[TrimmableTypeMap] Scanner unit tests (#10813)

Stacked on #10823. Adds comprehensive unit test coverage for the Java peer scanner.
Part of #10798

## What this PR adds

New `Microsoft.Android.Sdk.TrimmableTypeMap.Tests` project with xUnit tests:

### 1. Test fixtures
> `TestFixtures/StubAttributes.cs`, `TestFixtures/TestTypes.cs`

Stub Mono.Android attributes and a representative set of test types covering MCW bindings, user types with component attributes, generics, nested types, interfaces with invokers, and edge-case types (unregistered, empty namespace, deep nesting).

### 2. Foundational tests
> `Scanner/JavaPeerScannerTests.cs`

Core discovery assertions: all peers found, DoNotGenerateAcw flags, component types marked unconditional, interface/abstract/generic metadata, assembly name populated.

### 3. Behavior and contract tests
> `Scanner/JavaPeerScannerTests.Behavior.cs`

Marshal method collection, JNI signature decoding for all primitive types and arrays, activation constructor inheritance, base type chain resolution, compat JNI names, custom JNI name provider attributes, nested type discovery.

### 4. Edge-case regression tests
> `Scanner/JavaPeerScannerTests.EdgeCases.cs`

Generic TypeSpecification resolution, component-only base detection, unregistered nested type naming, 3-level deep nesting, empty namespace handling, plain subclass CRC64 naming, unregistered types with interfaces/exports.

