… all meaningful operations can be expressed in terms of the rebase command. Once you figure that out it all makes sense.

~ Linus Torvalds

Yes, Rebase

A comparison of merge and rebase workflows

Andrew Briening (abriening)

Prerequisites

You are probably...

  • a professional developer or designer
  • a user of Git, SVN or other revision control tool
  • familiar with git merge +/or rebase commands

Content

  • Why use an SCM or care about history?
  • Review SVN workflows (for comparison)
  • Review +/- of merge workflows
  • Review +/- of rebase workflows
  • Tools & Techniques

Why Use Source Control?

  • Source backup?
  • Deployment tracking?
  • Ease collaboration?
  • …

We don't accept Spaghetti Code

thedailywtf

Why accept spaghetti history?

Accountability

You should know when and why any changes were made.

This requires a clean history.

But what does that realy mean?

When are you cleaning history, or destroying it?

We'll come back to this later …

notes on clean history

Workflows

SVN Workflows

SVN publishes the recommended usage in their Svnbook.

Git on the other hand …


%> man git
GIT(1)
NAME
       git - the stupid content tracker
...

We'll come back to this later …

SVN: Merge-ish

Use svn update to pull-down the changes from the remote and apply them to your local working copy.


%> svn update
Updating '.':
Conflict discovered in 'sandwich.txt'.
Select: (p) postpone, (df) diff-full, (e) edit,
        (mc) mine-conflict, (tc) theirs-conflict,
        (s) show all options: p
C    sandwich.txt
Updated to revision 2.
Summary of conflicts:
  Text conflicts: 1

This usually leaves a messy set of conflicts if you have uncommitted changes.

You then resolve all of the conflicts and attempt to commit again.

svn examples from svnbook

SVN: Rebase-ish

The friendlier technique outlined in the book is to use svn status -u to review the upstream files/commits.


svn status -u -v
M      *        44        23    sally     README
M               44        20    harry     bar.c
       *        44        35    harry     stuff/trout.c
D               44        19    ira       stuff/fish.c
A                0         ?     ?        stuff/things/bloo.h
Status against revision:   46

This allows you to then update and resolve files one at a time using svn update stuff/trout.c.

SVN: Branches (Sqash-ish)

  • Merge Tracking added in v1.5; merges were previously maintained by the user
  • Recomended to merge often from trunk to the branch
  • These incremental merges are just to avoid Merge Hell
  • Merge back to trunk is one large patch
  • Delete the branch

Git Merge Workflows

Git-flow

Merge: Git-flow

  • Branch always
  • master: deployed version history
  • develop: Next to be deployed
  • Method for hotfixes to master
  • Release branches
  • Tagged releases

Merge: Git-flow

Merge: Mashion Workflow

  • Modified git-flow but without git extensions
  • Throwaway integration branches for testing multiple feature branches
  • …
  • More info

Merge: Advantages & Drawbacks

  • Yay! Can use git branch --merged to see if a branch is in master
  • Yay! Only one command to learn: git merge
  • Boo! Merge conflicts are easy to ignore, all conflicts occur at once
  • Boo! Merge conflicts can repeat if long-lived branches are continually merged
  • Boo! Easier to create Spaghetti History
  • Boo! Ladder merges

Ladder Merges

  • Don't merge upstream code at random points
  • Don't merge downstream code at random points either
  • The code you merge in should be for a specific purpose
  • At a specific point in the other branch's history

notes on clean history

Git Rebase Workflows

… all meaningful operations can be expressed in terms of the rebase command. Once you figure that out it all makes sense.

