[typemap] Trim unused listener implementors from existing bindings

src/Microsoft.Android.Sdk.TrimmableTypeMap/Generator/ModelBuilder.cs

@@ -235,14 +235,21 @@ static bool IsUnconditionalEntry (JavaPeerInfo peer)
 			return true;
 		}
 
-		// User-defined ACW types (not MCW bindings, not interfaces) are unconditional
-		// because Android can instantiate them from Java at any time.
-		if (!peer.IsFrameworkAssembly && !peer.DoNotGenerateAcw && !peer.IsInterface) {
+		// Types marked unconditional by the scanner (component attributes: Activity, Service, etc.)
+		if (peer.IsUnconditional) {
 			return true;
 		}
 
-		// Types marked unconditional by the scanner (component attributes: Activity, Service, etc.)
-		if (peer.IsUnconditional) {
+		// Binding-generated listener implementors are instantiated by the generated managed event
+		// accessors before being passed to Java. Existing binding assemblies can be recognized by
+		// their generated metadata shape, so their entries can follow managed reachability.
+		if (peer.IsBindingEventListenerImplementor) {
+			return false;
+		}
+
+		// User-defined ACW types (not MCW bindings, not interfaces) are unconditional
+		// because Android can instantiate them from Java at any time.
+		if (!peer.IsFrameworkAssembly && !peer.DoNotGenerateAcw && !peer.IsInterface) {
 			return true;
 		}
 

src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerInfo.cs

@@ -72,6 +72,13 @@ public sealed record JavaPeerInfo
 	/// </summary>
 	public bool DoNotGenerateAcw { get; init; }
 
+	/// <summary>
+	/// True when the type matches the existing binding-generator listener implementor shape:
+	/// a generated <c>mono/</c> ACW implementing a Java interface with the static
+	/// <c>__IsEmpty(TImplementor)</c> helper used by event removal.
+	/// </summary>
+	public bool IsBindingEventListenerImplementor { get; init; }
+
 	/// <summary>
 	/// True when the type was discovered via <c>[JniTypeSignatureAttribute]</c>
 	/// rather than <c>[RegisterAttribute]</c>.  Used to resolve cross-assembly

src/Microsoft.Android.Sdk.TrimmableTypeMap/Scanner/JavaPeerScanner.cs

@@ -388,6 +388,8 @@ void ScanAssembly (AssemblyIndex index, Dictionary<(string ManagedName, string A
 				IsInterface = isInterface,
 				IsAbstract = isAbstract,
 				DoNotGenerateAcw = doNotGenerateAcw,
+				IsBindingEventListenerImplementor = IsBindingEventListenerImplementor (
+					typeDef, index, jniName, fullName, isInterface, doNotGenerateAcw, implementedInterfaces),
 				IsFromJniTypeSignature = registerInfo?.IsFromJniTypeSignature ?? false,
 				IsUnconditional = isUnconditional,
 				CannotRegisterInStaticConstructor = cannotRegisterInStaticConstructor,
@@ -405,6 +407,41 @@ void ScanAssembly (AssemblyIndex index, Dictionary<(string ManagedName, string A
 		}
 	}
 
+	static bool IsBindingEventListenerImplementor (
+		TypeDefinition typeDef,
+		AssemblyIndex index,
+		string jniName,
+		string managedTypeName,
+		bool isInterface,
+		bool doNotGenerateAcw,
+		IReadOnlyList<string> implementedInterfaces)
+	{
+		if (isInterface ||
+		    doNotGenerateAcw ||
+		    !jniName.StartsWith ("mono/", StringComparison.Ordinal) ||
+		    implementedInterfaces.Count == 0 ||
+		    (typeDef.Attributes & TypeAttributes.Sealed) == 0) {
+			return false;
+		}
+
+		foreach (var methodHandle in typeDef.GetMethods ()) {
+			var methodDef = index.Reader.GetMethodDefinition (methodHandle);
+			if ((methodDef.Attributes & MethodAttributes.Static) == 0 ||
+			    index.Reader.GetString (methodDef.Name) != "__IsEmpty") {
+				continue;
+			}
+
+			var signature = methodDef.DecodeSignature (TypeRefSignatureTypeProvider.Instance, genericContext: index);
+			if (signature.ReturnType.ManagedTypeName == "System.Boolean" &&
+			    signature.ParameterTypes.Length == 1 &&
+			    signature.ParameterTypes [0].ManagedTypeName == managedTypeName) {
+				return true;
+			}
+		}
+
+		return false;
+	}
+
 	bool IsResolvableJavaPeerType (
 		TypeDefinitionHandle typeDefHandle,
 		AssemblyIndex index,

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Generator/TypeMapModelBuilderTests.cs

@@ -227,6 +227,31 @@ public void Build_UserAcwType_IsUnconditional ()
 			Assert.Null (mainEntry.TargetTypeReference);
 		}
 
