Merge requests¶

Merge requests are the basis of GitLab as a code collaboration and version control platform [ref].

A merge request is just a way of proposing a change that you have developed on a separate branch be merged into the default branch (master, or main). They enable any number of people to all simultaneously work on the same project without creating merge conflicts that are hard to resolve after-the-fact.

Always use forks and merge requests

The fork-branch-merge workflow should be used for all projects, regardless of scale or size.

Merge requests and pull requests

...are the same thing, 'Pull request' is just GitHub's name for what GitLab calls a 'Merge request'.

The fork-branch-merge-request workflow¶

The ideal workflow for development of any bug fix, or new feature, should be:

create a fork of the canonical repo

clone your fork and add the canonical repo as a remote

git clone git@git.igwn.org:<user>/<name>.git
git remote add upstream https://git.igwn.org/<group>/<name>.git

create a new feature branch for this feature

git checkout -b new-feature upstream/master

commit, commit, commit, then push
```
git push -u origin new-feature
```
open a merge request to propose these commits be integrated
discuss, review, and (hopefully) merge
if you need to update your feature branch relative to upstream changes
```
git pull --rebase upstream master
```
delete the feature branch (using the web interface)

merge request workflow

Examples¶

Merge requests on a single-developer project: https://git.ligo.org/lscsoft/gwdatafind/merge_requests/18
Merge requests on a small project: https://git.ligo.org/packaging/lscsoft-metapackages/merge_requests/16
Merge requests on a large project: https://git.ligo.org/lscsoft/lalsuite/merge_requests/981

Advanced features¶

Approvals¶

Projects can configure themselves to require a formal approval from one or more eligible contributors. This is extremely powerful as a way of enforcing code review, and disabling the ability for merge requests to be submitted and merged by the same person.

https://docs.gitlab.com/ee/user/project/merge_requests/merge_request_approvals.html

This has been configured in LALSuite via the Code Owners concept, whereby one or more project contributors are declared in a special file as the 'owner' of that file; any merge requests that propose changes to those files must be approved by one of the code owners.

Approvals have been configured in GWCelery by defining groups of contributors, including peers, librarians, and review committee; one member of each group must approve each merge request.