Static class functions can be erroneously removed in ADVANCED mode

[dfreedm]

In a simple example with ADVANCED optimizations enabled

class Foo {
  static print() {
    console.log('f');
  }
  constructor() {
    this.constructor.print();
  }
}

let x = new Foo();

The call to the print function remains, but the implementation is missing.

new function() {
  this.constructor.print();
};

Live Example

[brad4d]

What happens is this.

1. the ES6 class is transpiled into an ES5 class, so we end up with

   function Foo() {
    this.constructor.print();
   }
   Foo.print = function() { console.log('f'); }
   var x = new Foo();

2. Then CollapseProperties does it's thing to rename Foo.print to Foo$print, but it doesn't realize that this.constructor.print is the same object and fails to update that.
3. Finally Foo$print appears to be unused, so it gets removed.

[brad4d]

As a workaround, you can use the @nocollapse annotation to prevent collapsing the print function.

class Foo {
  /** @nocollapse */
  static print() {
    console.log('f');
  }
  constructor() {
    this.constructor.print();
  }
}

let x = new Foo();

[ChadKillingsworth]

I believe the situation may be a bit worse when the static method is on a super class. @azakus That's why #2286 exists.

[WearyMonkey]

This seems to happen anytime the static method is not called directly from the class.

Example:

class Foo {
   static foo() { 
     console.log('foo'); 
   }
}

function callStaticMethod(Foo) {
  Foo.foo();
}

callStaticMethod(Foo);

(function(){}).a();

The problem doesn't occur when the language_out is ECMASCRIPT_2015 +

$ java -jar compiler.jar --js example.js -O ADVANCED --language_out ECMASCRIPT_2015

'use strict';class a{static a(){console.log("foo")}}(function(b){b.a()})(a);

[theRobinator]

I'm running into this issue as well, from a slightly different angle. Demo link.
Input:

class Foo {
  static method() {
    return true;
  }
}

const Bar = {
  Foo: Foo
}

console.log(Bar.Foo.method());

Output:

console.log(function(){}.method());

[thebravoman]

A little different but probably connected case

/**
 * @nocollapse
 * @namespace
 */
var NN ={}

NN.Container = class {
  constructor() {
    console.log("some")
  }
  getId() { 
    return new Date()
  }
}
console.log(new NN.Container().getId())

when compiled with

 java -jar $CLOSURE_PATH --js steps3.js --compilation_level ADVANCED_OPTIMIZATIONS --output_wrapper "(function() {%output%}).call(window)" --formatting=pretty_print

results in

(function() {new {}.a;
console.log(new Date);
}).call(window)

Here console.log("some") is missing. The whole NN.Container constructor is missing.

So there should be a '@nocollapse' at the NN.Container level

[kjin]

Created Google internal issue http://b/143308051