[SR-7981] `self` available without backticks in let initialization closure of NSObject

[swift-ci]

Previous ID	SR-7981
Radar	None
Original Reporter	benpious (JIRA User)
Type	Bug
Status	Resolved
Resolution	Duplicate

Environment

Xcode 9.3.0.

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 8bc95e194233eeaad7dd08b80e745ab5

duplicates:

• [SR-4559] Method called 'self' can be confused with regular 'self' #47136

Issue Description:

This code compiles. In Xcode, it even colors self as though it's a keyword.

import UIKit

class C: NSObject {
    let button: UIButton = {
       let button = UIButton()
        button.addTarget(self,
                         action: #selector(f),
                         for: .touchUpInside)
        return button
    }()
    
    @objc
    func f() {   
    }
}

But self is actually NSObject.self, which is a function.

Note that in a non-NSObject subclass, this code does not compile, with the error "error: use of unresolved identifier 'self'". So I'm guessing that the compiler currently has a hack of some sort to prevent self from referring to NSObject.self as in the class object in this context, since that would be confusing. And that that's why the compiler allows NSObject.self to not be backticked.

Note that

class C {
    func self() {
    }
}

also doesn't compile, nor does refering to a func `self`() function without backticks, so allowing this is clearly wrong.