Attachment: Download

Issue Description:

The following code causes a compiler issue in 3.1, while it worked on 3.0: -
Here is the code:

import UIKit

public protocol Addable: class {
    static func +(lhs: Self, rhs: NSLayoutConstraint) -> NSLayoutConstraint
    static func +(lhs: Self, rhs: [NSLayoutConstraint]) -> [NSLayoutConstraint]
}

extension UIView : Addable {}
extension Addable where Self: UIView
{
    /// To add single constraint on the lhs view
    public static func +(lhs: Self, rhs: NSLayoutConstraint) -> NSLayoutConstraint {
            lhs.addConstraint(rhs)
            return rhs
    }
    
    /// To add multiple constraints on the lhs view
    public static func +(lhs: Self, rhs: [NSLayoutConstraint]) -> [NSLayoutConstraint] {
           return rhs.map { lhs + $0 }
    }
}

Note: - Now If we remove Second method of protocol & we also remove its implementation part from protocol extension then the remaining code is compilable.

As far as I know there is something wrong with — rhs.map { lhs + $0 } in the second method of Addable. means using the first method inside the second method.

If we use the same code with custom operators in the same way then the issue will remain same. Here is the link to my project KVConstraintKit in which I have made few custom operators and all of them having the same issues but works fine in swift 3.0.