__proto__ implementation does not quite match proposed ES6 spec

[A. Sundararajan]

Hi,

Thanks for writing. We are aware of current start of draft spec on this. 
But, the issue is that if Object.prototype.__proto__ is the way to 
implement, how will setting __proto__ to null or undefined do? If 
Object.prototype is not in proto chain of an object, what happens to 
__proto__ for such objects?

Current __proto__ impl is more of a fall back for scripts that do use 
__proto__. Since there is no definitive spec yet, it is going to be 
"wrong" one way or other. If it is finalized by ES6, we'll follow it. 
For now, I think we'll leave it "as is".

Thanks,
-Sundar

On Wednesday 18 September 2013 05:54 PM, André Bargull wrote:
> Official support for __proto__ was added recently, but the 
> implementation does not quite match the proposed ECMAScript 6 
> specification (rev18).
>
> The current consensus in TC39 is as follows:
>
> (1) __proto__ in object literals is treated as a special form to set 
> the [[Prototype]] internal data property of a new object. It is not 
> possible to disable this functionality (*).
>
> (2) Object.prototype.__proto__ is an accessor property with [[Get]] 
> and [[Set]] accessors. Also [[Enumerable]] is false, [[Configurable]] 
> is true.
>
> (*) Previously it was possible to disable it, see ES6 draft rev14.
>
> Certain details may still change over time when the ES6 spec gets 
> finalized, e.g. should `Object.setPrototypeOf(1,null)` throw a 
> TypeError because 1 is not an object or should this just perform 
> argument checks and then return (as proposed in rev18). Also see 
> https://bugs.ecmascript.org/show_bug.cgi?id=1586 for some recent 
> changes on this topic.
>
>
> - André
>
>
> Current issues for (1):
>
> 1.1:
> jjs> ({__proto__: (print("first"),{}), a: (print("second"),0)})
>
> Expected: print "first" and then "second"
> Actual: "second" and then "first"
>
> 1.2:
> jjs> ({__proto__: null})
>
> Expected: [[Prototype]] is set to null
> Actual: jjs is terminated (also reproducible with `jjs> 
> Object.create(null)`)
> Exception in thread "main" ECMAScript Exception: TypeError: Cannot get 
> default string value
>     at jdk.nashorn.internal.runtime.ECMAErrors.error(ECMAErrors.java:56)
>     at 
> jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:212)
>     at 
> jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:184)
>     at 
> jdk.nashorn.internal.objects.Global.getDefaultValue(Global.java:585)
>     at 
> jdk.nashorn.internal.runtime.ScriptObject.getDefaultValue(ScriptObject.java:1243)
>     ...
>
> 1.3:
> jjs> ({__proto__: void 0}).__proto__ === Object.prototype
>
> Expected: returns true
> Actual: TypeError: undefined is not an Object
> (Only Objects or null are allowed, other types are simply ignored. 
> This was changed in rev17 for backward compatibility reasons)
>
> 1.4:
> jjs> ({__proto__: 0})
> Exception in thread "main" java.lang.AssertionError: int is not 
> compatible with object
>     at 
> jdk.nashorn.internal.codegen.MethodEmitter.popType(MethodEmitter.java:235)
>     at 
> jdk.nashorn.internal.codegen.MethodEmitter.fixParamStack(MethodEmitter.java:1109)
>     at 
> jdk.nashorn.internal.codegen.MethodEmitter.invoke(MethodEmitter.java:1128)
>     at 
> jdk.nashorn.internal.codegen.MethodEmitter.invokevirtual(MethodEmitter.java:1168)
>     at 
> jdk.nashorn.internal.codegen.CompilerConstants$3.invoke(CompilerConstants.java:394)
>     ...
>
>
> Current issues for (2):
>
> 2.1:
> jjs> Object.getOwnPropertyDescriptor(Object.prototype, "__proto__")
>
> Expected: return accessor property descriptor
> Actual: returns undefined
>
> 2.2:
> jjs> (o = {}, o.__proto__ = void 0, o.__proto__ === Object.prototype)
>
> Expected: returns true
> Actual: returns false
> (Only Objects or null are allowed, other types are simply ignored. 
> This was changed in rev17 for backward compatibility reasons)
>
> 2.3:
> jjs> (o = {}, o.__proto__ = 0, o)
>
> Expected: returns o
> Actual: jjs is terminated
> jjs> (o = {}, o.__proto__ = 0, o)
> Exception in thread "main" ECMAScript Exception: TypeError: [object 
> Object] is not a Number
>     at jdk.nashorn.internal.runtime.ECMAErrors.error(ECMAErrors.java:56)
>     at 
> jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:212)
>     at 
> jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:184)
>     at 
> jdk.nashorn.internal.runtime.ECMAErrors.typeError(ECMAErrors.java:171)
>     at 
> jdk.nashorn.internal.objects.NativeNumber.getNumberValue(NativeNumber.java:341)
>     ...
>
> 2.4:
> jjs> 12["__proto__"] === Number.prototype
>
> Expected: returns true
> Actual: returns false