git-deps ======== `git-deps` is a tool for performing automatic analysis of dependencies between commits in a [git](http://git-scm.com/) repository. Background theory ----------------- It is fairly clear that two git commits within a single repo can be considered "independent" from each other in a certain sense, if they do not change the same files, or if they do not change overlapping parts of the same file(s). In contrast, when a commit changes a line, it is "dependent" on not only the commit which last changed that line, but also any commits which were responsible for providing the surrounding lines of context, because without those previous versions of the line and its context, the commit's diff might not cleanly apply (depending on how it's being applied, of course). So all dependencies of a commit can be programmatically inferred by running git-blame on the lines the commit changes, plus however many lines of context make sense for the use case of this particular dependency analysis. Therefore the dependency calculation is impacted by a "fuzz" factor parameter (c.f. [patch(1)](http://en.wikipedia.org/wiki/Patch_(Unix))), i.e. the number of lines of context which are considered necessary for the commit's diff to cleanly apply. As with many dependency relationships, these dependencies form edges in a DAG (directed acyclic graph) whose nodes correspond to commits. Note that a node can only depend on a subset of its ancestors. Motivation ---------- Sometimes it is useful to understand the nature of parts of this DAG, as its nature will impact the success or failure of operations including merge, rebase, cherry-pick etc. For example when porting a commit "A" between git branches via git cherry-pick, it can be useful to programmatically determine in advance the minimum number of other dependent commits which would also need to be cherry-picked to provide the context for commit "A" to cleanly apply. Another use case might be to better understand levels of specialism / cross-functionality within an agile team. If I author a commit which modifies (say) lines 34-37 and 102-109 of a file, the authors of the dependent commits forms a list which indicates the group of people I should potentially consider asking to review my commit, since I'm effectively changing "their" code. Monitoring those relationships over time might shed some light on how agile teams should best coordinate efforts on shared code bases. I'm sure there are other use cases I haven't yet thought of. At first I thought that it might provide a useful way to programmatically predict whether operations such as merge / rebase / cherry-pick would succeed, but actually it's probably cheaper and more reliable simply to perform the operation and then roll back. Note the dependency graph is likely to be semantically incomplete; for example it would not auto-detect dependencies between a commit A which changes code and another commit B which changes documentation or tests to reflect the code changes in commit A. (Although of course it's usually best practice to logically group such changes together in a single commit.) But this should not stop it from being useful. Usage ----- The tool is not yet fully documented, but usage is fairly self-explanatory if you run with `-h` or `--help`. By default it will output all dependencies of the given commit-ish(s), one per line. With `--recurse`, it will traverse dependencies of dependencies, and so on until it cannot find any more. In recursion mode, two SHA1s are output per line, indicating that the first depends on the second. Development / support / feedback -------------------------------- Any kind of feedback is very welcome. For bugs or issues, please first check: * https://github.com/aspiers/git-deps/issues and then file a new issue if yours is not already listed. Otherwise please mail [the `git` mailing list](http://vger.kernel.org/vger-lists.html#git) and cc: me ``. History ------- This tool was born from experiences at [SUSEcon](http://www.susecon.com/) 2013, when I attempted to help a colleague backport a bugfix in [OpenStack](http://www.openstack.org/) [Nova](http://docs.openstack.org/developer/nova/) from the `master` branch to a stable release branch. At first sight it looked like it would only require a trivial `git cherry-pick`, but that immediately revealed conflicts due to related code having changed in `master` since the release was made. I manually found the underlying commit which the bugfix required by using `git blame`, and tried another `cherry-pick`. The same thing happened again. Very soon I found myself in a quagmire of dependencies between commits, with no idea whether the end was in sight. In coffee breaks during the ensuing openSUSE conference at the same venue, I feverishly hacked together a prototype and it seemed to work. Then normal life intervened, and no progress was made for another year. Thanks to SUSE's generous [Hack Week](https://hackweek.suse.com/) policy, I have the luxury of being able to spending some of early January 2015 working to bring this tool to the next level. I have submitted a [Hack Week project page](https://hackweek.suse.com/11/projects/366) and [announced my intentions on the `git` mailing list](http://article.gmane.org/gmane.comp.version-control.git/262000).