Author: simonrozsival

Xamarin.Android.sln

@@ -59,6 +59,12 @@ Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Xamarin.ProjectTools", "src
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Xamarin.Android.Build.Tests", "src\Xamarin.Android.Build.Tasks\Tests\Xamarin.Android.Build.Tests\Xamarin.Android.Build.Tests.csproj", "{53E4ABF0-1085-45F9-B964-DCAE4B819998}"
 EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Android.Sdk.TrimmableTypeMap", "src\Microsoft.Android.Sdk.TrimmableTypeMap\Microsoft.Android.Sdk.TrimmableTypeMap.csproj", "{507759AE-93DF-411B-8645-31F680319F5C}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "Microsoft.Android.Sdk.TrimmableTypeMap.Tests", "tests\Microsoft.Android.Sdk.TrimmableTypeMap.Tests\Microsoft.Android.Sdk.TrimmableTypeMap.Tests.csproj", "{F9CD012E-67AC-4A4E-B2A7-252387F91256}"
+EndProject
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "TestFixtures", "tests\Microsoft.Android.Sdk.TrimmableTypeMap.Tests\TestFixtures\TestFixtures.csproj", "{C5A44686-3469-45A7-B6AB-2798BA0625BC}"
+EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "class-parse", "external\Java.Interop\tools\class-parse\class-parse.csproj", "{38C762AB-8FD1-44DE-9855-26AAE7129DC3}"
 EndProject
 Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "logcat-parse", "external\Java.Interop\tools\logcat-parse\logcat-parse.csproj", "{7387E151-48E3-4885-B2CA-A74434A34045}"
@@ -231,6 +237,18 @@ Global
 		{53E4ABF0-1085-45F9-B964-DCAE4B819998}.Debug|AnyCPU.Build.0 = Debug|Any CPU
 		{53E4ABF0-1085-45F9-B964-DCAE4B819998}.Release|AnyCPU.ActiveCfg = Release|Any CPU
 		{53E4ABF0-1085-45F9-B964-DCAE4B819998}.Release|AnyCPU.Build.0 = Release|Any CPU
+		{507759AE-93DF-411B-8645-31F680319F5C}.Debug|AnyCPU.ActiveCfg = Debug|Any CPU
+		{507759AE-93DF-411B-8645-31F680319F5C}.Debug|AnyCPU.Build.0 = Debug|Any CPU
+		{507759AE-93DF-411B-8645-31F680319F5C}.Release|AnyCPU.ActiveCfg = Release|Any CPU
+		{507759AE-93DF-411B-8645-31F680319F5C}.Release|AnyCPU.Build.0 = Release|Any CPU
+		{F9CD012E-67AC-4A4E-B2A7-252387F91256}.Debug|AnyCPU.ActiveCfg = Debug|Any CPU
+		{F9CD012E-67AC-4A4E-B2A7-252387F91256}.Debug|AnyCPU.Build.0 = Debug|Any CPU
+		{F9CD012E-67AC-4A4E-B2A7-252387F91256}.Release|AnyCPU.ActiveCfg = Release|Any CPU
+		{F9CD012E-67AC-4A4E-B2A7-252387F91256}.Release|AnyCPU.Build.0 = Release|Any CPU
+		{C5A44686-3469-45A7-B6AB-2798BA0625BC}.Debug|AnyCPU.ActiveCfg = Debug|Any CPU
+		{C5A44686-3469-45A7-B6AB-2798BA0625BC}.Debug|AnyCPU.Build.0 = Debug|Any CPU
+		{C5A44686-3469-45A7-B6AB-2798BA0625BC}.Release|AnyCPU.ActiveCfg = Release|Any CPU
+		{C5A44686-3469-45A7-B6AB-2798BA0625BC}.Release|AnyCPU.Build.0 = Release|Any CPU
 		{38C762AB-8FD1-44DE-9855-26AAE7129DC3}.Debug|AnyCPU.ActiveCfg = Debug|Any CPU
 		{38C762AB-8FD1-44DE-9855-26AAE7129DC3}.Debug|AnyCPU.Build.0 = Debug|Any CPU
 		{38C762AB-8FD1-44DE-9855-26AAE7129DC3}.Release|AnyCPU.ActiveCfg = Release|Any CPU
@@ -398,6 +416,8 @@ Global
 		{645E1718-C8C4-4C23-8A49-5A37E4ECF7ED} = {04E3E11E-B47D-4599-8AFC-50515A95E715}
 		{2DD1EE75-6D8D-4653-A800-0A24367F7F38} = {CAB438D8-B0F5-4AF0-BEBD-9E2ADBD7B483}
 		{53E4ABF0-1085-45F9-B964-DCAE4B819998} = {CAB438D8-B0F5-4AF0-BEBD-9E2ADBD7B483}
+		{F9CD012E-67AC-4A4E-B2A7-252387F91256} = {CAB438D8-B0F5-4AF0-BEBD-9E2ADBD7B483}
+		{C5A44686-3469-45A7-B6AB-2798BA0625BC} = {CAB438D8-B0F5-4AF0-BEBD-9E2ADBD7B483}
 		{38C762AB-8FD1-44DE-9855-26AAE7129DC3} = {864062D3-A415-4A6F-9324-5820237BA058}
 		{7387E151-48E3-4885-B2CA-A74434A34045} = {864062D3-A415-4A6F-9324-5820237BA058}
 		{8A6CB07C-E493-4A4F-AB94-038645A27118} = {E351F97D-EA4F-4E7F-AAA0-8EBB1F2A4A62}

build-tools/automation/yaml-templates/build-windows-steps.yaml

@@ -77,6 +77,21 @@ steps:
     testRunTitle: Microsoft.Android.Sdk.Analysis.Tests
   continueOnError: true
 
+- template: /build-tools/automation/yaml-templates/run-dotnet-preview.yaml@self
+  parameters:
+    command: test
+    project: tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests.csproj
+    arguments: -c $(XA.Build.Configuration) --logger trx --results-directory $(Agent.TempDirectory)/trimmable-typemap-tests
+    displayName: Test Microsoft.Android.Sdk.TrimmableTypeMap.Tests $(XA.Build.Configuration)
+
+- task: PublishTestResults@2
+  displayName: publish Microsoft.Android.Sdk.TrimmableTypeMap.Tests results
+  condition: always()
+  inputs:
+    testResultsFormat: VSTest
+    testResultsFiles: "$(Agent.TempDirectory)/trimmable-typemap-tests/*.trx"
+    testRunTitle: Microsoft.Android.Sdk.TrimmableTypeMap.Tests
+
 - task: BatchScript@1
   displayName: Test dotnet-local.cmd - create template
   inputs:

src/Microsoft.Android.Sdk.TrimmableTypeMap/Microsoft.Android.Sdk.TrimmableTypeMap.csproj

