Fix `missing_debug_implementations` in Xilem Core (#739)

This also updates to use `core::error::Error` now that it is stable.

xilem/src/driver.rs

@@ -52,8 +52,12 @@ impl RawProxy for MasonryProxy {
             }
         }
     }
+    fn dyn_debug(&self) -> &dyn std::fmt::Debug {
+        self
+    }
 }
 
+#[derive(Debug)]
 pub struct MasonryProxy(pub(crate) EventLoopProxy);
 
 impl MasonryProxy {

xilem_core/src/any_view.rs

@@ -166,6 +166,7 @@ where
 /// The state used by [`AnyView`].
 #[doc(hidden)]
 #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+#[derive(Debug)]
 pub struct AnyViewState {
     inner_state: Box<dyn Any>,
     /// The generation is the value which is shown

xilem_core/src/deferred.rs

@@ -3,7 +3,7 @@
 
 use alloc::boxed::Box;
 use alloc::sync::Arc;
-use core::fmt::Display;
+use core::fmt::{Debug, Display};
 use core::marker::PhantomData;
 
 use crate::{DynMessage, Message, NoElement, View, ViewId, ViewPathTracker};
@@ -47,9 +47,18 @@ pub trait RawProxy<Message = DynMessage>: Send + Sync + 'static {
     //
     // e.g. an `Option<Arc<dyn FnMut(ProxyError, ProxyMessageId?)>>`?
     fn send_message(&self, path: Arc<[ViewId]>, message: Message) -> Result<(), ProxyError>;
+    /// Get the debug formatter for this proxy type.
+    fn dyn_debug(&self) -> &dyn Debug;
+}
+
+impl<Message: 'static> Debug for dyn RawProxy<Message> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        self.dyn_debug().fmt(f)
+    }
 }
 
 /// A way to send a message of an expected type to a specific view.
+#[derive(Debug)]
 pub struct MessageProxy<M: Message> {
     proxy: Arc<dyn RawProxy<DynMessage>>,
     path: Arc<[ViewId]>,
@@ -109,10 +118,8 @@ pub enum ProxyError {
     ///
     /// This likely requires async error handling to happen.
     ViewExpired(DynMessage, Arc<[ViewId]>),
-    #[allow(missing_docs)]
-    Other(&'static str),
-    // TODO: When core::error::Error is stabilised
-    // Other(Box<dyn core::error::Error + Send>),
+    /// An error specific to the driver being used.
+    Other(Box<dyn core::error::Error + Send>),
 }
 
 // Is it fine to use thiserror in this crate?
@@ -123,17 +130,16 @@ impl Display for ProxyError {
             ProxyError::ViewExpired(_, _) => {
                 f.write_fmt(format_args!("the corresponding view is no longer present"))
             }
-
-            ProxyError::Other(inner) => inner.fmt(f),
+            ProxyError::Other(inner) => Display::fmt(inner, f),
         }
     }
 }
 
-// impl std::error::Error for ProxyError {
-//     fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-//         match self {
-//             ProxyError::Other(inner) => inner.source(),
-//             _ => None,
-//         }
-//     }
-// }
+impl core::error::Error for ProxyError {
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
+        match self {
+            ProxyError::Other(inner) => inner.source(),
+            _ => None,
+        }
+    }
+}

xilem_core/src/docs.rs

@@ -38,6 +38,7 @@
 use crate::{run_once, View, ViewPathTracker};
 
 /// A type used for documentation
+#[derive(Debug)]
 pub enum Fake {}
 
 impl ViewPathTracker for Fake {
@@ -63,6 +64,7 @@ pub trait DocsView<State, Action = ()>: View<State, Action, Fake> {}
 impl<V, State, Action> DocsView<State, Action> for V where V: View<State, Action, Fake> {}
 
 /// A state type usable in a component
+#[derive(Debug)]
 pub struct State;
 
 /// A minimal component.

