Re: [PATCH 0/3] merge -Xindex-only

> Michael Haggerty <mhagger@alum.mit.edu> writes:
> 
>> [Resend because of address confusion in replied-to email.]
>>
>> On 07/07/2013 08:00 PM, Thomas Rast wrote:
>>> I recently looked into making merge-recursive more useful as a modular
>>> piece in various tasks, e.g. Michael's git-imerge and the experiments
>>> I made in showing evil merges.
>>>
>>> This miniseries is the extremely low-hanging fruit.  If it makes a
>>> good first step for git-imerge, perhaps it can go in like this.  It's
>>> not a big speedup (about 2.2s vs 2.4s in a sample conflicting merge in
>>> git.git), but it does feel much cleaner to avoid touching the worktree
>>> unless actually necessary.
>>>
>>> Otherwise it's probably not worth it just yet; for what I want to do
>>> with it, we need some more reshuffling of things.
>>
>> Interesting.
>>
>> For git-imerge, it would be nice to speed up merges by skipping the
>> working tree updates.  10% might not be so noticeable, but every little
>> bit helps :-)
>>
>> But the killer benefit would be if git-imerge could do some of its
>> automatic merge-testing and autofilling in the background while the user
>> is resolving conflicts in the main index and working tree.
>>
>> Is it possible to use this option with an alternate index file (e.g.,
>> via the GIT_INDEX_FILE environment variable)?  Can it be made to leave
>> other shared state (e.g., MERGE_HEAD) alone?  If so, maybe it's already
>> there.
> 
> GIT_INDEX_FILE yes, that one works out of the box.
> 
> I think for the shared state, the following is a (probably) ridiculously
> unsupported yet magic way of achieving this:
> 
>   mkdir -p unshared/.git
>   cd unshared/.git
>   for f in ../../.git/*; do
>     case "$f" in
>       *HEAD | index)
>         cp "$f" .
>         ;;
>       *)
>         ln -s "$f" .
>         ;;
>     esac
>   done
> 
> That gives you a repository that propagates ref changes and object
> writing, but does not propagate changes to index, HEAD, FETCH_HEAD or
> MERGE_HEAD.  Which might just be what you need?
> 
> Note that as far as I'm concerned, this is a live handgrenade.  It could
> blow up in your face at any time, but it probably has its applications...