include description of bindings in the reference

[nikomatsakis]

This describes the behavior implemented in https://github.com/rust-lang/rust/pull/63376.

cc @Centril

[ehuss]

@nikomatsakis I was looking to merge this with the minor editorial changes, but I see that this example doesn't compile (aside from the syntax issues). I assume this is because of https://github.com/rust-lang/rust/issues/63618.

IIUC, the rules for defaults for associated types are not implemented at all? If that is correct, then I personally would prefer to document what is implemented, instead of what is intended in this case. (Following the same kind of logic that we don't document unstable features, future intentions, unimplemented RFCs, etc.)

If there are cases that are implemented, then I think it would be better to use those as examples. If they are not implemented at all, then I would prefer to remove the associated type rules for now and change the example to make it clear that it fails to infer.

We can very easily add the rules back once they are implemented.

[nikomatsakis]

@ehuss oof, I totally forgot about this PR.

[Havvy]

What's the status on this?