[java.interop] address some "easy" trimmer warnings

Context: dotnet#1157

On the path to enabling `IsAotCompatible`, we can enable some settings
to get started:

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

This opts into the analyzers without declaring the assembly is fully
AOT-compatible.

Starting out, I got 33 warnings: this is an attempt to address the
ones that don't require too much thinking. Unfortunately, solving 1
warning likely will create dozens more -- as you have to update all
callers.

This results in 24 warnings remaining. Since `Release` builds have
`$(TreatWarningsAsErrors)`, I will wait to enable the analyzers until
all warnings are addressed.

~~ Example Warnings ~~

`System.Linq.Expression` usage:

    src\Java.Interop\Java.Interop\JniRuntime.JniValueManager.cs(672,58):
    warning IL2026: Using member 'System.Linq.Expressions.Expression.Property(Expression, String)' which has 'RequiresUnreferencedCodeAttribute' can break functionality when trimming application code. Creating Expressions requires unreferenced code because the members being referenced by the Expression may be trimmed.

I decorated this one with:

    [RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]

`Type.GetNestedType()` usage:

    src\Java.Interop\Java.Interop\JniRuntime.JniTypeManager.cs(447,28):
    warning IL2070: 'this' argument does not satisfy 'DynamicallyAccessedMemberTypes.NonPublicNestedTypes' in call to 'System.Type.GetNestedType(String, BindingFlags)'. The parameter 'type' of method 'Java.Interop.JniRuntime.JniTypeManager.TryLoadJniMarshalMethods(JniType, Type, String)' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.

Added:

    [DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.NonPublicNestedTypes)]

`Activator.CreateInstance()` usage:

    src\Java.Interop\Java.Interop\JniRuntime.JniValueManager.cs(542,33): warning IL2072: 'type' argument does not satisfy 'DynamicallyAccessedMemberTypes.PublicParameterlessConstructor' in call to 'System.Activator.CreateInstance(Type)'. The return value of method 'Java.Interop.JniValueMarshalerAttribute.MarshalerType.get' does not have matching annotations. The source value must declare at least the same requirements as those declared on the target location it is assigned to.

Added:

    [return: DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicParameterlessConstructor)]

~~ Code that Actually Changed ~~

As I enabled more attributes, these snowball into more and more
warnings! I eventually had to make `GetPeerType()` look like:

    [return: DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)]
    static Type GetPeerType ([DynamicallyAccessedMembers (DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors)] Type type)

The analyzer was not able to understand code like:

    static  readonly    KeyValuePair<Type, Type>[]      PeerTypeMappings = new []{
        new KeyValuePair<Type, Type>(typeof (object),           typeof (JavaObject)),
        new KeyValuePair<Type, Type>(typeof (IJavaPeerable),    typeof (JavaObject)),
        new KeyValuePair<Type, Type>(typeof (Exception),        typeof (JavaException)),
    };
    //...
    foreach (var m in PeerTypeMappings) {
        if (m.Key == type)
            return m.Value;
    }

Simply removing the `PeerTypeMappings` array and using `if` statements
solved the warnings. This may be the only real code change if any.

src/Java.Interop/Java.Interop.csproj

@@ -14,6 +14,10 @@
     <AllowUnsafeBlocks>true</AllowUnsafeBlocks>
     <Nullable>enable</Nullable>
     <ProduceReferenceAssembly>true</ProduceReferenceAssembly>
+    <EnableSingleFileAnalyzer>true</EnableSingleFileAnalyzer>
+    <!-- TODO: enable these when all warnings are solved -->
+    <!--<IsTrimmable>true</IsTrimmable>-->
+    <!--<EnableAotAnalyzer>true</EnableAotAnalyzer>-->
     <MSBuildWarningsAsMessages>NU1702</MSBuildWarningsAsMessages>
   </PropertyGroup>
   <PropertyGroup Condition=" '$(Configuration)' == 'Debug' ">

src/Java.Interop/Java.Interop/JavaArray.cs

@@ -12,6 +12,8 @@ namespace Java.Interop
 {
 	public abstract class JavaArray<T> : JavaObject, IList, IList<T>
 	{
+		internal const DynamicallyAccessedMemberTypes ConstructorsAndInterfaces = DynamicallyAccessedMemberTypes.PublicConstructors | DynamicallyAccessedMemberTypes.NonPublicConstructors | DynamicallyAccessedMemberTypes.Interfaces;
+
 		internal delegate TArray ArrayCreator<TArray> (ref JniObjectReference reference, JniObjectReferenceOptions transfer)
 			where TArray : JavaArray<T>;
 
@@ -362,7 +364,7 @@ public void Dispose ()
 		}
 	}
 
-	public abstract class JavaPrimitiveArray<T> : JavaArray<T> {
+	public abstract class JavaPrimitiveArray<[DynamicallyAccessedMembers (ConstructorsAndInterfaces)] T> : JavaArray<T> {
 
 		internal JavaPrimitiveArray (ref JniObjectReference reference, JniObjectReferenceOptions transfer)
 			: base (ref reference, transfer)

src/Java.Interop/Java.Interop/JavaObjectArray.cs

@@ -1,4 +1,4 @@
-#nullable enable
+#nullable enable
 
 using System;
 using System.Collections.Generic;
@@ -7,7 +7,7 @@
 
 namespace Java.Interop
 {
-	public class JavaObjectArray<T> : JavaArray<T>
+	public class JavaObjectArray<[DynamicallyAccessedMembers (ConstructorsAndInterfaces)] T> : JavaArray<T>
 	{
 		internal    static  readonly    ValueMarshaler   Instance           = new ValueMarshaler ();
 
