Items defined in a function inherit the stability of the function and trigger lint checker

[elinorbgr]

Example code:

#[deprecated = "You shouldn't double 42"]
fn double_of_42() -> uint {

    fn compute_42() -> uint {
        42u
    }

    2*compute_42()
}

generates the warning:

<anon>:8:7: 8:17 warning: use of deprecated item: You shouldn't double 42, #[warn(deprecated)] on by default
<anon>:8     2*compute_42()
               ^~~~~~~~~~

Which is quite confusing as the warning message is hardly related to the code warned against.
And I would not expect a warning being generated in such a case.

[alexcrichton]

Interesting! It appears that the inheritance of stability levels does... interesting things here! cc @aturon