Specify the discriminant for enum variants

[desm86]

#[repr(u8)]
#[derive(Serialize, Deserialize)]
pub enum Enum {
	Variant1(...),
	Variant3(...) = 2
}

Expected result:

Enum::Variant3(...) -> [2, ...]

[jamesmunns]

Hi there @desm86, as far as I am aware: serde doesn't actually use the discriminant value, even if it is specified like this.

Serde provides an integer that is the zero-indexed item, so in your example Variant1 will always be 0 and Variant3 will always be 1.

This is not something postcard can address, unless I am mistaken.

[33KK]

Would this PR be relevant? serde-rs/serde#2354