@@ -11,6 +11,7 @@
   <ItemGroup>
     <PackageReference Include="System.IO.Hashing" Version="$(SystemIOHashingPackageVersion)" />
     <PackageReference Include="System.Reflection.Metadata" Version="$(SystemReflectionMetadataPackageVersion)" />
+    <InternalsVisibleTo Include="Microsoft.Android.Sdk.TrimmableTypeMap.Tests" />
   </ItemGroup>
 
   <ItemGroup>

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

@@ -105,6 +105,13 @@ void Build ()
 					applicationAttributeInfo.BackupAgent = TryGetTypeProperty (ca, "BackupAgent");
 					applicationAttributeInfo.ManageSpaceActivity = TryGetTypeProperty (ca, "ManageSpaceActivity");
 				}
+			} else if (attrInfo is null && ImplementsJniNameProviderAttribute (ca)) {
+				// Custom attribute implementing IJniNameProviderAttribute (e.g., user-defined [CustomJniName])
+				var name = TryGetNameProperty (ca);
+				if (name is not null) {
+					attrInfo = new TypeAttributeInfo (attrName);
+					attrInfo.JniName = name.Replace ('.', '/');
+				}
 			}
 		}
 
@@ -129,6 +136,36 @@ static TypeAttributeInfo CreateTypeAttributeInfo (string attrName)
 
 	static bool IsKnownComponentAttribute (string attrName) => KnownComponentAttributes.Contains (attrName);
 
+	/// <summary>
+	/// Checks whether a custom attribute's type implements <c>Java.Interop.IJniNameProviderAttribute</c>.
+	/// Only works for attributes defined in the assembly being scanned (MethodDefinition constructors).
+	/// </summary>
+	bool ImplementsJniNameProviderAttribute (CustomAttribute ca)
+	{
+		if (ca.Constructor.Kind != HandleKind.MethodDefinition) {
+			return false;
+		}
+		var methodDef = Reader.GetMethodDefinition ((MethodDefinitionHandle)ca.Constructor);
+		var typeDef = Reader.GetTypeDefinition (methodDef.GetDeclaringType ());
+		foreach (var implHandle in typeDef.GetInterfaceImplementations ()) {
+			var impl = Reader.GetInterfaceImplementation (implHandle);
+			if (impl.Interface.Kind == HandleKind.TypeReference) {
+				var typeRef = Reader.GetTypeReference ((TypeReferenceHandle)impl.Interface);
+				if (Reader.GetString (typeRef.Name) == "IJniNameProviderAttribute" &&
+				    Reader.GetString (typeRef.Namespace) == "Java.Interop") {
+					return true;
+				}
+			} else if (impl.Interface.Kind == HandleKind.TypeDefinition) {
+				var ifaceDef = Reader.GetTypeDefinition ((TypeDefinitionHandle)impl.Interface);
+				if (Reader.GetString (ifaceDef.Name) == "IJniNameProviderAttribute" &&
+				    Reader.GetString (ifaceDef.Namespace) == "Java.Interop") {
+					return true;
+				}
+			}
+		}
+		return false;
+	}
+
 	internal static string? GetCustomAttributeName (CustomAttribute ca, MetadataReader reader)
 	{
 		if (ca.Constructor.Kind == HandleKind.MemberReference) {

tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests/Microsoft.Android.Sdk.TrimmableTypeMap.Tests.csproj

