Reintroduce backend selection through ICED_BACKEND env var

graphics/src/error.rs

@@ -1,5 +1,7 @@
+//! See what can go wrong when creating graphical backends.
+
 /// An error that occurred while creating an application's graphical context.
-#[derive(Debug, thiserror::Error)]
+#[derive(Debug, Clone, PartialEq, Eq, thiserror::Error)]
 pub enum Error {
     /// The requested backend version is not supported.
     #[error("the requested backend version is not supported")]
@@ -11,9 +13,30 @@ pub enum Error {
 
     /// A suitable graphics adapter or device could not be found.
     #[error("a suitable graphics adapter or device could not be found")]
-    GraphicsAdapterNotFound,
+    GraphicsAdapterNotFound {
+        /// The name of the backend where the error happened
+        backend: &'static str,
+        /// The reason why this backend could not be used
+        reason: Reason,
+    },
 
     /// An error occurred in the context's internal backend
     #[error("an error occurred in the context's internal backend")]
     BackendError(String),
+
+    /// Multiple errors occurred
+    #[error("multiple errors occurred: {0:?}")]
+    List(Vec<Self>),
+}
+
+/// The reason why a graphics adapter could not be found
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum Reason {
+    /// The backend did not match the preference
+    DidNotMatch {
+        /// The preferred backend
+        preferred_backend: String,
+    },
+    /// The request to create the backend failed
+    RequestFailed(String),
 }