Runtime crash in AnyKeyPath.debugDescription when using @dynamicMemberLookup

[mbrandonw]

Description

The following code defines a wrapper struct around a value and uses @dynamicMemberLookup to expose access to the underlying value:

@dynamicMemberLookup
struct Wrapper<Value> {
  let value: Value
  subscript<OtherValue>(dynamicMember keyPath: KeyPath<Value, OtherValue>) -> OtherValue {
    self.value[keyPath: keyPath]
  }
}

In Swift 5.8, if we try to access a key path's debugDescription on Wrapper that goes through the dynamic member, we get a runtime crash:

let kp = \Wrapper<String>.count
print(kp.debugDescription)  // 🛑 Bad access

Steps to reproduce

Run the above code in any Swift environment.

Expected behavior

It should print out something like "\Wrapper<String>.count".

Environment

• swift-driver version: 1.75.2 Apple Swift version 5.8 (swiftlang-5.8.0.124.2 clang-1403.0.22.11.100)
• Xcode 14.3, Build version 14E222b
• Deployment target: iOS 16.4

[mbrandonw]

Hi @benpious, I saw you pitched and implemented SE-0369 so thought you might be interested in this edge case that we ran into.