Re: A rebase regression in Git 2.18.0

Hi Elijah,

On Thu, 30 Aug 2018, Elijah Newren wrote:

On Tue, Aug 28, 2018 at 9:58 AM Junio C Hamano [off-list ref] wrote:

quoted

Elijah Newren [off-list ref] writes:

quoted

  - Add a flag to turn off directory rename detection, and set the
flag for every call from am.c in order to avoid problems like this.

I'd say this is the only practical solution, before you deprecate
the "pipe format-patch output to am -3" style of "git rebase" (and
optionally replace with something else).

I posted a patch a while back to add an --am flag to "git rebase",
make "--am" be implied by options which are still am-specific
(--whitespace, --committer-date-is-author-date, and -C), and change
--merge to be the default.

Didn't you also post a patch to fold --merge into the --interactive
backend? What's your current state of thinking about this?

As to switching from --am as the default: I still think that --am has
serious speed advantages over --merge (or for that matter, --interactive).
I have no numbers to back that up, though, and I am currently really busy
with working on the CI, so I won't be able to measure these numbers,
either...

Also please note: I converted the `am` backend to pure C (it is waiting at
https://github.com/gitgitgadget/git/pull/24, to be submitted after the
v2.19.0 RC period). Switching to `--merge` as the default would force me
to convert that backend, too ;-)

I'll post it as an RFC again after the various rebase-rewrite series
have settled and merged down...along with my other rebase cleanups
that I was waiting on to avoid conflicts with GSoC stuff.

Thanks for waiting! Please note that I am interested, yet I will be on
vacation for a couple of weeks in September. Don't let that stop you,
though!

quoted

The whole point of "am -3" is to do _better_ than just "patch" with
minimum amount of information available on the pre- and post- image
blobs, without knowing the remainder of the tree that the patch did
not touch.  It is not surprising that the heuristics that look at
the unchanging part of the tree to infer renames that may or may not
exist guesses incorrectly, either with false positive or negative.
In the context of "rebase", we always have all the trees that are
involved.  We should be able to do better than "am -3".

Right. I think that Elijah's right, and --merge is that "do better"
solution.

Ciao,
Dscho