[Xamarin.Android.Build.Tasks] Support HandleKind.TypeSpecification (#9373)

Fixes: #9369

[C# 11 added support for generic custom attributes][0]:

	[AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
	public class GenericTestAttribute<T> : Attribute {
	}

which means generic types can now be used as assembly-level attributes:

	[assembly: GenericTestAttribute<string>]

Unfortunately, attempting to do this would result in an
`InvalidCastException` from the `<FilterAssemblies/>` task:

	System.InvalidCastException: Die angegebene Umwandlung ist ungültig.
	error XAFLT7007:    bei System.Reflection.Throw.InvalidCast()
	error XAFLT7007:    bei System.Reflection.Metadata.TypeReferenceHandle.op_Explicit(EntityHandle handle)
	error XAFLT7007:    bei Xamarin.Android.Tasks.MetadataExtensions.GetCustomAttributeFullName(MetadataReader reader, CustomAttribute attribute)
	error XAFLT7007:    bei Xamarin.Android.Tasks.FilterAssemblies.IsAndroidAssembly(AssemblyDefinition assembly, MetadataReader reader)
	error XAFLT7007:    bei Xamarin.Android.Tasks.FilterAssemblies.ProcessAssembly(ITaskItem assemblyItem, List`1 output)
	error XAFLT7007:    bei Xamarin.Android.Tasks.FilterAssemblies.RunTask()
	error XAFLT7007:    bei Microsoft.Android.Build.Tasks.AndroidTask.Execute()

This happens because when System.Reflection.Metadata comes across an
Attribute which has a generic type parameter, it does *not* return a
[`TypeReferenceHandle`][1], but instead a
[`TypeSpecificationHandle`][2].

Update `MetadataExtensions.GetCustomAttributeFullName()` to support
[`HandleKind.TypeSpecification`][3]

[0]: https://learn.microsoft.com/dotnet/csharp/whats-new/csharp-11#generic-attributes
[1]: https://learn.microsoft.com/dotnet/api/system.reflection.metadata.typereferencehandle?view=net-8.0
[2]: https://learn.microsoft.com/dotnet/api/system.reflection.metadata.typespecificationhandle?view=net-8.0
[3]: https://learn.microsoft.com/dotnet/api/system.reflection.metadata.handlekind?view=net-8.0

Author: dellis1972

samples/HelloWorld/HelloLibrary/LibraryActivity.cs

@@ -16,8 +16,12 @@
 using Android.Views;
 using Android.Widget;
 
+[assembly: HelloLibrary.GenericTest<string>]
 namespace HelloLibrary
 {
+    [AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
+    public class GenericTestAttribute<T> : Attribute { }
+
     [Activity(Label = "Library Activity", Name="mono.samples.hello.LibraryActivity")]
     public class LibraryActivity : Activity
     {

src/Xamarin.Android.Build.Tasks/Tasks/BuildApk.cs

@@ -493,7 +493,7 @@ void DoAddAssembliesFromArchCollection (AndroidTargetArch arch, Dictionary<strin
 				// Thus, we no longer just store them in the apk but we call the `GetCompressionMethod` method to find out whether
 				// or not we're supposed to compress .so files.
 				foreach (ITaskItem assembly in assemblies.Values) {
-					if (MonoAndroidHelper.IsReferenceAssembly (assembly.ItemSpec)) {
+					if (MonoAndroidHelper.IsReferenceAssembly (assembly.ItemSpec, Log)) {
 						Log.LogCodedWarning ("XA0107", assembly.ItemSpec, 0, Properties.Resources.XA0107, assembly.ItemSpec);
 					}
 

src/Xamarin.Android.Build.Tasks/Tasks/FilterAssemblies.cs

@@ -102,7 +102,7 @@ bool IsAndroidAssembly (AssemblyDefinition assembly, MetadataReader reader)
 		{
 			foreach (var handle in assembly.GetCustomAttributes ()) {
 				var attribute = reader.GetCustomAttribute (handle);
-				var name = reader.GetCustomAttributeFullName (attribute);
+				var name = reader.GetCustomAttributeFullName (attribute, Log);
 				switch (name) {
 					case "System.Runtime.Versioning.TargetFrameworkAttribute":
 						string targetFrameworkIdentifier = null;

