Public struct fields do not (always) get "this node does not have a stability attribute" error

[huonw]

#![feature(staged_api)]
#![staged_api]
#![crate_type = "lib"]

#![stable(feature = "rust1", since = "1.0.0")]

#[stable(feature = "rust1", since = "1.0.0")]
pub struct Foo {
    pub bar: u8,
}

#[stable(feature = "rust1", since = "1.0.0")]
pub struct Baz(pub u8);

compiles without any error.

Notably this isn't a regression from #22803: I noticed it because core::iter::Scan has a public state field that has had no stability attribute from far before #22803. However, that PR did pick up some structs with missing stability attributes, I'm unsure of the exact circumstances when fields will get the errors or when they will not.

[huonw]

As @alexcrichton points out in #22952 (comment) this isn't a bug; I didn't realise that stability propagation literally just ignores #[stable], meaning core::iter::Scan::state is unstable due to the #[unstable] on core. Closing.