Re: GSoC draft proposal: Line-level history browser

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

Hi,

On Tue, Mar 23, 2010 at 9:49 PM, Jakub Narebski <jnareb@gmail.com> wrote:
> Try to come with the result of line-level history for some line in
> git sources "by hand": this would help in discussion about what
> line-level history browser should do, and perhaps even be first test
> of it (see e.g. tests for git-blame).

Thanks for your advice of coming with a real example, Jakub! And I can
give a not too trivial one, :)

If you look at the pretty.c line 1032 line, you will find a line like:

format_commit_message(commit, user_format, sb, context);

Take for example, we will trace the history of this line.
We will find that the first time this line appears:

@@ -900,18 +900,18 @@ char *reencode_commit_message(const struct
commit *commit, const char **encoding
...skipped...
        if (fmt == CMIT_FMT_USERFORMAT) {
-               format_commit_message(commit, user_format, sb, dmode);
+               format_commit_message(commit, user_format, sb, context);
                return;
        }
And we should trace the preimage, something like:
        if (fmt == CMIT_FMT_USERFORMAT) {
               format_commit_message(commit, user_format, sb, dmode);

We will find these below:
@@ -770,7 +775,7 @@ void pretty_print_commit(enum cmit_fmt fmt, const struct com
        const char *encoding;

        if (fmt == CMIT_FMT_USERFORMAT) {
-               format_commit_message(commit, user_format, sb);
+               format_commit_message(commit, user_format, sb, dmode);
                return;
        }

Again:
+
+       if (fmt == CMIT_FMT_USERFORMAT) {
+               format_commit_message(commit, user_format, sb);
+               return;
+       }
+

Here, we find that the line is added from scratch and line level
history browser will do a code movement and copy matching try to find
whether this line if moved from other files.

And it is. In commit 93fc05eb9(Split off the pretty print stuff into
its own file), some code is moved from commit.c to pretty.c and this
line if from commit.c .

Ok, now, we will trace into commit.c for this line.
Again:
        char *reencoded;
        const char *encoding;
-       char *buf;

-       if (fmt == CMIT_FMT_USERFORMAT)
-               return format_commit_message(commit, user_format,
buf_p, space_p);
+       if (fmt == CMIT_FMT_USERFORMAT) {
+               format_commit_message(commit, user_format, sb);
+               return;
+       }

        encoding = (git_log_output_encoding
                    ? git_log_output_encoding

Now, we will trace the commit which produce the above preimage of the
diff hunk. And because there are four lines of the preimage in our
tracing window. We should follow any commit which intersect with these
four lines. Fortunately, there is only one commit.

@@ -1165,7 +1166,7 @@ unsigned long pretty_print_commit(enum cmit_fmt fmt,
        char *buf;

        if (fmt == CMIT_FMT_USERFORMAT)
-               return format_commit_message(commit, msg, buf_p, space_p);
+               return format_commit_message(commit, user_format,
buf_p, space_p);

        encoding = (git_log_output_encoding
                    ? git_log_output_encoding


Again, we find:

        if (fmt == CMIT_FMT_USERFORMAT)
-               return format_commit_message(commit, msg, buf, space);
+               return format_commit_message(commit, msg, buf_p, space_p);

        encoding = (git_log_output_encoding

Again:
        char *encoding;

+       if (fmt == CMIT_FMT_USERFORMAT)
+               return format_commit_message(commit, msg, buf, space);
+
        encoding = (git_log_output_encoding
                    ? git_log_output_encoding

And here, finally, we reach a place where the code is added from
scratch and not copied/moved from other place.

Line level history browser will just display all the related diff to
users and trace the code modification/move/copy.

It traces the preimage of the minimum related diff hunk carefully, if
there is any case that there are more than one commit intersect with
the preimage, we will stop and ask the users to select which way to go
on tracing.

I hope this can help us to discuss the problem, thanks!

Regards!
Bo