Re: Bring together merge and rebase

From: Theodore Ts'o <tytso@mit.edu>
Date: Dec 26, 2017, 18:04 UTC
Message-ID: <20171226180436.GA28565@thunk.org>
In-Reply-To: <20171226011638.GA16552@Carl-MBP.ecbaldwin.net>

On Mon, Dec 25, 2017 at 06:16:40PM -0700, Carl Baldwin wrote:

Show 9 quoted lines

> At this point, you might wonder why I'm not proposing to simply add a
> "change-id" to the commit object. The short answer is that the
> "change-id" Gerrit uses in the commit messages cannot stand on its own.
> It depends on data stored on the server which maintains a relationship
> of commits to a review number and a linear ordering of commits within
> the review (hopefully I'm not over simplifying this). The "replaces"
> reference is an attempt to make something which can stand on its own. I
> don't think we need to solve the problem of where to keep comments at
> this point.

I strongly disagree, and one way to see that is by doing a real-life experiment. If you take a look at a gerrit change that, which in my experience can have up to ten or twelve revisions, and strip out the comments, so all you get to look at it is half-dozen or more revisions. How useful is it *really*? How does it get used in practice? What development problem does it help to solve?

And when you say that it is a bug that the Gerrit Change-Id does not stand alone, consider that it can also be a *feature*. If you keep all of this in the main repo, the number of commits can easily grow by an order of magnitude. And these are commits that you have to keep forever, which means it slows down every subsequent git clone, git gc operation, git tag --contains search, etc.

So what are the benefits, and what are the costs? If the benefits were huge, then perhaps it would be worthwhile. But if you lose a huge amount of the value because you are missing the *why* between the half-dozen to dozen past revisions of the commit, then is it really worth it to adopt that particular workflow?

It seems to me your argument is contrasting a "replaces" pointer versus the github PR. But compared to the Gerrit solution, I don't think the "replaces" pointer proposal is as robust or as featureful. Also, please keep in mind that just because it's in core git doesn't guarantee that Github will support it. As far as I know github has zero support notes, for example.

						- Ted