Make BindingExpression and ExpressionObserver internal.

src/Avalonia.Base/Avalonia.Base.csproj

@@ -47,6 +47,9 @@
     <InternalsVisibleTo Include="Avalonia.DesignerSupport, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Direct2D1.RenderTests, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.LeakTests, PublicKey=$(AvaloniaPublicKey)" />
+    <InternalsVisibleTo Include="Avalonia.Markup, PublicKey=$(AvaloniaPublicKey)" />
+    <InternalsVisibleTo Include="Avalonia.Markup.Xaml, PublicKey=$(AvaloniaPublicKey)" />
+    <InternalsVisibleTo Include="Avalonia.Markup.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Markup.Xaml.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Skia.RenderTests, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Skia.UnitTests, PublicKey=$(AvaloniaPublicKey)" />

src/Avalonia.Base/Data/Core/BindingExpression.cs

@@ -13,7 +13,7 @@ namespace Avalonia.Data.Core
     /// that are sent and received.
     /// </summary>
     [RequiresUnreferencedCode(TrimmingMessages.TypeConvertionRequiresUnreferencedCodeMessage)]
-    public class BindingExpression : LightweightObservableBase<object?>, IAvaloniaSubject<object?>, IDescription
+    internal class BindingExpression : LightweightObservableBase<object?>, IAvaloniaSubject<object?>, IDescription
     {
         private readonly ExpressionObserver _inner;
         private readonly Type _targetType;

src/Avalonia.Base/Data/Core/ExpressionObserver.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Data.Core
     /// <summary>
     /// Observes and sets the value of an expression on an object.
     /// </summary>
-    public class ExpressionObserver : LightweightObservableBase<object?>, IDescription
+    internal class ExpressionObserver : LightweightObservableBase<object?>, IDescription
     {
         /// <summary>
         /// An ordered collection of property accessor plugins that can be used to customize

src/Markup/Avalonia.Markup.Xaml/MarkupExtensions/CompiledBindingExtension.cs

@@ -35,7 +35,7 @@ namespace Avalonia.Markup.Xaml.MarkupExtensions
             };
         }
 
-        protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty targetProperty, object anchor, bool enableDataValidation)
+        private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty targetProperty, object anchor, bool enableDataValidation)
         {
             if (Source != null)
             {

src/Markup/Avalonia.Markup/Avalonia.Markup.csproj

@@ -19,6 +19,7 @@
   <Import Project="..\..\..\build\TrimmingEnable.props" />
 
   <ItemGroup Label="InternalsVisibleTo">
+    <InternalsVisibleTo Include="Avalonia.Markup.Xaml, PublicKey=$(AvaloniaPublicKey)" />
     <InternalsVisibleTo Include="Avalonia.Markup.UnitTests, PublicKey=$(AvaloniaPublicKey)" />
   </ItemGroup>
 </Project>

src/Markup/Avalonia.Markup/Data/Binding.cs

@@ -56,7 +56,7 @@ namespace Avalonia.Data
         /// </summary>
         public Func<string, string, Type>? TypeResolver { get; set; }
 
-        protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty? targetProperty, object? anchor, bool enableDataValidation)
+        private protected override ExpressionObserver CreateExpressionObserver(AvaloniaObject target, AvaloniaProperty? targetProperty, object? anchor, bool enableDataValidation)
         {
             _ = target ?? throw new ArgumentNullException(nameof(target));
 

src/Markup/Avalonia.Markup/Data/BindingBase.cs

@@ -70,7 +70,7 @@ namespace Avalonia.Data
 
         public WeakReference<INameScope>? NameScope { get; set; }
 
-        protected abstract ExpressionObserver CreateExpressionObserver(
+        private protected abstract ExpressionObserver CreateExpressionObserver(
             AvaloniaObject target,
             AvaloniaProperty? targetProperty,
             object? anchor,
@@ -127,7 +127,7 @@ namespace Avalonia.Data
             return new InstancedBinding(subject, Mode, Priority);
         }
 
-        protected ExpressionObserver CreateDataContextObserver(
+        private protected ExpressionObserver CreateDataContextObserver(
             AvaloniaObject target,
             ExpressionNode node,
             bool targetIsDataContext,
@@ -162,7 +162,7 @@ namespace Avalonia.Data
             }
         }
 
-        protected ExpressionObserver CreateElementObserver(
+        private protected ExpressionObserver CreateElementObserver(
             StyledElement target,
             string elementName,
             ExpressionNode node)
@@ -178,7 +178,7 @@ namespace Avalonia.Data
             return result;
         }
 
-        protected ExpressionObserver CreateFindAncestorObserver(
+        private protected ExpressionObserver CreateFindAncestorObserver(
             StyledElement target,
             RelativeSource relativeSource,
             ExpressionNode node)
@@ -211,7 +211,7 @@ namespace Avalonia.Data
                 null);
         }
 
-        protected ExpressionObserver CreateSourceObserver(
+        private protected ExpressionObserver CreateSourceObserver(
             object source,
             ExpressionNode node)
         {
@@ -220,7 +220,7 @@ namespace Avalonia.Data
             return new ExpressionObserver(source, node);
         }
 
-        protected ExpressionObserver CreateTemplatedParentObserver(
+        private protected ExpressionObserver CreateTemplatedParentObserver(
             AvaloniaObject target,
             ExpressionNode node)
         {

src/Markup/Avalonia.Markup/Markup/Parsers/ExpressionObserverBuilder.cs

@@ -6,7 +6,7 @@ using Avalonia.Utilities;
 
 namespace Avalonia.Markup.Parsers
 {
-    public static class ExpressionObserverBuilder
+    internal static class ExpressionObserverBuilder
     {
         [RequiresUnreferencedCode(TrimmingMessages.ReflectionBindingRequiresUnreferencedCodeMessage)]
         internal static (ExpressionNode Node, SourceMode Mode) Parse(string expression, bool enableValidation = false, Func<string, string, Type>? typeResolver = null,