Replace stateful widgets with new `iced_pure` API

1 files changed, 176 insertions, 132 deletions

diff --git a/lazy/src/component.rs b/lazy/src/component.rs
index eac7e8ee..ea4d7311 100644
--- a/lazy/src/component.rs
+++ b/lazy/src/component.rs
@@ -1,17 +1,16 @@
 //! Build and reuse custom widgets using The Elm Architecture.
-use crate::{Cache, CacheBuilder};
-
 use iced_native::event;
 use iced_native::layout::{self, Layout};
 use iced_native::mouse;
 use iced_native::overlay;
 use iced_native::renderer;
+use iced_native::widget::tree::{self, Tree};
 use iced_native::{
     Clipboard, Element, Length, Point, Rectangle, Shell, Size, Widget,
 };
 
 use ouroboros::self_referencing;
-use std::cell::RefCell;
+use std::cell::{Ref, RefCell};
 use std::marker::PhantomData;
 
 /// A reusable, custom widget that uses The Elm Architecture.
@@ -28,17 +27,24 @@ use std::marker::PhantomData;
 /// Additionally, a [`Component`] is capable of producing a `Message` to notify
 /// the parent application of any relevant interactions.
 pub trait Component<Message, Renderer> {
+    /// The internal state of this [`Component`].
+    type State: Default;
+
     /// The type of event this [`Component`] handles internally.
     type Event;
 
     /// Processes an [`Event`](Component::Event) and updates the [`Component`] state accordingly.
     ///
     /// It can produce a `Message` for the parent application.
-    fn update(&mut self, event: Self::Event) -> Option<Message>;
+    fn update(
+        &mut self,
+        state: &mut Self::State,
+        event: Self::Event,
+    ) -> Option<Message>;
 
     /// Produces the widgets of the [`Component`], which may trigger an [`Event`](Component::Event)
     /// on user interaction.
-    fn view(&mut self) -> Element<'_, Self::Event, Renderer>;
+    fn view(&self, state: &Self::State) -> Element<'_, Self::Event, Renderer>;
 }
 
 /// Turns an implementor of [`Component`] into an [`Element`] that can be
@@ -48,6 +54,7 @@ pub fn view<'a, C, Message, Renderer>(
 ) -> Element<'a, Message, Renderer>
 where
     C: Component<Message, Renderer> + 'a,
+    C::State: 'static,
     Message: 'a,
     Renderer: iced_native::Renderer + 'a,
 {
@@ -56,36 +63,48 @@ where
             StateBuilder {
                 component: Box::new(component),
                 message: PhantomData,
-                cache_builder: |state| {
-                    Some(
-                        CacheBuilder {
-                            element: state.view(),
-                            overlay_builder: |_| None,
-                        }
-                        .build(),
-                    )
-                },
+                state: PhantomData,
+                element_builder: |_| None,
             }
             .build(),
         )),
     })
 }
 
-struct Instance<'a, Message, Renderer, Event> {
-    state: RefCell<Option<State<'a, Message, Renderer, Event>>>,
+struct Instance<'a, Message, Renderer, Event, S> {
+    state: RefCell<Option<State<'a, Message, Renderer, Event, S>>>,
 }
 
 #[self_referencing]
-struct State<'a, Message: 'a, Renderer: 'a, Event: 'a> {
-    component: Box<dyn Component<Message, Renderer, Event = Event> + 'a>,
+struct State<'a, Message: 'a, Renderer: 'a, Event: 'a, S: 'a> {
+    component:
+        Box<dyn Component<Message, Renderer, Event = Event, State = S> + 'a>,
     message: PhantomData<Message>,
+    state: PhantomData<S>,
 
-    #[borrows(mut component)]
+    #[borrows(component)]
     #[covariant]
-    cache: Option<Cache<'this, Event, Renderer>>,
+    element: Option<Element<'this, Event, Renderer>>,
 }
 
