dead_code lint misses some expressions

[canndrew]

#![feature(never_type)]

use std::error::Error;

pub trait Deserialize: Sized {
  fn deserialize() -> Result<Self, Box<Error>>;
}

impl Deserialize for ! {
  fn deserialize() -> Result<!, Box<Error>> {
    Err("oh geez")?;
    panic!()
  }
}

fn foo() -> Result<usize, Box<Error>> {
  Deserialize::deserialize()?;
  Ok(22)
}

In this code, the Ok(22) is unreachable. This should raise a warning but it currently doesn't.

[nikomatsakis]

since we decided to stabilize, this doesn't matter