@@ -0,0 +1,38 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <TargetFramework>$(DotNetStableTargetFramework)</TargetFramework>
+    <LangVersion>latest</LangVersion>
+    <Nullable>enable</Nullable>
+    <IsPackable>false</IsPackable>
+    <RootNamespace>Microsoft.Android.Sdk.TrimmableTypeMap.Tests</RootNamespace>
+  </PropertyGroup>
+
+  <!-- Exclude TestFixtures subdirectory — it's a separate project compiled independently -->
+  <ItemGroup>
+    <Compile Remove="TestFixtures\**" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="3.0.2" />
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.5.0" />
+  </ItemGroup>
+
+  <ItemGroup>
+    <ProjectReference Include="..\..\src\Microsoft.Android.Sdk.TrimmableTypeMap\Microsoft.Android.Sdk.TrimmableTypeMap.csproj" />
+    <ProjectReference Include="TestFixtures\TestFixtures.csproj">
+      <!-- Don't add as a compile-time reference — we only need the built DLL as scanner test input -->
+      <ReferenceOutputAssembly>false</ReferenceOutputAssembly>
+    </ProjectReference>
+  </ItemGroup>
+
+  <!-- Copy TestFixtures output to our output directory so tests can find it -->
+  <Target Name="_CopyTestFixturesOutput" AfterTargets="Build">
+    <ItemGroup>
+      <_TestFixtureFiles Include="TestFixtures\bin\$(Configuration)\$(DotNetStableTargetFramework)\TestFixtures.dll" />
+    </ItemGroup>
+    <Copy SourceFiles="@(_TestFixtureFiles)" DestinationFolder="$(OutputPath)" SkipUnchangedFiles="true" />
+  </Target>
+
+</Project>

