#[serde(default)] fields are non-optional

[andrewbaxter]

In serde

struct X {
    #[serde(default)]
    o: bool,
}

makes e.g. {} a valid json value for the above struct - o becomes optional.

With #[derive(Serialize, Deserialize, TS)] the generated typescript doesn't have o?: bool or o: bool | undefined or whatever, the o field is mandatory on any objects declared of type X.

The serde-compat section of the readme claims that the default attribute is supported, and there are no notes qualifying that, so I believe this behavior is incorrect.

I tried to work around it but #[ts(optional)] complains about needing IsOption or something and doesn't appear to work on non-option types AFAICT.

I'm not sure if this is a bug or something that's difficult to achieve parity on and should have a specific call-out in the documentation. In the meantime though, is there a way to work around this at the attribute level (i.e. without changes to structure definitions?).

[gustavo-shigueo]

Hey @andrewbaxter! This is not a bug, #[ts(optional)] only works with the Option type. That's why you see the IsOption error.
You can use #[ts(as = "Option<_>", optional)] to achieve the result you want

[andrewbaxter]

Ah great! Is there a reason that isn't documented in the serde compat section?

[gustavo-shigueo]

Not really, we probably just forgot about it lol. On another note, #[serde(default, skip_serializing)] and #[serde(default, skip_serializing_if = "...")] will also add the ?