Contributing to GitLab after move to a single codebase

What this post added

This post details the transition to a single codebase for GitLab Community (CE) and Enterprise (EE) Editions. It explains that this consolidation simplifies the contribution workflow by providing a single place for issues and merge requests. The post also clarifies that licenses remain the same (CE under MIT, EE proprietary) and that this change primarily impacts contributions to the main GitLab repository, not other related projects like Charts, GitLab Design System, GitLab UI, Omnibus, or Runner. It highlights the elimination of `ee_compat_check` errors for contributors.