Could we offload all the checks that are done on match guards wrt them mutably borrowing their surroundings onto mir-borrowck? There's some weird interactions between the two (https://github.com/rust-lang/rust/pull/60125#discussion_r277136282) and aren't match guards essentially
Fn closures that are called immediately?
We can't do that -- at minimum -- until the NLL transition is complete, @oli, but I do believe we plan to do that
(cc @pnkfelix and @Matthew Jasper)