Re: [PATCH v5 3/3] builtin/grep.c: walking tree instead of expanding index with --sparse

[Junio C Hamano <gitster@pobox.com>]

Shaoxuan Yuan <shaoxuan.yuan02@gmail.com> writes:

> +
> +	/*
> +	 * NEEDSWORK: when reading a submodule, the sparsity settings in the
> +	 * superproject are incorrectly forgotten or misused. For example:
> +	 *
> +	 * 1. "command_requires_full_index"
> +	 * 	When this setting is turned on for `grep`, only the superproject
> +	 *	knows it. All the submodules are read with their own configs
> +	 *	and get prepare_repo_settings()'d. Therefore, these submodules
> +	 *	"forget" the sparse-index feature switch. As a result, the index
> +	 *	of these submodules are expanded unexpectedly.

Is this fundamental, or is it just this version of the patch is
incomplete in that it still does not propagate the bit from
the_repository->settings to submodule's settings?  Should a change
to propagate the bit be included for this topic to be complete?

To put it another way, when grep with this version of the patch
recurses into a submodule, does it work correctly even without
flipping command_requires_full_index on in the "struct repository"
instance for the submodule?  If so, then the NEEDSWORK above may be
just performance issue.  If it behaves incorrectly, then it means
we cannot safely make "git grep" aware of sparse index yet.  It is
hard to tell which one you meant in the above.

I think the same question needs to be asked for other points
(omitted from quoting) in this list.

Thanks.