Refuses to serialize Rc<RefCell<Item>> field - despite #[serde(skip_serializing)]

[cambiata]

When using the "rc" feature flag, serializing structs with Vec<Rc<Child>> fields works fine.

However, if I add a field to the same struct that shouldn't be serialized (using #[serde(skip_serializing)] for that) containing a RefCell (for example a Rc<RefCell<Child>>), it doesn't compile.

#[derive(Debug, PartialEq, Eq, Hash, serde::Deserialize, serde::Serialize)]
struct Child {
    data: i32,
}

#[derive(Debug, PartialEq, Eq, Hash, serde::Deserialize, serde::Serialize)]
struct Parent {
    // persistent field - should be serialized
    children: Vec<Rc<Child>>,

    // computed field - shouldn't be serialized
    // As soon as I add the child field below
    #[serde(skip_serializing)]
    child: Rc<RefCell<Child>>, // <- causes compile error `RefCell<Child>: Hash` not satisified
}

Is there a way to allow non-serialized fields containing RefCells in an otherwise serialized struct?

[jonasbb]

That is a problem with the Hash derive macro, that ships with the Rust standard library. It has nothing to do with serde.
These derive macros offer no customization. You will need to implement Hash by hand or look for a crate.

[Mingun]

The problem is because RefCell does not implement Hash. A possible workaround is to use newtype wrapper for Rc<RefCell<Child>> and implement Hash for it manually. But I recommend to google first, why RefCell doesn't implement Hash for the first place -- maybe there is some non-obvious obstacles

[cambiata]

Thanks guys! I get that RefCell doesn't implement Hash, but - as mentioned - I don't need to serialize any field using RefCells.
When adding #[serde(skip_serializing)] to a field, I was expecting that field to be completely ignored - regardless using RefCell or not.

It would be very nice if the serde docs could provide some info about this limitation, and - at best - some examples on how to get around it.

[dtolnay]

I am locking the issue because, as already pointed out above, this has literally nothing to do with serde.

You can remove all serde attributes and derives from this code and still get the same error.