[Rule Request] Weak Computed Property

[marcelofabri]

New Issue Checklist

• Updated SwiftLint to the latest version
• I searched for existing GitHub issues

New rule request

1. Why should this rule be added? Share links to existing discussion about what
   the community thinks about this.

weak on a computed property doesn't do anything.

There are discussions about adding a warning on the compiler directly.

2. Provide several examples of what would and wouldn't trigger violations.

class A {
    var b1: B { return B() } // ok
    weak var b2: B? // ok

    weak var b3: B? { return nil } // warning
    weak var b4: B? {  // warning
        get { return b3 }
        set { b3 = newValue }
    }
}

3. Should the rule be configurable, if so what parameters should be configurable?

Just severity

4. Should the rule be opt-in or enabled by default? Why?
   See README.md for guidelines on when to mark a rule as opt-in.

I think it should be enabled by default. The only reasonable case for allowing this is to document the behavior, but since it's really not enforced by the compiler I'm not sure if it's worth the possible confusion.