feat: gitlab_project module - Allow to update project default branch

[lgatellier]

SUMMARY

This PR allow gitlab_project module to update a GitLab project's default branch.

ISSUE TYPE

• Feature Pull Request

COMPONENT NAME

gitlab_project module

ADDITIONAL INFORMATION

Fixes #5995

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[felixfontein]

You also need to update the documentation for default_branch.

The gitlab_project module always stated that default_branch is only using during creation. Some users might rely on that and be very surprised if it suddenly starts using that value to update. So this should be marked as a breaking change, and not backported to stable-7.

Out of curiosity, what happens if you provide a name that doesn't exist as a branch? Does the API rename the current default branch to the new name? Or will it simply create the new branch based on the current default branch? Or will it simply fail?

[lgatellier]

Thanks @felixfontein for your feedback. I updated the documentation.

It's clearly a breaking change, since the module will update a field it did not before this PR.

If the provided branch does not exist, the GitLab API will return an HTTP 400 error like that :

fatal: [localhost]: FAILED! => {"changed": false, "msg": "Failed update project: 400: {'base': ["Could not change HEAD: branch 'nonexistingbranch' does not exist"]} "}

A branch rename (like git branch -m) is not possible with GitLab, you have to create the new branch, update project's default branch, and all branch protection rules.

[felixfontein]

I would extend the changelog fragment a bit to point out in which cases users could see unexpected breaking changes; besides that everything looks good!

[lgatellier]

@felixfontein I applied your suggestions, thanks !

[felixfontein]

LGTM! I will merge this in a few days if nobody objects.

[felixfontein]

@lgatellier thanks for implementing this!