Re: [WIP v3 0/7] mv: fix out-of-cone file/directory move logic

[Shaoxuan Yuan <shaoxuan.yuan02@gmail.com>]

On 6/24/2022 12:19 AM, Junio C Hamano wrote:
 > Derrick Stolee <derrickstolee@github.com> writes:
 >
 >> On 6/21/2022 7:30 PM, Victoria Dye wrote:
 >>> Shaoxuan Yuan wrote:
 >>>> But I think it worth discuss if we should implement in-cone to
 >>>> out-of-cone move, since it will be nice (naturally) to have it 
working.
 >>>>
 >>>> However, I noticed this from the mv man page:
 >>>>
 >>>> "In the second form, the last argument has to be an existing 
directory;
 >>>> the given sources will be moved into this directory."
 >>>>
 >>>> I think trying to move out-of-cone, the last argument has to be an 
non-existent
 >>>> directory? I'm a bit confused: should we update some of mv basic 
logic to
 >>>> accomplish this?
 >>>>
 >>>
 >>> I suspect this requirement is related to the POSIX 'mv' [1] (and
 >>> corresponding 'rename()', used in 'git mv'), which also requires 
that the
 >>> destination directory exists. I personally don't think this requirement
 >>> needs to apply to 'git mv' at all, but note that changing the 
behavior would
 >>> require first creating the necessary directories before calling 
'rename()'.
 >>>
 >>> As a more conservative solution, you could do the parent directory 
creation
 >>> *only* in the case of moving to a sparse contents-only directory (using
 >>> something like the 'check_dir_in_index()' function you introduced to
 >>> identify).
 >>>
 >>> I'm also interested in hearing what others have to say, especially 
regarding
 >>> historical context/use cases of 'git mv'.
 >>>
 >>> [1] https://pubs.opengroup.org/onlinepubs/9699919799/utilities/mv.html
 >>
 >> I wanted to reply here to maybe get more attention on this point.
 >>
 >> My personal opinion is that `git mv` should move to the location 
requested,
 >> even if it requires adding parent directories. Changing that 
behavior might
 >> need to come as its own topic, before doing the 
in-cone-to-out-of-cone work.
 >> Knowing if this behavior can change (or must stay the same) informs 
how that
 >> sparse case will work.
 >
 > When a particular checkout excludes directory, say, Documentation/,
 > from its cone of interest, we may not have that directory in the
 > working tree.  In such a scenario, if you did
 >
 >     $ git mv new.txt Documentation/technical/
 >
 > the index may not even know if "Documentation/" (which most likely
 > is represented as a sparse "tree entry in the index") has the
 > "technical" subdirectory in it, so it may have to expand it
 > on-demand.  I do not have an objection against making it easier for
 > users to do this.
 >
 > As part of its implementation, you may have to do an equivalent of
 > "mkdir -p Documentation/technical/" before you can even materialize
 > the "new.txt" file in the directory.  I do not think that breaks the
 > parallel to POSIX "mv" in that case, as Documentation/technical/ is
 > *NOT* really a destination directory that does not exist.
 > Conceptually, the directory (and all the directories in the full
 > tree) exists---it is just the sparse-checkout is hiding it from the
 > view.
 >
 > A corollary to the above is what should happen when you did
 >
 >     $ git mv new.txt Documentation/no-such-directory/
 >
 > i.e. you try to do a move that would fail even if you weren't using
 > the sparse-checkout feature.  I think that *SHOULD* fail, if we
 > wanted to be parallel to what POSIX "mv" does.
 >
 > Thanks.

Agree.

Thanks & Regards,
Shaoxuan