Skipped enum variants still contribute to bounds

[dtolnay]

There should be no bounds placed on T in this example, just like there wouldn't be with skip_serializing / skip_deserializing on a field.

#[macro_use]
extern crate serde_derive;

extern crate serde;
use serde::Serialize;

#[derive(Serialize)]
enum E<T> {
    #[serde(skip_serializing)]
    T(T),
    Unit,
}

struct Not;

fn main() {
    fn assert<T: Serialize>() {}
    assert::<E<Not>>();
}

error[E0277]: the trait bound `Not: serde::Serialize` is not satisfied
  --> src/main.rs:18:5
   |
18 |     assert::<E<Not>>();
   |     ^^^^^^^^^^^^^^^^ the trait `serde::Serialize` is not implemented for `Not`
   |
   = note: required because of the requirements on the impl of `serde::Serialize` for `E<Not>`
   = note: required by `main::assert`

[dtolnay]

Fixed in c4181f4.