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

@@ -0,0 +1,133 @@
+using System.Linq;
+using Xunit;
+
+namespace Microsoft.Android.Sdk.TrimmableTypeMap.Tests;
+
+public partial class JavaPeerScannerTests
+{
+	[Theory]
+	[InlineData ("android/app/Activity", "OnCreate", "onCreate", "(Landroid/os/Bundle;)V")]
+	[InlineData ("android/app/Activity", "OnStart", "onStart", "()V")]
+	[InlineData ("my/app/MainActivity", "OnCreate", "onCreate", "(Landroid/os/Bundle;)V")]
+	[InlineData ("my/app/AbstractBase", "DoWork", "doWork", "()V")]
+	[InlineData ("java/lang/Throwable", "Message", "getMessage", "()Ljava/lang/String;")]
+	[InlineData ("my/app/TouchHandler", "OnTouch", "onTouch", "(Landroid/view/View;I)Z")]
+	[InlineData ("my/app/TouchHandler", "OnFocusChange", "onFocusChange", "(Landroid/view/View;Z)V")]
+	[InlineData ("my/app/TouchHandler", "OnScroll", "onScroll", "(IFJD)V")]
+	[InlineData ("my/app/TouchHandler", "SetItems", "setItems", "([Ljava/lang/String;)V")]
+	public void Scan_MarshalMethod_HasCorrectSignature (string javaName, string managedName, string jniName, string jniSig)
+	{
+		var peers = ScanFixtures ();
+		var method = FindByJavaName (peers, javaName)
+			.MarshalMethods.FirstOrDefault (m => m.ManagedMethodName == managedName || m.JniName == jniName);
+		Assert.NotNull (method);
+		Assert.Equal (jniName, method.JniName);
+		Assert.Equal (jniSig, method.JniSignature);
+	}
+
+	[Fact]
+	public void Scan_MarshalMethod_ConstructorsAndSpecialCases ()
+	{
+		var peers = ScanFixtures ();
+
+		var ctors = FindByJavaName (peers, "my/app/CustomView")
+			.MarshalMethods.Where (m => m.IsConstructor).ToList ();
+		Assert.Equal (2, ctors.Count);
+		Assert.Equal ("()V", ctors [0].JniSignature);
+		Assert.Equal ("(Landroid/content/Context;)V", ctors [1].JniSignature);
+
+		Assert.DoesNotContain (FindByJavaName (peers, "my/app/MyHelper").MarshalMethods, m => m.IsConstructor);
+
+		var exportMethod = FindByJavaName (peers, "my/app/ExportExample").MarshalMethods.Single ();
+		Assert.Equal ("myExportedMethod", exportMethod.JniName);
+		Assert.Null (exportMethod.Connector);
+
+		var onStart = FindByJavaName (peers, "android/app/Activity")
+			.MarshalMethods.FirstOrDefault (m => m.JniName == "onStart");
+		Assert.NotNull (onStart);
+		Assert.Equal ("", onStart.Connector);
+
+		var onClick = FindByManagedName (peers, "Android.Views.IOnClickListener")
+			.MarshalMethods.FirstOrDefault (m => m.JniName == "onClick");
+		Assert.NotNull (onClick);
+		Assert.Equal ("(Landroid/view/View;)V", onClick.JniSignature);
+
+		Assert.Equal ("Android.Views.IOnClickListenerInvoker",
+			FindByManagedName (peers, "Android.Views.IOnClickListener").InvokerTypeName);
+	}
+
+	[Theory]
+	[InlineData ("android/app/Activity", "Android.App.Activity")]
+	[InlineData ("my/app/SimpleActivity", "Android.App.Activity")]
+	[InlineData ("my/app/MyButton", "MyApp.MyButton")]
+	public void Scan_ActivationCtor_InheritsFromNearestBase (string javaName, string expectedDeclaringType)
+	{
+		var peers = ScanFixtures ();
+		var peer = FindByJavaName (peers, javaName);
+		Assert.NotNull (peer.ActivationCtor);
+		Assert.Equal (expectedDeclaringType, peer.ActivationCtor.DeclaringTypeName);
+	}
+
+	[Theory]
+	[InlineData ("java/lang/Object", null)]
+	[InlineData ("android/app/Activity", "java/lang/Object")]
+	[InlineData ("my/app/MainActivity", "android/app/Activity")]
+	[InlineData ("java/lang/Throwable", "java/lang/Object")]
+	[InlineData ("java/lang/Exception", "java/lang/Throwable")]
+	[InlineData ("my/app/MyButton", "android/widget/Button")]
+	public void Scan_BaseJavaName_ResolvesCorrectly (string javaName, string? expectedBase)
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal (expectedBase, FindByJavaName (peers, javaName).BaseJavaName);
+	}
+
+	[Fact]
+	public void Scan_MultipleInterfaces_AllResolved ()
+	{
+		var peers = ScanFixtures ();
+
+		var multi = FindByJavaName (peers, "my/app/MultiInterfaceView");
+		Assert.Contains ("android/view/View$OnClickListener", multi.ImplementedInterfaceJavaNames);
+		Assert.Contains ("android/view/View$OnLongClickListener", multi.ImplementedInterfaceJavaNames);
+		Assert.Equal (2, multi.ImplementedInterfaceJavaNames.Count);
+
+		Assert.Contains ("android/view/View$OnClickListener",
+			FindByJavaName (peers, "my/app/ClickableView").ImplementedInterfaceJavaNames);
+		Assert.Empty (FindByJavaName (peers, "my/app/MyHelper").ImplementedInterfaceJavaNames);
+	}
+
+	[Theory]
+	[InlineData ("android/app/Activity", "android/app/Activity")]
+	[InlineData ("my/app/MainActivity", "my/app/MainActivity")]
+	public void Scan_CompatJniName (string javaName, string expectedCompat)
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal (expectedCompat, FindByJavaName (peers, javaName).CompatJniName);
+	}
+
+	[Fact]
+	public void Scan_CompatJniName_UnregisteredType_UsesRawNamespace ()
+	{
+		var peers = ScanFixtures ();
+		var unregistered = FindByManagedName (peers, "MyApp.UnregisteredHelper");
+		Assert.StartsWith ("crc64", unregistered.JavaName);
+		Assert.Equal ("myapp/UnregisteredHelper", unregistered.CompatJniName);
+	}
+
+	[Fact]
+	public void Scan_CustomJniNameProviderAttribute_UsesNameFromAttribute ()
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal ("com/example/CustomWidget",
+			FindByManagedName (peers, "MyApp.CustomWidget").JavaName);
+	}
+
+	[Theory]
+	[InlineData ("my/app/Outer$Inner", "MyApp.Outer+Inner")]
+	[InlineData ("my/app/ICallback$Result", "MyApp.ICallback+Result")]
+	public void Scan_NestedType_IsDiscovered (string javaName, string managedName)
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal (managedName, FindByJavaName (peers, javaName).ManagedTypeName);
+	}
+}

