We've found that there are quite a few defects introduced when files that need to be changed together are not. To address this, we're working on bringing the code together, so the change can be made in one place and unit-tested. We have a git repository, and we'd like to know which files change most often and which files are changed together so that we can be sure that we're collecting the right code together. It's no problem to rank the files by the number of changes made. It's not so easy to cluster the files into groups that are usually changed together.
Do you know of a tool for analyzing a git repository that would help identify the files that get changed together?