macos: only hide dock on the screen with the dock

macos/Sources/Helpers/NSScreen+Extension.swift

@@ -0,0 +1,36 @@
+import Cocoa
+
+extension NSScreen {
+    // Returns true if the given screen has a visible dock. This isn't
+    // point-in-time visible, this is true if the dock is always visible
+    // AND present on this screen.
+    var hasDock: Bool {
+        // If the dock autohides then we don't have a dock ever.
+        if let dockAutohide = UserDefaults.standard.persistentDomain(forName: "com.apple.dock")?["autohide"] as? Bool {
+            if (dockAutohide) { return false }
+        }
+
+        // There is no public API to directly ask about dock visibility, so we have to figure it out
+        // by comparing the sizes of visibleFrame (the currently usable area of the screen) and
+        // frame (the full screen size). We also need to account for the menubar, any inset caused
+        // by the notch on macbooks, and a little extra padding to compensate for the boundary area
+        // which triggers showing the dock.
+
+        // If our visible width is less than the frame we assume its the dock.
+        if (visibleFrame.width < frame.width) {
+            return true
+        }
+
+        // We need to see if our visible frame height is less than the full
+        // screen height minus the menu and notch and such.
+        let menuHeight = NSApp.mainMenu?.menuBarHeight ?? 0
+        let notchInset: CGFloat = if #available(macOS 12, *) {
+            safeAreaInsets.top
+        } else {
+            0
+        }
+        let boundaryAreaPadding = 5.0
+
+        return visibleFrame.height < (frame.height - max(menuHeight, notchInset) - boundaryAreaPadding)
+    }
+}