xilem_web: Fix message type of AnyDomView and add .boxed() combin…

…ator (linebender#460)

I guess I missed this when adding linebender#408, the doc-test should ensure that
`Box<AnyDomView>` is now really a `DomView`.

---------

Co-authored-by: Daniel McNab <[email protected]>

xilem_web/src/lib.rs

@@ -88,7 +88,7 @@ where
 }
 
 /// A view which can have any [`DomView`] type, see [`AnyView`] for more details.
-pub type AnyDomView<State, Action = ()> = dyn AnyView<State, Action, ViewCtx, AnyPod>;
+pub type AnyDomView<State, Action = ()> = dyn AnyView<State, Action, ViewCtx, AnyPod, DynMessage>;
 
 /// The central [`View`] derived trait to represent DOM nodes in xilem_web, it's the base for all [`View`]s in xilem_web
 pub trait DomView<State, Action = ()>:
@@ -97,6 +97,25 @@ pub trait DomView<State, Action = ()>:
     type DomNode: DomNode<Self::Props>;
     type Props;
 
+    /// Returns a boxed type erased [`AnyDomView`]
+    ///
+    /// # Examples
+    /// ```
+    /// use xilem_web::{elements::html::div, DomView};
+    ///
+    /// # fn view<State: 'static>() -> impl DomView<State> {
+    /// div("a label").boxed()
+    /// # }
+    /// ```
+    fn boxed(self) -> Box<AnyDomView<State, Action>>
+    where
+        State: 'static,
+        Action: 'static,
+        Self: Sized,
+    {
+        Box::new(self)
+    }
+
     /// See [`adapt`](`core::adapt`)
     fn adapt<ParentState, ParentAction, ProxyFn>(
         self,