Keeping master green and ensuring the stability of collaboration on branches is vitally important. GitLab has introduced Merge Trains as an important way to accomplish this. When merge trains are used, each merge request joins as the last item in that train. Each merge request is processed in order and is added to the merge result of the last successful merge request. The merge request adds its changes, and starts the pipeline immediately under the assumption that everything is going to pass. If the merge request fails, it is kicked out of the train and the next merge request continues the pipeline of the last successful merge result.
Up next we are working on gitlab#28821 which will add more informative context to the position of the merge request in the merge train. When a merge request is added to a merge train, it reveals the position in which it was added, but this information is static and does not update as the train progresses. This issue will improve the user experience by adding more real-time information, so that you can tell what is going on with your merge request.
This category is currently at the "Viable" maturity level, and our next maturity target is Complete (see our definitions of maturity levels). We currently have basic capabilities and want to continue and extend these in the upcoming releases.
Key deliverables to achieve this are:
Parallel execution strategy for Merge Trains (Complete)
It looks like GitLab is the first to provide this functionality, but GitHub has a partial solution and we are aware that other competitors will be able to catch up. We will be monitoring this space closely.
The most popular issue is gitlab#35628. When selecting to work with Fast Forward Merge without using merge trains, a user is offered to rebase master manually, in case master has advanced. Merge Train supporting fast forward merge would reconstruct train and re-run pipelines automatically.
One very useful functionality that has been requested by our own team while dogfooding the feature, is the ability to use merge quick action to add an MR to a merge train gitlab#32336.
In an effort to dogfood our own features, we are actively working on using merge trains internally on gitlab-org gitlab#195.
Our top vision item is Merge Trains should support fast forward merge as this will eliminate the frequent need for manually rebasing. We have heard from many developers that a large portion of their day is dedicated to this activity, and with this functionality, Merge trains will take care of this for them.