Fix warnings introduced in newer Rust Nightly

This does not (yet) upgrade ./rust-toolchain

The warnings:

* dead_code "field is never read"
* redundant_semicolons "unnecessary trailing semicolon"
* non_fmt_panic "panic message is not a string literal, this is no longer accepted in Rust 2021"
* unstable_name_collisions "a method with this name may be added to the standard library in the future"
* legacy_derive_helpers "derive helper attribute is used before it is introduced" https://github.com/rust-lang/rust/issues/79202

ports/libsimpleservo/api/src/lib.rs

@@ -174,7 +174,7 @@ pub struct ServoGlue {
     // and exit if it is empty afterwards.
     browsers: Vec<BrowserId>,
     events: Vec<WindowEvent>,
-    current_url: Option<ServoUrl>,
+
     context_menu_sender: Option<IpcSender<ContextMenuResult>>,
 }
 
@@ -306,7 +306,6 @@ pub fn init(
             browser_id: None,
             browsers: vec![],
             events: vec![],
-            current_url: Some(url.clone()),
             context_menu_sender: None,
         };
         let browser_id = BrowserId::new();
@@ -636,7 +635,6 @@ impl ServoGlue {
                     self.callbacks
                         .host_callbacks
                         .on_url_changed(entries[current].clone().to_string());
-                    self.current_url = Some(entries[current].clone());
                 },
                 EmbedderMsg::LoadStart => {
                     self.callbacks.host_callbacks.on_load_started();

ports/libsimpleservo/capi/src/lib.rs

@@ -188,7 +188,7 @@ where
         Some(ref mut s) => (f)(s),
         None => Err("Servo not available in this thread"),
     }) {
-        Err(e) => panic!(e),
+        Err(e) => panic!("{}", e),
         Ok(r) => r,
     }
 }

ports/winit/browser.rs

@@ -42,21 +42,13 @@ pub struct Browser<Window: WindowPortsMethods + ?Sized> {
     browsers: Vec<BrowserId>,
 
     title: Option<String>,
-    status: Option<String>,
-    favicon: Option<ServoUrl>,
-    loading_state: Option<LoadingState>,
+
     window: Rc<Window>,
     event_queue: Vec<WindowEvent>,
     clipboard_ctx: Option<ClipboardContext>,
     shutdown_requested: bool,
 }
 
-enum LoadingState {
-    Connecting,
-    Loading,
-    Loaded,
-}
-
 impl<Window> Browser<Window>
 where
     Window: WindowPortsMethods + ?Sized,
@@ -67,9 +59,6 @@ where
             current_url: None,
             browser_id: None,
             browsers: Vec::new(),
-            status: None,
-            favicon: None,
-            loading_state: None,
             window: window,
             clipboard_ctx: match ClipboardContext::new() {
                 Ok(c) => Some(c),
@@ -278,8 +267,8 @@ where
     pub fn handle_servo_events(&mut self, events: Vec<(Option<BrowserId>, EmbedderMsg)>) {
         for (browser_id, msg) in events {
             match msg {
-                EmbedderMsg::Status(status) => {
-                    self.status = status;
+                EmbedderMsg::Status(_status) => {
+                    // FIXME: surface this status string in the UI somehow
                 },
                 EmbedderMsg::ChangePageTitle(title) => {
                     self.title = title;
@@ -440,11 +429,11 @@ where
                 EmbedderMsg::SetCursor(cursor) => {
                     self.window.set_cursor(cursor);
                 },
-                EmbedderMsg::NewFavicon(url) => {
-                    self.favicon = Some(url);
+                EmbedderMsg::NewFavicon(_url) => {
+                    // FIXME: show favicons in the UI somehow
                 },
                 EmbedderMsg::HeadParsed => {
-                    self.loading_state = Some(LoadingState::Loading);
+                    // FIXME: surface the loading state in the UI somehow
                 },
                 EmbedderMsg::HistoryChanged(urls, current) => {
                     self.current_url = Some(urls[current].clone());
@@ -453,10 +442,10 @@ where
                     self.window.set_fullscreen(state);
                 },
                 EmbedderMsg::LoadStart => {
-                    self.loading_state = Some(LoadingState::Connecting);
+                    // FIXME: surface the loading state in the UI somehow
                 },
                 EmbedderMsg::LoadComplete => {
-                    self.loading_state = Some(LoadingState::Loaded);
+                    // FIXME: surface the loading state in the UI somehow
                 },
                 EmbedderMsg::CloseBrowser => {
                     // TODO: close the appropriate "tab".