feat: Support sub-menus in context menus (#21)

Author: jbmorley

Package.swift

@@ -17,7 +17,7 @@ let package = Package(
     dependencies: [
         .package(path: "MacResources"),
         .package(url: "https://github.com/apple/swift-docc-plugin", from: "1.0.0"),
-        .package(url: "https://github.com/inseven/interact.git",  .upToNextMajor(from: "2.19.14")),
+        .package(url: "https://github.com/inseven/interact.git",  .upToNextMajor(from: "2.20.1")),
         .package(url: "https://github.com/inseven/licensable.git", .upToNextMajor(from: "0.0.1")),
         .package(url: "https://github.com/tribalworldwidelondon/CassowarySwift.git", from: "2.0.0"),
     ],

Sources/SelectableCollectionView/Views/CollectionViewContainer.swift

@@ -195,14 +195,7 @@ public class CollectionViewContainer<Element: Hashable, Content: View>: NSView,
         action()
     }
 
-    func collectionView(_ collectionView : InteractiveCollectionView,
-                        contextMenuForSelection _: Set<IndexPath>) -> NSMenu? {
-
-        guard let menuItems = delegate?.collectionViewContainer(self, menuItemsForElements: selectedElements),
-              !menuItems.isEmpty
-        else {
-            return nil
-        }
+    func contextMenu(for menuItems: [MenuItem]) -> NSMenu {
         let menu = NSMenu()
         menu.items = menuItems.map { menuItem in
             switch menuItem.itemType {
@@ -214,11 +207,26 @@ public class CollectionViewContainer<Element: Hashable, Content: View>: NSView,
                 return menuItem
             case .separator:
                 return NSMenuItem.separator()
+            case .menu(let title, let menuItems):
+                let menuItem = NSMenuItem(title: title, action: nil, keyEquivalent: "")
+                menuItem.submenu = contextMenu(for: menuItems)
+                return menuItem
             }
         }
         return menu
     }
 
+    func collectionView(_ collectionView : InteractiveCollectionView,
+                        contextMenuForSelection _: Set<IndexPath>) -> NSMenu? {
+
+        guard let menuItems = delegate?.collectionViewContainer(self, menuItemsForElements: selectedElements),
+              !menuItems.isEmpty
+        else {
+            return nil
+        }
+        return contextMenu(for: menuItems)
+    }
+
     var selectedElements: Set<Element> {
         return Set(collectionView.selectionIndexPaths.compactMap { dataSource?.itemIdentifier(for: $0) })
     }