({...R}, a = R) => {}
({X: Y,...R}, {a = {Y}}) => {}
(a = R, {...R}) => {}
({...R}, e, c = 2, a = R, f = q) => { let q; }
({...R}, a = f(R)) => {}
({...R}, { [R.key]: a = 42 }) => {}

({...R}, {a = {R: b}}) => {}
({...R}, {a = R => R} = {b: R => R}) => {}