Babel throws confusing error when private property is used as computed key

[JLHwung]

Bug Report

• I would like to work on a fix!

Current Behavior
The following snippet, after transformed, throws

Cannot read property 'get' of undefined

Input Code

• REPL

class Toggle {
  #prop = "disabled";
  [this.#prop] = false
}

Expected behavior/code
It should throw

attempted to get private field on non-instance

Environment
REPL

Possible Solution

We should also check if privateMap is undefined in

babel/packages/babel-helpers/src/helpers.js

Line 1121 in a6e8b38

export default function _classPrivateFieldGet(receiver, privateMap) {

Additional context/Screenshots
Found this issue when reviewing PR 11405.

[babel-bot]

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[jridgewell]

Once #11405 has landed, this will be a very simple fix. All that's needed is to rearrange https://github.com/babel/babel/blob/070ec201/packages/babel-helper-create-class-features-plugin/src/index.js#L185-L186, so that the private name nodes are inserted before the key nodes.

I think this is a GFI.

[AjayPoshak]

I would like to take it up.