Typed throws that rely on a type's generic placeholder crash the compiler.

[JessyCatterwaul]

Description

I was trying to add strong error typing (the (UnwrapError) part) to this. It sadly didn't work.

extension Optional {
  /// Represents that an `Optional` was `nil`.
  public struct UnwrapError: Swift.Error & Equatable {
    public init() { }
  }

  @inlinable public var wrappedValue: Wrapped {
     get throws(UnwrapError) {
      switch self {
      case let wrapped?: return wrapped
      case nil: throw UnwrapError()
      }
    }
  }
}

Reproduction

This all compiles fine.

struct GenericError<T>: Error {
  init() { }
}

struct S<T> {
  var property: Void {
    get throws(GenericError<Void>) { }
  }

  func method() throws(GenericError<Void>) { }
}

But change the <Voids> to <T>s, and the compiler crashes.

struct S<T> {
  var property: Void {
    get throws(GenericError<T>) { }
  }

  func method() throws(GenericError<T>) { }
}

Stack dump

Command SwiftCompile failed with a nonzero exit code

Expected behavior

throws() supports all errors that can be thrown.

Environment

swift-driver version: 1.109.2 Apple Swift version 6.0 (swiftlang-6.0.0.3.300 clang-1600.0.20.10)
Target: arm64-apple-macosx14.0

Additional information

No response

[JessyCatterwaul]

The compiler has moved on to the point now where the examples above compile. Good work! But having the signatures compile, alone, does not result in usability, as the errors are still not usable. I.e. adding in throw .init() is now what results in the compiler crash.

struct GenericError<T>: Error {
  init() { }
}

struct S<T> {
  var property: Void {
    get throws(GenericError<T>) { throw .init() }
  }

  func method() throws(GenericError<T>) { throw .init() }
}

[slavapestov]

Oops, sorry.