Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/52802/

CI errors are related.
This fix might be a little hard to do, as the current _removeFromScope also has issues, I have an open PR but it hasn't been updated in a long time, I think I can probably go ahead with it.

@liuxingbaoyu what are the current issues with _removeFromScope? I looked through that whole code path and it seems pretty straightforward.

One problem I see with my current PR is assertions in _replaceWith could fail after I've removed the scope bindings. (_replaceWith seems to have no reason for separate existence; it's only called by replaceWith according to TS...)

Do you have any hunch why removing bindings from the scope is causing regressions like this? I would think the extraneous variable _temp would get generated if a binding is dangling, not the other way around...

    - Expected
    + Received
    
    @@ -1,9 +1,9 @@
      function classFactory() {
    -   var _class, _foo, _bar;
    +   var _class, _foo, _bar, _temp;
    
    -   return _foo = /*#__PURE__*/babelHelpers.classPrivateFieldLooseKey("foo"), _bar = /*#__PURE__*/babelHelpers.classPrivateFieldLooseKey("bar"), (_class = class Foo {
    +   return _foo = /*#__PURE__*/babelHelpers.classPrivateFieldLooseKey("foo"), _bar = /*#__PURE__*/babelHelpers.classPrivateFieldLooseKey("bar"), (_temp = _class = class Foo {

#14430
Perhaps because _removeFromScope does not perform reference analysis, it will cause the Binding to be removed unexpectedly or not removed.

Yeah I was just going through in the debugger and saw with my own eyes how getBindingIdentifiers() was returning the lhs of an AssignmentExpression 👍

I'm surprised the dangling bindings after replacement apparently aren't causing loads of other problems

There are some reports of this, but most circumvent the problem by doing it manually.
It might be harder to fix it at the root, so I've been wanting to fix it, but haven't actually worked on it.