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

[Thomas Rast <trast@inf.ethz.ch>]

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...

-- 
Thomas Rast
trast@{inf,student}.ethz.ch