Using a immerable class with a getter without a setter

[dalcib]

In an immerable class with a getter without the corresponding setter, assigning a value to any field using the getter value within a class method causes the following error:

#TypeError#
Cannot set property bar of # which has only a getter

It only happens with non-primitive getter values and with setUseProxies(true)
It can be fixed in userland creating an empty setter (set prop(v) {})
This PR makes the markChangedProxy function to skip the assignment copy[key]=value when there is a getter without a setter.

It fixes #439 and replaces #438

Links to Repro (updated to immer 6.0.2)

https://codesandbox.io/s/small-rain-inotu
https://codesandbox.io/s/useimmer-tic-tac-ci6qq

To Reproduce

import { produce, immerable } from "immer";
class Obj {
  [immerable] = true;
  foo = 0;
  _bar = { baz: 1 };
  get bar() {return this._bar}
  syncFoo() {
    return produce(this, state => {
      state.foo = state.bar.baz;
    });
  }
}
const obj = new Obj();
const obj2 = obj.syncFoo();

[codesandbox-ci]

This pull request is automatically built and testable in CodeSandbox.

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Latest deployment of this branch, based on commit 081fff1:

Sandbox	Source
Immer sandbox	Configuration
staging-rain-vybit	PR
useImmer - Tic Tac	PR

[mweststrate]

Direction feels solid to me :) left a question and two ideas for better test coverage. Thanks for diving into this!

[mweststrate]

Merged into #593, changed the implementation there to be a bit more efficient, and fix the problem and trap rather than at finalize time, still wip, but seems we can solve some other issues with it as well

[aleclarson]

🎉 This issue has been resolved in version 7.0.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

Your semantic-release bot 📦🚀

[mweststrate]

Sorry it took so long @dalcib! This rabbit hole went way deeper to do it entirely correct than I expected, but I think the current solution in Immer 7 should work in general!