xilem_core/src/element.rs

@@ -87,6 +87,7 @@ where
 /// correct `State` and `Action` types), as they do not need to actually add an element to the sequence.
 ///
 /// These views can also as the `alongside_view` in [`fork`](crate::fork).
+#[derive(Debug)]
 pub struct NoElement;
 
 impl ViewElement for NoElement {

xilem_core/src/lib.rs

@@ -24,7 +24,6 @@
 #![warn(clippy::print_stdout, clippy::print_stderr)]
 // TODO: Remove any items listed as "Deferred"
 #![deny(clippy::trivially_copy_pass_by_ref)]
-#![expect(missing_debug_implementations, reason = "Deferred: Noisy")]
 #![expect(unused_qualifications, reason = "Deferred: Noisy")]
 #![expect(single_use_lifetimes, reason = "Deferred: Noisy")]
 #![expect(clippy::exhaustive_enums, reason = "Deferred: Noisy")]

xilem_core/src/message.rs

@@ -11,7 +11,7 @@ use core::ops::Deref;
 /// The possible outcomes from a [`View::message`]
 ///
 /// [`View::message`]: crate::View::message
-#[derive(Default)]
+#[derive(Default, Debug)]
 pub enum MessageResult<Action, Message = DynMessage> {
     /// An action for a parent message handler to use
     ///

xilem_core/src/sequence.rs

@@ -197,6 +197,7 @@ where
 
 /// The state used to implement `ViewSequence` for `Option<impl ViewSequence>`
 #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+#[derive(Debug)]
 pub struct OptionSeqState<InnerState> {
     /// The current state.
     ///
@@ -341,6 +342,7 @@ where
 // This is managed in [`create_generational_view_id`] and [`view_id_to_index_generation`]
 #[doc(hidden)]
 #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+#[derive(Debug)]
 pub struct VecViewState<InnerState> {
     inner_states: Vec<InnerState>,
 

xilem_core/src/view.rs

@@ -206,6 +206,7 @@ where
 }
 
 #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+#[derive(Debug)]
 pub struct RcState<ViewState> {
     view_state: ViewState,
     /// This is a flag that is set, when an inner view signifies that it requires a rebuild (via [`MessageResult::RequestRebuild`]).

xilem_core/src/views/adapt.rs

@@ -6,6 +6,7 @@ use core::marker::PhantomData;
 use crate::{MessageResult, Mut, View, ViewId, ViewMarker, ViewPathTracker};
 
 /// A view that wraps a child view and modifies the state that callbacks have access to.
+#[derive(Debug)]
 pub struct Adapt<
     ParentState,
     ParentAction,
@@ -37,6 +38,7 @@ pub struct Adapt<
 ///
 /// The closure passed to [`Adapt`] should call this thunk with the child's
 /// app state.
+#[derive(Debug)]
 pub struct AdaptThunk<'a, ChildState, ChildAction, Context, ChildView, Message>
 where
     Context: ViewPathTracker,

xilem_core/src/views/fork.rs

@@ -20,6 +20,7 @@ pub fn fork<Active, Alongside>(
 }
 
 /// The view for [`fork`].
+#[derive(Debug)]
 pub struct Fork<Active, Alongside> {
     active_view: Active,
     alongside_view: Alongside,

xilem_core/src/views/map_action.rs

@@ -1,23 +1,38 @@
 // Copyright 2024 the Xilem Authors
 // SPDX-License-Identifier: Apache-2.0
 
-use core::marker::PhantomData;
+use core::{fmt::Debug, marker::PhantomData};
 
 use crate::{Mut, View, ViewId, ViewMarker, ViewPathTracker};
 
 /// A view that maps a child [`View<State,ChildAction,_>`] to [`View<State,ParentAction,_>`] while providing mutable access to `State` in the map function.
 ///
-/// This is very similar to the Elm architecture, where the parent view can update state based on the action message from the child view.
+/// This is very similar to the Elm architecture, where the parent view can update state based on the action message from the child view
 pub struct MapAction<
+    V,
     State,
     ParentAction,
     ChildAction,
-    V,
+    Context,
+    Message,
+    // This default only exists for documentation purposes.
     F = fn(&mut State, ChildAction) -> ParentAction,
 > {
     map_fn: F,
     child: V,
-    phantom: PhantomData<fn() -> (State, ParentAction, ChildAction)>,
+    phantom: PhantomData<fn() -> (State, ParentAction, ChildAction, Context, Message)>,
+}
+
+impl<V, State, ParentAction, ChildAction, Context, Message, F> Debug
+    for MapAction<V, State, ParentAction, ChildAction, Context, Message, F>
+where
+    V: Debug,
+{
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("MapAction")
+            .field("child", &self.child)
+            .finish_non_exhaustive()
+    }
 }
 
