Failing test of class computed method name yield with argument

[benjamn]

I was tempted to add this test to #408, but after some debugging I believe this is a bug with @babel/plugin-transform-classes, as demonstrated by this babeljs.io/repl example.

Specifically, when this code is compiled with only @babel/plugin-transform-classes:

function *gen() {
  return class {
    *[yield 123](x) {
      return yield x;
    }
  }
}

the generated code wraps the class creation code in a non-generator function expression, but accidentally preserves the yield 123 expression within that function:

function* gen() {
  return /*#__PURE__*/function () {
    function _class() {
      _classCallCheck(this, _class);
    }

    _createClass(_class, [{
      key: yield 123, // Parse error!
      value: function* (x) {
        return yield x;
      }
    }]);

    return _class;
  }();
}

If Regenerator is used without the class transform, everything works (thanks to #408; see test/class.regenerator.js).

To get this right, I think we would want to generate the following code (or something similar):

function* gen() {
  return /*#__PURE__*/function (t0) {
    function _class() {
      _classCallCheck(this, _class);
    }

    _createClass(_class, [{
      key: t0,
      value: function* (x) {
        return yield x;
      }
    }]);

    return _class;
  }(yield 123);
}

Passing arguments to the IIFE makes sense to me because that's how extends superclass expressions are handled, but if the combination of those features is tricky for some reason, the following code could work as well:

function* gen() {
  const t0 = yield 123;
  return /*#__PURE__*/function () {
    function _class() {
      _classCallCheck(this, _class);
    }

    _createClass(_class, [{
      key: t0,
      value: function* (x) {
        return yield x;
      }
    }]);

    return _class;
  }();
}

@nicolo-ribaudo I can file this bug over at the Babel repo, but let me know if you have any other ideas!

[nicolo-ribaudo]

This is babel/babel#8300. That bug never got fixed because I accidentally found it but no one ever complained 😂
I'll work on it next week.