Re: git status: small difference between stating whole repository and small subdirectory

> Nguyen Thai Ngoc Duy <pclouds@gmail.com> writes:
>
>>> diff --git a/builtin/checkout.c b/builtin/checkout.c
>>> index 5bf96ba..c06287a 100644
>>> --- a/builtin/checkout.c
>>> +++ b/builtin/checkout.c
>>> @@ -319,6 +319,10 @@ static void show_local_changes(struct object *head, struct diff_options *opts)
>>>                die(_("diff_setup_done failed"));
>>>        add_pending_object(&rev, head, NULL);
>>>        run_diff_index(&rev, 0);
>>> +       if (!DIFF_OPT_TST(&rev.diffopt, HAS_CHANGES)) {
>>> +               struct tree *tree = parse_tree_indirect(head->sha1);
>>> +               prime_cache_tree(&active_cache_tree, tree);
>>> +       }
>>>  }
>
> I think this patch is wrong on at least two counts.
>
>  * The run_diff_index(&rev, 0) you reused is doing "diff HEAD" and not
>   "diff --cached HEAD".  The added check does not say anything about the
>   comparison between the index and the tree at the HEAD.
>
>  * Even if we added an extra run_diff_index(&rev, 1) there, or added a
>   call to index_differs_from() to run "diff --cached HEAD" to check what
>   needs to be checked, it is still not quite right.
>
> On the latter point, imagine what happens in the two invocations of
> checkout in the following sequence:
>
>   $ git reset --hard master
>   $ git checkout master
>   $ git checkout master
>
> The second one should notice that the cache tree is fully valid, so the
> internal "diff --cached" it runs should only open the top-level tree
> and scan entries in it, without recursing into any of the subtrees, and
> realize that the index is in sync with "HEAD", which should be a very
> cheap operation (that is the whole point of the current topic of our
> discussion looking at the cache-tree).  Then the new code calls
> prime_cache_tree() to read _everything_?
>
> Probably cache_tree_fully_valid() should be called before deciding that we
> need to re-populate the cache tree from "HEAD".