Reinstating weak_clone and non-weak callbacks

Somehow I missed that my changes for weak callbacks broke the theme
editor. I thought I had it working with the try_get changes, but I
discovered several flaws in this approach.

In the end, ownership has been transferred to the CallbackHandle, and a
CallbackHandle can relinquish its reference to create weak graphs. This
is how weak_clone now works.

examples/theme.rs

@@ -213,28 +213,26 @@ fn optional_editor(label: &str, color: &Dynamic<ColorSource>) -> (Dynamic<bool>,
 }
 
 fn color_editor(color: &Dynamic<ColorSource>) -> impl MakeWidget {
-    let hue = color.map_each(|color| color.hue.into_positive_degrees());
+    let hue = color.map_each_cloned(|color| color.hue.into_positive_degrees());
     hue.for_each_cloned({
         let color = color.clone();
         move |hue| {
-            if let Ok(mut source) = color.try_get() {
-                source.hue = OklabHue::new(hue);
-                color.set(source);
-            }
+            let mut source = color.get();
+            source.hue = OklabHue::new(hue);
+            color.set(source);
         }
     })
     .persist();
 
     let hue_text = hue.linked_string();
-    let saturation = color.map_each(|color| color.saturation);
+    let saturation = color.map_each_cloned(|color| color.saturation);
     saturation
         .for_each_cloned({
             let color = color.clone();
             move |saturation| {
-                if let Ok(mut source) = color.try_get() {
-                    source.saturation = saturation;
-                    color.set(source);
-                }
+                let mut source = color.get();
+                source.saturation = saturation;
+                color.set(source);
             }
         })
         .persist();

src/debug.rs

@@ -53,7 +53,7 @@ impl DebugContext {
             section.values.lock().push(Box::new(RegisteredValue {
                 label: label.into(),
                 value: reader.clone(),
-                widget: make_observer(value.clone()).make_widget(),
+                widget: make_observer(value.weak_clone()).make_widget(),
             }))
         });
         let this = self.clone();

src/value.rs

@@ -290,6 +290,30 @@ pub trait Source<T> {
         mapped
     }
 
+    /// Returns a new [`Dynamic`] that contains a clone of each value from
+    /// `self`.
+    ///
+    /// The returned dynamic does not hold a strong reference to `self`,
+    /// ensuring that `self` can be cleaned up even if the returned dynamic
+    /// still exists.
+    fn weak_clone(&self) -> Dynamic<T>
+    where
+        T: Clone + Send + 'static,
+    {
+        let mapped = Dynamic::new(self.get());
+        let mapped_weak = mapped.downgrade();
+
+        mapped.set_source(
+            self.for_each_cloned_try(move |value| {
+                let mapped = mapped_weak.upgrade().ok_or(CallbackDisconnected)?;
+                *mapped.lock() = value.clone();
+                Ok(())
+            })
+            .weak(),
+        );
+        mapped
+    }
+
     /// Returns a new dynamic that is updated using `U::from(T.clone())` each
     /// time `self` is updated.
     #[must_use]
@@ -510,7 +534,7 @@ impl<T> Source<T> for Arc<DynamicData<T>> {
             + 'static,
     {
         let this = WeakDynamic(Arc::downgrade(self));
-        DynamicData::for_each(self, move || {
+        dynamic_for_each(self, move || {
             let this = this.upgrade().ok_or(CallbackDisconnected)?;
             this.map_generational(&mut for_each)?;
             Ok(())
@@ -523,7 +547,7 @@ impl<T> Source<T> for Arc<DynamicData<T>> {
         F: FnMut(GenerationalValue<T>) -> Result<(), CallbackDisconnected> + Send + 'static,
     {
         let this = WeakDynamic(Arc::downgrade(self));
-        DynamicData::for_each(self, move || {
+        dynamic_for_each(self, move || {
             let this = this.upgrade().ok_or(CallbackDisconnected)?;
 
             if let Ok(value) = this.try_map_generational(GenerationalValue::clone) {
@@ -726,6 +750,7 @@ impl<T> Source<T> for Owned<T> {
         let mut callbacks = self.callbacks.active.lock().ignore_poison();
         CallbackHandle(CallbackHandleInner::Single(CallbackHandleData {
             id: Some(callbacks.push(Box::new(for_each))),
+            owner: None,
             callbacks: self.callbacks.clone(),
         }))
     }
@@ -944,9 +969,10 @@ impl<T> Dynamic<T> {
             Ok(())
         }));
 
