I tried this code:
https://play.rust-lang.org/?version=stable&mode=debug&edition=2018&gist=b8f15edf4886c9c8bb753636feb70ec2

pub mod foo {
    #[derive(Debug, Copy, Clone)]
    pub struct Foo {
        x: (),
    }
}

pub static FOO: foo::Foo = FOO;

fn main() {
    dbg!(FOO);
}

I expected the code to fail to compile with a cycle error.

Instead, it compiled and ran,printing the value of FOO .

Meta

I was able to verify that this bug happens for the 1.42.0 stable, 1.43-beta.5, and 1.44.0-nightly(2020-04-11 e82734e) versions.

Trying this code in rust.godbolt.org it errors up to 1.36.0,and doesn't error anymore from 1.37.0 onwards.