No Love For Rebase

thanks r38y

Rebase: Hashrocket Worflow

With a feature branch:


* 3dcd585 Adding Comment model, migrations, spec
* 9f5c362 Adding Comment controller, helper, spec
* dcd4813 Adding Comment relationship with Post
* 977a754 Comment belongs to a User
* 9ea48e3 Comment form on Post show page

It will get merged as one commit with a message like:


[#3275] User Can Add A Comment To a Post

* Adding Comment model, migrations, spec
* Adding Comment controller, helper, spec
* Adding Comment relationship with Post
* Comment belongs to a User
* Comment form on Post show page
  • Squash workflow
  • Branch commits destroyed; applied as one patch to master
  • Look familiar?
  • More info

Rebase: Neomind Workflow

Modified git-flow without the extensions.

  • Master => Production, Develop => Master
  • Timestamped release tags, git datetag
  • release-2012-12-11T01.39.50
  • Throwaway integration branches for testing multiple feature branches

Rebase: Neomind Workflow

Modified git-flow without the extensions.

  • Rebase feature and bug branches against master before merging
  • Use octopus merge for several branches at once
  • Use no-fast-forward for several related commits

A Rebased History Is Boring

Delineate Branch History With No-Fast-Forward

Octopus Merges Are Fun

Rebase: Advantages & Drawbacks

  • Yay! A clean history!
  • Yay! Rebase conflicts occur one at a time
  • Yay! No Ladder merges
  • Boo! More commands to learn
  • Boo! Recovering from mistakes is difficult for beginners

Long-Lived Branches

What about long-lived branches?

Don't use long-lived branches

Long-Lived Branches

No, really, what about long-lived branches?

  • Decompose your features into negotiable chunks
  • Sometimes unavoidable. ex re-design
  • Merge may be the best solution…
  • but avoid ladders, merge with purpose
  • Assign a gatekeeper
  • Feature Toggle
  • A Microcosm Workflow

The Microcosm Workflow


microcosm/next        » ancestor of master
microcosm/feature-456 » decendent of microcosm/next
microcosm/bug-123     » decendent of microcosm/next
microcosm/integration » throw-away integration
  • next acts like master
  • Always branch from next
  • Features and bugs are merged into next
  • Create integration branches for staging & testing

Safety Equipment

Some tools & techniques to keep you safe while merging & rebasing.

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!

More info

Reuse Recorded Resolution

If you start using throw-away integration branches then git rerere will be your new best friend.


%> git merge i18n-world
Auto-merging hello.rb
CONFLICT (content): Merge conflict in hello.rb
Recorded preimage for 'hello.rb'
Automatic merge failed; fix conflicts and then commit the result.
          

%> git add hello.rb
%> git commit
Recorded resolution for 'hello.rb'.
[master 68e16e5] Merge branch 'i18n'

More info

No Fast-Forward

git merge --no-ff

Don't Fear Destroying History

You can always make more branches.


git checkout -b feature-123-b feature-123
git rebase master

Reflog

And ther is always the reflog

git reflog


b64f807 HEAD@{0}: commit: Silence warning about VERSION...
a2083ca HEAD@{1}: commit: Adds gem dependency on json 1...
adc1095 HEAD@{2}: commit: Adds backup example
ef1c4ab HEAD@{3}: commit: Updates validations & error m...
cf681af HEAD@{4}: commit: Updates validations & error m...
e97f1f3 HEAD@{5}: commit: Updates carpenter binary to e...
d9ac66a HEAD@{6}: checkout: moving from validation_unit...
3322ef8 HEAD@{7}: commit: Unit tests for validation
d9ac66a HEAD@{8}: checkout: moving from experimental to...
d9ac66a HEAD@{9}: checkout: moving from d9ac66a69cabee1...
d9ac66a HEAD@{10}: pull : Fast-forward
c5bd0ab HEAD@{11}: merge allow-alternate-definitions-di...

git reset --hard a2083ca

Stash / Interrupted Workflow

git stash; git stash pop

git save; git restore


# .gitconfig
[alias]
  save = !git add . && git commit -a -m"WIP"
  restore = !git reset --soft HEAD^ && git reset

More info

Just Remember, Git Is Stupid

Pay attention & be safe.

HEAD@{0}