perf(wasm): Enable trimming for external drag and drop

build/cSpell.json

@@ -111,6 +111,7 @@
 	"Udemy",
 	"UNOB",
 	"winui",
+	"illinker",
   ],
   "patterns": [
 	{

build/uno.winui.common.targets

@@ -8,6 +8,17 @@
 		<_IsUnoPlatform>true</_IsUnoPlatform>
 	</PropertyGroup>
 
+	<!-- Feature configuration -->
+	<PropertyGroup>
+		<UnoDragDropExternalSupport Condition="'$(UnoDragDropExternalSupport)'==''">true</UnoDragDropExternalSupport>
+	</PropertyGroup>
+	<ItemGroup>
+
+		<RuntimeHostConfigurationOption Include="Windows.ApplicationModel.DataTransfer.DragDrop.ExternalSupport"
+										Value="$(UnoDragDropExternalSupport)"
+										Trim="true" />
+	</ItemGroup>
+
 	<Target Name="ValidateUnoUIAndUnoWinUIExclusion" BeforeTargets="BeforeBuild">
 		<Error Code="UNOB0001"
 		Text="Cannot build with both Uno.WinUI and Uno.UI nuget packages referenced."
@@ -211,5 +222,4 @@
 			">
 		<Error Text="Building for the iOS Simulator requires the use of the static registrar. Make sure that `MtouchExtraArgs` contains `--registrar:static`. See https://github.com/unoplatform/uno/issues/9430 for more details." />
 	</Target>
-
 </Project>

doc/articles/features/using-il-linker-webassembly.md

@@ -1,4 +1,26 @@
-# Using the IL Linker for WebAssembly
+---
+uid: articles.features.illinker
+---
+
+# Using the IL Linker
+
+### Support for features
+
+In order to improve the size of the application, some platforms are providing the ability to unconditionally disable features if the app is known not to use them.
+
+|Feature|MSBuild property|Description|
+|-----|----|---|
+|External Drag and Drop|`UnoDragDropExternalSupport`|Enables or disables drag and dropping content from **outside** the app using this property. Drag and Drop **inside** the app is always available when disabled.|
+
+For example, to disable external drag and drop support on WebAssembly, add the following to your csproj:
+
+```xml
+<PropertyGroup>
+    <UnoDragDropExternalSupport>false</UnoDragDropExternalSupport>
+</PropertyGroup>
+```
+
+## WebAssembly
 
 The [linker step](https://github.com/mono/linker/tree/master/docs) (also known as tree shaking, or IL Trimming) is responsible for the detection and removal of code that may not be used at runtime. This step is particularly important when targeting WebAssembly or native code in general, to reduce significantly the final package size.
 

src/SourceGenerators/Uno.UI.Tasks/Content/Uno.UI.Tasks.targets

@@ -103,6 +103,7 @@
 		AfterTargets="CoreCompile">
 
 		<ItemGroup>
+			<_SubstitutionFiles Include="@(UnoLinkerSubstitution)" />
 			<_SubstitutionFiles Include="$(IntermediateOutputPath)\Substitutions\*.Substitutions.xml" />
 		</ItemGroup>
 

src/Uno.Foundation/Extensions/LinkerAttributes.cs

@@ -3,7 +3,7 @@
 
 #nullable enable
 
-#if NETSTANDARD2_0
+#if !NET6_0_OR_GREATER || NETSTANDARD
 namespace System.Diagnostics.CodeAnalysis
 {
 	/// <summary>

src/Uno.UI/LinkerDefinition.Wasm.xml

@@ -16,9 +16,6 @@
 	<type fullname="Windows.UI.Xaml.Input.FocusManager">
 	  <method name="ReceiveFocusNative" />
 	</type>
-	<type fullname="Windows.ApplicationModel.DataTransfer.DragDrop.Core.DragDropExtension">
-	  <method name="OnNativeDropEvent" />
-	</type>
 	<type fullname="Windows.UI.Xaml.Application">
 	  <method name="DispatchSuspending" />
       <method name="DispatchSystemThemeChange" />
@@ -92,5 +89,4 @@
 	<type fullname="System.ComponentModel.*Converter" />
 	<type fullname="System.*Converter" />
   </assembly>
-
 </linker>