+		[Fact]
+		public void Build_BindingEventListenerImplementor_IsTrimmable ()
+		{
+			var peer = MakeAcwPeer ("mono/example/ListenerImplementor", "Example.ListenerImplementor", "Binding") with {
+				IsBindingEventListenerImplementor = true,
+			};
+			var model = BuildModel ([peer]);
+
+			Assert.False (model.Entries [0].IsUnconditional);
+			Assert.Equal ("Example.ListenerImplementor, Binding", model.Entries [0].TargetTypeReference);
+		}
+
+		[Fact]
+		public void Build_BindingEventListenerImplementor_MarkedUnconditional_IsUnconditional ()
+		{
+			var peer = MakeAcwPeer ("mono/example/ListenerImplementor", "Example.ListenerImplementor", "Binding") with {
+				IsBindingEventListenerImplementor = true,
+				IsUnconditional = true,
+			};
+			var model = BuildModel ([peer]);
+
+			Assert.True (model.Entries [0].IsUnconditional);
+			Assert.Null (model.Entries [0].TargetTypeReference);
+		}
+
 		[Fact]
 		public void Build_FrameworkAcwType_IsTrimmable ()
 		{
@@ -754,21 +779,20 @@ public void Fixture_AcwType_HasProxy (string javaName, string expectedProxyName)
 	public class FixtureImplementorsAndDispatchers
 	{
 		[Theory]
-		[InlineData ("mono/android/view/View_IOnClickListenerImplementor", "Implementor")]
-		[InlineData ("mono/android/view/View_ClickEventDispatcher", "EventDispatcher")]
-		public void Fixture_HelperType_IsUnconditional (string javaName, string kind)
+		[InlineData ("mono/android/view/View_IOnClickListenerImplementor", true)]
+		[InlineData ("mono/android/view/View_ClickEventDispatcher", false)]
+		public void Fixture_HelperType_UsesGeneratedShapeDetection (string javaName, bool isBindingEventListenerImplementor)
 		{
 			var peer = FindFixtureByJavaName (javaName);
 			Assert.False (peer.DoNotGenerateAcw);
 			Assert.False (peer.IsInterface);
+			Assert.Equal (isBindingEventListenerImplementor, peer.IsBindingEventListenerImplementor);
 
 			var model = BuildModel (new [] { peer }, "TypeMap");
 
 			var entry = model.Entries.FirstOrDefault ();
 			Assert.NotNull (entry);
-			// Implementor/EventDispatcher types are treated as unconditional ACW types.
-			// Future optimization (see #10911) may make them trimmable.
-			Assert.True (entry.IsUnconditional, $"{kind} should be unconditional");
+			Assert.Equal (!isBindingEventListenerImplementor, entry.IsUnconditional);
 		}
 	}
 

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Scanner/JavaPeerScannerTests.cs

@@ -92,6 +92,15 @@ public void Scan_InvokerAndInterface_ShareJavaName ()
 		Assert.Contains (clickListenerPeers, p => p.DoNotGenerateAcw);
 	}
 
+	[Fact]
+	public void Scan_DetectsBindingEventListenerImplementorShape ()
+	{
+		Assert.True (FindFixtureByJavaName ("mono/android/view/View_IOnClickListenerImplementor").IsBindingEventListenerImplementor);
+		Assert.False (FindFixtureByJavaName ("mono/android/view/FakeListenerPeer").IsBindingEventListenerImplementor);
+		Assert.False (FindFixtureByJavaName ("mono/android/view/View_ClickEventDispatcher").IsBindingEventListenerImplementor);
+		Assert.False (FindFixtureByJavaName ("my/app/MainActivity").IsBindingEventListenerImplementor);
+	}
+
 	[Fact]
 	public void Scan_AllTypes_HaveAssemblyName ()
 	{

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/TestFixtures/TestTypes.cs

@@ -111,6 +111,18 @@ namespace Android.Views
 	public class View : Java.Lang.Object
 	{
 		protected View (IntPtr handle, JniHandleOwnership transfer) : base (handle, transfer) { }
+
+		[Register ("mono/android/view/View_IOnClickListenerImplementor")]
+		internal sealed class IOnClickListenerImplementor : Java.Lang.Object, IOnClickListener
+		{
+			#pragma warning disable 0649
+			public EventHandler? Handler;
+			#pragma warning restore 0649
+
+			public IOnClickListenerImplementor (IntPtr handle, JniHandleOwnership transfer) : base (handle, transfer) { }
+			public void OnClick (View v) => Handler?.Invoke (this, EventArgs.Empty);
+			internal static bool __IsEmpty (IOnClickListenerImplementor value) => value.Handler is null;
+		}
 	}
 
 	[Register ("android/view/View$OnClickListener", "", "Android.Views.IOnClickListenerInvoker")]
@@ -186,10 +198,11 @@ public interface INamedClickListener : IOnClickListener
 		string? Label { get; }
 	}
 
-	[Register ("mono/android/view/View_IOnClickListenerImplementor")]
-	public class View_IOnClickListenerImplementor : Java.Lang.Object
+	[Register ("mono/android/view/FakeListenerPeer")]
+	internal sealed class FakeListenerPeer : Java.Lang.Object, IOnClickListener
 	{
-		public View_IOnClickListenerImplementor (IntPtr handle, JniHandleOwnership transfer) : base (handle, transfer) { }
+		public FakeListenerPeer (IntPtr handle, JniHandleOwnership transfer) : base (handle, transfer) { }
+		public void OnClick (View v) { }
 	}
 
 	[Register ("mono/android/view/View_ClickEventDispatcher")]