Re: GSoC draft proposal: Line-level history browser

[Bo Yang <struggleyb.nku@gmail.com>]

Hi,
> Hmm, I can imagine some (mutually inconsistent) heuristics:
>
>  - Suppose in the blamed commit a single isolated line changed.  Then
>   it is clear where to look next.
>
>  - If the mystery code is at the beginning of the file (resp.
>   beginning of a diff -C0 hunk), maybe it was based on the line at the
>   same position within the previous commit.
>
>  - Take the line with the lowest Levenshtein distance from the mystery
>   code.
>
>  - Expect certain common patterns of change: substituted words,
>   whitespace changes, added arguments for a function, things like that.
>
> That said, I still don’t have a clear picture of a basic strategy.

I can't understand fully about your above strategy. I think we can
category the code change into two cases:
1. The diff looks like:

@@ -1008,29 +1000,29 @@ int cmd_format_patch(int argc, const char
**argv, const char *prefix)
                add_signoff = xmemdupz(committer, endpos - committer + 1);
        }

-       for (i = 0; i < extra_hdr_nr; i++) {
-               strbuf_addstr(&buf, extra_hdr[i]);
+       for (i = 0; i < extra_hdr.nr; i++) {
+               strbuf_addstr(&buf, extra_hdr.items[i].string);
                strbuf_addch(&buf, '\n');
        }


ie: there is both deletion and addition in a change. And this means we
modify some lines of the code. So, what we do will be tracing the two
'minus' lines and then find another diff. Start trace from that diff
recursively.
Yes, the new added code may also be moved or copied from other place.
But, I think here, we should focus on the lines before this changeset.

2. The diff looks like:

@@ -879,9 +885,12 @@ int cmd_grep(int argc, const char **argv, const
char *prefix)
        opt.regflags = REG_NEWLINE;
        opt.max_depth = -1;

+       strcpy(opt.color_context, "");
        strcpy(opt.color_filename, "");
+       strcpy(opt.color_function, "");
        strcpy(opt.color_lineno, "");
        strcpy(opt.color_match, GIT_COLOR_BOLD_RED);

This means, the code here is added from scratch. Here, I think we have
three options.
1. Find if the new code is moved here from other place.
2. Find if the new code is copied from other place.
3. We find the end of the history, so stop here.

The problems remain how do we find the copied/moved code. The new
added code may be copied/moved from multiple place with little
changes.

I hope I understand the requirement of the line-level browser, could
you please point it out if I have made some mistake?

Regards!
Bo