fix(class-properties): replace new.target in static properties with undefined

[colinaaa]

Q	A
Fixed Issues?	Fixes #12737
Patch: Bug Fix?	👍
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	👍
Documentation PR Link
Any Dependency Changes?
License	MIT

When we meet a static class property, we traverse to visit all new.target with a MetaProperty visitor.

Then we find out if or not this new.target is associated with a class by:

const func = path.findParent((path) => {
  if (path.isClass()) return true;
  if (path.isFunction() && !path.isArrowFunctionExpression()) {
    return true;
  }
  return false;
});

Now, if func is a child of prop, we do nothing. If not, that means new.target now is leaked to upper new.target, we just replace it by undefined / void 0.

if (!func.findParent((path) => path === prop)) {
  // if func is not child of prop, which means
  // `new.target` is leaked to the upper `new.target` values.
  // thus we should replace it with `undefined` (`void 0` here)
  path.replaceWith(scope.buildUndefinedNode());
}

[babel-bot]

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[JLHwung]

We can now enable tests packages/babel-plugin-proposal-class-static-block/test/fixtures/integration/.new-target/exec.js , once disabled in #12738. You can rename .new-target to new-target.

[nicolo-ribaudo]

Thanks!

[nicolo-ribaudo]

Nit: you can delete this comment from input.js

[JLHwung]

Thanks!