src/Uno.UI/LinkerSubstitution.Wasm.xml

@@ -0,0 +1,13 @@
+<linker>
+	<assembly fullname="Uno.UI">
+		<type fullname="Windows.ApplicationModel.DataTransfer.DragDrop.Core.DragDropExtension">
+
+			<method signature="System.Boolean get_IsExternalDragAndDropSupported()"
+					feature="Windows.ApplicationModel.DataTransfer.DragDrop.ExternalSupport"
+					body="stub"
+					value="false"
+					featurevalue="false" />
+
+		</type>
+	</assembly>
+</linker>

src/Uno.UI/UI/Xaml/DragDrop/DragDropExtension.wasm.cs

@@ -28,6 +28,7 @@
 using Uno.Storage.Internal;
 using Uno.UI;
 using Uno.UI.Xaml;
+using System.Diagnostics.CodeAnalysis;
 
 // As IDragDropExtension is internal, the generated registration cannot be used.
 // [assembly: ApiExtension(typeof(Windows.ApplicationModel.DataTransfer.DragDrop.Core.IDragDropExtension), typeof(Windows.ApplicationModel.DataTransfer.DragDrop.Core.DragDropExtension))]
@@ -42,17 +43,29 @@ internal class DragDropExtension : IDragDropExtension
 
 		private static DragDropExtension? _current;
 
+		/// <summary>
+		/// Conditional support for external drag and drop. See the UnoDragDropExternalSupport msbuild property.
+		/// </summary>
+		public static bool IsExternalDragAndDropSupported { get; } = true;
+
 		public static DragDropExtension GetForCurrentView()
 		{
 			// Note: We use the GetForCurrentView naming pattern, but we don't support multi-threading yet
 			//		 and the '_current' is actually just static.
 
 			if (_current is null && Interlocked.CompareExchange(ref _current, new DragDropExtension(), null) is null)
 			{
-				// For now we enable the D&DExtension sync at creation and we don't support disable.
-				// This allow us to prevent a drop of a content on an app which actually don't support D&D
-				// (would drive the browser to open the dragged file and "dismiss" the app).
-				_current.Enable();
+				if (IsExternalDragAndDropSupported)
+				{
+					// For now we enable the D&DExtension sync at creation and we don't support disable.
+					// This allow us to prevent a drop of a content on an app which actually don't support D&D
+					// (would drive the browser to open the dragged file and "dismiss" the app).
+					_current.Enable();
+				}
+				else
+				{
+					EnableExternalWarning();
+				}
 			}
 
 			return _current;
@@ -70,6 +83,7 @@ private DragDropExtension()
 				?? throw new InvalidOperationException("No CoreDragDropManager available for current thread.");
 		}
 
+		[DynamicDependency(nameof(OnNativeDropEvent))]
 		private void Enable()
 		{
 			if (Interlocked.CompareExchange(ref _isInitialized, 1, 0) == 0)
@@ -84,6 +98,11 @@ private void Enable()
 			}
 		}
 
+		private static void EnableExternalWarning()
+		{
+			WebAssemblyRuntime.InvokeJS("Windows.ApplicationModel.DataTransfer.DragDrop.Core.DragDropExtension.registerNoOp();");
+		}
+
 		/// <inheritdoc />
 		void IDragDropExtension.StartNativeDrag(CoreDragInfo info)
 		{

src/Uno.UI/Uno.UI.Wasm.csproj

@@ -59,6 +59,8 @@
 	</ItemGroup>
 
 	<ItemGroup>
+	  <None Include="LinkerSubstitution.Wasm.xml" />
+	  <UnoLinkerSubstitution Include="LinkerSubstitution.Wasm.xml" />
 	  <EmbeddedResource Include="LinkerDefinition.Wasm.xml">	
 			<LogicalName>$(AssemblyName).xml</LogicalName>
 	  </EmbeddedResource>

src/Uno.UI/ts/Windows/ApplicationModel/DataTransfer/DragAndDropExtension.ts

@@ -61,6 +61,17 @@
 			document.removeEventListener("drop", this._dropHandler);
 		}
 
+		public static registerNoOp() {
+			let notifyDisabled = (evt: DragEvent) => {
+				evt.dataTransfer.dropEffect = "none";
+				console.debug("DragAndDrop from external sources is disabled. See the UnoDragDropExternalSupport msbuild property.");
+
+				document.removeEventListener("dragenter", notifyDisabled);
+			};
+
+			document.addEventListener("dragenter", notifyDisabled);
+		}
+
 		private dispatchDropEvent(evt: DragEvent): any {
 			if (evt.type == "dragleave"
 				&& evt.clientX > 0