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

On Sat, Sep 24, 2011 at 10:19 PM, Dmitry Ivankov [off-list ref] wrote:

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

quoted

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)?

I started by using --force, but I did not want to completely disable
these checks. The idea of the drop command is to add support to the
exceptions that require non-fastforward updates.

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.

I think you are not considering the possibility that checkpoints could
have been done along the way. I use them frequently to be able to
analyse branches with diff-tree. As soon as a checkpoint is done,
update-branches will issue an error (commit A is not part of branch A').

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.

Not exactly true if there is a checkpoint done after step 1.

My scenario is:

1) import topic
2) checkpoint
3) diff-tree and processing
4) exit if processing returns ok
5) reset topic to another HEAD
6) goto 1)

-- 
Vitor Antunes