[Java.Interop] Add JniRuntime.JniValueManager.ActivatePeer() (#784)

Context: dotnet/android#5400

The `Java.Interop.ManagedPeer` type uses `System.Linq.Expressions`
in order to invoke a constructor as part of Java-side activation;
see also 8c83f64.

The use of `System.Linq.Expressions` and
`JniRuntime.JniMarshalMemberBuilder.CreateConstructActivationPeerFunc()`
increases Xamarin.Android `.apk` size by ~136KB, which is undesirable
as ~no Xamarin.Android apps *use* `ManagedPeer`, other than the
`Mono.Android-Tests` unit test app.

Add a new `JniRuntime.JniValueManager.ActivatePeer()` method, which
`ManagedPeer.Construct()` can now call instead of
`CreateConstructActivationPeerFunc()`.  This allows the
`CreateConstructActivationPeerFunc()` invocation to be moved into
`Java.Runtime.Environment.dll`.  (Xamarin.Android instead uses
`System.Reflection.Emit`, and doesn't use `System.Linq.Expressions`.)

This in turn means that `System.Linq.Expressions` is no longer used
in the "default" Xamarin.Android app case, allowing smaller `.apk`s.

Author: radekdoulik

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

@@ -86,6 +86,8 @@ protected virtual void Dispose (bool disposing)
 
 			public abstract List<JniSurfacedPeerInfo>   GetSurfacedPeers ();
 
+			public abstract void ActivatePeer (IJavaPeerable? self, JniObjectReference reference, ConstructorInfo cinfo, object? []? argumentValues);
+
 			public void ConstructPeer (IJavaPeerable peer, ref JniObjectReference reference, JniObjectReferenceOptions options)
 			{
 				if (peer == null)

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

@@ -93,31 +93,17 @@ static void Construct (
 
 				var ptypes  = GetParameterTypes (JniEnvironment.Strings.ToString (n_constructorSignature));
 				var pvalues = GetValues (runtime, new JniObjectReference (n_constructorArguments), ptypes);
-				var ctor    = type.GetConstructors (BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
-					.FirstOrDefault (c =>
-						c.GetParameters ().Select (p => p.ParameterType).SequenceEqual (ptypes));
-				if (ctor == null) {
+				var cinfo = type.GetConstructor (ptypes);
+				if (cinfo == null) {
 					throw CreateMissingConstructorException (type, ptypes);
 				}
+
 				if (self != null) {
-					ctor.Invoke (self, pvalues);
+					cinfo.Invoke (self, pvalues);
 					return;
 				}
 
-				try {
-					var f = JniEnvironment.Runtime.MarshalMemberBuilder.CreateConstructActivationPeerFunc (ctor);
-					f (ctor, new JniObjectReference (n_self), pvalues);
-				}
-				catch (Exception e) {
-					var m = string.Format ("Could not activate {{ PeerReference={0} IdentityHashCode=0x{1} Java.Type={2} }} for managed type '{3}'.",
-							r_self,
-							runtime.ValueManager.GetJniIdentityHashCode (r_self).ToString ("x"),
-							JniEnvironment.Types.GetJniTypeNameFromInstance (r_self),
-							type.FullName);
-					Debug.WriteLine (m);
-
-					throw new NotSupportedException (m, e);
-				}
+				JniEnvironment.Runtime.ValueManager.ActivatePeer (self, new JniObjectReference (n_self), cinfo, pvalues);
 			}
 			catch (Exception e) when (JniEnvironment.Runtime.ExceptionShouldTransitionToJni (e)) {
 				envp.SetPendingException (e);
@@ -127,29 +113,33 @@ static void Construct (
 			}
 		}
 
-		static Exception CreateJniLocationException ()
-		{
-			using (var e = new JavaException ()) {
-				return new JniLocationException (e.ToString ());
-			}
-		}
-
-		static Exception CreateMissingConstructorException (Type type, Type[] ptypes)
+		static Exception CreateMissingConstructorException (Type type, Type [] ptypes)
 		{
 			var message = new StringBuilder ();
 			message.Append ("Unable to find constructor ");
 			message.Append (type.FullName);
 			message.Append ("(");
+
 			if (ptypes.Length > 0) {
 				message.Append (ptypes [0].FullName);
 				for (int i = 1; i < ptypes.Length; ++i)
 					message.Append (", ").Append (ptypes [i].FullName);
 			}
+
 			message.Append (")");
 			message.Append (". Please provide the missing constructor.");
+
 			return new NotSupportedException (message.ToString (), CreateJniLocationException ());
 		}
 
