closure-compiler seems to delete static getter fields

[sbc100]

When working on #24190 I ran into an issue where closure compiler was completely removing the parameterDescriptors static getter:

    static get parameterDescriptors() {                                              
      return audioParams;                                                            
    }    

This field seems to be required to be static getter field: https://developer.mozilla.org/en-US/docs/Web/API/AudioWorkletProcessor/parameterDescriptors

As a horrible workaround I mangle this code before passing to closure and then unmangle it afterwards.

[brad4d]

Can closure-compiler see the code that uses the parameterDescriptors field?
I would guess that it cannot, and for that reason it removed its definition, believing it was unused.

I'm guessing this code is implementing part of a standard API (e.g. a DOM API) and expecting the field to be used by code that closure-compiler cannot see.
If so, the answer is probably to write an externs file that explicitly declares that API to closure-compiler, so it will know that it should consider this definition as untouchable.

https://github.com/google/closure-compiler/wiki/How-do-I-make-closure-compiler-stop-breaking-my-API-by-removing-and-renaming-things%3F

[brad4d]

Another possibility is that you need to use the command line flag --assume_static_inheritance_is_not_used=false

https://github.com/google/closure-compiler/wiki/Flags-and-Options#miscellaneous

[sbc100]

I don't think the issue is that closure think its unused because:

(a) I did try adding to one of our externs files.
(b) Renaming the method such that it is no longer prefixed with static get fixes the issue.

I will try that flag.

[sbc100]

BTW we are using the last public npm release to closure compiler with is ~1 year old now I think (In case that matters).

[sbc100]

If I add AudioWorkletProcessor.prototype.parameterDescriptors; to the externs and declare parameterDescriptors as a normal method it is correctly preserved.

Perhaps for a static getter I need a different sync to just AudioWorkletProcessor.prototype.parameterDescriptors; ?

[sbc100]

Ah! Its look maybe not using the prototype fixes it. If that is the fix, sorry for the noise.. i should have figured that out.

[sbc100]

Yup that was it, thanks!

[brad4d]

So, the problem was that your custom externs file declared AudioWorkletNode.prototype.parameterDescriptors when it should have declared AudioWorkletNode.parameterDescriptors. Is that correct?

[sbc100]

So, the problem was that your custom externs file declared AudioWorkletNode.prototype.parameterDescriptors when it should have declared AudioWorkletNode.parameterDescriptors. Is that correct?

Exactly. I guess because static properties are not part of the prototype?

[brad4d]

Correct.

class MyClass {
  instanceMethod() {}

  static staticMethod() {}
}

// is mostly equivalent to this
/** @constructor */
function MyClass() {}
MyClass.prototype.instanceMethod = function() {};
MyClass.staticMethod = function() {};

// ... and our externs are still mostly written in this older ES5 syntax.