Bo Yang <struggleyb.nku@xxxxxxxxx> writes:
> +A call to `git-blame <rev> -- <file>` works as follows:
> +
> +- Look at `git diff <rev>^ <rev>` to see what the commit did.
> +
> +- Discard all `-` lines in the diff, since they are no longer part of
> + `<file>`.
> +
> +- Take blame for all `+` lines; i.e., the newly added lines according
> + to the diff are attributed to `<rev>`.
I hate to say it, but this is horrifying; it works quite the other way
around.
The name of the game is not "take blame by looking at the diff to see what
we introduced"; it is "avoid taking blame at all cost, by looking at the
diff to see what we might have inherited from our parents".
A description closer to the truth would be:
- Look at output of "git diff <rev>^$n <rev>" for each parent ($n runs
from 1 to number of parents);
- Ignore all +/- lines. The context ' ' lines and lines outside of diff
hunks are known to have been inherited from $n-th parent and they are
not our fault. We can happily pass blame for these lines to our
parent.
- Do the above for all the parents. We (grudgingly) take blame for lines
that we failed to find corresponding lines in our parents.
The -M option affects what happens between the second and the third step.
We try to see if the lines that we did not pass blame to <rev>^$n might
have come from <rev>^$n by running diff between the remainder and the blob
in <rev>^$n *again*. This lets us catch code movement within the blob,
hence the name of the option -M.
The -C option affects the choice of the blob in <rev>^$n. Usually, we
internally run an equivalent of "git diff -M <rev>^$n <rev>" to notice
that the file F that we are analyzing used to be called F' in $n-th
parent, and run the diff against it, but -C allows us to check with paths
other than that, and additional -C enlarges the search space. This is to
notice code movement (with a single -C) or copies (with more -Cs) across
paths.
For illustrated description, read the classic:
http://thread.gmane.org/gmane.comp.version-control.git/28826
Almost all the hits in the first page from this query would help, too:
http://search.gmane.org/?query=On+blame%2Fpickaxe&author=Junio+C+Hamano&group=gmane.comp.version-control.git&sort=revdate&DEFAULTOP=and&[=2&xP=blame%09pickaxe&xFILTERS=Gcomp.version-control.git-Ac-Ahamano-Ajunio---A
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html