'cargo fix --edition-idioms' deletes the crate in '#[cfg_attr(test, macro_use)] extern crate foo;'

[ExpHP]

Running cargo fix --edition-idioms on the following causes cargo to delete the text extern crate itertools; as shown, leaving behind an orphaned attribute and trailing whitespace. Needless to say, this transformation is not correct.

Cargo.toml

[package]
name = "lollol"
version = "0.1.0"
edition = "2018"

[dependencies]
itertools = "0.7.11"

src/main.rs

- #[cfg_attr(test, macro_use)] extern crate itertools;
+ #[cfg_attr(test, macro_use)] 
  use itertools::Itertools;

  fn main() {
      println!("{:?}", (0..1).collect_vec());
  }

  #[test]
  fn test() {
      println!("{:?}", izip!((0..1), (0..1)).collect_vec());
  }

Besides the orphaned attribute that is now incorrectly applied to the use on the next line, tests now fail to compile due to missing izip!.

---

cargo 1.32.0-nightly (b3d0b2e54 2018-11-15)

[alexcrichton]

Thanks for the report! I've moved this upstream to rustc as rust-lang/rust#56328