fix: devtool warning by adding parent view, closes #273 (#654)

* fix: devtool warning by adding parent view, closes #273

Previously, we would just inject the webview into the contentView of the
NSWindow. When devtools would inject the subView into this top-level content
view, a warning would be displayed.

* Move parent view to macOS only

Co-authored-by: Yu-Wei Wu <wusyong9104@gmail.com>

src/webview/wkwebview/mod.rs

@@ -495,11 +495,22 @@ r#"Object.defineProperty(window, 'ipc', {
       // Inject the web view into the window as main content
       #[cfg(target_os = "macos")]
       {
+        // Create a view to contain the webview, without it devtools will try to
+        // inject a subview into the frame causing an obnoxious warning.
+        // See https://github.com/tauri-apps/wry/issues/273
+        let parent_view: id = msg_send![class!(NSView), alloc];
+        let _: () = msg_send![parent_view, init];
+        parent_view.setAutoresizingMask_(NSViewHeightSizable | NSViewWidthSizable);
+        let _: () = msg_send![parent_view, addSubview: webview];
+
         // Tell the webview we use layers (macOS only)
         let _: () = msg_send![webview, setWantsLayer: YES];
         // inject the webview into the window
         let ns_window = window.ns_window() as id;
-        let _: () = msg_send![ns_window, setContentView: webview];
+        // NOTE: We ignore the fact that we may get back the existing view as we
+        // expect tao::Window to hold a handle to it and release it for us
+        // eventually.
+        let _: () = msg_send![ns_window, setContentView: parent_view];
 
         // make sure the window is always on top when we create a new webview
         let app_class = class!(NSApplication);