Add skip support for newtype enum variants

[johanholmerin]

The logic that filtered skipped fields didn't run on newtype variants due to an early return. I added the same logic, which will treat newtype variants with a skipped field as a unit field, and added some tests for different types of enum variants and for internally tagged enums since I couldn't find any.

[siefkenj]

@johanholmerin Thanks for the contribution!

It looks like a skipped newtype results in the inner type being undefined rather than null. This makes sense to me. Could you please verify that that is the actual behavior and change the test accordingly?

[johanholmerin]

The output differed between js & json. I've added missing_as_null as a fix

[siefkenj]

JSON doesn't have a null, but undefined becomes null in JSON.

Is having the null important? I think it makes more sense not to have the option and have missing fields be undefined. After all { a: 10 }.b === undefined in Javascript.

[johanholmerin]

I'm not sure what you mean, JSON has null but not undefined. I used the same code that's used for Style::Unit but I can change it if you have a better suggestion.

[siefkenj]

I'm not sure what you mean, JSON has null but not undefined. I used the same code that's used for Style::Unit but I can change it if you have a better suggestion.

I mean "{\"foo\": undefined}" is not JSON, but "{\"foo\": null}" is JSON

[siefkenj]

Sorry, I didn't read your previous message correctly.

My question is, when is JSON with null being produced via rust code? It is my understanding that if you serialize

struct Foo {
 #[serde(skip)]
 a: usize,
 b: usize
}

it will produce something like {b: 48739} rather than {a: null, b: 48739}

[johanholmerin]

No worries. I checked the results for both serde_json & serde-wasm-bindgen and you're right about the fields being skipped rather than being null for struct and tuple variants. For the externally tagged newtype it should however be generated the same way as the tuple, i.e. a string. I had assumed it would be enough to change parse_fields to return the same value as for Unit but I actually had to change what style was used. It should work correctly now.

[siefkenj]

Thanks!