IdentifierPattern's right-hand side Pattern cannot be an IdentifierPattern

[Ekleog]

https://github.com/rust-lang-nursery/reference/blob/master/src/patterns.md currently mentions that IdentifierPattern's right-hand side is a Pattern, which is allowed to be an IdentifierPattern.

However, the following code doesn't parse let x @ y @ () = (); println!("{:?} {:?}", x, y); (playground) due to pattern bindings not being allowed after the @.

As a consequence, I think the reference should be updated to mention that an IdentifierPattern's right-hand-side Pattern is not actually a full Pattern, but is instead not allowed to be another IdentifierPattern.

[petrochenkov]

Syntactically, PAT in ident @ PAT is indeed a full pattern, so x @ y @ () parses successfully.

However, there's a semantic restriction (probably due to necessary support being missing in borrow checker or something) preventing introduction of fresh bindings anywhere inside PAT.
So, something like x @ MyVariant(y, ..) is prohibited as well.