extern crate foo with use self::foo doesn't work inside a function

[durka]

EDIT (@steveklabnik) see #27626 (comment)

This code fails and rustc doesn't tell you why:

fn main() {
    extern crate rand;
    use self::rand::Rng;
}

(playpen)

I think it should at least warn, assuming there is some reason why it can't do what it looks like it does.

[tomjakubowski]

It's not true that it does nothing at all (playpen)

#![feature(rand)]

fn main() {
    extern crate rand;
    let rng = rand::chacha::ChaChaRng::new_unseeded();
}

[durka]

Huh. Fascinating. And you can use trait methods that way without importing the trait, as long as you use UFCS, which I thought was supposed to be impossible. So, I count this as another confusion caused by use paths being different from all other paths.

[durka]

Well, maybe I'll leave the issue open, in case there's any way to fix the diagnostic.

[steveklabnik]

Given that nobody has commented in over a year, I'm going to give this one a close; a better diagnostic here would be nice, but since nobody else has run into it, and this is a very niche case, I don't think we need to track it. If you feel super strongly, we can re-open I guess, but I doubt this is going to be fixed.

[durka]

Would you object if I opened a new bug at least about the ridiculous suggestion "did you mean `self::self::rand`"? Or maybe there's already an issue about that.

…

On Wed, Nov 30, 2016 at 1:27 PM, Steve Klabnik ***@***.***> wrote: Closed #27626 <#27626>. — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#27626 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAC3n5eo9k-1uu-ES8HBL2iJ8-oanH-tks5rDb_-gaJpZM4FocuD> .

[steveklabnik]

I am not sure if there is; let's re-open this one for that then, I guess.

[durka]

I suppose an easy fix is just to omit the suggestion when the path already begins with `self::`.

…

On Wed, Nov 30, 2016 at 1:38 PM, Steve Klabnik ***@***.***> wrote: Reopened #27626 <#27626>. — You are receiving this because you modified the open/close state. Reply to this email directly, view it on GitHub <#27626 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAC3nxyB8O5GgYcaaxWOsMqziTevpBiuks5rDcKLgaJpZM4FocuD> .

[steveklabnik]

Triage: this error message has gotten a bit weirder:

error[E0432]: unresolved import `self::rand`
 --> src\main.rs:3:15
  |
3 |     use self::rand::Rng;
  |               ^^^^ maybe a missing `extern crate rand;`?

warning: unused import: `self::rand::Rng`
 --> src\main.rs:3:9
  |
3 |     use self::rand::Rng;
  |         ^^^^^^^^^^^^^^^
  |
  = note: #[warn(unused_imports)] on by default

It seems like the import both works and doesn't work, simultaneously?

Given that extern crate is no longer needed in the 2018 edition, I doubt people are going to run into this bug.

[Mark-Simulacrum]

I'm going to go ahead and close this; the error today in a project that just has rand in Cargo.toml seems mostly acceptable for this niche case, if the extern crate is moved to root scope then things just work, as expected.