@@ -164,7 +164,7 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<T>> {
 
-			public override IList<T> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<T> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<T>.CreateValue (ref reference, options, targetType, (ref JniObjectReference h, JniObjectReferenceOptions t) => new JavaObjectArray<T> (ref h, t) {
 					forMarshalCollection    = true,
@@ -194,7 +194,7 @@ partial class JniEnvironment {
 		[SuppressMessage ("Design", "CA1034", Justification = "https://github.com/xamarin/Java.Interop/commit/bb7ca5d02aa3fc2b447ad57af1256e74e5f954fa")]
 		partial class Arrays {
 
-			public static JavaObjectArray<T>? CreateMarshalObjectArray<T> (IEnumerable<T>? value)
+			public static JavaObjectArray<T>? CreateMarshalObjectArray<[DynamicallyAccessedMembers (JavaArray<T>.ConstructorsAndInterfaces)] T> (IEnumerable<T>? value)
 			{
 				if (value == null) {
 					return null;

src/Java.Interop/Java.Interop/JavaPrimitiveArrays.cs

@@ -244,14 +244,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaBooleanArray) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers(JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Boolean>> {
 
-			public override IList<Boolean> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Boolean> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Boolean>.CreateValue (
 						ref reference,
@@ -276,6 +276,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Boolean> val
 				JavaArray<Boolean>.DestroyArgumentState<JavaBooleanArray> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaBooleanArray.CreateMarshaledValue;
@@ -439,14 +440,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaSByteArray) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<SByte>> {
 
-			public override IList<SByte> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<SByte> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<SByte>.CreateValue (
 						ref reference,
@@ -471,6 +472,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<SByte> value
 				JavaArray<SByte>.DestroyArgumentState<JavaSByteArray> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaSByteArray.CreateMarshaledValue;
@@ -634,14 +636,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaCharArray) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Char>> {
 
-			public override IList<Char> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Char> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Char>.CreateValue (
 						ref reference,
@@ -666,6 +668,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Char> value,
 				JavaArray<Char>.DestroyArgumentState<JavaCharArray> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaCharArray.CreateMarshaledValue;
@@ -829,14 +832,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaInt16Array) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Int16>> {
 
-			public override IList<Int16> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Int16> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Int16>.CreateValue (
 						ref reference,
@@ -861,6 +864,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Int16> value
 				JavaArray<Int16>.DestroyArgumentState<JavaInt16Array> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaInt16Array.CreateMarshaledValue;
@@ -1024,14 +1028,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaInt32Array) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Int32>> {
 
-			public override IList<Int32> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Int32> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Int32>.CreateValue (
 						ref reference,
@@ -1056,6 +1060,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Int32> value
 				JavaArray<Int32>.DestroyArgumentState<JavaInt32Array> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaInt32Array.CreateMarshaledValue;
@@ -1219,14 +1224,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaInt64Array) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Int64>> {
 
-			public override IList<Int64> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Int64> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Int64>.CreateValue (
 						ref reference,
@@ -1251,6 +1256,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Int64> value
 				JavaArray<Int64>.DestroyArgumentState<JavaInt64Array> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaInt64Array.CreateMarshaledValue;
@@ -1414,14 +1420,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaSingleArray) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Single>> {
 
-			public override IList<Single> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Single> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Single>.CreateValue (
 						ref reference,
@@ -1446,6 +1452,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Single> valu
 				JavaArray<Single>.DestroyArgumentState<JavaSingleArray> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaSingleArray.CreateMarshaledValue;
@@ -1609,14 +1616,14 @@ internal override bool TargetTypeIsCurrentType (Type? targetType)
 				typeof (JavaDoubleArray) == targetType;
 		}
 
-		public static object? CreateMarshaledValue (IntPtr handle, Type? targetType)
+		public static object? CreateMarshaledValue (IntPtr handle, [DynamicallyAccessedMembers (JniValueMarshaler.ConstructorsAndInterfaces)] Type? targetType)
 		{
 			return ArrayMarshaler.CreateValue (handle, targetType);
 		}
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<Double>> {
 
-			public override IList<Double> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<Double> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<Double>.CreateValue (
 						ref reference,
@@ -1641,6 +1648,7 @@ public override void DestroyGenericArgumentState ([AllowNull] IList<Double> valu
 				JavaArray<Double>.DestroyArgumentState<JavaDoubleArray> (value, ref state, synchronize);
 			}
 
+			[RequiresUnreferencedCode (ExpressionRequiresUnreferencedCode)]
 			public override Expression CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize = 0, Type? targetType = null)
 			{
 				Func<IntPtr, Type?, object?>  m = JavaDoubleArray.CreateMarshaledValue;

src/Java.Interop/Java.Interop/JavaPrimitiveArrays.tt

@@ -248,7 +248,7 @@ namespace Java.Interop {
 
 		internal sealed class ValueMarshaler : JniValueMarshaler<IList<<#= info.TypeModifier #>>> {
 
-			public override IList<<#= info.TypeModifier #>> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, Type? targetType)
+			public override IList<<#= info.TypeModifier #>> CreateGenericValue (ref JniObjectReference reference, JniObjectReferenceOptions options, [DynamicallyAccessedMembers (ConstructorsAndInterfaces)] Type? targetType)
 			{
 				return JavaArray<<#= info.TypeModifier #>>.CreateValue (
 						ref reference,