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+`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 (`git at adamspiers dot org`).
+
+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 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).