Hide binding plugins and disable Data Annotations validation by default (#20623)

* Make binding plugin API internal.

Making everything pluggable like has performance implications even if the plugins are never customized (which will be the 99% case).

`IPropertyAccessor` is used in `CompiledBindingPathBuilder` so needs to be kept public for the moment.

* Disable Data Annotations validation by default.

It [conflicts with `CommunityToolkit.Mvvm`](https://github.com/AvaloniaUI/Avalonia/issues/8397) which is now the default MVVM framework, so require it to be enabled in the `AppBuilder`.

* Update API supressions.

* Add back missing using

---------

Co-authored-by: Julien Lebosquain <julien@lebosquain.net>

api/Avalonia.nupkg.xml

@@ -25,6 +25,60 @@
     <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.BindingPlugins</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.DataValidationBase</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.ExceptionValidationPlugin</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IDataValidationPlugin</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IndeiValidationPlugin</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IPropertyAccessorPlugin</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IStreamPlugin</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.PropertyAccessorBase</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.PropertyError</Target>
+    <Left>baseline/Avalonia/lib/net10.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net10.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0001</DiagnosticId>
     <Target>T:Avalonia.Diagnostics.AppliedStyle</Target>
@@ -253,6 +307,60 @@
     <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
     <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
   </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.BindingPlugins</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.DataValidationBase</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.ExceptionValidationPlugin</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IDataValidationPlugin</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IndeiValidationPlugin</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IPropertyAccessorPlugin</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.IStreamPlugin</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.PropertyAccessorBase</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
+  <Suppression>
+    <DiagnosticId>CP0001</DiagnosticId>
+    <Target>T:Avalonia.Data.Core.Plugins.PropertyError</Target>
+    <Left>baseline/Avalonia/lib/net8.0/Avalonia.Base.dll</Left>
+    <Right>current/Avalonia/lib/net8.0/Avalonia.Base.dll</Right>
+  </Suppression>
   <Suppression>
     <DiagnosticId>CP0001</DiagnosticId>
     <Target>T:Avalonia.Diagnostics.AppliedStyle</Target>

src/Avalonia.Base/Data/Core/Plugins/BindingPlugins.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Data.Core.Plugins
     /// Holds a registry of plugins used for bindings.
     /// </summary>
     [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
-    public static class BindingPlugins
+    internal static class BindingPlugins
     {
         internal static readonly List<IPropertyAccessorPlugin> s_propertyAccessors = new()
         {
@@ -17,7 +17,6 @@ namespace Avalonia.Data.Core.Plugins
 
         internal static readonly List<IDataValidationPlugin> s_dataValidators = new()
         {
-            new DataAnnotationsValidationPlugin(),
             new IndeiValidationPlugin(),
             new ExceptionValidationPlugin(),
         };

src/Avalonia.Base/Data/Core/Plugins/DataValidationBase.cs

@@ -11,7 +11,7 @@ namespace Avalonia.Data.Core.Plugins
     /// and convert any values received from the inner property accessor into
     /// <see cref="BindingNotification"/>s.
     /// </remarks>
-    public abstract class DataValidationBase : PropertyAccessorBase, IObserver<object?>
+    internal abstract class DataValidationBase : PropertyAccessorBase, IObserver<object?>
     {
         private readonly IPropertyAccessor _inner;
 

src/Avalonia.Base/Data/Core/Plugins/ExceptionValidationPlugin.cs

@@ -7,7 +7,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// Validates properties that report errors by throwing exceptions.
     /// </summary>
-    public class ExceptionValidationPlugin : IDataValidationPlugin
+    internal class ExceptionValidationPlugin : IDataValidationPlugin
     {
         /// <inheritdoc/>
         public bool Match(WeakReference<object?> reference, string memberName) => true;

src/Avalonia.Base/Data/Core/Plugins/IDataValidationPlugin.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// Defines how data validation is observed by an <see cref="BindingExpression"/>.
     /// </summary>
-    public interface IDataValidationPlugin
+    internal interface IDataValidationPlugin
     {
         /// <summary>
         /// Checks whether this plugin can handle data validation on the specified object.

