Bioclipse git experiences #2: Create patches for individual plugins/features

Carrying around git patches is hard work.
Source: Auckland War Memorial Museum, CC-SA.

This is a series of two posts repeating some content I wrote up back in the Bioclipse days (see also this Scholia page). They both deal with something we were facing: restructuring of version control repositories, while actually keeping the history. For example, you may want to copy or move code from one repository to another. A second use case can be a file that must be removed (there are valid reasons for that). Because these posts are based on Bioclipse work, there will be some specific terminology, but the approach I regularly apply in other situations.

This second post talks about how to migrate code from one repository to another.

Create patches for individual plugins/features

While the above works pretty well, a good alternative in situations where you only need to get a repository-with-history for a few plugins, is to use patch sets.

• first, initialize a new git repository, e.g. bioclipse.rdf:

 mkdir bioclipse.rdf
 cd bioclipse.rdf
 git init
 nano README
 git commit -m "Added README with some basic info about the new repository" README

• then, for each plugin discover you need what the commit was where the plugins was first commited, using the git-svn repository created earlier:

 cd your.gitsvn.checkout
 git log --pretty=oneline externals/com.hp.hpl.jena/ | tail -1

• then create patches for the last tree before that last patch by appending '^1' to the commit hash. For example, the first patch of the Jena libraries was 06d0eb0542377f958d06892860ea3363e3316389, so I type:

 rm 00*.patch
 git format-patch 06d0eb0542377f958d06892860ea3363e3316389^1 -- externals/com.hp.hpl.jena

(tune the filter when removing old patches if there are more than 99!)

The previous two steps can be combined into a Perl script:

#!/usr/bin/perl
use diagnostics;
use strict;

my $plugin = $ARGV[0];

if (!$plugin) {
  print "Syntax: gfp <plugin|feature>\n";
  exit(0);
}

die "Cannot find plugin or feature $plugin !" if (!(-e $plugin));

`rm -f *.patch`;
my $hash = `git log --follow --pretty=oneline $plugin | tail -1 | cut -d' ' -f1`;
$hash =~ s/\n|\r//g;

print "Plugin: $plugin \n";
print "Hash: $hash \n";
`git format-patch $hash^1 -- $plugin`;

• move these patches into your new repository:

 mv 00*.patch ../bioclipse.rdf

(tune the filter when moving the patches if there are more than 99! Also customize the target folder name to match your situation)

• apply the new patches in your new git repository:

 cd ../bioclipse.rdf
 git am 00*.patch

(You're on your own if that fails... and you may have to default to the other alternative then)

• repeat those two steps for all plugins you want in your new repository