src/Xamarin.Android.Build.Tasks/Tests/Xamarin.Android.Build.Tests/BuildTest2.cs

@@ -1461,5 +1461,48 @@ public void BuildWithJavaToolOptions ()
 				Environment.SetEnvironmentVariable ("JAVA_TOOL_OPTIONS", oldEnvVar);
 			}
 		}
+
+		[Test]
+		public void LibraryWithGenericAttribute ()
+		{
+			var path = Path.Combine ("temp", TestContext.CurrentContext.Test.Name);
+			var lib = new XamarinAndroidLibraryProject {
+				ProjectName = "Library1",
+				IsRelease = true,
+				Sources = {
+					new BuildItem.Source ("Class1.cs") {
+						TextContent = () => """
+							namespace Library1;
+							public class Class1 { }
+						"""
+					},
+					new BuildItem.Source ("GenericTestAttribute.cs") {
+						TextContent = () => """
+							using System;
+							[assembly: GenericTestAttribute<Guid>]
+							[AttributeUsage(AttributeTargets.Assembly, AllowMultiple = true, Inherited = false)]
+							public class GenericTestAttribute<T> : Attribute { }
+						""",
+					},
+				},
+			};
+			var proj = new XamarinAndroidApplicationProject {
+				ProjectName = "App1",
+				IsRelease = true,
+				Sources = {
+					new BuildItem.Source ("Class2.cs") {
+						TextContent= () => """
+							namespace App1;
+							class Class2 : Library1.Class1 { }
+						""",
+					},
+				},
+			};
+			proj.AddReference (lib);
+			using var libb = CreateDllBuilder (Path.Combine (path, "Library1"));
+			Assert.IsTrue (libb.Build (lib), "Library1 Build should have succeeded.");
+			using var b = CreateApkBuilder (Path.Combine (path, "App1"));
+			Assert.IsTrue (b.Build (proj), "App1 Build should have succeeded.");
+		}
 	}
 }

src/Xamarin.Android.Build.Tasks/Utilities/MetadataExtensions.cs

@@ -3,17 +3,37 @@
 using System.IO;
 using System.Reflection.Metadata;
 using System.Reflection.PortableExecutable;
+using Microsoft.Build.Utilities;
+using Microsoft.Android.Build.Tasks;
 
 namespace Xamarin.Android.Tasks
 {
 	public static class MetadataExtensions
 	{
-		public static string GetCustomAttributeFullName (this MetadataReader reader, CustomAttribute attribute)
+		public static string GetCustomAttributeFullName (this MetadataReader reader, CustomAttribute attribute, TaskLoggingHelper log)
 		{
 			if (attribute.Constructor.Kind == HandleKind.MemberReference) {
 				var ctor = reader.GetMemberReference ((MemberReferenceHandle)attribute.Constructor);
-				var type = reader.GetTypeReference ((TypeReferenceHandle)ctor.Parent);
-				return reader.GetString (type.Namespace) + "." + reader.GetString (type.Name);
+				try {
+					if (ctor.Parent.Kind == HandleKind.TypeReference) {
+						var type = reader.GetTypeReference ((TypeReferenceHandle)ctor.Parent);
+						return reader.GetString (type.Namespace) + "." + reader.GetString (type.Name);
+					} else if (ctor.Parent.Kind == HandleKind.TypeSpecification) {
+						var type = reader.GetTypeSpecification ((TypeSpecificationHandle)ctor.Parent);
+						BlobReader blobReader = reader.GetBlobReader (type.Signature);
+						SignatureTypeCode typeCode = blobReader.ReadSignatureTypeCode ();
+						EntityHandle typeHandle = blobReader.ReadTypeHandle ();
+						TypeReference typeRef = reader.GetTypeReference ((TypeReferenceHandle)typeHandle);
+						return reader.GetString (typeRef.Namespace) + "." + reader.GetString (typeRef.Name);
+					} else {
+						log.LogDebugMessage ($"Unsupported EntityHandle.Kind: {ctor.Parent.Kind}");
+						return null;
+					}
+				}
+				catch (InvalidCastException ex) {
+					log.LogDebugMessage ($"Unsupported EntityHandle.Kind `{ctor.Parent.Kind}`: {ex}");
+					return null;
+				}
 			} else if (attribute.Constructor.Kind == HandleKind.MethodDefinition) {
 				var ctor = reader.GetMethodDefinition ((MethodDefinitionHandle)attribute.Constructor);
 				var type = reader.GetTypeDefinition (ctor.GetDeclaringType ());

src/Xamarin.Android.Build.Tasks/Utilities/MonoAndroidHelper.cs

@@ -364,15 +364,15 @@ public static bool HasMonoAndroidReference (MetadataReader reader)
 			return false;
 		}
 
-		public static bool IsReferenceAssembly (string assembly)
+		public static bool IsReferenceAssembly (string assembly, TaskLoggingHelper log)
 		{
 			using (var stream = File.OpenRead (assembly))
 			using (var pe = new PEReader (stream)) {
 				var reader = pe.GetMetadataReader ();
 				var assemblyDefinition = reader.GetAssemblyDefinition ();
 				foreach (var handle in assemblyDefinition.GetCustomAttributes ()) {
 					var attribute = reader.GetCustomAttribute (handle);
-					var attributeName = reader.GetCustomAttributeFullName (attribute);
+					var attributeName = reader.GetCustomAttributeFullName (attribute, log);
 					if (attributeName == "System.Runtime.CompilerServices.ReferenceAssemblyAttribute")
 						return true;
 				}

src/Xamarin.Android.Build.Tasks/Utilities/ResourceDesignerImportGenerator.cs

@@ -85,7 +85,7 @@ string GetResourceDesignerClass (MetadataReader reader)
 			var assembly = reader.GetAssemblyDefinition ();
 			foreach (var handle in assembly.GetCustomAttributes ()) {
 				var attribute = reader.GetCustomAttribute (handle);
-				var fullName = reader.GetCustomAttributeFullName (attribute);
+				var fullName = reader.GetCustomAttributeFullName (attribute, Log);
 				if (fullName == "Android.Runtime.ResourceDesignerAttribute") {
 					var values = attribute.GetCustomAttributeArguments ();
 					foreach (var arg in values.NamedArguments) {