Difference between revisions of "Development/Tutorials/Git/Feature Development Workflow/Branch Development With Merge"

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Latest revision as of 20:43, 24 March 2012

noframe
 
Warning
This page refers to a draft policy which is still to be agreed and implemented. Please take it as a reference for a work in progress project.


This tutorial is aimed to get core developers with more-than-average git knowledge started for developing their own branches, and get them merged and integrated.

This tutorial require you to have a good understanding of git, especially regarding rebasing, merging and committing.

Before you start, you are strongly advised to read the following documents:

Contents

[edit] Merging your branch into integration/master

Merging your branch is a critical part, and it is a delicate process you should undertake only if you are confident with what you are doing and knowing what it implies. The merging process is done with the following several steps.

[edit] Rebase the branch onto master

[edit] The Recipe
git checkout add-hello-button
git fetch --all
git rebase integration/master
[edit] The Explanation

Checkout your branch by issuing

git checkout add-hello-button

Before performing the actual rebase, make sure all your remotes are synced with latest changes. To do that, issue

git fetch --all

Now, fetch from integration to retrieve the changes:

git fetch integration

At this point, you can rebase your branch onto master. Issue

git rebase integration/master

When rebasing, all the commits of your branch are put on top of the commits of the branch you are rebasing. This allows to keep a clean and linear history.

Of course, at this stage conflicts might occur. Be sure to have your branch cleanly rebased before proceeding. A good practice is to verify if the history is now linear as expected. You can use git log or any git UI for doing that.

[edit] Merge the branch into master

[edit] The Recipe
git checkout integration-master
git reset --hard integration/master
git merge --no-ff add-hello-button
[edit] The Explanation

First of all, get back to your local branch tracking integration/master by issuing

git checkout integration-master

You now need to make sure that your local branch matches 1:1 the remote integration/master branch. For this reason, you have to reset the local branch to the remote one.

noframe
 
Warning
This process will erase any local change you made to your local integration-master branch which has not been pushed to integration/master. This is the main reason why you should never do any work in integration-master, except for merging!


This is done when issuing

git reset --hard integration/master

It is now time to perform the actual merge. Due to our rebase, the merge will be fast-forward (if you are here, you should know what it means, and why this happens). However, our policy implies to have a merge commit containing relevant information belonging to the branch we are merging. For this, we have to tell git to perform a non-fast-forward merge. This is done through this command:

git merge --no-ff add-hello-button


[edit] Repositories and projects complying with this policy

The following repositories/projects follow these guidelines. Any project not mentioned here is unaffected by what described

  • kde-workspace
  • kde-runtime
  • kdelibs (plasma only)

[edit] Rationale

This approach is meant to implement proper quality evaluation into the main repositories, still allowing developers to work on anything they want, and providing a sane merging strategy which does not require any specific knowledge from the developer's side.

To learn more about the rationale behind this approach, please read the Rationale article.

[edit] Setting up the development environment

In the following steps, we will assume your system is set up as shown in the git.kde.org user manual, especially regarding automatic URL rewriting for KDE repositories enabled.

In the following tutorial, we'll refer to kdelibs as the main target, but this applies to any other repository using this policy.

[edit] Cloning the repository and adding integration

To clone the repository, issue

git clone kde:kdelibs

This will create a kdelibs directory containing the whole repository. You now need to add a separate remote for handling integration. A remote is a repository URL, and your local clone can contain multiple repositories to track different branches. To add kdelibs' integration repository, issue inside kdelibs' clone:

git remote add integration kde:clones/kdelibs/dafre/kdelibs-integration

Now, fetch from integration to retrieve the changes:

git fetch integration
noframe
 
Note
When working with multiple remotes, you can issue git fetch --all to update all the remotes tracked by your local copy

[edit] Creating branches

You now need to get your branches set up, in particular integration/master. In this example, we are creating a new branch named integration-master which would serve for this purpose in particular:

git checkout -b integration-master integration/master

This command creates a local branch set to track a remote one. This branch should be the branch you'll be basing your work upon: origin/master is not meant for development!

[edit] Using integration vs. using your own clone

It is strongly advised to push your work to integration, but under some circumstances (your work is extremely big in size, you do not have a KDE Development account, etc.), it is allowed to push your branches to a separate personal clone. All work should end up into integration for being reviewed anyway.

[edit] Developing a new feature

We'll now walk through the process needed to develop a new feature. We'll suppose you want to add a button which says "hello" to a specific part of code.

[edit] Creating a new branch

First thing to do is creating a new branch on which to base your work on. This branch must be based upon integration/master. To make sure this happens, start by issuing

git checkout integration-master

Now create your branch. Give it a self-exeplainatory name: try to keep branches as atomic as possible, and possibly split big changes throughout multiple branches divided as per topic. In our case, we want to name our branch add-hello-button. To do that, we do:

git checkout -b add-hello-button

That will create our personal branch which is going to contain our work. Push your branch to integration by issuing

git push integration add-hello-button

[edit] Synchronizing the branch with master

When you create a branch (like you did), you are not receiving incremental updates from other people working in the repository (so in the master branch). This is usually not an issue, and instead an advantage: you can work on your code without being affected by other changes.

However, there are some cases in which synchronizing your code with what's been going on with master is required. Git gives you two ways for doing that: merging or rebasing. Both have upsides and downsides, and both come at a cost.

For this reason, you are strongly invited to avoid merging or rebasing on top of master while developing your feature whenever possible. Although, if you need to, you are supposed to merge your branch with master, and not to rebase it. What you need to do is the following:

git fetch --all
git merge integration/master

This command merges your work with the very latest code from integration/master. This process comes with a cost: your branch will not be a candidate for a clean rebase, and each merge makes the history more complex.

Again, this means that you should try to avoid this process if possible, and if you absolutely need to do that, you should try and keep the number of merges you'll do in your branch as low as possible. More than 3 merges start to create a very cluttered history.

To learn more about merging, rebasing, and what this implies to your branch and to our merge strategy, you are invited to read Rebasing vs. merging: why and how

[edit] Getting the branch reviewed

Once you are done with your changes, you are ready to get your branch reviewed. In the review process, the project's core developers will evaluate your code's quality, and will help you in making it perfect before it gets integrated. Here's how to do it.

[edit] Push your changes to integration

If you have a KDE developer account, simply

git push integration add-hello-button

from within your add-hello-button branch.

If you do not have a KDE Developer account, please get in touch with the core developer who is mentoring you, or with one of the repository's maintainers to get your changes pushed into integration.

[edit] Submit the branch for review

Use Reviewboard for getting your branch reviewed. You can read KDE Reviewboard+Git tutorial for getting started and understanding the steps involved.

It is critical that you specify in the review request whether your branch has ever been merged with master or not.

[edit] Modifying the branch

Everytime you update your review request with new code, please remember to push changes to integration with your new code. That will help developers in reviewing and maintainers in handling your request.

[edit] Getting your branch integrated

Once your review request has been marked as "Ship it!", your job is done. The maintainers will take care of merging the branch into integration/master, stage it for release, and make it reach origin in the end.

It is critical at this point to have your branch frozen. You should not commit anything else to your branch and you should consider it dead. Maintainers will take over its commits and will delete it when merging occurs.

If you are curious to find out what happens to your commit after your code is accepted, read Merge strategies to and from integration


This page was last modified on 24 March 2012, at 20:43. This page has been accessed 1,675 times. Content is available under Creative Commons License SA 3.0 as well as the GNU Free Documentation License 1.2.
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