SVN to Git/Piston Migration

Why migrate?

The main reason for migrating a project from SVN externals to Git/Piston is to make it easier to apply future updates. The SilverStripe codebase is now on github, so any future updates will have to be applied using "piston update".

Any project that is currently on SVN branches/2.4 or is being upgraded to SilverStripe 2.4+ should be migrated to Git/Piston.

Project branches

If a project is on its own project branch, then migrating to Piston is difficult. This task involves switching the project to piston and merging any project-specific commits back into the repository (or integrating them into core, if they are relevant fixes).

Ideally, we combined this work with upgrading of the project to the latest version of SilverStripe. So, best to propose an upgrade to the client.

The way to handle switching from a project branch is to first change the svn:externals to a branch or tag (who's equivalent can be found on github), then run the script, then re-apply all the commits in the project branch, as necessary.

Installation

Requirements:

PHP: http://php.net/manual/en/install.php
Git: http://book.git-scm.com/2_installing_git.html
Subversion: http://subversion.apache.org/
Ruby Gem: http://fak3r.com/geek/ruby-on-rails-gem-install-versus-apt-get/
Pear: http://pear.php.net/manual/en/installation.getting.php
Piston: http://piston.rubyforge.org/index.html

Install this script by running the following commands:

sudo gem install piston

sudo pear upgrade --force PEAR
sudo pear channel-discover pear.phing.info
sudo pear install phing/phing

git clone git://github.com/candidasa/piston-migrator.git piston-migrator

Then run the script by running:

phing -f piston-migrator/build.xml

Script

Here is what the script does:

Reads in the existing svn:externals
Scans externals to see which have equivalent git repositories with the same branch/tag used in the external
Generates all the commands to run to swap the externals to git/piston
Displays a list of the commands it will run, asking for confirmation
Runs the commands to do the following:
- remove externals from svn:externals
- delete the externals' folders
- commit the removed svn:externals
- run the piston import commands to import the new code
- commit the new git/piston imported externals