-        let t_weak = self.downgrade();
+        // The linked dynamic holds a reference to the original, since it's
+        // being created from the original.
+        let t = self.clone();
         self.set_source(r.for_each_try(move |r| {
-            let t = t_weak.upgrade().ok_or(CallbackDisconnected)?;
             if let Some(update) = r_into_t(r).into() {
                 let _result = t.replace(update);
             }
@@ -1388,18 +1414,20 @@ impl<T> DynamicData<T> {
 
         Ok(old)
     }
+}
 
-    pub fn for_each<F>(&self, map: F) -> CallbackHandle
-    where
-        F: for<'a> FnMut() -> Result<(), CallbackDisconnected> + Send + 'static,
-    {
-        let state = self.state().expect("deadlocked");
-        let mut data = state.callbacks.callbacks.lock().ignore_poison();
-        CallbackHandle(CallbackHandleInner::Single(CallbackHandleData {
-            id: Some(data.callbacks.push(Box::new(map))),
-            callbacks: state.callbacks.clone(),
-        }))
-    }
+fn dynamic_for_each<T, F>(this: &Arc<DynamicData<T>>, map: F) -> CallbackHandle
+where
+    F: for<'a> FnMut() -> Result<(), CallbackDisconnected> + Send + 'static,
+    T: Send + 'static,
+{
+    let state = this.state().expect("deadlocked");
+    let mut data = state.callbacks.callbacks.lock().ignore_poison();
+    CallbackHandle(CallbackHandleInner::Single(CallbackHandleData {
+        id: Some(data.callbacks.push(Box::new(map))),
+        owner: Some(this.clone()),
+        callbacks: state.callbacks.clone(),
+    }))
 }
 
 /// A callback function is no longer connected to its source.
@@ -1467,8 +1495,12 @@ enum CallbackHandleInner {
     Multi(Vec<CallbackHandleData>),
 }
 
+trait ReferencedDynamic: Sync + Send + 'static {}
+impl<T> ReferencedDynamic for T where T: Sync + Send + 'static {}
+
 struct CallbackHandleData {
     id: Option<LotId>,
+    owner: Option<Arc<dyn ReferencedDynamic>>,
     callbacks: Arc<dyn CallbackCollection>,
 }
 
@@ -1508,6 +1540,33 @@ impl CallbackHandle {
             }
         }
     }
+
+    /// Drops any references to owning [`Dynamic`]s associated with this
+    /// callback.
+    ///
+    /// This enables creating weak connections between callback graphs.
+    pub fn forget_owners(&mut self) {
+        match &mut self.0 {
+            CallbackHandleInner::None => {}
+            CallbackHandleInner::Single(handle) => {
+                handle.owner = None;
+            }
+            CallbackHandleInner::Multi(handles) => {
+                for handle in handles {
+                    handle.owner = None;
+                }
+            }
+        }
+    }
+
+    /// Drops any references to owning [`Dynamic`]s associated with this
+    /// callback, and returns self.
+    ///
+    /// This uses [`Self::forget_owners()`].
+    pub fn weak(mut self) -> Self {
+        self.forget_owners();
+        self
+    }
 }
 
 impl Eq for CallbackHandle {}
@@ -1539,6 +1598,7 @@ impl Drop for CallbackHandleData {
         }
     }
 }
+
 impl PartialEq for CallbackHandleData {
     fn eq(&self, other: &Self) -> bool {
         self.id == other.id && Arc::ptr_eq(&self.callbacks, &other.callbacks)
@@ -2932,7 +2992,7 @@ macro_rules! impl_tuple_for_each_cloned {
         }
     };
     ($self:ident $for_each:ident $handles:ident [] [$type:ident $field:tt $var:ident]) => {
-        $handles += $self.$field.for_each(move |field: &$type| $for_each((field.clone(),)));
+        $handles += $self.$field.for_each_cloned(move |field| $for_each((field,)));
     };
     ($self:ident $for_each:ident $handles:ident [] [$($type:ident $field:tt $var:ident),+]) => {
         let $for_each = Arc::new(Mutex::new($for_each));