Dynamic member lookup fails to autocomplete sendable key path

[stephencelis]

Description

If a type with dynamic member lookup is constrained to sendable key paths, then the compiler fails to show autocomplete for the members.

Reproduction

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

func f(_ s: S<String>) {
  s.count  // Compiles, but members do not show up when autocompleting from 's.'
}

Expected behavior

I expect autocomplete to show the members.

Related bug: I can add an unavailable overload for non-sendable key paths, and it restores autocomplete, but it also allows such accesses to compile even though they should be unavailable:

extension S {
  @available(*, unavailable)
  subscript<B>(dynamicMember keyPath: KeyPath<A, B>) -> S<B> {
    fatalError()
  }
}

struct T {
  @MainActor var p = 0
}

func f(_ s: S<T>) {
  s.p  // Compiles, but it shouldn't
}

Environment

swift-driver version: 1.115 Apple Swift version 6.0.2 (swiftlang-6.0.2.1.2 clang-1600.0.26.4)
Target: arm64-apple-macosx15.0

Additional information

No response

[stephencelis]

@xedin Another key path sendability bug...

[xedin]

cc @ahoppen, this might be a code completion issue since the signature of dynamic member subscript is allowed to provide & Sendable and code completion might not handle protocol compositions correctly in some situations?…

Re: s.p that is most likely due to concurrency checker not diagnosing synthesized code, if completion issue turns up to be non-typecker I think you should file a new one for s.p example specifically.

[ahoppen]

Yes, it’s indeed a code completion issue. Removing & Sendable makes the result show up.