Re: Could this be done simpler?

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Jun 25, 2009, 22:50 UTC
Message-ID: <alpine.LFD.2.01.0906251544030.3605@localhost.localdomain>
In-Reply-To: <7vprcsymjd.fsf@alter.siamese.dyndns.org>

On Thu, 25 Jun 2009, Junio C Hamano wrote:

Show 6 quoted lines

> 
> Such a decomposed octopus would _only_ be necessary during bisection, only
> when the user chooses to test two tips at once (instead of testing one by
> one), _and_ only its tree is needed for that purpose.  In other words, we
> should be able to do this _without_ creating an extra commit, let alone
> replace mechanism.

Keep in mind, though, that realistically, I don't think we've ever seen any bisection attempts that end at an octopus.

Sure, I suspect that being really clever about decomposing an octopus merge might allow us to bisect things _faster_ to one of the branches involved in the merge, but the amount of smarts to do that just for that reason seems pretty outlandish.

And if we ever do end up with an actual bug being bisected to the octopus merge itself, at that point I don't think it's unreasonable to take the same approach we do with any normal merge: just try to figure out what the conflict is all about (clearly it's not a data conflict, since the octopus wouldn't have succeeded in that case, but subtle merge errors can be due to two branches each introducing their own assumptions without actually ever clashing on a source file level).

With regular merges, if you really don't see what the conceptual conflict is, you could try to do a temporary rebase to try to figure it out, and I suspect that that is what you'd want to do with an octopus merge too - rather than try to decompose the octopus merge into multiple simpler merges, you'd like to try to linearize history and then re-do the bisection attempt on that totally modified/simplified history.

			Linus