Thank you! If the arrow function in the key is immediately invoked, do we throw a TDZ error?

I think we can't statically infer whether a class binding can be resolved. For example

class C {
  [f = () => C, Math.random() > .5 ? f() : Promise.resolve().then(f)]
}

will either throw a TDZ error or pass with roughly equal possibility.

Here is an approach if we would like to seriously match the tdz behaviour.

First we create an intermediate object so that we can intercept the binding identifier:

let _C = {
  get _ () { throw new ReferenceError("C can not be accessed before initialization") },
  set _ (_) { throw new ReferenceError("C is a constant binding") }
}

Then we overwrite the _ getterOrSetter when a class binding is assigned. For decorator transforms, this can be inserted immediately after the applyDecs call

Object.defineProperty(_C, "_", { value: modified_class, writable: false })

Then we can replace all the reference identifiers from the inner binding C to _C._.