Re: Detecting redundant commits

On Mon, Jan 04, 2016 at 09:59:09AM -0600, greened@obbligato.org wrote:

I am attempting to teach cherry-pick to handle redundant commits
gracefully (via a new --skip-redundant-commits option) instead of
aborting.  However, I'm struggling a bit with how to check if the
changes in a commit will become redundant when appied to the new HEAD.

I found diff_tree_sha1 which seems promising.  Am I on the right track?
If not, what's the best way to determine whether a commit object is
redundant with respect to HEAD?

Do you mean commits that are in the cherry-pick range but have matching
commits already in HEAD? For that, you'd want to use patch-ids.[ch], but
I think we already do.

Or do you mean commits that, when applied, we find turn out to have
empty changes (e.g., because we have a set of commits that have
different patch-ids, but do roughly the same thing)? I don't think you
can find that with a straight end-to-end diff. You have try to apply and
then look at the result. I think we already catch that case (see
--allow-empty), though I think the only options are "preserve" or
"abort", not "silently skip" (and it sounds like the latter is what you
would want).

Or am I missing the point completely? :)

-Peff