[Java.Interop] ignore remaining trimming warnings (dotnet#1190)

Fixes: dotnet#1157

The remaining trimmer warnings are around usage of System.Reflection
such as:

  * Creating an `Invoker` type from an original type via
    `Type.Assembly.GetType()`, within
    `JniRuntime.JniValueManager.GetInvokerType()`.

  * Create a `JniValueMarshaler` corresponding to
    `ParameterInfo.ParameterType` in
    `JniRuntime.JniMarshalMemberBuilder.GetParameterMarshaler()`.

  * Create a value corresponding to `ParameterInfo.ParameterType` in
    `ManagedPeer.GetValues()`.

  * Use `typeof(JavaObjectArray<>).MakeGenericType()` in
    `JniRuntime.JniTypeManager.GetTypes(JniTypeSignature)`.

  * Use `Type.MakeArrayType()` in
    `JniRuntime.JniTypeManager.GetTypes(JniTypeSignature)`.

The trimming warnings themselves all indicate that these types "might
be trimmed", in that nothing explicitly preserves them.  However, we
have a plethora of custom trimmer steps that work to preserve these
types involved in Java interop, such as:

  * https://github.com/xamarin/xamarin-android/blob/71b6fcc92f9e86246e0fe575bc1f44bbf73c3132/src/Microsoft.Android.Sdk.ILLink/PreserveApplications.cs
  * https://github.com/xamarin/xamarin-android/blob/71b6fcc92f9e86246e0fe575bc1f44bbf73c3132/src/Microsoft.Android.Sdk.ILLink/PreserveExportedTypes.cs
  * https://github.com/xamarin/xamarin-android/blob/71b6fcc92f9e86246e0fe575bc1f44bbf73c3132/src/Microsoft.Android.Sdk.ILLink/PreserveJavaExceptions.cs
  * https://github.com/xamarin/xamarin-android/blob/71b6fcc92f9e86246e0fe575bc1f44bbf73c3132/src/Microsoft.Android.Sdk.ILLink/PreserveJavaInterfaces.cs
  * https://github.com/xamarin/xamarin-android/blob/71b6fcc92f9e86246e0fe575bc1f44bbf73c3132/src/Microsoft.Android.Sdk.ILLink/PreserveRegistrations.cs

One day, in a perfect world, we could remove these trimmer steps and
completely rely on the trimmer's warnings & attributing mechanisms.
That day doesn't have to be today -- as our goal is begin surfacing
trimmer warnings to users in their own code and dependencies.

With these warnings ignored, we can fully enable analyzers with:

	<IsTrimmable>true</IsTrimmable>
	<EnableAotAnalyzer>true</EnableAotAnalyzer>

We can then remove:

	[assembly: AssemblyMetadata ("IsTrimmable", "True")]

As the MSBuild property does this for us, in addition to enabling
analyzers.

I don't think we should enable `$(IsAotCompatible)` quite yet, as
`Java.Interop.dll` likely *won't work* yet on NativeAOT, and this
places metadata that says an assembly is supported.  We should just
use the `$(EnableAotAnalyzer)` analyzers for now, so we don't
introduce new issues.

src/Java.Interop/Java.Interop.csproj

@@ -15,9 +15,8 @@
     <Nullable>enable</Nullable>
     <ProduceReferenceAssembly>true</ProduceReferenceAssembly>
     <EnableSingleFileAnalyzer>true</EnableSingleFileAnalyzer>
-    <!-- TODO: enable these when all warnings are solved -->
-    <!--<IsTrimmable>true</IsTrimmable>-->
-    <!--<EnableAotAnalyzer>true</EnableAotAnalyzer>-->
+    <IsTrimmable>true</IsTrimmable>
+    <EnableAotAnalyzer>true</EnableAotAnalyzer>
     <MSBuildWarningsAsMessages>NU1702</MSBuildWarningsAsMessages>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">

src/Java.Interop/Java.Interop/JniRuntime.JniMarshalMemberBuilder.cs

@@ -152,6 +152,12 @@ string GetTypeSignature (ParameterInfo p)
 
 			public JniValueMarshaler GetParameterMarshaler (ParameterInfo parameter)
 			{
+				// Activator.CreateInstance requires DynamicallyAccessedMemberTypes.PublicParameterlessConstructor
+				// GetValueMarshaler requires DynamicallyAccessedMemberTypes.Interfaces
+				[UnconditionalSuppressMessage ("Trimming", "IL2072", Justification = "JniValueMarshalerAttribute is decorated with [DynamicallyAccessedMembers]")]
+				static JniValueMarshaler GetValueMarshaler (JniValueManager manager, ParameterInfo parameter) =>
+					manager.GetValueMarshaler (parameter.ParameterType);
+
 				if (parameter.ParameterType == typeof (IntPtr))
 					return IntPtrValueMarshaler.Instance;
 
