<!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> ### Proposal <!-- Use this section to explain the feature and how it will work. It can be helpful to add technical details, design proposals, and links to related epics or issues. --> [Delete merged branches API](https://docs.gitlab.com/ee/api/branches.html#delete-merged-branches) endpoint doesn't have any "preview" or "dry run" counterpart in API as far as I can tell, so if one wants to evaluate *what* is to be deleted - the only way I can see it "kind" of being done is: query for all `merged` MRs, query existing branches, cross-reference the two manually and use intersection as the resulting list. But that's a rather roundabout way and not necessarily aligned with inner works of [Delete merged branches API](https://docs.gitlab.com/ee/api/branches.html#delete-merged-branches). Proposal is to add a way to "preview" this destructive transaction either by providing additional endpoint or by extending [Delete merged branches API](https://docs.gitlab.com/ee/api/branches.html#delete-merged-branches) with `dry_run` option. <!-- Consider adding related issues and epics to this issue. You can also reference the Feature Proposal Template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal%20-%20detailed.md) for additional details to consider adding to this issue. Additionally, as a data oriented organization, when your feature exits planning breakdown, consider adding the `What does success look like, and how can we measure that?` section. --> <!-- Label reminders Use the following resources to find the appropriate labels: - https://gitlab.com/gitlab-org/gitlab/-/labels - https://about.gitlab.com/handbook/product/categories/features/ -->