Migrate GenerateProguardConfiguration from ILLink step to MSBuild task

src/Xamarin.Android.Build.Tasks/Microsoft.Android.Sdk/targets/Microsoft.Android.Sdk.ILLink.targets

@@ -9,6 +9,8 @@ This file contains the .NET 5-specific targets to customize ILLink
 
 <Project xmlns="http://schemas.microsoft.com/developer/msbuild/2003">
 
+  <UsingTask TaskName="Xamarin.Android.Tasks.GenerateProguardConfiguration" AssemblyFile="$(_XamarinAndroidBuildTasksAssembly)" />
+
   <Target Name="_PrepareLinking"
       Condition=" '$(PublishTrimmed)' == 'true' "
       AfterTargets="ComputeResolvedFilesToPublishList"
@@ -33,11 +35,6 @@ This file contains the .NET 5-specific targets to customize ILLink
         -->
       <_TrimmerCustomData Include="AndroidHttpClientHandlerType" Value="$(AndroidHttpClientHandlerType)" />
       <_TrimmerCustomData Include="AndroidCustomViewMapFile" Value="$(_OuterCustomViewMapFile)" />
-      <_TrimmerCustomData
-          Condition=" '$(_ProguardProjectConfiguration)' != '' "
-          Include="ProguardConfiguration"
-          Value="$(_ProguardProjectConfiguration)"
-      />
       <_TrimmerCustomData Include="SystemIOHashingAssemblyPath" Value="$(_SystemIOHashingAssemblyPath)" />
       <_TrimmerCustomSteps
         Include="$(_AndroidLinkerCustomStepAssembly)"
@@ -57,13 +54,6 @@ This file contains the .NET 5-specific targets to customize ILLink
       <_TrimmerCustomSteps Include="$(_AndroidLinkerCustomStepAssembly)" Type="Microsoft.Android.Sdk.ILLink.PreserveRegistrations" />
       <_TrimmerCustomSteps Include="$(_AndroidLinkerCustomStepAssembly)" Type="Microsoft.Android.Sdk.ILLink.PreserveJavaInterfaces" />
       <_TrimmerCustomSteps Include="$(_AndroidLinkerCustomStepAssembly)" Type="MonoDroid.Tuner.FixAbstractMethodsStep" />
-      <!-- Custom steps that run after MarkStep -->
-      <_TrimmerCustomSteps
-          Condition=" '$(_ProguardProjectConfiguration)' != '' "
-          Include="$(_AndroidLinkerCustomStepAssembly)"
-          AfterStep="CleanStep"
-          Type="Mono.Linker.Steps.GenerateProguardConfiguration"
-      />
       <_TrimmerCustomSteps
           Condition=" '$(AndroidAddKeepAlives)' == 'true' "
           Include="$(_AndroidLinkerCustomStepAssembly)"
@@ -121,4 +111,23 @@ This file contains the .NET 5-specific targets to customize ILLink
     <Touch Files="$(_AndroidLinkFlag)" AlwaysCreate="true" />
   </Target>
 
+  <Target Name="_PrepareLinkedAssembliesForProguard"
+      AfterTargets="ILLink"
+      Condition=" '$(PublishTrimmed)' == 'true' and '$(_ProguardProjectConfiguration)' != '' ">
+    <ItemGroup>
+      <_LinkedAssemblyForProguard Include="@(ManagedAssemblyToLink->'$(IntermediateLinkDir)%(Filename)%(Extension)')"
+                                   Condition="Exists('$(IntermediateLinkDir)%(Filename)%(Extension)')" />
+    </ItemGroup>
+  </Target>
+
+  <Target Name="_GenerateProguardConfiguration"
+      AfterTargets="_PrepareLinkedAssembliesForProguard"
+      Condition=" '$(PublishTrimmed)' == 'true' and '$(_ProguardProjectConfiguration)' != '' "
+      Inputs="@(_LinkedAssemblyForProguard)"
+      Outputs="$(_ProguardProjectConfiguration)">
+    <GenerateProguardConfiguration
+        LinkedAssemblies="@(_LinkedAssemblyForProguard)"
+        OutputFile="$(_ProguardProjectConfiguration)" />
+  </Target>
+
 </Project>

