`From<PrivateType> for PublicExternalType` suppresses `dead_code`

I tried this code:

mod private_module {
    pub struct UsedType;

    // This single line suppresses dead_code for ALL pub methods on UsedType.
    // Comment it out to see the warning on dead_pub_method.
    impl From<UsedType> for String {
        fn from(_: UsedType) -> String {
            String::new()
        }
    }

    impl UsedType {
        // This is never called — but NO warning because of the From impl above
        pub fn dead_pub_method(&self) -> u32 {
            42
        }

        pub fn called_method(&self) -> u32 {
            1
        }
    }
}

pub fn use_it() -> u32 {
    let x = private_module::UsedType;
    x.called_method()
}

I expected to see this happen: the Rust compiler warning about the unused function.

Instead, this happened: no warning.

Reproduce the behavior with the Rust code in the report and trace how the dead_code lint handles the From implementation. Add a regression test that warns about dead_pub_method while accepting called_method, then run the relevant compiler test suite.