Switching to GitUsing branches and pull requests

What’s the goal?

Ship code that is ready for production often.

• Build software that we are confident in shipping

• Ship code more often to address needs

• Become better developers through industry standard practices (with fewer bad habits)

Three kinds of tasks ...• Features (Add or change marketable

features)

• Bugs (Fix issues reported by users and staff)

• Hotfix (Fix very urgent issue with platform)

But how often has this happened?

Too much going on

Release Release

r100 r103 r101 r102

What if we could ...

Release Release

r100 r103 r101 r102

Release Release

You could make this work with subversion

• Create a branch for each task (feature, bug, hotfix)

• Reintegrate / release in whatever order is needed

• Slow process and lots of opportunity for errors.

Turns out, we are not alone in having this issue ...

... and there’s already a (better/best) practice

Most Important Slide™• Anything in the master branch is deployable

• To work on something new, create a descriptively named branch off of master (e.g. feature/new-oauth2-scopes)

• Commit to that branch locally and regularly push your work to the same named branch on the server

• When you need feedback or help, or you think the branch is ready for merging, open a pull request.

• After someone else has reviewed and signed off on the feature, you can merge it into master

• Once it is merged and pushed to master, you can and should deploy immediately

Stolen from http://scottchacon.com/2011/08/31/github-flow.html

What are git branches?• Files are blob objects in a database, stored

in .git/

• A branch is really just a pointer to those objects

• Switching branches is moving a pointer and replacing the files (milliseconds)

• Transparent to the file system

More on how it works at http://ftp.newartisans.com/pub/git.from.bottom.up.pdf

What is master?• The production-ready branch

• Not the same thing as /trunk, other than it is what all branches use as a parent

• Git tags are created on code merged into master, and those are then deployed to production servers

Clone the repository

$ cd ~/Sites/ $ git clone git@github.com/youruser/yourapp.git Cloning into ‘yourapp’ ...

• Grab a copy of the repository (only once)

Create a branch

$ git branch -l * master $ git checkout -b bug/5012-fix-oauth $ git branch -l * bug/5012-fix-oauth master

• When you start a specific task, every time

Make changes

$ git branch -l * bug/5012-fix-oauth master $ vim configuration/production.php $ git add configuration/production.php $ git commit -m “Fix OAuth secret for Twitter” $ vim configuration/production.php $ git add configuration/production.php $ git commit --amend -m “Fix OAuth secret for Twitter, fixes redmine #5012”

• Do the work, commit it (and amend if needed)

Push branch commits• Push to a named branch in the repository

$ git status # On branch bug/5012-fix-oauth nothing to commit, working directory clean $ git push origin bug/5012-fix-oauth Counting objects: 46, done. Delta compression using up to 4 threads. Compressing objects: 100% (22/22), done. Writing objects: 100% (24/24), 3.83 KiB | 0 bytes/s, done. Total 24 (delta 17), reused 8 (delta 1) To git@github.com:youruser/yourapp.git 06ff761..b3ea751 bug/5012-fix-oauth -> bug/5012-fix-oauth

Open a pull request• A pull request is used for integration or

feedback

Discuss pull request, merge accepted• Each pull request is a candidate for inclusion

in master, or at least a discussion about best approach

• Even “good” pull requests might have multiple revisions

• False starts happen – branches are “cheap”

Continuous integration testing• Pull requests will trigger a Jenkins build job and

add a contextual link to it within Github

• A “build” is a snapshot of the repository at a particular commit that is run through a testing regimen

• At minimum, committed files are run through linters and the results are reported back on the pull request via an API

Cleaning up• Once a branch is merged, it can be deleted

$ git branch --merged bug/5012-fix-oauth $ git branch --no-merge * master feature/top-secret $ git branch -d bug/5012-fix-oauth Deleted branch bug/5012-fix-oauth (was a705432).

Wait, what about forks?

Not necessary

Stolen from http://zachholman.com/talk/how-github-uses-github-to-build-github/

Pulling upstream changes

Get upstream changes• Pick up changes in the master branch

• Merge from another fork/branch of changes

$ git pull origin master remote: Counting objects: 18, done. remote: Compressing objects: 100% (5/5), done. remote: Total 11 (delta 8), reused 9 (delta 6) Unpacking objects: 100% (11/11), done. From git://github.com/youruser/yourapp bfbb16f..75737c6 master -> origin/master Updating bfbb16f..75737c6 Fast-forward src/unit/engine/PhpunitTestEngine.php | 2 +- src/workflow/ArcanistUnitWorkflow.php | 3 ++- 2 files changed, 3 insertions(+), 2 deletions(-)

Get another branch• Fetch all branches, checkout from origin

$ git fetch origin $ git checkout -b feature/acme origin/feature/acme remote: Counting objects: 18, done. remote: Compressing objects: 100% (5/5), done. remote: Total 11 (delta 8), reused 9 (delta 6) Unpacking objects: 100% (11/11), done.

A few tools to make the process easier

github/hub• Wrapper that shortens git commands for

GitHub

GitHub for Mac• Yes, there is a GUI, but learn to use the CLI

Quick recap• We’re switching to git to improve the code

review process and ship better code more often

• All code changes are done through pull requests and reviewed by appropriate developers

• Continuous integration testing framework through Jenkins works in tandem with pull requests

That’s it.