`use` of unstable function is not gated in import list

[bluss]

This compiles on stable:

use std::thread::{catch_panic};

but this does not:

use std::thread::catch_panic;
error: use of unstable library feature 'catch_panic': recent API addition

Fortunately, I can't find a way to actually use the import anyway, but it's a stability trap.

[brson]

Let's fix soon!

[brson]

This should be a matter of fixing the appropriate case in stability.rs and adding a test.

[apasel422]

This actually applies to all stability attributes and unused feature checks, and it looks like this is a result of ViewPathList being visited as a series of calls to visit_ident followed by a call to walk_path with only the path prefix. For example, when use-ing the deprecated std::iter::order this way:

foo.rs:

#![feature(iter_order)]
use std::iter::{order};
fn main() {}

Output:

foo.rs:1:12: 1:22 warning: unused or unknown feature, #[warn(unused_features)] on by default
foo.rs:1 #![feature(iter_order)]
                    ^~~~~~~~~~
foo.rs:3:17: 3:22 warning: unused import, #[warn(unused_imports)] on by default
foo.rs:3 use std::iter::{order};

[apasel422]

Compare that with:

#![feature(iter_order)]
use std::iter::order;
fn main() {}

Output:

foo.rs:2:5: 2:21 warning: unused import, #[warn(unused_imports)] on by default
foo.rs:2 use std::iter::order;
             ^~~~~~~~~~~~~~~~
foo.rs:2:5: 2:21 warning: use of deprecated item: use the equivalent methods on `Iterator` instead, #[warn(deprecated)] on by default
foo.rs:2 use std::iter::order;
             ^~~~~~~~~~~~~~~~

[terrynsun]

I'd like to try looking at this, if that's okay.

[apasel422]

@terrynsun Go for it!

[brson]

@terrynsun How's this going?

[terrynsun]

Sorry! I was struggling with the structure of the AST walking and couldn't figure it out.

[alexcrichton]

triage: P-high