isEmpty call on ProxyObject w/ size property throws '.get()' proxy assertion (3.1+)

[nickschot]

Having an ObjectProxy (or any object using unknownProperty) with a property named 'size' of type String isEmpty(myChangeset) results in the Assertion Failed: You attempted to access the 'size' property (of changeset:[object Object]). Since Ember 3.1 , this is usually fine as you no longer need to use '.get()'... error.

This is caused at:

ember.js/packages/@ember/-internals/metal/lib/is_empty.ts

Line 44 in f73d844

if (typeof obj.size === 'number') {

and only occurs in Ember 3.1+ (which is when the assertion was added) which also means that the assertion will trigger for any object with a "size" key that refers to a proxy.

Minimal reproduction: https://ember-twiddle.com/8e63470aa2e8ab8b07735334b169c96d?openFiles=controllers.application.js%2C

AFAIK .size is just used for Maps/Sets and the like? Might an extra check be necessary?

Somewhat similar to: #16259

cc @snewcomer

[pixelhandler]

@nickschot can you create an ember-twiddle as an example?

[nickschot]

@pixelhandler I did some more debugging and the test case is pretty simple. I will update the main post with my new findings. Meanwhile a reproduction can be found: https://ember-twiddle.com/d3b2742a7156454f2ece80d6c26d2581?openFiles=controllers.application.js%2C . Press the "validate" button once and the error is thrown in the console.

[nickschot]

I have created an updated test case which doesn't use changeset but a normal ObjectProxy in the example (as this is the more general case).

Updated minimal reproduction: https://ember-twiddle.com/8e63470aa2e8ab8b07735334b169c96d?openFiles=controllers.application.js%2C

The first post is also updated.

[nickschot]

I think the solution can be as simple as adding an unknownProperty check so that it falls through to the branch where get(obj, 'size') is used. This still conforms to the description:

If the value is an object with a size property of type number, it is used
to check emptiness.

Proposed fix:

  if (typeof obj.unknownProperty !== 'function' && typeof obj.size === 'number') {
    return !obj.size;
  }

This uses the same check as the assertion:

ember.js/packages/@ember/-internals/runtime/lib/system/core_object.js

Line 216 in 9881f0b

if (DEBUG && HAS_NATIVE_PROXY && typeof self.unknownProperty === 'function') {

[nickschot]

The same is true for an ObjectProxy with a property length. I think to conform with the description of isEmpty we need to apply the same fix to the branch testing for length.