Git commit generation numbers

Ok, so I see that the old discussion about generation numbers has resurfaced.

And I have to say, with six years of git use, I think it's not a coincidence that the notion of generation numbers has come up several times over the years: I think the lack of them is literally the only real design mistake we have.

And I absolutely *detest* the generation number cache thing I see on the list.

Maybe I missed the discussion that actually added them to the commits (I don't read the git mailing list regularly any more) but I think it's a mistake to add an external cache to work around the fact that I didn't add the generation numbers originally.

So I think we should just add the generation numbers now. We can make the rule be that if a commit doesn't have a generation number, we end up having to compute it (with no real need for caching). Yes, it's expensive. But it's going to be a *lot* less expensive over time as people start using a git version that adds the generation numbers to commits.

And we can easily mix this - there's no "flag-day" issues. Old versions of git will ignore the generation number and generate new commits that doesn't have it. New versions of git will generate them, and use them. And once the project starts having generation numbers in some commits, the "generating them" part will get cheaper over time.

I'll send out a patch that admittedly does not have much testing as a reply to this one. It ends up being really simple. Of course, maybe it's simple because I did something incredibly stupid, but please take a look.

                                 Linus