Rust: how do I patch a vendored crate in a pkgsrc package?

[Benny Siegert <bsiegert%gmail.com@localhost>]

Hi!

I need to patch something in a crate that wip/tealdeer depends on. I
managed to create the necessary patch by hand (with a path of
../vendor/x/y/z), matching the canonical example of www/geckodriver.
mkpatches (which I usually use) only acts in WRKSRC, but the vendor
directory is one level higher for some reason.

Is this a bug in cargo.mk? A bug in mkpatches? Working as intended?

-- 
Benny