Re: Merge with git-pasky II.

[Bram Cohen <bram@bitconjurer.org>]

Linus Torvalds wrote:

> On Tue, 26 Apr 2005, Bram Cohen wrote:
> >
> > If one person renames a file and another person modifies it then the
> > changes should be applied to the moved file.
>
> Bzzt. Wrong answer.

I'm trying to be polite. You're not making that easy.

> The _right_ answer is "if one person moves a function, and another person
> modifies the function, the changes should be applied to the moved
> function".

Now that you're done being dismissive, could you either (a) rebut my quite
detailed explanation of exactly why that functionality is both a dubious
idea and difficult to implement, or (b) admit that you have no plans
whatsoever for supporting any of this stuff? You can't have it both ways.

What I'd really like to hear is some explanation of why git is
reimplementing all of this stuff from scratch. Your implicit claims that
git will do more things than the other systems without having to reinvent
all of their functionality first are, honestly, naive, ill-informed
arrogance.

I'd like to reiterate that *nothing* out there supports moving lines
between files, and further predict, with total confidence, that if git
tries to support such functionality it will simply fail, either by giving
up or creating a system which can behave horribly. Before you get all
dismissive about this claim, please remember that I've spent years
thinking about merge algorithms, and have actually designed and
implemented them, and have spoken at length with other people who have
done the same, while you've merely thought about them for a few weeks.

> Which is clearly a _much_ more common case than file renames.

Even if we pretend that these are comparable features, that's far from
clearly true. Function moves within a file occur more frequently, but a
file rename moves *all* the functions within that file.

> In other words, if your algorithm doesn't handle the latter, then there is
> no point in handling the former either.

If someone offers you a dollar, no strings attached, do you turn them down
because they didn't offer you ten?

> And _if_ your algorithm handles the latter, then there's no point in
> handling file renames specially, since the algorithm will have done that
> too, as a small part of it.

In case these concepts got conflated, I'd like to point out that Codeville
merge both supports renames *and* does better than three-way merge can do
at merging a single, non-renamed file. In most cases three-way and
codeville merge give the same answer, but there are some cases where there
isn't a single appropriate LCA available, and in those cases codeville
will do the right thing while three-way can't.

-Bram