+
+		static Exception CreateJniLocationException ()
+		{
+			using (var e = new JavaException ()) {
+				return new JniLocationException (e.ToString ());
+			}
+		}
+
 		static Type[] GetParameterTypes (string? signature)
 		{
 			if (string.IsNullOrEmpty (signature))

src/Java.Interop/Properties/AssemblyInfo.cs

@@ -28,3 +28,10 @@
 	"814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0" +
 	"d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b" +
 	"2c9733db")]
+[assembly: InternalsVisibleTo (
+	"Java.Runtime.Environment, PublicKey=" +
+	"0024000004800000940000000602000000240000525341310004000011000000438ac2a5acfbf1" +
+	"6cbd2b2b47a62762f273df9cb2795ceccdf77d10bf508e69e7a362ea7a45455bbf3ac955e1f2e2" +
+	"814f144e5d817efc4c6502cc012df310783348304e3ae38573c6d658c234025821fda87a0be8a0" +
+	"d504df564e2c93b2b878925f42503e9d54dfef9f9586d9e6f38a305769587b1de01f6c0410328b" +
+	"2c9733db")]

src/Java.Runtime.Environment/Java.Interop/MonoRuntimeValueManager.cs

@@ -1,7 +1,11 @@
-using System;
+using System;
 using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+using System.Reflection;
 using System.Runtime.CompilerServices;
 using System.Runtime.InteropServices;
+using System.Text;
 
 namespace Java.Interop {
 
@@ -229,6 +233,32 @@ public override IJavaPeerable PeekPeer (JniObjectReference reference)
 			return null;
 		}
 
+		static Exception CreateJniLocationException ()
+		{
+			using (var e = new JavaException ()) {
+				return new JniLocationException (e.ToString ());
+			}
+		}
+
+		public override void ActivatePeer (IJavaPeerable self, JniObjectReference reference, ConstructorInfo cinfo, object [] argumentValues)
+		{
+			var runtime = JniEnvironment.Runtime;
+
+			try {
+				var f = runtime.MarshalMemberBuilder.CreateConstructActivationPeerFunc (cinfo);
+				f (cinfo, reference, argumentValues);
+			} catch (Exception e) {
+				var m = string.Format ("Could not activate {{ PeerReference={0} IdentityHashCode=0x{1} Java.Type={2} }} for managed type '{3}'.",
+						reference,
+						runtime.ValueManager.GetJniIdentityHashCode (reference).ToString ("x"),
+						JniEnvironment.Types.GetJniTypeNameFromInstance (reference),
+						cinfo.DeclaringType.FullName);
+				Debug.WriteLine (m);
+
+				throw new NotSupportedException (m, e);
+			}
+		}
+
 		public override void FinalizePeer (IJavaPeerable value)
 		{
 			var h = value.PeerReference;

tests/Java.Interop-Tests/Java.Interop/JniRuntime.JniValueManagerTests.cs

@@ -1,4 +1,5 @@
-using System;
+using System;
+using System.Reflection;
 using System.Collections.Generic;
 
 using Java.Interop;
@@ -59,6 +60,11 @@ public override IJavaPeerable PeekPeer (JniObjectReference reference)
 			{
 				return null;
 			}
+
+			public override void ActivatePeer (IJavaPeerable self, JniObjectReference reference, ConstructorInfo cinfo, object [] argumentValues)
+			{
+				throw new NotImplementedException ();
+			}
 		}
 
 		[Test]

tests/Java.Interop-Tests/Java.Interop/JniRuntimeTest.cs

@@ -1,4 +1,5 @@
 using System;
+using System.Reflection;
 using System.Collections.Generic;
 using System.Threading;
 
@@ -151,6 +152,11 @@ public override IJavaPeerable PeekPeer (JniObjectReference reference)
 				return null;
 			}
 
+			public override void ActivatePeer (IJavaPeerable self, JniObjectReference reference, ConstructorInfo cinfo, object [] argumentValues)
+			{
+				throw new NotImplementedException ();
+			}
+
 			public override void RemovePeer (IJavaPeerable peer)
 			{
 			}