Creating Patches
It can happen that you may need to manually modify an external dependency for it to work correctly in the context of a Omnibus embedded packaging, or even to fix an issue that the upstream maintainer have not either accepted or still taking longer to review and ship.
Bootstrapping
Omnibus has a specific DSL and conventions to ship and apply patches automatically as part of the building process.
You will store .patch files that contain the changes in a specific
directory structure and with the help of the patch DSL method, will apply
the file(s) to reflect the desired changes:
config/patches/<software-name>
As example, for a patch that will be applied during the execution of
gitlab-rails, you will store .patch files in:
config/patches/gitlab-rails
Creating a patch
There are two easy ways to create a patch file. You can use the diff command
and compare a original with a modified file (i.e. target.rb with
target.rb.original) or you can use Git to output a patch based one or more
commits.
Diff command
To create a patch file using the diff and the previous example, duplicate the file you are changing with a new name, and make the change to the old one.
diff -Naur target.rb.original target.rb > my_awesome_change.patch
Git command
To create a patch file based on Git commits, you must get the hash from both (or just the earliest one if you are comparing with base HEAD).
# to generate a patch between two commits
git diff commitid1 commitid2 > my_awesome_change.patch
# to generate a patch between the HEAD and a specific commits
git diff commitid1 > my_awesome_change.patch
Using the patch
To patch one or more files, you must first execute any operation in your software definition that provides the original files like downloading, bundle installing etc, and then add something similar to:
patch source: 'my_awesome_change.patch', target: "#{install_dir}/embedded/target_file.txt"