I'm curious if anyone can give an update on the status of Chalk (perhaps @scalexm or @nikomatsakis)?
Specifically, it seems that the trait system needs a lot of love, and I lot of bugs have come from either our lack of understanding of the current trait system or from bugs in the implementation (see for example https://github.com/rust-lang/rust/issues/57893 or Unsoundness in `Pin`). It seems like these sorts of bugs could have major disruptive impact on the rust ecosystem if we are not careful...