Description

When subclassing an open class from another module, Swift is not warning me if I have neglect to initialize all properties in my subclass. It unexpectedly builds fine but crashes at runtime.

Steps to reproduce

ModuleA:

open class MySuperclass {}

ModuleB:

import ModuleA
class MySubclass: MySuperclass {
    var hi: String
}

hi is never initialized, but this builds.

Expected behavior
I expect an error like: Class 'MySubclass' has no initializers: Stored property 'hi' without initial value prevents synthesized initializers. If I remove the inheritance clause from MySubclass I do get this error.

Environment

• swift-driver version: 1.87.1 Apple Swift version 5.9 (swiftlang-5.9.0.128.108 clang-1500.0.40.1)
  Target: arm64-apple-macosx14.0
• Xcode 15.0.1 / 15A507
• Deployment target: macOS 13