Incomplete documentation of `while let` syntax regarding lazy boolean operator expressions.

[steffahn]

Comparing the reference’s section on if let vs. the one on while let, the latter contains no note about top-level || and && being disallowed, even though this is the case by the corresponding RFC as well as in practice.

[Centril]

The corresponding RFC has not been stabilized, the syntax if p && let p = q { ... } is unstable. The reference only documents stable Rust.

[steffahn]

@Centril No. I’m talking about the part of the RFC that makes Rust2018 disallow certain expressions. This rule, that || and && cant appear inside if let or while let is part of stable Rust. It is even in the reference already, however only for if let, not for while let.

[Centril]

Oh you mean the Expression except struct or lazy boolean operator expression bit in if-let vs. while-let; yeah that needs to be updated. Want to send in a PR?

[steffahn]

Sure, I’ll do that. Playing around with this, there seems to be more to it though.. is seems as if the = changes precedence inside an if let. According to the reference it is supposed to be binding weaker than && and || and there’s also .. and ..= in between. Apparently the implementation of this part of the RFC changed things in a way that also disallows ..: see this playground.