preserve untracked cache, was Re: What's cooking in git.git (Jun 2017, #01; Thu, 1)

Hi Junio,

On Thu, 1 Jun 2017, Junio C Hamano wrote:

* dt/unpack-save-untracked-cache-extension (2017-05-20) 1 commit
  (merged to 'next' on 2017-05-23 at 3196d093d6)
 + unpack-trees: preserve index extensions

 When "git checkout", "git merge", etc. manipulates the in-core
 index, various pieces of information in the index extensions are
 discarded from the original state, as it is usually not the case
 that they are kept up-to-date and in-sync with the operation on the
 main index.  The untracked cache extension is copied across these
 operations now, which would speed up "git status" (as long as the
 cache is properly invalidated).

It was my understanding that Ben's analysis conclusively proved that the
patch as well as the test are sound, and Dave agreed.

What is holding this topic up? Anything Ben or I can do to move this
closer to `next` or even `master`?

Ciao,
Dscho