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

@@ -0,0 +1,69 @@
+using System.Linq;
+using Xunit;
+
+namespace Microsoft.Android.Sdk.TrimmableTypeMap.Tests;
+
+public partial class JavaPeerScannerTests
+{
+	[Fact]
+	public void Scan_GenericTypes_ResolveViaTypeSpecification ()
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal ("my/app/GenericBase",
+			FindByJavaName (peers, "my/app/ConcreteFromGeneric").BaseJavaName);
+		Assert.Contains ("my/app/IGenericCallback",
+			FindByJavaName (peers, "my/app/GenericCallbackImpl").ImplementedInterfaceJavaNames);
+	}
+
+	[Fact]
+	public void Scan_ComponentOnlyBase_BothBaseAndDerivedDiscovered ()
+	{
+		var peers = ScanFixtures ();
+
+		var baseType = FindByJavaName (peers, "my/app/BaseActivityNoRegister");
+		Assert.True (baseType.IsUnconditional);
+		Assert.Equal ("android/app/Activity", baseType.BaseJavaName);
+
+		var derived = FindByManagedName (peers, "MyApp.DerivedFromComponentBase");
+		Assert.StartsWith ("crc64", derived.JavaName);
+	}
+
+	[Theory]
+	[InlineData ("MyApp.RegisteredParent+UnregisteredChild", "my/app/RegisteredParent_UnregisteredChild")]
+	[InlineData ("MyApp.DeepOuter+Middle+DeepInner", "my/app/DeepOuter_Middle_DeepInner")]
+	public void Scan_UnregisteredNestedType_UsesParentJniPrefix (string managedName, string expectedJavaName)
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal (expectedJavaName, FindByManagedName (peers, managedName).JavaName);
+	}
+
+	[Fact]
+	public void Scan_EmptyNamespace_Handled ()
+	{
+		var peers = ScanFixtures ();
+		Assert.Equal ("GlobalType", FindByJavaName (peers, "my/app/GlobalType").ManagedTypeName);
+		Assert.Equal ("GlobalUnregisteredType",
+			FindByManagedName (peers, "GlobalUnregisteredType").CompatJniName);
+	}
+
+	[Theory]
+	[InlineData ("MyApp.PlainActivitySubclass")]
+	[InlineData ("MyApp.UnnamedActivity")]
+	[InlineData ("MyApp.UnregisteredClickListener")]
+	[InlineData ("MyApp.UnregisteredExporter")]
+	public void Scan_UnregisteredType_DiscoveredWithCrc64Name (string managedName)
+	{
+		var peers = ScanFixtures ();
+		Assert.StartsWith ("crc64", FindByManagedName (peers, managedName).JavaName);
+	}
+
+	[Fact]
+	public void Scan_ExportOnUnregisteredType_MethodDiscovered ()
+	{
+		var peers = ScanFixtures ();
+		var exportMethod = FindByManagedName (peers, "MyApp.UnregisteredExporter")
+			.MarshalMethods.FirstOrDefault (m => m.JniName == "doExportedWork");
+		Assert.NotNull (exportMethod);
+		Assert.Null (exportMethod.Connector);
+	}
+}