Optional-chained key path into nested optional returns wrong value

[stephencelis]

Description

Where an optional-chained key path to a nested optional should return nil, it somehow returns .some(nil) instead.

Reproduction

import Testing

@Test
func optionalChainedKeyPathToNestedOptional() {
  struct A {
    var str: String??
  }
  struct B {
    var a: A?
  }
  let b = B()
  #expect(b.a?.str == String??.none)              // ✅
  #expect(b[keyPath: \.a?.str] == String??.none)  // 🛑
  // .some(nil) != .none
}

Expected behavior

I expect the key path access to return the correct value.

Environment

swift-driver version: 1.115 Apple Swift version 6.0 (swiftlang-6.0.0.9.10 clang-1600.0.26.2)
Target: arm64-apple-macosx14.0

Additional information

No response

[stephencelis]

@Azoy This bug potentially overlaps with some of the key path performance issues you were working on.