Re: [RFC PATCH] unpack-trees: add the dry_run flag to unpack_trees_options

> Until now there was no way to test if unpack_trees() with update=1 would
> succeed without really updating the work tree. The reason for that is that
> setting update to 0 does skip the tests for new files and deactivates the
> sparse handling, thereby making that unsuitable as a dry run.
>
> Add the new dry_run flag to struct unpack_trees_options unpack_trees().
> Setting that together with the update flag will check if the work tree
> update would be successful without doing it for real.
>
> The only class of problems that is not detected at the moment are file
> system conditions like ENOSPC or missing permissions. Also the index
> entries of updated files are not as they would be after a real checkout
> because lstat() isn't run as the files aren't updated for real.
>
> Signed-off-by: Jens Lehmann <Jens.Lehmann@web.de>
> ---

> AFAICS this patch enables the user to achieve a dry run by calling
> unpack_trees() with both update and dry_run set.
>
> My "Teach read-tree the -n|--dry-run option" adapted to this new flag
> runs all tests successfully ...
>
>
>  unpack-trees.c |    4 ++--
>  unpack-trees.h |    3 ++-
>  2 files changed, 4 insertions(+), 3 deletions(-)