I would like this project to be able to handle building merge requests and regular pushes. In order to do this I need a way to configure the git plugin via code to merge two branches together before a build. Much like the RevisionParameterAction.java in the git plugin, we need a class that takes to branches, a source and a target, and can be passed as a build action. I have started an issue for the Git plugin here: https://issues.jenkins-ci.org/browse/JENKINS-23362 If you know of a way to do this please PM on twitter at @bass_rock. All the other necessary code exists in this repo and works.
Optionally, the plugin communicates with the Gitlab server in order to fetch additional information. At this moment, this information is limited to fetching the source project of a Merge Request, in order to support merging from forked repositories.
To enable this functionality, a user should be set up on Gitlab, which adequate permissions to access the repository. On the global configuration screen, supply the gitlab host url ``http://your.gitlab.server`` and the API token of the user of choice.
* Click ``Git`` and enter your Repository URL and in Advanced set its Name to ``origin``
* Add a second Repository with URL ``${gitlabSourceRepoURL}`` and name (in Advanced) ``${gitlabSourceRepoName}`` if you want to be able to merge from forked repositories (this **requires** configuring communication to the Gitlab server)
* For ``token`` put any random string (This is not yet functioning)
* For ``Project URL`` put ``http://JENKINS_URL/project/PROJECT_NAME``
* Click on ``Web Hooks``
* Add a ``Web Hook`` for ``Merge Request Events`` to ``http://JENKINS_URL/project/PROJECT_NAME`` (GitLab for some reason does not send a merge request event with the GitLab Service)
* Configure any other pre build, build or post build actions as necessary
Triggers from push events may be filtered based on the branch name, i.e. the build will only be allowed for selected branches. On the project configuration page, a list of all branches on the remote repository is displayed under ``Build when a change is pushed to GitLab.``, or an asterisk (*) indicating that no filtering will be applied. It is possible to select multiple branches by holding Ctrl and clicking.
This functionality requires accessing the Gitlab server (see [above](#configuring-access-to-gitlab)) and for the time being also a git repository url already saved in the project configuration. In other words, when creating a new project, the configuration needs to be saved *once* before being able to select the allowed branches. For existing projects, all branches are allowed to push by default.
* GitLab CI Merge Status pages says pending when there is no build scheduled, or the status is unknown. This is because I coded a workaround until this bug gets resolved: https://github.com/gitlabhq/gitlabhq/issues/7047