 /// A view that maps a child [`View<State,ChildAction,_>`] to [`View<State,ParentAction,_>`] while providing mutable access to `State` in the map function.
@@ -52,7 +67,7 @@ pub struct MapAction<
 pub fn map_action<State, ParentAction, ChildAction, Context: ViewPathTracker, Message, V, F>(
     view: V,
     map_fn: F,
-) -> MapAction<State, ParentAction, ChildAction, V, F>
+) -> MapAction<V, State, ParentAction, ChildAction, Context, Message, F>
 where
     State: 'static,
     ParentAction: 'static,
@@ -67,19 +82,21 @@ where
     }
 }
 
-impl<State, ParentAction, ChildAction, V, F> ViewMarker
-    for MapAction<State, ParentAction, ChildAction, V, F>
+impl<V, State, ParentAction, ChildAction, F, Context, Message> ViewMarker
+    for MapAction<V, State, ParentAction, ChildAction, Context, Message, F>
 {
 }
-impl<State, ParentAction, ChildAction, Context: ViewPathTracker, Message, V, F>
+impl<V, State, ParentAction, ChildAction, Context, Message, F>
     View<State, ParentAction, Context, Message>
-    for MapAction<State, ParentAction, ChildAction, V, F>
+    for MapAction<V, State, ParentAction, ChildAction, Context, Message, F>
 where
+    V: View<State, ChildAction, Context, Message>,
     State: 'static,
     ParentAction: 'static,
     ChildAction: 'static,
-    V: View<State, ChildAction, Context, Message>,
     F: Fn(&mut State, ChildAction) -> ParentAction + 'static,
+    Context: ViewPathTracker + 'static,
+    Message: 'static,
 {
     type ViewState = V::ViewState;
     type Element = V::Element;

xilem_core/src/views/map_state.rs

@@ -1,7 +1,7 @@
 // Copyright 2024 the Xilem Authors
 // SPDX-License-Identifier: Apache-2.0
 
-use core::marker::PhantomData;
+use core::{fmt::Debug, marker::PhantomData};
 
 use crate::{MessageResult, Mut, View, ViewId, ViewMarker, ViewPathTracker};
 
@@ -14,6 +14,18 @@ pub struct MapState<V, F, ParentState, ChildState, Action, Context, Message> {
     phantom: PhantomData<fn(ParentState) -> (ChildState, Action, Context, Message)>,
 }
 
+impl<V, F, ParentState, ChildState, Action, Context, Message> Debug
+    for MapState<V, F, ParentState, ChildState, Action, Context, Message>
+where
+    V: Debug,
+{
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("MapAction")
+            .field("child", &self.child)
+            .finish_non_exhaustive()
+    }
+}
+
 /// A view that "extracts" state from a [`View<ParentState,_,_>`] to [`View<ChildState,_,_>`].
 /// This allows modularization of views based on their state.
 ///

xilem_core/src/views/memoize.rs

@@ -1,8 +1,8 @@
 // Copyright 2024 the Xilem Authors
 // SPDX-License-Identifier: Apache-2.0
 
-use core::marker::PhantomData;
 use core::mem::size_of;
+use core::{fmt::Debug, marker::PhantomData};
 
 use crate::{MessageResult, Mut, View, ViewId, ViewMarker, ViewPathTracker};
 
@@ -10,10 +10,22 @@ use crate::{MessageResult, Mut, View, ViewId, ViewMarker, ViewPathTracker};
 ///
 /// The story of Memoization in Xilem is still being worked out,
 /// so the details of this view might change.
-pub struct Memoize<Data, InitView, State, Action> {
+pub struct Memoize<Data, InitView, State, Action, Context, Message> {
     data: Data,
     init_view: InitView,
-    phantom: PhantomData<fn() -> (State, Action)>,
+    phantom: PhantomData<fn() -> (State, Action, Context, Message)>,
+}
+
+impl<Data, InitView, State, Action, Context, Message> Debug
+    for Memoize<Data, InitView, State, Action, Context, Message>
+where
+    Data: Debug,
+{
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("Memoize")
+            .field("data", &self.data)
+            .finish_non_exhaustive()
+    }
 }
 
