Add explicit error handling to image loading

runtime/src/image.rs

@@ -3,13 +3,13 @@ use crate::core::image::Handle;
 use crate::futures::futures::channel::oneshot;
 use crate::task::{self, Task};
 
-pub use crate::core::image::Allocation;
+pub use crate::core::image::{Allocation, Error};
 
 /// An image action.
 #[derive(Debug)]
 pub enum Action {
     /// Allocates the given [`Handle`].
-    Allocate(Handle, oneshot::Sender<Allocation>),
+    Allocate(Handle, oneshot::Sender<Result<Allocation, Error>>),
 }
 
 /// Allocates an image [`Handle`].
@@ -17,7 +17,7 @@ pub enum Action {
 /// When you obtain an [`Allocation`] explicitly, you get the guarantee
 /// that using a [`Handle`] will draw the corresponding image immediately
 /// in the next frame.
-pub fn allocate(handle: impl Into<Handle>) -> Task<Allocation> {
+pub fn allocate(handle: impl Into<Handle>) -> Task<Result<Allocation, Error>> {
     task::oneshot(|sender| {
         crate::Action::Image(Action::Allocate(handle.into(), sender))
     })

runtime/src/task.rs

@@ -390,6 +390,20 @@ impl<T, E> Task<Result<T, E>> {
             result.map_or_else(|error| Task::done(Err(error)), &f)
         })
     }
+
+    /// Maps the error type of this [`Task`] to a different one using the given
+    /// function.
+    pub fn map_err<E2>(
+        self,
+        f: impl Fn(E) -> E2 + MaybeSend + 'static,
+    ) -> Task<Result<T, E2>>
+    where
+        T: MaybeSend + 'static,
+        E: MaybeSend + 'static,
+        E2: MaybeSend + 'static,
+    {
+        self.map(move |result| result.map_err(&f))
+    }
 }
 
 impl<T> Default for Task<T> {