Re: [GSoC 2011] Git Sequencer

From: Daniel Barkalow <barkalow@iabervon.org>
Date: Apr 3, 2011, 19:49 UTC
Message-ID: <alpine.LNX.2.00.1104031407480.14365@iabervon.org>
In-Reply-To: <20110403172054.GA10220@kytes>

On Sun, 3 Apr 2011, Ramkumar Ramachandra wrote:

Show 26 quoted lines

> Hi,
> 
> I'd like to re-apply this year as a student because I really want to
> see (among other things), a sequencer in git.git.  Also, since I
> worked on areas related to fast-import and remote helpers last year, I
> thought I should work on something completely orthogonal this year.
> 
> I now have a draft of my proposal ready, and I'd really appreciate
> feedback.  Also, could someone mentor me?
> 
> ======================================================================
> Project Proposal: Git Sequencer
> Student: Ramkumar Ramachandra
> Mentor: ?
> 
> == The Objective ==
> 
> To write git-sequencer, a new builtin command, and implement existing
> commands on top of that.  This should give the commands more
> functionality, improve their error handling, and make them faster.
> The project can only be considered successful if all (or most) of the
> code written gets merged into upstream.
> 
> The Git Sequencer was a 2008 GSoC project as well; unfortunately most
> of the code did not get merged into git.git.  The learning from all
> that work should serve as a huge headstart this year.

One of the things that is hard about sequencer is that it is ultimately a complete replacement for several differently-implemented programs in different languages, with different temporary file formats and differrent supported operations. As such, you could probably spend an entire summer just getting it reviewed, revised, and accepted, starting with a working implementation.

So I think your proposal is good in how [1/5] includes getting something useful merged. My suspicion is that the outcome will be something like that you implemented all 7 tasks and got 4 of them merged, assuming that you really push getting things merged as soon as they're ready, without spending too much time porting other things to use the core and getting the ports reviewed before the core is accepted.

I actually think that it would be a worthwhile feature for git's library code to have a uniform mechanism for communicating that it is requesting human intervention in the middle of a particular operation, where library operations which conflict with being able to continue this operation are either blocked or abort the operation, and the library is able to be told in general that the human intervention is done and the library operation should be finished now (or produce complaints about the user's work). That is, a library-level, single-interrupted-step "sequencer". For that matter, it should also apply to the common '"git merge" gets a conflict' case, and it would be useful to get some representational uniformity between that and cherry-pick getting a conflict.

I think replacing existing multi-step processes is going to be a lot more contentious and involve user-visible changes which involve matters of taste and such. But I think you can make a valuable contribution in how a single current step is handled before getting tangled in that, and be much more likely to get a useful outcome than if you try to tackle the whole problem.

	-Daniel
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