@dynamicMemberLookup
struct S<T> {
  subscript<U>(dynamicMember keyPath: KeyPath<T, U> & Sendable) -> U {
    fatalError()
  }
}

public struct Foo {
  subscript<T>(bar bar: T) -> Int { 42 }
}

public struct NonSendable: Hashable {}

func f() {
  let s = S<Foo>()
  s[dynamicMember: \.[bar: NonSendable()]]  // ❌ Fails to compile
  s[bar: NonSendable()]                     // ✅ Compiles when it shouldn't
}