Inconsistency when try to access an property inside the "with" scope

[gfablima]

Hi,
there's an inconsistence when we try to access an property inside the "with" scope.

OS: Ubuntu 16.04 x64
Chakra: 1.10.0.0-beta

Step to reproduce:

var o = { f: "foo" };
with (o) {
  var desc = Object.getOwnPropertyDescriptor(this, "f");
  function f() {
    return "bar";
  }
  if (!(desc.value === undefined)) {
    throw new Error('expected: undefined, got: ' + desc.value);
  }
}

Actual results:
Error: expected: undefined, got: function f() {
return "bar";
}

Expected results:
Pass without failures

V8 and Spidermonkey pass as expected, but Chakra and JavascriptCore returns the function f() inside "with" scope.

[fatcerberus]

Isn't this the expected behavior? function f() gets hoisted and since it's in global scope it's assigned to the global object to be picked up by getOwnPropertyDescriptor. V8 and SpiderMonkey's behavior seems stranger to me.

[fatcerberus]

With that said, your repro crashes outright in Node.js v10:

D:\temp>node f.js
D:\temp\f.js:7
  if (!(desc.value === undefined)) {
             ^

TypeError: Cannot read property 'value' of undefined
    at Object.<anonymous> (D:\temp\f.js:7:14)
    at Module._compile (internal/modules/cjs/loader.js:678:30)
    at Object.Module._extensions..js (internal/modules/cjs/loader.js:689:10)
    at Module.load (internal/modules/cjs/loader.js:589:32)
    at tryModuleLoad (internal/modules/cjs/loader.js:528:12)
    at Function.Module._load (internal/modules/cjs/loader.js:520:3)
    at Function.Module.runMain (internal/modules/cjs/loader.js:719:10)
    at startup (internal/bootstrap/node.js:228:19)
    at bootstrapNodeJSCore (internal/bootstrap/node.js:575:3)

[dilijev]

Confirmed behavior difference.

## Source
var o = { f: "foo" };
with (o) {
  var desc = Object.getOwnPropertyDescriptor(this, "f");
  function f() {
    return "bar";
  }
  if (!(desc.value === undefined)) {
    print('expected: undefined, got: ' + desc.value);
  }
}
print('done')


#### jsvu-d8, jsvu-sm
done

#### jsvu-ch, jsvu-jsc
expected: undefined, got: function f() {
    return "bar";
  }
done

[pleath]

Chakra's is the behavior I would expect in sloppy mode. A binding for f is added to the global object.

[dilijev]

Maybe @bterlson can weigh in on spec?

[fatcerberus]

Chakra's is the behavior I would expect in sloppy mode. A binding for f is added to the global object.

Now that I look at the repro a second time I'm not so sure; per ES6+ specification function declarations inside {} are block-scoped (like let) IIRC.

[pleath]

You're right, they're scoped like let, but the sloppy-mode behavior has a wrinkle. Along with the let binding, a var binding with the same name is created on function entry and initialized when the block scope is entered. That's to support existing scripts like this:

if (t) {
function f() {...}
}
f();

[zenparsing]

Yes, the sloppy-mode behavior for this case is specified in B3.3.2.

[fatcerberus]

@zenparsing So in that case, this is not a bug in ChakraCore but instead V8 and SpiderMonkey are doing the wrong thing here, correct?

[pleath]

Last I looked, V8 had left some aspects of block-scoped functions unimplemented due to compat concerns, though that may no longer be true.