[SR-15121] Segfault when KeyPath expression as function used for functions on classes

[DeFrenZ]

Previous ID	SR-15121
Radar	None
Original Reporter	@DeFrenZ
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s
Labels	Bug
Assignee	None
Priority	Medium

md5: 1b2bc84d40d51034214b603bf5e65311

Issue Description:

final class WorkItem {
    let work: () -> Void    
    init(work: @escaping () -> Void) {
        self.work = work
    }
}


var items: [WorkItem] = [
    .init(work: { print("foo") }),
]


items.forEach(\.work) // SEGFAULT
items.forEach({ $0.work() }) // WORKS

This doesn't crash if `WorkItem` is a `struct` instead, but doesn't print either (without the correct call).

The last stack item before the crash is "libswiftCore.dylib`swift::metadataimpl::ValueWitnesses<(anonymous namespace)::ThickFunctionBox>::initializeWithTake"

The issue is that it probably shouldn't compile at all with the expression, since the type mismatches

[LucianoPAlmeida]

On main I see that the this is properly diagnosed(I think this was fixed by #36531 @DeFrenZ can you verify using the main snapshot? Since its been a long time, this probably fixed on 5.5 and available on Xcode 13 beta, but not sure...

[typesanitizer]

Yep, it looks like we have a proper diagnostic for Xcode 13 beta.