Derive macros fail with new "explicit discriminants on enums with fields"

[timwie]

Rust 1.66 was just released, along with Explicit discriminants on enums with fields. The given example does not compile when adding bincode (2.0.0-rc.2) derive macros to the enum:

$ cargo -V
# cargo 1.66.0 (d65d197ad 2022-11-15)

#[derive(Decode, Encode)]
#[repr(u8)]
enum Foo {
    A(u8),
    B(i8),
    C(bool) = 42,
}

# error: Invalid rust syntax, expected ident, got Some(Punct { ch: '=', spacing: Alone, span: #0 bytes(334..335) })

[VictorKoenders]

Step 1 would be to implement this in virtue: issue

After that we should see how serde implements this. With normal discriminants serde does not actually respect the value. e.g.

enum Foo {
    A = 5,
    B = 3,
}

Will still be encoded as 0 and 1 (See #592 for the reason why). I suspect this new syntax will also not actually respect the values, but instead use the index.