src/Avalonia.Base/Data/Core/Plugins/IPropertyAccessor.cs

@@ -3,8 +3,7 @@ using System;
 namespace Avalonia.Data.Core.Plugins
 {
     /// <summary>
-    /// Defines an accessor to a property on an object returned by a 
+    /// Defines an accessor to a property on an object.
-    /// <see cref="IPropertyAccessorPlugin"/>
     /// </summary>
     public interface IPropertyAccessor : IDisposable
     {

src/Avalonia.Base/Data/Core/Plugins/IPropertyAccessorPlugin.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// Defines how a member is read, written and observed by a binding.
     /// </summary>
-    public interface IPropertyAccessorPlugin
+    internal interface IPropertyAccessorPlugin
     {
         /// <summary>
         /// Checks whether this plugin can handle accessing the properties of the specified object.

src/Avalonia.Base/Data/Core/Plugins/IStreamPlugin.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// Defines a plugin that handles the '^' stream binding operator.
     /// </summary>
-    public interface IStreamPlugin
+    internal interface IStreamPlugin
     {
         /// <summary>
         /// Checks whether this plugin handles the specified value.

src/Avalonia.Base/Data/Core/Plugins/IndeiValidationPlugin.cs

@@ -9,7 +9,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// Validates properties on objects that implement <see cref="INotifyDataErrorInfo"/>.
     /// </summary>
-    public class IndeiValidationPlugin : IDataValidationPlugin
+    internal class IndeiValidationPlugin : IDataValidationPlugin
     {
         private static readonly WeakEvent<INotifyDataErrorInfo, DataErrorsChangedEventArgs>
             ErrorsChangedWeakEvent = WeakEvent.Register<INotifyDataErrorInfo, DataErrorsChangedEventArgs>(

src/Avalonia.Base/Data/Core/Plugins/PropertyAccessorBase.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// Defines a default base implementation for a <see cref="IPropertyAccessor"/>.
     /// </summary>
-    public abstract class PropertyAccessorBase : IPropertyAccessor
+    internal abstract class PropertyAccessorBase : IPropertyAccessor
     {
         private Action<object?>? _listener;
 

src/Avalonia.Base/Data/Core/Plugins/PropertyError.cs

@@ -5,7 +5,7 @@ namespace Avalonia.Data.Core.Plugins
     /// <summary>
     /// An <see cref="IPropertyAccessor"/> that represents an error.
     /// </summary>
-    public class PropertyError : IPropertyAccessor
+    internal class PropertyError : IPropertyAccessor
     {
         private readonly BindingNotification _error;
 

src/Avalonia.Controls/AppBuilder.cs

@@ -1,10 +1,12 @@
 using System;
 using System.Diagnostics.CodeAnalysis;
+using System.Linq;
 using System.Reflection;
 using Avalonia.Controls.ApplicationLifetimes;
 using Avalonia.Platform;
 using Avalonia.Media;
 using Avalonia.Metadata;
+using Avalonia.Data.Core.Plugins;
 
 namespace Avalonia
 {
@@ -265,6 +267,17 @@ namespace Avalonia
             return Self;
         }
 
+        /// <summary>
+        /// Adds support for validation using <c>System.ComponentModel.DataAnnotations</c>.
+        /// </summary>
+        [RequiresUnreferencedCode(TrimmingMessages.PropertyAccessorsRequiresUnreferencedCodeMessage)]
+        public AppBuilder WithDataAnnotationsValidation()
+        {
+            if (!BindingPlugins.DataValidators.Any(x => x is DataAnnotationsValidationPlugin))
+                BindingPlugins.DataValidators.Insert(0, new DataAnnotationsValidationPlugin());
+            return Self;
+        }
+
         /// <summary>
         /// Registers an action that is executed with the current font manager.
         /// </summary>

tests/Avalonia.Base.UnitTests/Data/Core/BindingExpressionTests.DataValidation.cs

@@ -2,7 +2,9 @@
 using System.Collections;
 using System.Collections.Generic;
 using System.ComponentModel.DataAnnotations;
+using System.Linq;
 using Avalonia.Data;
+using Avalonia.Data.Core.Plugins;
 using Avalonia.UnitTests;
 using Xunit;
 
@@ -273,6 +275,9 @@ public partial class BindingExpressionTests
     [Fact]
     public void Updates_Data_Validation_For_Required_DataAnnotation()
     {
+        if (!BindingPlugins.DataValidators.Any(x => x is DataAnnotationsValidationPlugin))
+            BindingPlugins.DataValidators.Insert(0, new DataAnnotationsValidationPlugin());
+
         var data = new DataAnnotationsViewModel();
         var target = CreateTargetWithSource(
             data,