1616378 - Reimplement Function.prototype.caller

Status: NEW

(Core :: JavaScript Engine, task, P2)

Description

[Tom S [:evilpie]]

This reimplement Function.prototype.caller to closely follow the new proposed spec. More details soon.

Comment 1

[Tom S [:evilpie]]

Attachment: Bug 1616378 - Reimplement Function.prototype.caller

Comment 2

[Tom S [:evilpie]]

I think this should now hopefully correctly implement the draft spec. Removing the caller setter causes a number of test262 failures, I opened an issue to discuss that.

1. From an implementation perspective maybe we should change IsAllowedReceiverFunctionForCallerAndArguments to follow the spec and check for [[Constructor]] instead of the individual function types like generator, async etc.
2. The restrictions that require the getter realm to be equal to the |this| function realm and similarly the restriction requiring the caller realm to be equal to the getter realm are probably the biggest possible compatibility fallout. I am not even sure if this works with the browser, I need to do some test runs.
3. I think there was some concern around using the unwrapped function in AdvanceToActiveCallLinear. I think we don't need to unwrap at all, because in IsAllowedReceiverFunction we will just fail for different realms anyway.

Comment 3

[Claude Pache]

(In reply to Tom Schuster [:evilpie] from comment #2)

1. From an implementation perspective maybe we should change IsAllowedReceiverFunctionForCallerAndArguments to follow the spec and check for [[Constructor]] instead of the individual function types like generator, async etc.

The intention of the spec is to exclude everything but what you call IsSloppyNormalFunction() (with additional cross-realm restriction), at least if I’m guessing correctly what IsSloppyNormalFunction() is doing. From the spec side, it happens that it suffices to inspect the [[Strict]] and the [[Construct]] slots, but it is in fact a somewhat indirect way to have the intended semantics (the intention is given in the Note following the IsAllowedReceiverFunctionForCallerAndArguments algorithm).