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

@@ -0,0 +1,135 @@
+#nullable enable
+
+using System;
+using System.IO;
+using System.Reflection.Metadata;
+using System.Reflection.PortableExecutable;
+using Microsoft.Build.Framework;
+using Microsoft.Android.Build.Tasks;
+
+namespace Xamarin.Android.Tasks
+{
+	public class GenerateProguardConfiguration : AndroidTask
+	{
+		public override string TaskPrefix => "GPC";
+
+		[Required]
+		public ITaskItem[] LinkedAssemblies { get; set; } = [];
+
+		[Required]
+		public string OutputFile { get; set; } = "";
+
+		public override bool RunTask ()
+		{
+			var dir = Path.GetDirectoryName (OutputFile);
+			if (!Directory.Exists (dir))
+				Directory.CreateDirectory (dir);
+			using var writer = File.CreateText (OutputFile);
+
+			foreach (var assembly in LinkedAssemblies) {
+				ProcessAssembly (assembly.ItemSpec, writer);
+			}
+
+			return !Log.HasLoggedErrors;
+		}
+
+		void ProcessAssembly (string assemblyPath, TextWriter writer)
+		{
+			try {
+				using var stream = File.OpenRead (assemblyPath);
+				using var pe = new PEReader (stream);
+
+				if (!pe.HasMetadata)
+					return;
+
+				var reader = pe.GetMetadataReader ();
+
+				// Those assemblies that do not reference Mono.Android.dll (such as System.*
+				// assemblies and Mono.Android.dll itself) can be skipped.
+				// (Mono.Android.dll is special; android.jar is not part of classes.dex).
+				//
+				// FIXME: Those non-embedded jar bindings could visit here too, and they don't have to
+				// be part of proguard configuration. But they don't break (they will be NOTEd though).
+				if (!ReferencesMonoAndroid (reader))
+					return;
+
+				var assemblyName = reader.GetString (reader.GetAssemblyDefinition ().Name);
+				writer.WriteLine ($"# ACW for {assemblyName}");
+
+				foreach (var typeHandle in reader.TypeDefinitions) {
+					var type = reader.GetTypeDefinition (typeHandle);
+					ProcessType (reader, type, writer);
+				}
+			} catch (BadImageFormatException) {
+				// Skip non-managed assemblies
+			}
+		}
+
+		static bool ReferencesMonoAndroid (MetadataReader reader)
+		{
+			foreach (var refHandle in reader.AssemblyReferences) {
+				var reference = reader.GetAssemblyReference (refHandle);
+				if (reader.GetString (reference.Name) == "Mono.Android")
+					return true;
+			}
+			return false;
+		}
+
+		void ProcessType (MetadataReader reader, TypeDefinition type, TextWriter writer)
+		{
+			// RegisterAttribute can be applied to interfaces, but proguard rules are only needed for classes.
+			// Structs don't need to be checked because RegisterAttribute cannot be applied to them.
+			if ((type.Attributes & System.Reflection.TypeAttributes.Interface) != 0)
+				return;
+
+			string? javaTypeName = null;
+			foreach (var attrHandle in type.GetCustomAttributes ()) {
+				var attr = reader.GetCustomAttribute (attrHandle);
+				var attrName = reader.GetCustomAttributeFullName (attr, Log);
+				if (attrName == "Android.Runtime.RegisterAttribute") {
+					var args = attr.GetCustomAttributeArguments ();
+					if (args.FixedArguments.Length > 0 && args.FixedArguments[0].Value is string jtype) {
+						javaTypeName = jtype.Replace ('/', '.');
+					}
+					break;
+				}
+			}
+
+			if (javaTypeName == null)
+				return;
+
+			writer.WriteLine ($"-keep class {javaTypeName}");
+			writer.WriteLine ($"-keepclassmembers class {javaTypeName} {{");
+
+			foreach (var methodHandle in type.GetMethods ()) {
+				ProcessMethod (reader, methodHandle, writer);
+			}
+
+			writer.WriteLine ("}");
+			writer.WriteLine ();
+		}
+
+		void ProcessMethod (MetadataReader reader, MethodDefinitionHandle methodHandle, TextWriter writer)
+		{
+			var method = reader.GetMethodDefinition (methodHandle);
+
+			foreach (var attrHandle in method.GetCustomAttributes ()) {
+				var attr = reader.GetCustomAttribute (attrHandle);
+				var attrName = reader.GetCustomAttributeFullName (attr, Log);
+				if (attrName == "Android.Runtime.RegisterAttribute") {
+					var args = attr.GetCustomAttributeArguments ();
+					if (args.FixedArguments.Length >= 2 &&
+					    args.FixedArguments[0].Value is string jname &&
+					    args.FixedArguments[1].Value is string jargs) {
+						if (jname == ".ctor") {
+							writer.WriteLine ("   <init>(...);");
+						} else {
+							writer.WriteLine ($"   *** {jname}(...);");
+						}
+					}
+					break;
+				}
+			}
+		}
+	}
+}