Comment on unchanged lines in an unchanged file in a merge request
Changing one line of code can easily impact other lines of code, where a function is used, or where an expected behavior is violated. This can affect areas of the changed file (addressed by https://gitlab.com/gitlab-org/gitlab-ce/issues/13950) and unchanged files too. Although it is possible to reference these in a comment on the changed line in many instances it makes more sense to leave the comment on the place that should be changed. It is not possible to leave a comment on an unchanged file in a merge request.
Proposal
Add the ability to open a file from the Source branch (possibly using the new file tree or fuzzy file finder) in the merge request comparison. The diff will show everything as unchanged.
What does success look like, and how can we measure that?
Count the number of comments on unchanged files and add to the usage ping.
If we are successful we will make it easy for people to leave comments anywhere on the code in the merge request interface.