git-grep in sparse checkout

Hi,

During Git Summit it was mentioned that git-grep searches outside sparsity pattern which is not aligned with user expectation. I took a quick look at it and it seems the reason is builtin/grep.c:grep_cache() (which also greps worktree) will grep the object store when a given index entry has the CE_SKIP_WORKTREE bit turned on.

From what I understand, this bit is used exactly for sparse checkouts (as described in Documentation/technical/index-format.txt[1]). But should we perhaps ignore it in git-grep to have the expected behavior? I'll be happy to send the patch if so, but I wanted to check with you first.

Grepping with --cached or in given trees objects would still grep outside the cone, but that is what one would expect, right? Or should we filter out what is outside of the cone for cached grep as well?

Thanks, Matheus

[1]: https://github.com/git/git/blob/master/Documentation/technical/index-format.txt#L101