Wildcard import fails to resolve if a derive is present

[ennis]

The following snippet fails to compile with the error [E0412]: cannot find type Foo in this scope

https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=d954ef6f84f0d1df4e5c4791c7716da9

struct Foo;          // line 1

mod foo {
    use super::*;    // line 4
    
    // Commenting out the Debug derive makes it work
    #[derive(Debug)] // line 7
    pub struct Foo;
}

mod bar {
    use super::foo::*;
    
    fn bar(_: Foo) {}
}

Expected result: code compiles without issues

I can get it to compile by doing one of those:

• by removing use super::* on line 4
• by commenting #[derive(Debug)] at line 7
• by renaming struct Foo on line 1 to Foo2
• and curiously, by copy-pasting the generated Debug impl obtained with --pretty=expanded instead of using #[derive(Debug)]

The same issue happens with other derives (Clone,Eq,etc.). Seems like #[derive()] is confused when an item with the same name is visible?

[petrochenkov]

Looks like a legitimate bug.
It's also a regression from Rust 1.15 released almost 2 years ago :)

[spastorino]

Assigning P-medium as discussed as part of the Prioritization Working Group process and removing I-prioritize.