Allow merge method as configurable option in atlantis.yaml

[ahatzz11]

Community Note

• Please vote on this issue by adding a 👍 reaction to the original issue to help the community and maintainers prioritize this request. Searching for pre-existing feature requests helps us consolidate datapoints for identical requirements into a single place, thank you!
• Please do not leave "+1" or other comments that do not add relevant new information or questions, they generate extra noise for issue followers and do not help prioritize the request.
• If you are interested in working on this issue or have submitted a pull request, please leave a comment.

---

• I'd be willing to implement this feature (contributing guide)

Describe the user story
As an engineer, I'd like all of my automerged atlantis PRs to use the squash merge method without having to specify a flag on every atlantis apply command.

Describe the solution you'd like
I'd love to be able to set the automerge method alongside the automerge enabled/disabled flag in atlantis.yaml

An ideal configuration in the atlantis.yaml would look like:

version: 3
automerge: true
automerge-method: squash
projects:
  ...

---

Right now it's possible to set the --auto-merge-method flag on an atlantis apply command when automerge: true. It would be awesome to be able to set the automerge-method in the repo file so every atlantis apply uses that method. Our use case here is enforcing squash commits to our main branch, but atlantis automerging currently fails because the default merge method isn't allowed. This results in this error:

Automerging failed:

merging pull request: PUT https://api.github.com/repos/FigureTechnologies/figure-infra/pulls/530/merge: 405 Merge commits are not allowed on this repository. []

[X-Guardian]

Atlantis is a community project. Please feel free to look at the code and raise a PR to add this.