[GSoC] Proposal: turn git-add--interactive.perl into a builtin

Hi there. First of all, I'd like to thank all of the support up to now with my microproject :). Here's a first draft of my proposal for Google Summer of Code '17, based on the "Convert scripts to builtins" idea. Please let me know what you think.

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SYNOPSIS There are many advantages to converting parts of git that are still scripts to C builtins, among which execution speed, improved compatibility and code deduplication. This proposal aims to apply this to git-add--interactive, one of the most useful features of Git.

FEASIBILITY Many git scripts have attracted attention for being turned into builtins. There is ongoing work on git-stash (https://public-inbox.org/git/20170321053135.thk77soxc4irxbqj@sigill.intra.peff.net/), and porting interactive rebase is one of the ideas for this edition of GSoC. Not as much attention, however, has been directed to git-add--interactive.

There was only one discussion regarding the feasibility of its porting (https://public-inbox.org/git/CAP8UFD2PcBsU6=FK4OHVrB7E98ycohS_0pYcbCBar=of1HLx+Q@mail.gmail.com/). It resulted in a consensus that doing it would be a task too large – although interesting – for GSoC 2015 based on the amount of its lines of code. It is, however, only a few lines larger than git-rebase--interactive, which has been considered an appropriate idea. As such, it looks like a possible project for three months of full-time work.

Aside from the benefits cited above, turning git-add--interactive into a builtin can reduce Git's dependency on Perl to the point where no "common" command would continue to rely on it.

PROJECTED TIMELINE
- Prior to May 4
-- Refine my basic knowledge of Perl
-- Craft one or two small patches to some of Git's Perl components
(preferentially to git-add--interactive itself) to improve my
understanding of the language and of how Git's Perl scripts actually
work

- May 4 - May 30
-- Clarify implementation details with my mentor, and work on a more
detailed roadmap for the project
-- Investigate roughly how to replace command invocations from the
script with actual builtin functions; which Git APIs in Perl already
have functional equivalents in C; which parts will require a full
rewrite.

- May 30 - June 30 (start of coding period)
-- Define the architecture of the builtin within git (which
functions/interfaces will it have? where will its code reside?).
-- Implement a small subset of the builtin (to be defined with my
mentor) and glue it into the existing Perl script. Present this as a
first patch to get feedback early regarding the implementation and
avoid piling up mistakes early.
-- Do necessary changes based on this initial review.
-- Have roughly 1/3 of the script's functionality ported to C.

- June 30 - July 28
-- Port the remainder of the script to a builtin.
-- Have a weekly roadmap, sending a part of the patch every 15 days to
the mailing list for review and to avoid massive commits by the end of
GSoC.
-- Apply suggestions from community reviews when possible; if not,
save them for doing toward the end of GSoC (see below).
(Note: due to a previous commitment, during a five-day period of July
I will only be able to work part-time on GSoC. The actual week will be
known over the next weeks.)

- July 28 - August 29
-- By the start of this period, send a patch with the builtin fully
implemented to the mailing list.
-- Fix bugs, test extensively, possibly extend test coverage for
git-add--interactive.
-- Respond to the (predictably big) community feedback regarding the change.

I currently work full-time in a payments company (see below), but in case of being accepted I am willing to quit my job some months early to dedicate myself fully to GSoC starting June.

BIOGRAPHICAL INFORMATION My name is Daniel Ferreira and I'm a student from São Paulo, Brazil. I was accepted by Stanford University last year and I will start college this fall. I started coding C about six years ago writing up system modifications ("tweaks") for jailbroken iPhones. Since then, I have written/contributed to a couple of open-source projects like an IRC bot and other assorted things – all of them tracked on Git (https://github.com/theiostream). I have also developed a (closed-source) library in C for interacting with payment terminals in the company I have worked for over the last two years (Pagar.me). There, we use Git extensively for managing projects with around 20 people working concurrently.

MICROPROJECT I have sent a series of patches to complete the microproject of converting recursive calls to readdir() into calls to dir_iterator. The most recent version can be found in https://public-inbox.org/git/1490465551-71056-2-git-send-email-bnmvco@gmail.com/T/#u.

Thanks, -- Daniel.