Fixes/inline host change propagation (#14914)

* Add failing test

* Propagate InlineHost to children

src/Avalonia.Controls/Documents/InlineCollection.cs

@@ -159,6 +159,8 @@ namespace Avalonia.Controls.Documents
         {
             foreach (var child in this)
             {
+                child.InlineHost = newValue;
+
                 if (child is not InlineUIContainer container)
                 {
                     continue;

src/Avalonia.Controls/Documents/Span.cs

@@ -77,9 +77,6 @@ namespace Avalonia.Controls.Documents
 
         private void OnInlinesChanged(InlineCollection? oldValue, InlineCollection? newValue)
         {
-            void OnInlinesInvalidated(object? sender, EventArgs e)
-                => InlineHost?.Invalidate();
-
             if (oldValue is not null)
             {
                 oldValue.LogicalChildren = null;
@@ -93,6 +90,11 @@ namespace Avalonia.Controls.Documents
                 newValue.InlineHost = InlineHost;
                 newValue.Invalidated += OnInlinesInvalidated;
             }
+
+            return;
+
+            void OnInlinesInvalidated(object? sender, EventArgs e)
+                => InlineHost?.Invalidate();
         }
     }
 }

tests/Avalonia.Controls.UnitTests/TextBlockTests.cs

@@ -205,6 +205,23 @@ namespace Avalonia.Controls.UnitTests
             }
         }
 
+        [Fact]
+        public void Changing_InlineHost_Should_Propagate_To_Nested_Inlines()
+        {
+            using (UnitTestApplication.Start(TestServices.MockPlatformRenderInterface))
+            {
+                var target = new TextBlock();
+
+                var span = new Span { Inlines = new InlineCollection { new Run { Text = "World" } } };
+
+                var inlines = new InlineCollection{ new Run{Text = "Hello "}, span };
+
+                target.Inlines = inlines;
+
+                Assert.Equal(target, span.InlineHost);
+            }
+        }
+
         [Fact]
         public void Changing_Inlines_Should_Reset_VisualChildren()
         {