swift234

Diagnose Objective-C method overrides not reflected as Swift overrides.

Diagnose cases where the use of @objc will produce Objective-C methods
that end up overriding an Objective-C method in a superclass, when
that override is not properly represented as an override in the Swift
type system. This can happen when the Objective-C methods are produced
by different kinds of entities. For example:

  class Super {
    @objc var property: Int
  }

  class Sub : Super {
    @objc func setProperty(property: Int) { }
  }

In Swift, Sub.setProperty and Super.property are completely
unrelated. However, both produce an Objective-C instance method with
the selector "setProperty:", so we end up with unexpected overriding
behavior. Diagnose this whenever it occurs, regardless of the kind of
@objc entity that produced the Objective-C methods: initializers,
deinitializers, methods, properties, or subscripts.

Implements the rest of the intended functionality of
rdar://problem/18391046, with the caveat that there are two remaining
classes of bugs:
  1) Superclasses defined in a module (or imported from a Clang
  module) aren't handled properly yet; we might not see those methods.
  2) We won't properly detect all of these failures when the methods
  are scattered across different source files in the same module.

Swift SVN r23170