Re: [PATCH 0/1] Preserve the untracked cache across checkout, reset --hard, etc

> I recently sent out a request for assistance, after noticing that the
> untracked cache is simply thrown away after operations such as
> `git checkout` or `git reset --hard`:
>
> http://public-inbox.org/git/alpine.DEB.2.20.1705031202470.3480@virtualbox/
>
> Duy responded with some high-level reasoning that it should be possible
> to simply reuse the untracked cache data structure in the new index, as
> he had a gut feeling that "we do invalidation right".
>
> I did not have time to back that up by a thorough analysis of the code,
> but it turns out that it is unnecessary: Ben Peart pointed me to a patch
> of Dave Turner's that was submitted as part of the watchman series,
> addressing the very issue about which I was concerned.
>
> And I trust Dave to have validated the idea that the untracked cache
> invalidation "is done right" even when we simply move the pointer to a
> different index_state struct than originally.
>
> Seeing as the untracked cache being dropped unceremoniously when it
> should not be dropped, in a surprising number of operations, I think it
> is a sensible change, and important, too, and independent enough from
> the watchman patches to merit being separated out and applied pretty
> soon.
>
> So what I did was simply to drop the two lines from this patch that
> referred to index_state fields added by Dave's watchman patch series.
>
> Please do not mistake this for a sign that I am disinterested in
> watchman support, far from it... stay tuned ;-)
>
> Oh, and I adjusted Dave's email address. Dave, is that okay?
>
> As we are in a feature freeze phase, I was debating whether to send out
> this patch now or later.
>
> Having thought about it for quite a bit, I am now convinced that this
> patch fixes a bug in the untracked cache feature that is so critical as
> to render it useless: if you
>
> - have to switch between branches frequently, or
> - rebase frequently (which calls `git reset --hard`), or
> - stash frequently (which calls `git reset --hard`),
>
> it is as if you had not enabled the untracked cache at all. Even worse,
> Git will do a ton of work to recreate the untracked cache and to store
> it as an index extension, *just* to throw the untracked away in the end.
>
>
> David Turner (1):
>   unpack-trees: preserve index extensions
>
>  cache.h                           |  1 +
>  read-cache.c                      |  6 ++++++
>  t/t7063-status-untracked-cache.sh | 22 ++++++++++++++++++++++
>  unpack-trees.c                    |  1 +
>  4 files changed, 30 insertions(+)
>
>
> base-commit: 4fa66c85f11bc5a541462ca5ae3246aa0ce02e74
> Published-As: https://github.com/dscho/git/releases/tag/preserve-untracked-cache-v1
> Fetch-It-Via: git fetch https://github.com/dscho/git preserve-untracked-cache-v1
>
> --
> 2.12.2.windows.2.800.gede8f145e06
>