@@ -164,7 +170,7 @@ public JniValueMarshaler GetParameterMarshaler (ParameterInfo parameter)
 				if (attr != null) {
 					return (JniValueMarshaler) Activator.CreateInstance (attr.MarshalerType)!;
 				}
-				return Runtime.ValueManager.GetValueMarshaler (parameter.ParameterType);
+				return GetValueMarshaler (Runtime.ValueManager, parameter);
 			}
 
 			// Heuristic: if first two parameters are IntPtr, this is a "direct" wrapper.

src/Java.Interop/Java.Interop/JniRuntime.JniTypeManager.cs

@@ -269,8 +269,18 @@ protected virtual IEnumerable<string> GetSimpleReferences (Type type)
 
 			static  readonly    string[]    EmptyStringArray    = Array.Empty<string> ();
 			static  readonly    Type[]      EmptyTypeArray      = Array.Empty<Type> ();
+			const string NotUsedInAndroid = "This code path is not used in Android projects.";
 
+			// FIXME: https://github.com/xamarin/java.interop/issues/1192
+			[UnconditionalSuppressMessage ("AOT", "IL3050", Justification = NotUsedInAndroid)]
+			static Type MakeArrayType (Type type) => type.MakeArrayType ();
 
+			// FIXME: https://github.com/xamarin/java.interop/issues/1192
+			[UnconditionalSuppressMessage ("Trimming", "IL2055", Justification = NotUsedInAndroid)]
+			[UnconditionalSuppressMessage ("AOT",      "IL3050", Justification = NotUsedInAndroid)]
+			static Type MakeGenericType (Type type, Type arrayType) => type.MakeGenericType (arrayType);
+
+			[UnconditionalSuppressMessage ("Trimming", "IL2073", Justification = "Types returned here should be preserved via other means.")]
 			[return: DynamicallyAccessedMembers (MethodsConstructorsInterfaces)]
 			public  Type?    GetType (JniTypeSignature typeSignature)
 			{
@@ -309,7 +319,7 @@ IEnumerable<Type> CreateGetTypesEnumerator (JniTypeSignature typeSignature)
 						var rank        = typeSignature.ArrayRank;
 						var arrayType   = type;
 						while (rank-- > 0) {
-							arrayType   = typeof (JavaObjectArray<>).MakeGenericType (arrayType);
+							arrayType   = MakeGenericType (typeof (JavaObjectArray<>), arrayType);
 						}
 						yield return arrayType;
 					}
@@ -318,7 +328,7 @@ IEnumerable<Type> CreateGetTypesEnumerator (JniTypeSignature typeSignature)
 						var rank        = typeSignature.ArrayRank;
 						var arrayType   = type;
 						while (rank-- > 0) {
-							arrayType   = arrayType.MakeArrayType ();
+							arrayType   = MakeArrayType (arrayType);
 						}
 						yield return arrayType;
 					}
@@ -341,14 +351,14 @@ IEnumerable<Type> GetPrimitiveArrayTypesForSimpleReference (JniTypeSignature typ
 					var rank        = typeSignature.ArrayRank-1;
 					var arrayType   = t;
 					while (rank-- > 0) {
-						arrayType   = typeof (JavaObjectArray<>).MakeGenericType (arrayType);
+						arrayType   = MakeGenericType (typeof (JavaObjectArray<>), arrayType);
 					}
 					yield return arrayType;
 
 					rank            = typeSignature.ArrayRank-1;
 					arrayType       = t;
 					while (rank-- > 0) {
-						arrayType   = arrayType.MakeArrayType ();
+						arrayType   = MakeArrayType (arrayType);
 					}
 					yield return arrayType;
 				}
@@ -462,6 +472,11 @@ protected bool TryRegisterNativeMembers (
 
 			static Type [] registerMethodParameters = new Type [] { typeof (JniNativeMethodRegistrationArguments) };
 
