Implement Object ...rest Assignment in for of loop

[komyg]

Issue: #722

[load1n9]

LGTM but fix the metrics file

[komyg]

LGTM but fix the metrics file

Hey @load1n9, done!

[load1n9]

LGTM

[aapoalas]

Hey, thanks for the patch.

This isn't yet ready for prime time, though. Try eg. this code:

const source = {};
let target;
({ ...target } = source);
if (target === source) {
  throw "impossible";
}

This will throw the "impossible" string: we're not actually creating a new object for b here at all. Furthermore, this code currently does not support property omissions at all, eg.

({ x, ...target } = source);

even if target was a new object, with the code right now this would still create an object with x property copied into target from source.

It seems you'll rather need the CopyDataPropertiesIntoObject instruction. See bytecode_compiler.rs:1872 and especially the branches related to object_pattern.rest in that function.