Remove empty frames.

In doing so, merged `ValueStore.OnBindingCompleted` into `OnValueEntryRemoved` as they were doing the same thing.

src/Avalonia.Base/PropertyStore/ValueFrame.cs

@@ -4,6 +4,7 @@ using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using Avalonia.Data;
 using Avalonia.Utilities;
+using static Avalonia.Rendering.Composition.Animations.PropertySetSnapshot;
 
 namespace Avalonia.PropertyStore
 {
@@ -45,8 +46,9 @@ namespace Avalonia.PropertyStore
 
         public void OnBindingCompleted(IValueEntry binding)
         {
-            Remove(binding.Property);
-            Owner?.OnBindingCompleted(binding.Property, this);
+            var property = binding.Property;
+            Remove(property);
+            Owner?.OnValueEntryRemoved(this, property);
         }
 
         public virtual void Dispose()

src/Avalonia.Base/PropertyStore/ValueStore.cs

@@ -397,23 +397,6 @@ namespace Avalonia.PropertyStore
             }
         }
 
-        /// <summary>
-        /// Called by a <see cref="BindingEntryBase{TValue, TSource}"/> to re-evaluate the
-        /// effective value when the binding completes or terminates on error.
-        /// </summary>
-        /// <param name="property">The previously bound property.</param>
-        /// <param name="frame">The frame which contained the binding.</param>
-        public void OnBindingCompleted(AvaloniaProperty property, ValueFrame frame)
-        {
-            var priority = frame.Priority;
-
-            if (TryGetEffectiveValue(property, out var existing))
-            {
-                if (priority <= existing.Priority)
-                    ReevaluateEffectiveValue(property, existing);
-            }
-        }
-
         /// <summary>
         /// Called by a <see cref="ValueFrame"/> when its <see cref="ValueFrame.IsActive"/>
         /// state changes.
@@ -577,22 +560,14 @@ namespace Avalonia.PropertyStore
         /// <param name="property">The property whose value was removed.</param>
         public void OnValueEntryRemoved(ValueFrame frame, AvaloniaProperty property)
         {
-            Debug.Assert(frame.IsActive);
+            if (frame.EntryCount == 0)
+                _frames.Remove(frame);
 
             if (TryGetEffectiveValue(property, out var existing))
             {
                 if (frame.Priority <= existing.Priority)
                     ReevaluateEffectiveValue(property, existing);
             }
-            else
-            {
-                Logger.TryGet(LogEventLevel.Error, LogArea.Property)?.Log(
-                    Owner,
-                    "Internal error: ValueStore.OnEntryRemoved called for {Property} " +
-                    "but no effective value was found.",
-                    property);
-                Debug.Assert(false);
-            }
         }
 
         public bool RemoveFrame(ValueFrame frame)

tests/Avalonia.Base.UnitTests/PropertyStore/ValueStoreTests_Frames.cs

@@ -1,6 +1,6 @@
 using System.Collections.Generic;
-using System.Reactive;
 using System.Reactive.Subjects;
+using Avalonia.Data;
 using Avalonia.PropertyStore;
 using Avalonia.Styling;
 using Microsoft.Reactive.Testing;
@@ -80,7 +80,6 @@ namespace Avalonia.Base.UnitTests.PropertyStore
             var target = new Class1();
             var scheduler = new TestScheduler();
             var obs = scheduler.CreateColdObservable(OnNext(0, "bar"));
-            var result = new List<PropertyChange>();
             var style = new Style
             {
                 Setters =
@@ -99,6 +98,23 @@ namespace Avalonia.Base.UnitTests.PropertyStore
             Assert.NotEqual(Subscription.Infinite, obs.Subscriptions[0].Unsubscribe);
         }
 
+        [Fact]
+        public void Completing_Binding_Removes_ImmediateValueFrame()
+        {
+            var target = new Class1();
+            var source = new BehaviorSubject<BindingValue<string>>("foo");
+
+            target.Bind(Class1.FooProperty, source, BindingPriority.Animation);
+
+            var valueStore = target.GetValueStore();
+            Assert.Equal(1, valueStore.Frames.Count);
+            Assert.IsType<ImmediateValueFrame>(valueStore.Frames[0]);
+
+            source.OnCompleted();
+
+            Assert.Equal(0, valueStore.Frames.Count);
+        }
+
         private static StyleInstance InstanceStyle(Style style, StyledElement target)
         {
             var result = new StyleInstance(style, null);