Implement stub `Clipboard` in `iced_web`

We need to figure out browser permissions and use of unstable `web-sys`
APIs

src/application.rs

@@ -305,8 +305,12 @@ where
         self.0.title()
     }
 
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message> {
-        self.0.update(message)
+    fn update(
+        &mut self,
+        message: Self::Message,
+        clipboard: &mut Clipboard,
+    ) -> Command<Self::Message> {
+        self.0.update(message, clipboard)
     }
 
     fn subscription(&self) -> Subscription<Self::Message> {

web/src/clipboard.rs

@@ -0,0 +1,21 @@
+/// A buffer for short-term storage and transfer within and between
+/// applications.
+#[derive(Debug, Clone, Copy)]
+pub struct Clipboard;
+
+impl Clipboard {
+    /// Creates a new [`Clipboard`].
+    pub fn new() -> Self {
+        Self
+    }
+
+    /// Reads the current content of the [`Clipboard`] as text.
+    pub fn read(&self) -> Option<String> {
+        unimplemented! {}
+    }
+
+    /// Writes the given text contents to the [`Clipboard`].
+    pub fn write(&mut self, _contents: String) {
+        unimplemented! {}
+    }
+}

web/src/lib.rs

@@ -59,6 +59,7 @@ use dodrio::bumpalo;
 use std::{cell::RefCell, rc::Rc};
 
 mod bus;
+mod clipboard;
 mod element;
 mod hasher;
 
@@ -67,6 +68,7 @@ pub mod subscription;
 pub mod widget;
 
 pub use bus::Bus;
+pub use clipboard::Clipboard;
 pub use css::Css;
 pub use dodrio;
 pub use element::Element;
@@ -126,7 +128,11 @@ pub trait Application {
     /// this method.
     ///
     /// Any [`Command`] returned will be executed immediately in the background.
-    fn update(&mut self, message: Self::Message) -> Command<Self::Message>;
+    fn update(
+        &mut self,
+        message: Self::Message,
+        clipboard: &mut Clipboard,
+    ) -> Command<Self::Message>;
 
     /// Returns the widgets to display in the [`Application`].
     ///
@@ -156,6 +162,8 @@ pub trait Application {
         let document = window.document().unwrap();
         let body = document.body().unwrap();
 
+        let mut clipboard = Clipboard::new();
+
         let (sender, receiver) =
             iced_futures::futures::channel::mpsc::unbounded();
 
@@ -182,7 +190,8 @@ pub trait Application {
 
         let event_loop = receiver.for_each(move |message| {
             let (command, subscription) = runtime.enter(|| {
-                let command = application.borrow_mut().update(message);
+                let command =
+                    application.borrow_mut().update(message, &mut clipboard);
                 let subscription = application.borrow().subscription();
 
                 (command, subscription)