Re: [PATCH 1/8] update-index: add untracked cache notifications

> Christian Couder <christian.couder@gmail.com> writes:
>
>> Doing:
>>
>>   cd /tmp
>>   git --git-dir=/git/somewhere/else/.git update-index --untracked-cache
>>
>> doesn't work how one would expect. It hardcodes "/tmp" as the directory
>> that "works" into the index, so if you use the working tree, you'll
>> never use the untracked cache.
>
> I think your "expectation" needs to be more explicitly spelled out.
>
> "git -C /tmp --git-dir=/git/somewhere/else/.git" is a valid way to
> use that repository you have in somewhere else to track things under
> /tmp/ (as you are only passing GIT_DIR but not GIT_WORK_TREE, the
> cwd, i.e. /tmp, is the root level of the working tree), and for such
> a usage, the above command works as expected.  Perhaps
>
>     Attempting to flip the untracked-cache feature on for a random index
>     file with
>
>        cd /random/unrelated/place
>        git --git-dir=/somewhere/else/.git update-index --untracked-cache
>
>     would not work as you might expect.  Because flipping the
>     feature on in the index also records the location of the
>     corresponding working tree (/random/unrelated/place in the above
>     example), when the index is subsequently used to keep track of
>     files in the working tree in /somewhere/else, the feature is
>     disabled.
>
> may be an improvement.

> The index already implicitly records where the working tree was and
> that is not limited to untracked-cache option.  For example, if you
> have your repository and its working tree in /git/somewhere/else,
> which does not have a path X, then doing:
>
>     cd /tmp && >tmp/X
>     git --git-dir=/git/somewhere/else/.git update-index --add X
>
> would store X taken from /tmp in the index, so subsequent use of the
> index "knows" about X that was taken outside /git/somewhere/else/
> after the above command finishes and the subsequent use is made
> without the --git-dir parameter, e.g.
>
>     cd /git/somewhere/else/ && git diff-index --cached HEAD'
>
> would say that you added X, even though /git/somewhere/else/ may not
> have that X at all.  And this is not limited to update-index,
> either.  You can temporarily use --git-dir with "git add X" and the
> result would persist the same way in the index.
>
> I think the moral of the story is that you are not expected to
> randomly use git-dir and git-work-tree to point at different places
> without knowing what you are doing, and we may need a way to help
> people understand what is going on when it is done by a mistake.

> I wonder if it is easy to tell when the user is doing such an
> unnatural thing.  Off the top of my head, when the working tree is
> anywhere other than one level above $GIT_DIR, the user is doing
> something unusual; I do not know if there are cases where the user
> is doing something unnatural if $GIT_WORK_TREE is one level above
> $GIT_DIR, though.