Section on Object Safety does not explicitly mention when Self is a type parameter

[jmaargh]

The section on Object Safety defines that concept with a list of bullet points. That list does not include the case when the trait takes Self as a type parameter, but that is included as an example below the list.

// Not object safe if `Self` is a type argument.

I suggest adding a bullet of

• A generic parameter of this trait, or any of its supertraits, is not specified to be Self

together with an expanded example to show that this applies even when Self: ?Sized. An example of this in action is PartialEq not being object safe.

If I get the thumbs-up I'll make a PR

[ehuss]

Thanks for the report! Closing as a duplicate of #756.

Unfortunately I don't understand the rule introduced in rust-lang/rust#22452 well enough to articulate it in English. I'll try pinging the lang team again on Zulip.