Re: [TopGit PATCH] tg-create.sh: Introduce --add option to add a dependency.

From: Jonathan Nieder <jrnieder@uchicago.edu>
Date: Aug 13, 2008, 16:20 UTC
Message-ID: <Pine.GSO.4.62.0808131100280.1278@harper.uchicago.edu>
In-Reply-To: <1218637514.7561.30.camel@heerbeest>

Hi,

Jan Nieuwenhuizen wrote:

Show 6 quoted lines

> The bad thing is that this does not play well with tg undepend;
> it won't work to re-add a previously removed dependency.  This
> --add is implemented as a merge, and all merge commits are
> already present; it is only that lateron they are reverted.
> 
> Any ideas on how to fix that?

Interesting - I had imagined changing dependencies working in an entirely different way.

Let's say your history is

    B -- (some mess) -- P

where P is your current branch head, and B is the current top base, a merge of all your current dependencies. Now you change your dependencies drastically, and you end up with a new top base B'. Then ideally you want your new branch head P' to have the same tree as if you had run "git rebase --onto B' B P", but of course you want to preserve the history, so you could

	$ git checkout -b P' P
	$ git rebase --onto B' B
	$ git checkout P
	$ git merge --no-ff --no-commit B'   (*)
	$ git read-tree -u P'
	$ git commit
	$ git branch -D P'

or something like that. The line marked with a (*) doesn't work as it should in current git as far as I remember, but it would be a simple change. The point is to achieve the result

    B -- (some mess) -- old P -- P
                                /
                              B'

with the diff from B to old P being approximately the same as the diff from B' to P, even if we just dropped some dependencies.

The main problem I see with this story is that if B' is just B with some new changes added this is overly complicated. In other words, in the simple case of moving from (say) a patch based on master to a patch based on next, one would probably prefer

    B -- (some mess) -- old P -- P
     \                         /
      ---------------------- B'

and similarly for moving from depending on master+(one additional patch) to next+(that same patch).

Hope this helps, and sorry I don't have something more constructive to say. Thanks for starting this going.

Jonathan