[SR-16076] Compiler crashes in release mode when using compactMap with a key path to an @objc optional property

[davedelong]

Previous ID	SR-16076
Radar	None
Original Reporter	@davedelong
Type	Bug

Environment

Xcode 13.3 and Xcode 13.2.1

Additional Detail from JIRA

Votes	0
Component/s	swift
Labels	Bug
Assignee	@AnthonyLatsis
Priority	Medium

md5: 2b2d253ea8e84f4670e030c4b62dd6c5

Issue Description:

Given this code:

@objc protocol OptionalVar {
    @objc optional var name: String { get }
}

extension NSObject: OptionalVar { }

let objects = [
    NSObject(),
    NSObject(),
    NSObject()
] as Array<OptionalVar>

let names = objects.compactMap(\.name)
print("Names: \(names)")

This will build and run fine in debug mode (-Onone), but the compiler crashes when in building in release mode (-O).

[davedelong]

This can be easily worked around by not using a keypath:

let names = objects.compactMap { $0.name }

[slavapestov]

@swift-ci create

[AnthonyLatsis]

Crashes in the SIL verifier, managed to reduce it to the following:

@objc protocol OptionalVar {
    @objc optional var name: Bool { get }
}
do {
  let x: KeyPath<OptionalVar, Bool?> = \.name
}

It definitely has to do with optional somehow, but there are no function conversions at this point, so the fix in #41849 is unfortunately unrelated 🙁

[AnthonyLatsis]

Fixed in #42137