[Bug]: Nested options fail to deserialize at run-time

[hniksic]

Is there an existing issue for this?

• I have searched the existing issues

Code of Conduct

• I agree to follow this project's Code of Conduct

Current Behaviour

The following code fails to deserialize Some(None):

use serde::{Deserialize, Serialize};

#[derive(Debug, Serialize, Deserialize, PartialEq)]
struct Foo(Option<Option<bool>>);

fn main() {
    for o in [None, Some(None), Some(Some(true)), Some(Some(false))] {
        let o = Foo(o);
        let mut ser = vec![];
        ciborium::into_writer(&o, &mut ser).unwrap();
        let o2: Foo = ciborium::from_reader(&mut ser.as_slice()).unwrap();
        if o != o2 {
            println!("error: {o:?} deserialized as {o2:?}");
        }
    }
}

Running the above code prints:

error: Foo(Some(None)) deserialized as Foo(None)

Expected Behaviour

I expected Some(None) to round-trip through ciborium as Some(None) (i.e. the above program to output nothing). We are investigating ciborium for types that use deserialize_any(), and inability to deserialize nested options is an issue.

I control the code that does the (de-)serialization, so if it's a matter of setting up some configuration, that'd work for me.

Environment Information

$ uname -a
Linux snijeg 5.15.0-107-generic #117-Ubuntu SMP Fri Apr 26 12:26:49 UTC 2024 x86_64 x86_64 x86_64 GNU/Linux
$ enarx --version
zsh: command not found: enarx

Steps To Reproduce

Run the included code, and observe the result.