+			// https://github.com/xamarin/xamarin-android/blob/5472eec991cc075e4b0c09cd98a2331fb93aa0f3/src/Microsoft.Android.Sdk.ILLink/PreserveRegistrations.cs#L85
+			const string MarshalMethods = "'jni_marshal_methods' is preserved by the PreserveRegistrations trimmer step.";
+
+			[UnconditionalSuppressMessage ("Trimming", "IL2072", Justification = MarshalMethods)]
+			[UnconditionalSuppressMessage ("Trimming", "IL2075", Justification = MarshalMethods)]
 			bool TryLoadJniMarshalMethods (
 					JniType nativeClass,
 					[DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]

src/Java.Interop/Java.Interop/JniRuntime.JniValueManager.cs

@@ -359,18 +359,36 @@ static Type GetPeerType ([DynamicallyAccessedMembers (Constructors)] Type type)
 			static Type? GetInvokerType (Type type)
 			{
 				const string suffix = "Invoker";
+
+				// https://github.com/xamarin/xamarin-android/blob/5472eec991cc075e4b0c09cd98a2331fb93aa0f3/src/Microsoft.Android.Sdk.ILLink/MarkJavaObjects.cs#L176-L186
+				const string assemblyGetTypeMessage = "'Invoker' types are preserved by the MarkJavaObjects trimmer step.";
+				const string makeGenericTypeMessage = "Generic 'Invoker' types are preserved by the MarkJavaObjects trimmer step.";
+
+				[UnconditionalSuppressMessage ("Trimming", "IL2026", Justification = assemblyGetTypeMessage)]
+				[UnconditionalSuppressMessage ("Trimming", "IL2073", Justification = assemblyGetTypeMessage)]
+				[return: DynamicallyAccessedMembers (Constructors)]
+				static Type? AssemblyGetType (Assembly assembly, string typeName) =>
+					assembly.GetType (typeName);
+
+				// FIXME: https://github.com/xamarin/java.interop/issues/1192
+				[UnconditionalSuppressMessage ("Trimming", "IL2055", Justification = makeGenericTypeMessage)]
+				[UnconditionalSuppressMessage ("AOT",      "IL3050", Justification = makeGenericTypeMessage)]
+				[return: DynamicallyAccessedMembers (Constructors)]
+				static Type MakeGenericType (Type type, Type [] arguments) =>
+					type.MakeGenericType (arguments);
+
 				Type[] arguments = type.GetGenericArguments ();
 				if (arguments.Length == 0)
-					return type.Assembly.GetType (type + suffix);
+					return AssemblyGetType (type.Assembly, type + suffix);
 				Type definition = type.GetGenericTypeDefinition ();
 				int bt = definition.FullName!.IndexOf ("`", StringComparison.Ordinal);
 				if (bt == -1)
 					throw new NotSupportedException ("Generic type doesn't follow generic type naming convention! " + type.FullName);
-				Type? suffixDefinition = definition.Assembly.GetType (
+				Type? suffixDefinition = AssemblyGetType (definition.Assembly,
 						definition.FullName.Substring (0, bt) + suffix + definition.FullName.Substring (bt));
 				if (suffixDefinition == null)
 					return null;
-				return suffixDefinition.MakeGenericType (arguments);
+				return MakeGenericType (suffixDefinition, arguments);
 			}
 
 			public object? CreateValue (
@@ -634,9 +652,17 @@ public JniValueMarshaler GetValueMarshaler (
 
