Missing impl blocks when rustdoc inlines a type and -Zforce-unstable-if-unmarked is turned on

[notriddle]

Compare the following pages:

• https://doc.rust-lang.org/nightly/nightly-rustc/rustc_errors/struct.FatalError.html
• https://doc.rust-lang.org/nightly/nightly-rustc/rustc_span/fatal_error/struct.FatalError.html

The issue can also be reproduced by setting up two crates, one with a type that has an inherent impl:

pub struct FatalError;
impl FatalError {
    pub fn raise(self) -> ! { loop {} }
}

And the other re-exports it:

pub use parent::FatalError;

And compile them with, specifically, the following CLI parameters:

RUSTFLAGS=-Zforce-unstable-if-unmarked cargo +dev doc

I expect raise to show up both in the original crate, and in the crate that re-exports it. Instead, it only shows blanket and auto trait impls.