-impl<'a, Message, Renderer, Event> Instance<'a, Message, Renderer, Event> {
+impl<'a, Message, Renderer, Event, S> Instance<'a, Message, Renderer, Event, S>
+where
+    S: Default,
+{
+    fn rebuild_element(&self, state: &S) {
+        let heads = self.state.borrow_mut().take().unwrap().into_heads();
+
+        *self.state.borrow_mut() = Some(
+            StateBuilder {
+                component: heads.component,
+                message: PhantomData,
+                state: PhantomData,
+                element_builder: |component| Some(component.view(state)),
+            }
+            .build(),
+        );
+    }
+
     fn with_element<T>(
         &self,
         f: impl FnOnce(&Element<'_, Event, Renderer>) -> T,
@@ -101,34 +120,43 @@ impl<'a, Message, Renderer, Event> Instance<'a, Message, Renderer, Event> {
             .borrow_mut()
             .as_mut()
             .unwrap()
-            .with_cache_mut(|cache| {
-                let mut element = cache.take().unwrap().into_heads().element;
-                let result = f(&mut element);
-
-                *cache = Some(
-                    CacheBuilder {
-                        element,
-                        overlay_builder: |_| None,
-                    }
-                    .build(),
-                );
-
-                result
-            })
+            .with_element_mut(|element| f(element.as_mut().unwrap()))
     }
 }
 
-impl<'a, Message, Renderer, Event> Widget<Message, Renderer>
-    for Instance<'a, Message, Renderer, Event>
+impl<'a, Message, Renderer, Event, S> Widget<Message, Renderer>
+    for Instance<'a, Message, Renderer, Event, S>
 where
+    S: 'static + Default,
     Renderer: iced_native::Renderer,
 {
+    fn tag(&self) -> tree::Tag {
+        struct Tag<T>(T);
+        tree::Tag::of::<Tag<S>>()
+    }
+
+    fn state(&self) -> tree::State {
+        tree::State::new(S::default())
+    }
+
+    fn children(&self) -> Vec<Tree> {
+        self.rebuild_element(&S::default());
+        self.with_element(|element| vec![Tree::new(element)])
+    }
+
+    fn diff(&self, tree: &mut Tree) {
+        self.rebuild_element(tree.state.downcast_ref());
+        self.with_element(|element| {
+            tree.diff_children(std::slice::from_ref(&element))
+        })
+    }
+
     fn width(&self) -> Length {
-        self.with_element(|element| element.width())
+        self.with_element(|element| element.as_widget().width())
     }
 
     fn height(&self) -> Length {
-        self.with_element(|element| element.height())
+        self.with_element(|element| element.as_widget().height())
     }
 
     fn layout(
@@ -136,11 +164,14 @@ where
         renderer: &Renderer,
         limits: &layout::Limits,
     ) -> layout::Node {
-        self.with_element(|element| element.layout(renderer, limits))
+        self.with_element(|element| {
+            element.as_widget().layout(renderer, limits)
+        })
     }
 
     fn on_event(
         &mut self,
+        tree: &mut Tree,
         event: iced_native::Event,
         layout: Layout<'_>,
         cursor_position: Point,
@@ -152,7 +183,8 @@ where
         let mut local_shell = Shell::new(&mut local_messages);
 
         let event_status = self.with_element_mut(|element| {
-            element.on_event(
+            element.as_widget_mut().on_event(
+                &mut tree.children[0],
                 event,
                 layout,
                 cursor_position,
@@ -165,37 +197,31 @@ where
         local_shell.revalidate_layout(|| shell.invalidate_layout());
 
         if !local_messages.is_empty() {
-            let mut component = self
-                .state
-                .borrow_mut()
-                .take()
-                .unwrap()
-                .into_heads()
-                .component;
-
-            for message in local_messages
-                .into_iter()
-                .filter_map(|message| component.update(message))
-            {
+            let mut heads = self.state.take().unwrap().into_heads();
+
+            for message in local_messages.into_iter().filter_map(|message| {
+                heads
+                    .component
+                    .update(tree.state.downcast_mut::<S>(), message)
+            }) {
                 shell.publish(message);
             }
 
