@@unscopables should not apply to the global environment record

[rossberg]

According to the current spec, the following program should produce undefined:

this[Symbol.unscopables] = {Object: true}
Object  // undefined

Of all 3 browsers that implement @@unscopables (Chrome, Edge, Safari), none seems to handle that. And there is a likely reason: it would be disastrous for performance, at least unless very complicated measures are taken in VMs. That's because every access to a conventional global variable x would require also looking up window[@@unscopables].x, i.e., two extra property look-ups. Worse, as a consequence, all existing (and essential) optimisations around global variable access are invalidated by this semantics.

I'm not sure if this semantics was intended, or where it would be useful (@@unscopables was introduced for dealing with with legacy). But given the implications and the noteworthy failure of all browsers to implement it correctly, I propose removing @@unscopables filtering for the global environment.

[anba]

The "If the withEnvironment flag of envRec is false, return true." step handles this case. (withEnvironment is false for the object environment of the global environment.)

[anba]

The "If the withEnvironment flag of envRec is false, return true." step handles this case. (withEnvironment is false for the object environment of the global environment.)

[rossberg]

@anba, argh, you're right, how did I miss that! Sorry for the noise.

[rossberg]

@anba, argh, you're right, how did I miss that! Sorry for the noise.