Replacement for UIView.hitTest(_:with:) that detects hits on subviews outside the bounds of the parent view

UIView+HitTest.swift

//
//  UIView+HitTest.swift
//
//  Created by Drew Olbrich on 2/5/20.
//  Copyright © 2022 Lunar Skydiving LLC. All rights reserved.
//
//  MIT License
//
//  Permission is hereby granted, free of charge, to any person obtaining a copy
//  of this software and associated documentation files (the "Software"), to deal
//  in the Software without restriction, including without limitation the rights
//  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
//  copies of the Software, and to permit persons to whom the Software is
//  furnished to do so, subject to the following conditions:
//
//  The above copyright notice and this permission notice shall be included in all
//  copies or substantial portions of the Software.
//
//  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
//  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
//  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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//  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
//  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
//

import UIKit

public extension UIView {
    
    /// Returns the frontmost visible subview of the receiver that contains `point`, or
    /// the receiver itself if it contains `point`.
    ///
    /// This method differs from the default implementation of `hitTest(_:with:)` in
    /// that points that lie outside the receiver’s bounds are reported as hits if they
    /// actually lie within one of the receiver’s subviews.
    ///
    /// See https://developer.apple.com/library/archive/qa/qa2013/qa1812.html
    ///
    /// Example usage:
    /// 
    ///     override func hitTest(_ point: CGPoint, with event: UIEvent?) -> UIView? {
    ///         return hitTestIncludingSubviewsWithoutBoundsCheck(point, with: event)
    ///     }
    ///
    /// - Parameters:
    ///   - point: A point specified in the receiver’s local coordinate system (bounds).
    ///   - event: The event that warranted a call to this method. If you are calling this
    ///     method from outside your event-handling code, you may specify nil.
    /// - Returns: The frontmost visible subview of the receiver, or the receiver,
    ///     that contains `point`, even if that subview lies outside the receiver's bounds.
    ///     Returns `nil` if `point` does not lie within any of the receiver's subviews.
    func hitTestIncludingSubviewsWithoutBoundsCheck(_ point: CGPoint, with event: UIEvent?) -> UIView? {
        // It might be tempting to refactor this function to apply its test recursively,
        // but this would this interact badly with system controls that contain internal
        // views that have different expectations about the hit test. For example,
        // `UISlider` manages an internal view for its thumb whose `hitTest` method always
        // returns `nil`, and if it returns otherwise, the slider will no longer work.
        //
        // Instead, this method should be manually applied to each problematic view in a
        // hierarchy.
        
        guard !isHidden && isUserInteractionEnabled && alpha >= 0.01 else {
            return nil
        }
        
        // Test the frontmost subview first.
        for subview in subviews.reversed() {
            let pointInSubview = subview.convert(point, from: self)
            if let hitSubview = subview.hitTest(pointInSubview, with: event) {
                return hitSubview
            }
        }
        
        if self.point(inside: point, with: event) {
            return self
        }
        
        return nil
    }

}