 const NON_CAPTURING_CLOSURE: &str = "
@@ -41,7 +53,7 @@ It's not possible in Rust currently to check whether the (content of the) callba
 pub fn memoize<State, Action, Context, Message, Data, V, InitView>(
     data: Data,
     init_view: InitView,
-) -> Memoize<Data, InitView, State, Action>
+) -> Memoize<Data, InitView, State, Action, Context, Message>
 where
     Data: PartialEq + 'static,
     InitView: Fn(&Data) -> V + 'static,
@@ -59,19 +71,24 @@ where
 }
 
 #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+#[derive(Debug)]
 pub struct MemoizeState<V, VState> {
     view: V,
     view_state: VState,
     dirty: bool,
 }
 
-impl<Data, ViewFn, State, Action> ViewMarker for Memoize<Data, ViewFn, State, Action> {}
+impl<Data, ViewFn, State, Action, Context, Message> ViewMarker
+    for Memoize<Data, ViewFn, State, Action, Context, Message>
+{
+}
 impl<State, Action, Context, Data, V, ViewFn, Message> View<State, Action, Context, Message>
-    for Memoize<Data, ViewFn, State, Action>
+    for Memoize<Data, ViewFn, State, Action, Context, Message>
 where
     State: 'static,
     Action: 'static,
-    Context: ViewPathTracker,
+    Context: ViewPathTracker + 'static,
+    Message: 'static,
     Data: PartialEq + 'static,
     V: View<State, Action, Context, Message>,
     ViewFn: Fn(&Data) -> V + 'static,
@@ -140,6 +157,12 @@ pub struct Frozen<InitView, State, Action> {
     phantom: PhantomData<fn() -> (State, Action)>,
 }
 
+impl<InitView, State, Action> Debug for Frozen<InitView, State, Action> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("Frozen").finish_non_exhaustive()
+    }
+}
+
 /// This view can be used, when the view returned by `init_view` doesn't access the `State`, other than in event callbacks
 /// It only evaluates the `init_view` once, when it's being created.
 ///

xilem_core/src/views/one_of.rs

@@ -22,6 +22,7 @@ pub trait PhantomElementCtx: ViewPathTracker {
 
 /// A [`View`] which can be one of nine inner view types.
 #[allow(missing_docs)] // On variants
+#[derive(Debug)]
 pub enum OneOf<A = (), B = (), C = (), D = (), E = (), F = (), G = (), H = (), I = ()> {
     A(A),
     B(B),
@@ -552,6 +553,7 @@ mod hidden {
     use crate::{View, ViewMarker};
 
     #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+    #[derive(Debug)]
     pub enum Never {}
 
     impl ViewMarker for Never {}
@@ -592,6 +594,7 @@ mod hidden {
     }
     /// The state used to implement `View` for `OneOfN`
     #[allow(unnameable_types)] // reason: Implementation detail, public because of trait visibility rules
+    #[derive(Debug)]
     pub struct OneOfState<A, B, C, D, E, F, G, H, I> {
         /// The current state of the inner view or view sequence.
         pub(super) inner_state: super::OneOf<A, B, C, D, E, F, G, H, I>,

xilem_core/src/views/run_once.rs

@@ -75,6 +75,12 @@ pub struct RunOnce<F> {
     once: F,
 }
 
+impl<F> Debug for RunOnce<F> {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        f.debug_struct("RunOnce").finish_non_exhaustive()
+    }
+}
+
 impl<F> ViewMarker for RunOnce<F> {}
 impl<F, State, Action, Context, Message> View<State, Action, Context, Message> for RunOnce<F>
 where

xilem_web/src/lib.rs

@@ -218,7 +218,10 @@ pub trait DomView<State, Action = ()>:
     }
 
     /// See [`map_action`](`core::map_action`)
-    fn map_action<ParentAction, F>(self, f: F) -> MapAction<State, ParentAction, Action, Self, F>
+    fn map_action<ParentAction, F>(
+        self,
+        f: F,
+    ) -> MapAction<Self, State, ParentAction, Action, ViewCtx, DynMessage, F>
     where
         State: 'static,
         ParentAction: 'static,