Apple Swift version 5.3.2 (swiftlang-1200.0.45 clang-1200.0.32.28)
Target: x86_64-apple-darwin20.1.0

Issue Description:

class C {
    var callback: ((C) -> Void)!
    
    func setCallback(_ callback: @escaping (Self) -> Void) {
        self.callback = callback // Cannot assign to property: 'self' is immutable
    }
}

From what I can tell, this assignment should be disallowed (since for any potential subclass, Self will differ from C), unless C is made final (should that be a separate bug)?

In any case, this diagnostic message is incorrect, though I'm not sure what the wording should be.

Is there a term for the process of taking a Self and converting it to a place where the literal type name is used?