initial situation

I have the following code:

var NS = {};  // namespace

NS.myEnum = {
    foo: 1,
    bar: 2
};

var extendedNS = Object.create(NS);

extendedNS.myAlert = function (x) { alert(x); };

extendedNS.myAlert(extendedNS.myEnum.foo);

      

        
        
        
      

    

It compiles successfully with this command (no warnings or errors):

java -jar compiler-20150609.jar --js test.js --compilation_level ADVANCED --warning_level VERBOSE

      

        
        
        
      

    

Question 1

According to the docs forJSC_UNSAFE_NAMESPACE

, I think Advanced optimization can replace NS.myEnum

with NS$myEnum

and then remove NS

.

So why doesn't the compiler raise a warning for this line?

var extendedNS = Object.create(NS);

      

        
        
        
      

    

Isn't that a dangerous namespace reference NS

? Shouldn't the compiler warn: "incomplete alias generated for namespace NS

"?

Calling like @enum compiled output

Now I mark NS.myEnum

as an enum:

/**
 * @enum {number}
 */
NS.myEnum = {
    foo: 1,
    bar: 2
};

      

        
        
        
      

    

According to this old SO answer , the compiler expects to collapse the enum value into separate variables. So I think the compiler can now collapse NS.myEnum

to:

NS$myEnum$foo = 1;
NS$myEnum$bar = 2;

      

        
        
        
      

    

The compiler now issues a warning:

WARNING - incomplete alias created for namespace NS
var extendedNS = Object.create(NS);
                               ^

      

        
        
        
      

    

I think I understand why: Optimization Advanced removed NS

after collapsing enum values.

The compiled output is indeed broken:

var a = Object.create({});
a.a = function() {
  alert(a.c.b);      // a.c.b doesn't exist, so a runtime error will occur
};
a.a();

      

        
        
        
      

    

Question 2

Now I add a tag @nocollapse

to the enum ("Indicates a property that should not be collapsed into a variable by the compiler. If you annotate a property that is an object with @nocollapse

, all its properties will also remain mismatched."):

/**
 * @enum {number}
 * @nocollapse
 */
NS.myEnum = {
    foo: 1,
    bar: 2
};

      

        
        
        
      

    

The compiled output is now valid code:

var a = Object.create({c:{a:1, f:2}});
a.b = function() {
  alert(a.c.a);      // a.c.a does exist
};
a.b();

      

        
        
        
      

    

But the compiler raises a warning anyway JSC_UNSAFE_NAMESPACE

:

WARNING - incomplete alias created for namespace NS
var extended = Object.create(NS);
                             ^

      

        
        
        
      

    

Why? Is there another tag to add to NS.myEnum

to prevent this warning?

(Note: I would prefer no @suppress

warning. I would like to understand and correct the cause of the warning.)