`BorshSerialize` failure to compile derive with `#[borsh_skip]` on struct variant field

[dj8yfo]

While resolving #110 , the following snippet fails to compile (in the BorshSerialize part). It must be more or less obvious bug, as derive of BorshDeserialize succeeds (as well as BorshSerialize for tuple struct variants).

use borsh::{self, BorshSerialize, BorshDeserialize};

#[derive(BorshDeserialize)]
enum AA {
    B {
        #[borsh_skip]
        c: i32,

        d: u32,
    },

    NegatedVariant {
        beta: u8,
    }
}

#[derive(BorshDeserialize)]
enum AAT {
    B(#[borsh_skip] i32, u32),

    NegatedVariant {
        beta: u8,
    }
}

#[derive(BorshSerialize)]
enum AATB {
    B(#[borsh_skip] i32, u32),

    NegatedVariant {
        beta: u8,
    }
}

#[derive(BorshSerialize)]
enum AATTB {
    B(#[borsh_skip] i32, #[borsh_skip] u32),

    NegatedVariant {
        beta: u8,
    }
}
// ERROR!
#[derive(BorshSerialize)]
enum AB {
    B {
        #[borsh_skip]
        c: i32,

        d: u32,
    },

    NegatedVariant {
        beta: String,
    }
}
// ERROR!
#[derive(BorshSerialize)]
enum AAB {
    B {
        #[borsh_skip]
        c: i32,

        #[borsh_skip]
        d: u32,
    },

    NegatedVariant {
        beta: String,
    }
}

fn main() {

}

 1  error: expected field pattern, found `_`
   --> src/main.rs:44:10
 2  error: expected `}`, found `c`
   --> src/main.rs:48:9
 3  error: proc-macro derive produced unparsable tokens
   --> src/main.rs:44:10
 4  error: expected field pattern, found `_`
   --> src/main.rs:58:10
 5  error: expected `}`, found `c`
   --> src/main.rs:62:9
 6  error: proc-macro derive produced unparsable tokens
   --> src/main.rs:58:10
 7  error[E0425]: cannot find value `d` in this scope
   --> src/main.rs:50:9

[dj8yfo]

https://github.com/dj8yfo/struct_variant_field_borsh_skip_derive_fail - this is a crate, identical to snippet in header