Replace Command with a new Task API with chain support

runtime/src/lib.rs

@@ -10,7 +10,6 @@
 )]
 #![cfg_attr(docsrs, feature(doc_auto_cfg))]
 pub mod clipboard;
-pub mod command;
 pub mod font;
 pub mod keyboard;
 pub mod overlay;
@@ -22,6 +21,8 @@ pub mod window;
 #[cfg(feature = "multi-window")]
 pub mod multi_window;
 
+mod task;
+
 // We disable debug capabilities on release builds unless the `debug` feature
 // is explicitly enabled.
 #[cfg(feature = "debug")]
@@ -34,8 +35,81 @@ mod debug;
 pub use iced_core as core;
 pub use iced_futures as futures;
 
-pub use command::Command;
 pub use debug::Debug;
-pub use font::Font;
 pub use program::Program;
+pub use task::Task;
 pub use user_interface::UserInterface;
+
+use crate::core::widget;
+use crate::futures::futures::channel::oneshot;
+
+use std::borrow::Cow;
+use std::fmt;
+
+/// An action that the iced runtime can perform.
+pub enum Action<T> {
+    /// Output some value.
+    Output(T),
+
+    /// Load a font from its bytes.
+    LoadFont {
+        /// The bytes of the font to load.
+        bytes: Cow<'static, [u8]>,
+        /// The channel to send back the load result.
+        channel: oneshot::Sender<Result<(), font::Error>>,
+    },
+
+    /// Run a widget operation.
+    Widget(Box<dyn widget::Operation<()> + Send>),
+
+    /// Run a clipboard action.
+    Clipboard(clipboard::Action),
+
+    /// Run a window action.
+    Window(window::Action),
+
+    /// Run a system action.
+    System(system::Action),
+}
+
+impl<T> Action<T> {
+    /// Creates a new [`Action::Widget`] with the given [`widget::Operation`].
+    pub fn widget(operation: impl widget::Operation<()> + 'static) -> Self {
+        Self::Widget(Box::new(operation))
+    }
+
+    fn output<O>(self) -> Result<T, Action<O>> {
+        match self {
+            Action::Output(output) => Ok(output),
+            Action::LoadFont { bytes, channel } => {
+                Err(Action::LoadFont { bytes, channel })
+            }
+            Action::Widget(operation) => Err(Action::Widget(operation)),
+            Action::Clipboard(action) => Err(Action::Clipboard(action)),
+            Action::Window(action) => Err(Action::Window(action)),
+            Action::System(action) => Err(Action::System(action)),
+        }
+    }
+}
+
+impl<T> fmt::Debug for Action<T>
+where
+    T: fmt::Debug,
+{
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self {
+            Action::Output(output) => write!(f, "Action::Output({output:?})"),
+            Action::LoadFont { .. } => {
+                write!(f, "Action::LoadFont")
+            }
+            Action::Widget { .. } => {
+                write!(f, "Action::Widget")
+            }
+            Action::Clipboard(action) => {
+                write!(f, "Action::Clipboard({action:?})")
+            }
+            Action::Window(_) => write!(f, "Action::Window"),
+            Action::System(action) => write!(f, "Action::System({action:?})"),
+        }
+    }
+}