-            *self.state.borrow_mut() = Some(
+            self.state = RefCell::new(Some(
                 StateBuilder {
-                    component,
+                    component: heads.component,
                     message: PhantomData,
-                    cache_builder: |state| {
-                        Some(
-                            CacheBuilder {
-                                element: state.view(),
-                                overlay_builder: |_| None,
-                            }
-                            .build(),
-                        )
+                    state: PhantomData,
+                    element_builder: |state| {
+                        Some(state.view(tree.state.downcast_ref::<S>()))
                     },
                 }
                 .build(),
-            );
+            ));
+
+            self.with_element(|element| {
+                tree.diff_children(std::slice::from_ref(&element))
+            });
 
             shell.invalidate_layout();
         }
@@ -205,6 +231,7 @@ where
 
     fn draw(
         &self,
+        tree: &Tree,
         renderer: &mut Renderer,
         theme: &Renderer::Theme,
         style: &renderer::Style,
@@ -213,7 +240,8 @@ where
         viewport: &Rectangle,
     ) {
         self.with_element(|element| {
-            element.draw(
+            element.as_widget().draw(
+                &tree.children[0],
                 renderer,
                 theme,
                 style,
@@ -226,13 +254,15 @@ where
 
     fn mouse_interaction(
         &self,
+        tree: &Tree,
         layout: Layout<'_>,
         cursor_position: Point,
         viewport: &Rectangle,
         renderer: &Renderer,
     ) -> mouse::Interaction {
         self.with_element(|element| {
-            element.mouse_interaction(
+            element.as_widget().mouse_interaction(
+                &tree.children[0],
                 layout,
                 cursor_position,
                 viewport,
@@ -241,63 +271,72 @@ where
         })
     }
 
-    fn overlay(
-        &mut self,
+    fn overlay<'b>(
+        &'b self,
+        tree: &'b mut Tree,
         layout: Layout<'_>,
         renderer: &Renderer,
-    ) -> Option<overlay::Element<'_, Message, Renderer>> {
-        let has_overlay = self
-            .state
-            .borrow_mut()
-            .as_mut()
-            .unwrap()
-            .with_cache_mut(|cache| {
-                let element = cache.take().unwrap().into_heads().element;
-
-                *cache = Some(
-                    CacheBuilder {
-                        element,
-                        overlay_builder: |element| {
-                            element.overlay(layout, renderer)
-                        },
-                    }
-                    .build(),
-                );
-
-                cache
+    ) -> Option<overlay::Element<'b, Message, Renderer>> {
+        let overlay = OverlayBuilder {
+            instance: self,
+            instance_ref_builder: |instance| instance.state.borrow(),
+            tree,
+            types: PhantomData,
+            overlay_builder: |instance, tree| {
+                instance
                     .as_ref()
                     .unwrap()
-                    .borrow_overlay()
+                    .borrow_element()
                     .as_ref()
-                    .map(|overlay| overlay.position())
-            });
+                    .unwrap()
+                    .as_widget()
+                    .overlay(&mut tree.children[0], layout, renderer)
+            },
+        }
+        .build();
+
+        let has_overlay = overlay.with_overlay(|overlay| {
+            overlay.as_ref().map(overlay::Element::position)
+        });
 
         has_overlay.map(|position| {
             overlay::Element::new(
                 position,
-                Box::new(Overlay { instance: self }),
+                Box::new(OverlayInstance {
+                    overlay: Some(overlay),
+                }),
             )
         })
     }
 }
 
-struct Overlay<'a, 'b, Message, Renderer, Event> {
-    instance: &'b mut Instance<'a, Message, Renderer, Event>,
+#[self_referencing]
+struct Overlay<'a, 'b, Message, Renderer, Event, S> {
+    instance: &'a Instance<'b, Message, Renderer, Event, S>,
+    tree: &'a mut Tree,
+    types: PhantomData<(Message, Event, S)>,
+
+    #[borrows(instance)]
+    #[covariant]
+    instance_ref: Ref<'this, Option<State<'a, Message, Renderer, Event, S>>>,
+
+    #[borrows(instance_ref, mut tree)]
+    #[covariant]
+    overlay: Option<overlay::Element<'this, Event, Renderer>>,
+}
+
+struct OverlayInstance<'a, 'b, Message, Renderer, Event, S> {
+    overlay: Option<Overlay<'a, 'b, Message, Renderer, Event, S>>,
 }
 
