Open Radar

 
Summary:
When an NSObject subclass defines a subscript operator, the Swift compiler accepts invalid code that crashes at runtime.

Steps to Reproduce:
Run the following code (in a Playground or in a project):

    import Foundation

    class Polluter : NSObject {
        subscript (key: String) -> Polluter {
            return self
        }
        func hello() { print("Hello") }
    }


    let dict: [String: AnyObject] = ["foo": "bar"]
    let anyDict = dict as AnyObject

    let v = anyDict["foo"]!         // Inferred type: Polluter
    print(String(reflecting: v))    // "bar"
    v.hello()                       // Compiles, and crash at runtime



Expected Results:
1. The variable v is not inferred to be of type `Polluter`.
2. The `v.hello()` line should not compile.
3. There is no runtime crash.


Actual Results:
1. The variable v is inferred to be of type `Polluter`.
2. The `v.hello()` line compiles.
3. There is a runtime crash.


Version:
Xcode  7.0 (7A218)
OSX 10.10.5 (14F27)