 			static JniValueMarshaler GetObjectArrayMarshaler (Type elementType)
 			{
+				const string makeGenericMethodMessage = "This code path is not used in Android projects.";
+
+				// FIXME: https://github.com/xamarin/java.interop/issues/1192
+				[UnconditionalSuppressMessage ("Trimming", "IL2060", Justification = makeGenericMethodMessage)]
+				[UnconditionalSuppressMessage ("AOT",      "IL3050", Justification = makeGenericMethodMessage)]
+				static MethodInfo MakeGenericMethod (MethodInfo method, Type type) =>
+					method.MakeGenericMethod (type);
+
 				Func<JniValueMarshaler> indirect = GetObjectArrayMarshalerHelper<object>;
-				var reifiedMethodInfo = indirect.Method.GetGenericMethodDefinition ()
-					.MakeGenericMethod (elementType);
+				var reifiedMethodInfo = MakeGenericMethod (
+						indirect.Method.GetGenericMethodDefinition (), elementType);
 				Func<JniValueMarshaler> direct = (Func<JniValueMarshaler>) Delegate.CreateDelegate (typeof (Func<JniValueMarshaler>), reifiedMethodInfo);
 				return direct ();
 			}

src/Java.Interop/Java.Interop/JniValueMarshalerAttribute.cs

@@ -1,4 +1,4 @@
-#nullable enable
+#nullable enable
 
 using System;
 using System.Diagnostics.CodeAnalysis;
@@ -8,13 +8,16 @@ namespace Java.Interop {
 
 	[AttributeUsage (Targets, AllowMultiple=false)]
 	public class JniValueMarshalerAttribute : Attribute {
+		const DynamicallyAccessedMemberTypes ParameterlessConstructorsInterfaces = DynamicallyAccessedMemberTypes.PublicParameterlessConstructor | DynamicallyAccessedMemberTypes.Interfaces;
 
 		const   AttributeTargets    Targets =
 			AttributeTargets.Class | AttributeTargets.Enum |
 			AttributeTargets.Interface | AttributeTargets.Struct |
 			AttributeTargets.Parameter | AttributeTargets.ReturnValue;
 
-		public JniValueMarshalerAttribute (Type marshalerType)
+		public JniValueMarshalerAttribute (
+				[DynamicallyAccessedMembers (ParameterlessConstructorsInterfaces)]
+				Type marshalerType)
 		{
 			if (marshalerType == null)
 				throw new ArgumentNullException (nameof (marshalerType));
@@ -27,7 +30,7 @@ public JniValueMarshalerAttribute (Type marshalerType)
 		}
 
 		public  Type    MarshalerType   {
-			[return: DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]
+			[return: DynamicallyAccessedMembers (ParameterlessConstructorsInterfaces)]
 			get;
 		}
 	}

src/Java.Interop/Java.Interop/ManagedPeer.cs

@@ -229,6 +229,11 @@ static List<Type>[] GetConstructorCandidateParameterTypes (string signature)
 
 		static object?[]? GetValues (JniRuntime runtime, JniObjectReference values, ConstructorInfo cinfo)
 		{
+			// https://github.com/xamarin/xamarin-android/blob/5472eec991cc075e4b0c09cd98a2331fb93aa0f3/src/Microsoft.Android.Sdk.ILLink/MarkJavaObjects.cs#L51-L132
+			[UnconditionalSuppressMessage ("Trimming", "IL2072", Justification = "Constructors are preserved by the MarkJavaObjects trimmer step.")]
+			static object? ValueManagerGetValue (JniRuntime runtime, ref JniObjectReference value, ParameterInfo parameter) =>
+				runtime.ValueManager.GetValue (ref value, JniObjectReferenceOptions.CopyAndDispose, parameter.ParameterType);
+
 			if (!values.IsValid)
 				return null;
 
@@ -240,7 +245,7 @@ static List<Type>[] GetConstructorCandidateParameterTypes (string signature)
 			var pvalues = new object? [len];
 			for (int i = 0; i < len; ++i) {
 				var n_value = JniEnvironment.Arrays.GetObjectArrayElement (values, i);
-				var value   = runtime.ValueManager.GetValue (ref n_value, JniObjectReferenceOptions.CopyAndDispose, parameters [i].ParameterType);
+				var value   = ValueManagerGetValue (runtime, ref n_value, parameters [i]);
 				pvalues [i] = value;
 			}
 

src/Java.Interop/Properties/AssemblyInfo.cs

@@ -6,7 +6,6 @@
 [assembly: AssemblyDescription ("")]
 [assembly: AssemblyCulture ("")]
 [assembly: AssemblyTrademark ("Microsoft Corporation")]
-[assembly: AssemblyMetadata ("IsTrimmable", "True")]
 
 [assembly: InternalsVisibleTo (
 	"Java.Interop.GenericMarshaler, PublicKey=" +