Last updated by 2 years ago

Page: Creating Patches From Git, Version:0

Most Grails-related source is hosted on GitHub, including the core source code, the functional test suite, and the source for the user guide. If you want to provide patches for any of these projects, then you should use git to generate them.

Getting hold of git

Before you can use git, you need to install it on your computer. This step is of course platform-dependent, but a few suggestions for some common operating systems follow.

Windows

Download and run the msysgit installer. This will provide a shortcut from which you can start a command prompt dedicated to git. Once running, you execute git as you would for any other OS.

Mac OS X

You have a couple of options. You can grab the dmg package or use MacPorts:

sudo port install git-core +svn+bash_completion

This will allow you work against Subversion repositories (via git svn@) and give you bash completion.

Linux

You can get RPM and Debian packages from the git download site, but it's usually easier to use @apt-get or @yum@:

sudo apt-get install git-core
# or
su -c 'yum install git-core'

Once you have git installed, you can fetch the source you want to work on from GitHub.

Cloning the repository

If you just want to create a patch for a project, then all you need is a read-only clone of the relevant project. You can find the URLs on the GitHub pages for each project. The HTTP URL is recommended since it works with HTTP proxies. So, let's take the Grails core project as an example:

git clone http://github.com/grails/grails-core.git

The above command will create a new directory called "grails-core" and populate it with a clone of the project source. You won't be able to push changes back to the remote repository on GitHub, but that's not what we're trying to do.

Creating a patch

Before you start hacking away and making changes to the code, wait! It's often a good idea to work on local branches. So, once you've cloned the repository, run this from within the project directory: 

git checkout -b myChanges
This will create a local branch called "myChanges" and switch your working copy to it. You can now hack away to your heart's content!

Once you have committed the changes that you want to your local branch, it's time to create the patch. But first, make sure you're synchronised with the latest code: 

git checkout master
git pull
git checkout myChanges
git rebase master
Your local branch will now have the latest code. For the next step, you have a couple of options. If you have created only one commit, then you can run: 
git format-patch -1
This will generate a file in the current directory with the name "001-*.patch". Assuming that an issue exists or you have created one for this change, you can attach the patch file to it.

On the other hand, if you have more than one commit you can generate multiple patch files. Simply execute git log and find the commit immediately preceding the first one you want to generate a patch for. You can then run: 

git format-patch 8b0e042a7523558244ea1ac405e145c859ef0370
All commits in git are identified by a long hash like this. It look scary, but copy & paste is your friend! And that's how you generate a patch.