XS: Object rest incorrectly accepts complex assignment targets

[bakkot]

There's an Early Error which forbids ({ ...{} } = {}), but XS allows it.

({ ...[a = 0] } = {}) is also forbidden by the grammar, but instead of being a Syntax Error, XS gives me TypeError: (host): C: xsCall: no function.

Same thing for bindings.

I think a reasonably complete listing of cases is

// legal
({ ...a } = {});
({ ...(a) } = {});
({ ...((a)) } = {});
({ ...a.b } = {});
({ ...(a.b) } = {});
let { ...a } = {};

// forbidden
({ ...{} } = {});
({ ...[] } = {});
({ ...a = 0 } = {});
let { ...{} } = {};
let { ...[] } = {};
let { ...a } = {};
let { ...(a) } = {};
let { ...a.b } = {};

I'm guessing some of these are missing from test262.