Run commands only on git update with Ansible

I have recently switched my automation workflow from Chef to Ansible, and just bumped into a simple issue.

I wanted to run some commands only when the git repository had been updated, and do nothing if it was already up to date.

I did not find anything in the documentation, but after looking a little at the source code, I found out that when using register, myvar.changed was set to true or false depending on whether the repository had been updated or not.

So, to get the result I wanted, I just had to write something like this:

- name: Fetch project
  git: repo= accept_hostkey=yes dest=
  register: gitclone

- name: Build project
  command: make
  when: gitclone.changed
  args:
    chdir: ""

I did not found a lot in the documentation about what can be used with register, but I found out that it was easy enough to get this info from the source code, as it is a simple as looking for module.exit_json calls in the module. For example for the git module.