Re: [PATCH 4/8] read-cache: add invalidate parameter to remove_marked_cache_entries

On Mon, Dec 10, 2018 at 10:19 AM Duy Nguyen [off-list ref] wrote:

On Mon, Dec 10, 2018 at 7:09 PM Elijah Newren [off-list ref] wrote:

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For the two current callsites, unpack-trees seems to do this
invalidation itself internally.

I'm still a bit scared of this invalidation business in unpack-trees.
The thing is, we handle two separate index_state there, src_index and
result and invalidation has to be done on the right one (because index
extensions are on src_index until the very end of unpack-trees;
invalidating on 'result' would be no-op and wrong).
remove_marked_cache_entries() seems to be called on 'result' while
invalidate_ce_path() is on src_index, hm....

Is Thomas avoiding problems here simply because merge is the only
caller of unpack_trees with src_index != dst_index?  Or does src_index
== dst_index for checkout not actually help?

I think it would not help. 'result' is a temporary index where we copy
things to (and it does not have anything from the beginning). If you
invalidate stuff in there, you invalidate nothing, regardless whether
dst_index == src_index.

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If that does help with the checkout case, then allow me to find a
different way to muddy the waters...  I think I might want to make use
of this function in the merge machinery at some point, so I either
need to figure out how to convince you to verify if all this cache
tree invalidation stuff is sane, or somehow figure out all the
cache_tree stuff stuff myself so I can figure out what is right here.
:-)

I'm not the unpack-trees man (I think that would still be Junio). And
I'm not saying it's sane either. I think it's just some leftover
things since Linus split "the index" in unpack-tree operation to
'src', 'result' and 'dst' many years ago and nobody was brave enough
to clean it up (then I piled on with untracked cache and split index,
but I did not see it clearly either). That person could be you ;-)

Hmm, might make a good New Year's resolution: Enter the abyss, find
out if one can return from it...  or maybe I could just sanely run
away screaming.  We'll see.