Fast-forward merge check for submodules.

New in this release

This version includes a new merge check to ensure that all submodules can be merged in fast-forward mode. If we didn't merge the submodule before merging the main repository, we'd be able to do it afterward in fast-forward mode, and the link to the submodule will remain unchanged.

Please note that validation is performed only at the first level of a submodule, and nested submodules will not be checked.

Merge-check must first be enabled in the project or repository settings.