-impl<'a, 'b, Message, Renderer, Event>
-    Overlay<'a, 'b, Message, Renderer, Event>
+impl<'a, 'b, Message, Renderer, Event, S>
+    OverlayInstance<'a, 'b, Message, Renderer, Event, S>
 {
     fn with_overlay_maybe<T>(
         &self,
         f: impl FnOnce(&overlay::Element<'_, Event, Renderer>) -> T,
     ) -> Option<T> {
-        self.instance
-            .state
-            .borrow()
-            .as_ref()
-            .unwrap()
-            .borrow_cache()
+        self.overlay
             .as_ref()
             .unwrap()
             .borrow_overlay()
@@ -306,27 +345,21 @@ impl<'a, 'b, Message, Renderer, Event>
     }
 
     fn with_overlay_mut_maybe<T>(
-        &self,
+        &mut self,
         f: impl FnOnce(&mut overlay::Element<'_, Event, Renderer>) -> T,
     ) -> Option<T> {
-        self.instance
-            .state
-            .borrow_mut()
+        self.overlay
             .as_mut()
             .unwrap()
-            .with_cache_mut(|cache| {
-                cache
-                    .as_mut()
-                    .unwrap()
-                    .with_overlay_mut(|overlay| overlay.as_mut().map(f))
-            })
+            .with_overlay_mut(|overlay| overlay.as_mut().map(f))
     }
 }
 
-impl<'a, 'b, Message, Renderer, Event> overlay::Overlay<Message, Renderer>
-    for Overlay<'a, 'b, Message, Renderer, Event>
+impl<'a, 'b, Message, Renderer, Event, S> overlay::Overlay<Message, Renderer>
+    for OverlayInstance<'a, 'b, Message, Renderer, Event, S>
 where
     Renderer: iced_native::Renderer,
+    S: 'static + Default,
 {
     fn layout(
         &self,
@@ -401,32 +434,43 @@ where
         local_shell.revalidate_layout(|| shell.invalidate_layout());
 
         if !local_messages.is_empty() {
-            let mut component =
-                self.instance.state.take().unwrap().into_heads().component;
-
-            for message in local_messages
-                .into_iter()
-                .filter_map(|message| component.update(message))
-            {
+            let overlay = self.overlay.take().unwrap().into_heads();
+            let mut heads = overlay.instance.state.take().unwrap().into_heads();
+
+            for message in local_messages.into_iter().filter_map(|message| {
+                heads
+                    .component
+                    .update(overlay.tree.state.downcast_mut::<S>(), message)
+            }) {
                 shell.publish(message);
             }
 
-            self.instance.state = RefCell::new(Some(
+            *overlay.instance.state.borrow_mut() = Some(
                 StateBuilder {
-                    component,
+                    component: heads.component,
                     message: PhantomData,
-                    cache_builder: |state| {
-                        Some(
-                            CacheBuilder {
-                                element: state.view(),
-                                overlay_builder: |_| None,
-                            }
-                            .build(),
-                        )
+                    state: PhantomData,
+                    element_builder: |state| {
+                        Some(state.view(overlay.tree.state.downcast_ref::<S>()))
                     },
                 }
                 .build(),
-            ));
+            );
+
+            overlay.instance.with_element(|element| {
+                overlay.tree.diff_children(std::slice::from_ref(&element))
+            });
+
+            self.overlay = Some(
+                OverlayBuilder {
+                    instance: overlay.instance,
+                    instance_ref_builder: |instance| instance.state.borrow(),
+                    tree: overlay.tree,
+                    types: PhantomData,
+                    overlay_builder: |_, _| None,
+                }
+                .build(),
+            );
 
             shell.invalidate_layout();
         }