[SR-2289] Dynamic casts of CoreFoundation types don't work

[gribozavr]

Previous ID	SR-2289
Radar	rdar://problem/27116100
Original Reporter	@gribozavr
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, Runtime
Assignee	@tbkka
Priority	Medium

md5: 540dd3cbf15c2fc1a75d48b4738ea25f

Issue Description:

See disabled test cases in {test/1_stdlib//Casts.swift}. Dynamic casts from CoreFoundation types to protocol existentials (for protocols that they implement) don't work.

[belkadan]

Also see the XFAILed tests in https://github.com/apple/swift/pull/3253/commits/3b6e40c0308b44dc77a41e651fe04fd6ad893f6c.

[tbkka]

The test cases in question attempt to:

• Extend a CF class with a protocol conformance

• Create an CF object

• Cast it to the protocol in question

This turns out to be a somewhat ambiguous thing to try to do: When dealing with references to class objects, the runtime caster will normalize the object types. For most CF objects, this results in the caster working with the corresponding Objective-C type instead of the CF type. One possible solution would be for the runtime dynamic cast code to try both the provided (CF) type and the normalized (Obj-C) type in such cases.

[tbkka]

#33561 should fix this for the non-optimized case (where the cast is being handled by the runtime). There may still be issues with optimized casts, though.

[tbkka]

I believe the PR mentioned above has resolved this. Please let me know if you see any further problems in this area.