Re: [PATCH v0] fast-import: Add drop command

On Sun, Sep 25, 2011 at 1:37 AM, Jonathan Nieder [off-list ref] wrote:

Vitor Antunes wrote:

quoted

The drop command deletes the given branch reference, allowing
fast-import to actively ignore it in the final checks.

Thanks.  I must have missed the earlier discussion.  What are the
semantics of this command and its intended purpose?

My guess is that if fast-import is used to manage a set of "remote"
branches, it should be able to delete branches. Then, it should
be allowed to do non-fastforward updates too (--force). Why can't
it just ignore branches deletion (considering --force)?

Random thoughts:
1. once 'drop' is executed, fast-import can't tell if the branch was
actually deleted. And moreover any attempt to read this branch
head becomes illegal (either it's missing in .git or fast-import is
instructed to use a dropped branch).
2. 'reset' command is a bit like proposed 'drop' but it never deletes
a branch ref. Consider following imports:
1) import branch topic
2) reset topic
3) import branch topic2 starting at topic (incorrect import)
If 1-3) is done in one fast-import process, the error is reported.
If 3) is done separately, it succeeds but the result is strange:
topic2 isn't started from scratch but from old "erased" topic.
So, maybe, reset should be fixed to erase branches on --force.

One more scenario is:
1) import topic
2) reset topic
3) import topic
If 1-3) go together - no error
If 3) goes separate - no error, but non-fastforward update.
Much more harmless, but still may look strange.

For example, what
happens if the branch already existed or if there is a checkpoint
(perhaps triggered by the impatient user sending SIGUSR1 to
fast-import) before the "drop" command is processed?

I think that actual ref deletion should take place in update_branch().
So all the cases would be handled as usual.

Jonathan