Make Application and Sandbox return a Result

src/application.rs

@@ -1,6 +1,5 @@
-use crate::{
-    window, Color, Command, Element, Executor, Settings, Subscription,
-};
+use crate::window;
+use crate::{Color, Command, Element, Executor, Settings, Subscription};
 
 /// An interactive cross-platform application.
 ///
@@ -59,7 +58,7 @@ use crate::{
 /// ```no_run
 /// use iced::{executor, Application, Command, Element, Settings, Text};
 ///
-/// pub fn main() {
+/// pub fn main() -> iced::Result {
 ///     Hello::run(Settings::default())
 /// }
 ///
@@ -204,12 +203,13 @@ pub trait Application: Sized {
     /// Runs the [`Application`].
     ///
     /// On native platforms, this method will take control of the current thread
-    /// and __will NOT return__.
+    /// and __will NOT return__ unless there is an [`Error`] during startup.
     ///
     /// It should probably be that last thing you call in your `main` function.
     ///
     /// [`Application`]: trait.Application.html
-    fn run(settings: Settings<Self::Flags>)
+    /// [`Error`]: enum.Error.html
+    fn run(settings: Settings<Self::Flags>) -> crate::Result
     where
         Self: 'static,
     {
@@ -226,15 +226,19 @@ pub trait Application: Sized {
                 ..crate::renderer::Settings::default()
             };
 
-            crate::runtime::application::run::<
+            Ok(crate::runtime::application::run::<
                 Instance<Self>,
                 Self::Executor,
                 crate::renderer::window::Compositor,
-            >(settings.into(), renderer_settings);
+            >(settings.into(), renderer_settings)?)
         }
 
         #[cfg(target_arch = "wasm32")]
-        <Instance<Self> as iced_web::Application>::run(settings.flags);
+        {
+            <Instance<Self> as iced_web::Application>::run(settings.flags);
+
+            Ok(())
+        }
     }
 }
 

src/error.rs

@@ -0,0 +1,34 @@
+use iced_futures::futures;
+
+/// An error that occurred while running an application.
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    /// The futures executor could not be created.
+    #[error("the futures executor could not be created")]
+    ExecutorCreationFailed(futures::io::Error),
+
+    /// The application window could not be created.
+    #[error("the application window could not be created")]
+    WindowCreationFailed(Box<dyn std::error::Error>),
+
+    /// A suitable graphics adapter or device could not be found.
+    #[error("a suitable graphics adapter or device could not be found")]
+    GraphicsAdapterNotFound,
+}
+
+#[cfg(not(target_arch = "wasm32"))]
+impl From<iced_winit::Error> for Error {
+    fn from(error: iced_winit::Error) -> Error {
+        match error {
+            iced_winit::Error::ExecutorCreationFailed(error) => {
+                Error::ExecutorCreationFailed(error)
+            }
+            iced_winit::Error::WindowCreationFailed(error) => {
+                Error::WindowCreationFailed(Box::new(error))
+            }
+            iced_winit::Error::GraphicsAdapterNotFound => {
+                Error::GraphicsAdapterNotFound
+            }
+        }
+    }
+}

src/lib.rs

@@ -181,6 +181,8 @@
 #![cfg_attr(docsrs, feature(doc_cfg))]
 mod application;
 mod element;
+mod error;
+mod result;
 mod sandbox;
 
 pub mod executor;
@@ -225,7 +227,9 @@ pub use widget::*;
 
 pub use application::Application;
 pub use element::Element;
+pub use error::Error;
 pub use executor::Executor;
+pub use result::Result;
 pub use sandbox::Sandbox;
 pub use settings::Settings;
 

src/result.rs

@@ -0,0 +1,6 @@
+use crate::Error;
+
+/// The result of running an [`Application`].
+///
+/// [`Application`]: trait.Application.html
+pub type Result = std::result::Result<(), Error>;

src/sandbox.rs

@@ -1,5 +1,6 @@
+use crate::executor;
 use crate::{
-    executor, Application, Color, Command, Element, Settings, Subscription,
+    Application, Color, Command, Element, Error, Settings, Subscription,
 };
 
 /// A sandboxed [`Application`].
@@ -64,7 +65,7 @@ use crate::{
 /// ```no_run
 /// use iced::{Element, Sandbox, Settings, Text};
 ///
-/// pub fn main() {
+/// pub fn main() -> iced::Result {
 ///     Hello::run(Settings::default())
 /// }
 ///
@@ -159,7 +160,7 @@ pub trait Sandbox {
     /// It should probably be that last thing you call in your `main` function.
     ///
     /// [`Sandbox`]: trait.Sandbox.html
-    fn run(settings: Settings<()>)
+    fn run(settings: Settings<()>) -> Result<(), Error>
     where
         Self: 'static + Sized,
     {