duplicates:

• SR-993 Objc class extensions don't support stored type properties, error message is confusing

Issue Description:

When adding a static stored property to an Objective-C classes in an extension, the compiler fails with the error message A declaration cannot be both 'final' and 'dynamic' which is not associated with any source location.

import Foundation

public class TestClass: NSObject {
}

extension TestClass {
  class let x = 5
}

If TestClass does not inherit from NSObject (and is hence not @objc) the code compiles fine.

If you write class let x = 5 instead of static let x = 5, the compiler fails with the error message Class stored properties not supported in classes; did you mean 'static'? suggesting the static keyword.

If adding static stored properties to @objc classes is not supported in extensions, we should produce a diagnostic that clearly points out the issue (including a source location).