`#[zeroize(drop)]` no-op in zeroize_derive v1.1 for `enum`s

[daxpedda]

I discovered a bug where #[zeroize(drop)] doesn't generate a Drop implementation when used on enums. It seems to me that it was accidentally fixed by #847 in zeroize_derive version 1.2. The bug still exists in version 1.1.

If I'm not missing something and this bug is real, version 1.1 should probably be yanked and a report filed at the RustSec Advisory Database.

Cargo.toml:

[dependencies]
zeroize = { version = "=1.4.2", features = ["zeroize_derive"] }
zeroize_derive = "=1.1"

lib.rs:

use zeroize::Zeroize;

#[derive(Zeroize)]
#[zeroize(drop)]
pub struct Works {
    field: Vec<u8>,
}

// This doesn't compile, because a conflicting implementation generated by `#[zeroize(drop)]`.
impl Drop for Works {
    fn drop(&mut self) {
        todo!()
    }
}

#[derive(Zeroize)]
#[zeroize(drop)]
pub enum Fails {
    Variant(Vec<u8>),
}

// This does compile with zeroize_derive version 1.1, meaning `#[zeroize(drop)]` didn't implement `Drop`.
impl Drop for Fails {
    fn drop(&mut self) {
        todo!()
    }
}

[tony-iqlusion]

Confirmed via cargo expand. Thanks for the report.

Input:

#[derive(Zeroize)]
#[zeroize(drop)]
pub enum Foo {
    A(u8),
    B(u16),
    C(u32)
}

zeroize_derive v1.1 output:

#[allow(non_upper_case_globals)]
#[doc(hidden)]
const _DERIVE_zeroize_Zeroize_FOR_Foo: () = {
    extern crate zeroize;
    impl zeroize::Zeroize for Foo {
        fn zeroize(&mut self) {
            match self {
                Foo::A(ref mut __binding_0) => {
                    __binding_0.zeroize();
                }
                Foo::B(ref mut __binding_0) => {
                    __binding_0.zeroize();
                }
                Foo::C(ref mut __binding_0) => {
                    __binding_0.zeroize();
                }
            }
        }
    }
};

zeroize_derive v1.2 output:

#[allow(non_upper_case_globals)]
#[doc(hidden)]
const _DERIVE_zeroize_Zeroize_FOR_Foo: () = {
    extern crate zeroize;
    impl zeroize::Zeroize for Foo {
        fn zeroize(&mut self) {
            match self {
                Foo::A(ref mut __binding_0) => {
                    __binding_0.zeroize();
                }
                Foo::B(ref mut __binding_0) => {
                    __binding_0.zeroize();
                }
                Foo::C(ref mut __binding_0) => {
                    __binding_0.zeroize();
                }
            }
        }
    }
};
#[doc(hidden)]
#[allow(non_upper_case_globals)]
const _DERIVE_Drop_FOR_Foo: () = {
    impl Drop for Foo {
        fn drop(&mut self) {
            self.zeroize();
        }
    }
};

I have yanked all of the releases of zeroize_derive prior to v1.2.0.

[tony-iqlusion]

Assigned RUSTSEC-2021-0115