Re: [PATCH v2 00/11] Clarify API for dir.[ch] and unpack-trees.[ch] -- mark relevant fields as internal

> Changes since v1 (thanks to Jonathan Tan for the careful reviews!)
>
>  * Clear o->pl when freeing pl, to avoid risking use-after-free.
>  * Initialize o->result in update_sparsity() since it is actually used (by
>    check_ok_to_remove()).
>
> Some time ago, I noticed that struct dir_struct and struct
> unpack_trees_options both have numerous fields meant for internal use only,
> most of which are not marked as such. This has resulted in callers
> accidentally trying to initialize some of these fields, and in at least one
> case required a fair amount of review to verify other changes were okay --
> review that would have been simplified with the apriori knowledge that a
> combination of multiple fields were internal-only[1]. Looking closer, I
> found that only 6 out of 18 fields in dir_struct were actually meant to be
> public[2], and noted that unpack_trees_options also had 11 internal-only
> fields (out of 36).