Re: GSoC draft proposal: Line-level history browser

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Mar 20, 2010, 11:30 UTC
Message-ID: <alpine.DEB.1.00.1003201209260.7596@pacific.mpi-cbg.de>
In-Reply-To: <41f08ee11003200218u59c45b6dl82a8eb56cc289256@mail.gmail.com>

Hi,

On Sat, 20 Mar 2010, Bo Yang wrote:

> I am very interested in the project 'Line-level history browser', after 
> some days consideration, now I made up a draft of my proposal, I think 
> it is helpful to send it to the list before submitting it. Could you 
> please give me some advise?

I like it very much already! You obviously put in a substantial amount of time to learn intricate details about the way Git operates, and what is already available.

And you also provided a patch (unrelated to line-level history browser), so you proved that you actually cloned Git, and that you can actually patch it and use Git itself to send a patch to this list.

Very good.

Just a few constructive criticisms (inlined):

> This project will add a new utility for git called 'git line-log'. It 
> can trace the history of any line range of certain file at any revision.

I think that that might be good for starters, but one could imagine that an integration into "git log" might be even better, so that gitk can use this without any further changes.

> For simplity, users can run the command like: ' git line-log 
> builtin/diff.c 6..8 ', he will get the change history of code between 
> line 6 and line 8 of the diff.c file.

It would be good if the code looked harder after failing with the simple strategy, such as looking for code removed in other files, fuzzy matching (optional), and looking for code duplication (i.e. literal copying, or slightly modified copying).

The fuzzy matching might be necessary to catch things like a Java class moving from one file into another (and changing its name): the first line changes, but not completely.

> After reading some libxdiff document and code, I find that libxdiff 
> output all the diff blocks as string into a memory file.

Almost.

Just have a look at the word-level diff (--color-words):

http://repo.or.cz/w/git/dscho.git/blob/bc1ed6aafd9ee4937559535c66c8bddf1864bec6:/diff.c#l382

You will see that there is a function fn_out_diff_words_aux(), which is passed to xdi_diff_outf(). That latter function calls xdiff such that the former function receives a complete line at a time. And this is what I would suggest doing in the line-level log, too.

Ciao, Dscho