[unnecessary_lazy_eval]: reduce applicability if closure has return type annotation

[y21]

Fixes #11672

We already check if closure parameters don't have type annotations and reduce the applicability to MaybeIncorrect if they do, since those help type inference and removing them breaks code. We didn't do this for return type annotations however. This PR adds it. This doesn't change it to produce a fix that will compile, but it will prevent rustfix from auto-applying it.

(In general I'm not sure if we can suggest a fix that will compile. In this specific example, it might be possible to suggest &[] as &[u8], but as-casts won't always work, e.g. Default::default() as &[u8] is a compile error, so just reducing applicability should be a safe fix in any case for now)

changelog: [unnecessary_lazy_eval]: reduce applicability to MaybeIncorrect if closure has return type annotation

[rustbot]

r? @Manishearth

(rustbot has picked a reviewer for you, use r? to override)

[Manishearth]

@bors r+

thanks!

[bors]

📌 Commit bb6516a has been approved by Manishearth

It is now in the queue for this repository.

[bors]

⌛ Testing commit bb6516a with merge 9f27b15...

[bors]

☀️ Test successful - checks-action_dev_test, checks-action_remark_test, checks-action_test
Approved by: Manishearth
Pushing 9f27b15 to master...