feature
branches
fix

fix
feature
fix
even though good
enough for master...

fix
feature
Don’t merge ANY
feature branches
fix

You can merge feature topics into ‘next’ for integration of
them while ‘master’ is frozen. So you don’t have to stop
developing for the code-freeze.
merging feature
branches are OKay
fix
feature
fix

merging fix branches
are also OKay
fix
feature
fix

rebase
rebasing active topics
are OKay

reverting or dropping
active branches are also
OKay
revert

reverting or dropping
active branches are also
OKay

The code-freeze period has done. Now you will make
feature-release.

Before tagging, make sure ‘maint’ is fully merged into
‘master’ by git merge maint on ‘master’. If not merged,
some fixes will be missing from the new release.
Already fully merged
into master in this case

Now release it. Tag v1.1.0 on ‘master’ for the feature-
release and push it.
tag
v1.
1.0

New release has done. But you have some tasks for the
‘next’ and ‘maint’ after feature-release

Let’s do for ‘next’.
At first reset ‘next’ to ‘master’
reset to
master
leave a tag for in
case messed up

Then merge active topics they weren’t included in the last
release. (And rebuild ‘pu’ if needed)
merge active
branches

check diff for
making sure that
they are
equivalentdiff

rebuild pu

This rewind and reconstruction of ‘next’ is for cleaning up the
history of it. Actually you can do this anytime with an
announcement. But it is good point to do this right after a
feature release.

Next, let’s see about ‘maint’
The task for ‘maint’ is simple. Just fast-forward ‘maint’ to
‘master’.
Fast-Foward
to master

This is done by git merge --ff-only master on
‘maint’. If it fail, the last release is missing some fixes
because ‘maint’ must have some commits that are not in
‘master’.
Fast-Foward
to master

If you merge ‘maint’ into ‘master’ before the release like
already shown, the fast-forward will succeed.

Note that if you want keep maintenance branch for the
previous feature-release, you can leave another maint
branch, e.g. maint-1.0, for it.
maint-1.0

After the feature-release, repeat the same workflows
already shown. This is the gitworkflows(7). Keep on
developing with it.
New topic and...

Conclusion (1/2)
● Use throw-away integration branch like pu
● Merge topics into the throw-away(TA) first
● Test in TAs before merging topics into master
● You can use hybrid of TA and non-TA like
next
● next can be reset with announcements.
● master and maint cannot be reset

Conclusion (2/2)
● Don’t base your work on pu or next
● Fork off topics from the oldest integ-branch
which the topics will be finally merged into
● Merge integration branches upwards
● Tag master for feature-releases
● Tag maint for fix-releases

See also
● gitworkflows(7)
● Documentation/SubmittingPatches
in Git source tree
● MaintNote in ‘todo’ branch of git.git
● the Git Blame blog by Junio C Hamano

Q: What is the difference between next and pu?
A: It depends.
gitworkflows(7) saids pu, throw-away, is for testing the
interaction of topics but according to the recent MaintNotes in
the git.git, pu is a sort of reminder for the maintainer. next is
said to be for testing/polishing for master in both documents.
IMHO pu is a working space and next is a staging area for
master. It looks like working tree and index of Git itself.

Q: Do I have to keep {‘pu’, ‘next’, ‘maint’}
A: No, you don’t.
Just create and keep them if you need. But I recommend you
to use a throw-away at least. You may keep it in your local
repos only (i.e. make sure tests are succeeded and then
push master).
I’ve seen a project that have only ‘master’, ‘pu’ and another
project that have ‘master’, ‘master-pu’, ‘maint’, ‘maint-pu’.

Q: Do I have to keep so many topics?
A: Yes.
You have to keep them until they’ve been merged into
‘master’ or ‘maint’
But you can assign someone you trust to maintain a certain
subsystem with gitworkflows. Then you can just merge
his/her ‘master’ into your ‘master’. (actually you need a
throw-away)
This is the reason why gitworkflows is thought to be scalable.

Q: Do I have to merge a single branch repeatedly?
A: Yes.
When you become tired of resolving identical conflicts,
enable git-rerere(1). The ‘rerere’ stands for Reuse Recorded
Resolution. It will help you to resolve conflicts that have been
resolved once before.

Q: May I use GitHub pull requests with gitworkflows?
A: Yes, of course.
For the git.git, GitHub pull requests are simply ignored but it’s
just a policy of the project.
“Merge Workflow” in the online manual gitworkflows(7) will
suit for GitHub users.

The gitworkflows(7) illustrated

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