[Java.Interop] Value Marshaling with Expressions

Fixes: dotnet#8

Extend the JniValueMarshaler abstraction from commit 77a6bf8 so that
JniValueMarshaler can *also* marshal from/to Java via
System.Linq.Expressions expression trees:

	partial class JniValueMarshaler {
		public  virtual Type        MarshalType {get;}

		public  virtual Expression  CreateParameterToManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize, Type targetType);
		public  virtual Expression  CreateParameterFromManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue, ParameterAttributes synchronize);
		public  virtual Expression  CreateReturnValueFromManagedExpression (JniValueMarshalerContext context, ParameterExpression sourceValue);
	}

The members:

  * MarshalType: The JNI type that this marshaler marshals from/to.
    The default value is typeof(IntPtr), making it suitable for
    marshaling reference types.

  * CreateParameterToManagedExpression():
    Java > Managed marshaler.
    Convert the Java parameter `sourceValue`, of type `MarshalType`,
    to the managed type `targetType`.

  * CreateParameterFromManagedExpression():
    Managed > Java marshaler.
    Convert the managed parameter `sourceValue` to `MarshalType`.

  * CreateReturnValueFromManagedExpression():
    Managed > Java marshaler, for return values (not parameters).
    Convert the managed parameter `sourceValue` to `MarshalType`,
    suitable for use when returning to Java.

The default implementation of these methods uses the marshaling
behavior provided by the abstract JniValueMarshaler.CreateValue(),
JniValueMarshaler.CreateArgumentState(), and
JniValueMarshaler.DestroyArgumentState() methods.
CreateParameterToManagedExpression() uses CreateValue(), while
CreateParameterFromManagedExpression() and
CreateReturnValueFromManagedExpression() uses both
CreateArgumentState() and DestroyArgumentState() to marshal values.

The purpose of using expression trees is to permit optimizations:
Java.Interop.ExportedMemberBuilder uses expression trees in order to
generate the Java > Managed marshaling code, so by extending
JniValueMarshaler to use expression trees it's possible to use a
smarter marshaling algorithm for specific types.

For example, the builtin types don't need to do *anything*, as they're
binary compatible with the JNI types. Conseequently, they only need to
return the source parameter, instead of actually using
JniValueManager.CreateValue()/etc.

Similarly, the IJavaPeerable value marshaler can directly use
JniRuntime.JniValueManager.GetValue<T>() for Java > managed marshaling
and IJavaPeerable.PeerReference for Managed > Java marshaling.

Finally, this doesn't *fully* fix Issue dotnet#8, but it fixes "enough" to
close the issue. What's missing, but can be done later, is:

> Do in conjunction w/ Java.Interop.Dynamic

While Java.Interop.Dynamic can (should!) use
JniValueManager.CreateParameterFromManagedExpression(), it doesn't
currently because it doesn't even perform the JNI invocation via
expression trees; it uses expression trees to invoke the intermediate
helper method JavaClassInfo.TryInvokeMember().

This can be fixed, but doesn't need to be done yet.

> Need to permit use of custom attributes on return types, parameter
> types, "inline" into marshal methods.

This will be done in a separate commit for a JniValueManagerAttribute
custom attribute. (Let's try to keep commits single purpose, right?)

> Use Expression<TDelegate> to make it easier to write marshalers.

This isn't needed for the currently supported marshalers.

Author: jonpryor

lib/mono.linq.expressions

@@ -6,6 +6,8 @@
 using System.Reflection;
 using System.Text;
 
+using Java.Interop.Expressions;
+
 namespace Java.Interop {
 
 	public class ExportedMemberBuilder : JniRuntime.JniExportedMemberBuilder
@@ -108,89 +110,73 @@ public virtual LambdaExpression CreateMarshalFromJniMethodExpression (JavaCallab
 			CheckMarshalTypesMatch (method, export.Signature, methodParameters);
 
 			var jnienv  = Expression.Parameter (typeof (IntPtr), "__jnienv");
-			var context = Expression.Parameter (typeof (IntPtr), "__context");
+			var context = Expression.Parameter (typeof (IntPtr), method.IsStatic ? "__class" : "__this");
 
 			var envp        = Expression.Variable (typeof (JniTransition), "__envp");
+			var jvm         = Expression.Variable (typeof (JniRuntime), "__jvm");
 			var envpVars    = new List<ParameterExpression> () {
 				envp,
+				jvm,
 			};
 
 			var envpBody    = new List<Expression> () {
 				Expression.Assign (envp, CreateJniTransition (jnienv)),
 			};
 
-			var jvm         = Expression.Variable (typeof (JniRuntime), "__jvm");
-			var variables   = new List<ParameterExpression> () {
-				jvm,
-			};
-
 			var marshalBody = new List<Expression> () {
 				Expression.Assign (jvm, GetRuntime ()),
 			};
 
-			ParameterExpression self = null;
+			Expression self = null;
+			var marshalerContext    = new JniValueMarshalerContext (jvm);
 			if (!method.IsStatic) {
-				self    = Expression.Variable (type, "__this");
-				variables.Add (self);
-				marshalBody.Add (Expression.Assign (self, GetThis (jvm, type, context)));
+				var selfMarshaler   = Runtime.ValueManager.GetValueMarshaler (type);
+				self                = selfMarshaler.CreateParameterToManagedExpression (marshalerContext, context, 0, type);
 			}
 
 			var marshalParameters   = new List<ParameterExpression> (methodParameters.Length);
-			var invokeParameters    = new List<ParameterExpression> (methodParameters.Length);
+			var invokeParameters    = new List<Expression> (methodParameters.Length);
 			for (int i = 0; i < methodParameters.Length; ++i) {
-				var jni = GetMarshalFromJniParameterType (methodParameters [i].ParameterType);
-				if (jni == methodParameters [i].ParameterType) {
-					var p   = Expression.Parameter (jni, methodParameters [i].Name);
-					marshalParameters.Add (p);
-					invokeParameters.Add (p);
-				}
-				else {
-					var np      = Expression.Parameter (jni, "native_" + methodParameters [i].Name);
-					var p       = Expression.Variable (methodParameters [i].ParameterType, methodParameters [i].Name);
-					var fromJni = GetMarshalFromJniExpression (jvm, p.Type, np);
-					if (fromJni == null)
-						throw new NotSupportedException (string.Format ("Cannot convert from '{0}' to '{1}'.", jni, methodParameters [i].ParameterType));
-					variables.Add (p);
-					marshalParameters.Add (np);
-					invokeParameters.Add (p);
-					marshalBody.Add (Expression.Assign (p, fromJni));
-				}
+				var marshaler   = Runtime.ValueManager.GetValueMarshaler (methodParameters [i].ParameterType);
+				var np          = Expression.Parameter (marshaler.MarshalType, methodParameters [i].Name);
+				var p           = marshaler.CreateParameterToManagedExpression (marshalerContext, np, methodParameters [i].Attributes, methodParameters [i].ParameterType);
+				marshalParameters.Add (np);
+				invokeParameters.Add (p);
 			}
 
+			marshalBody.AddRange (marshalerContext.CreationStatements);
+
 			Expression invoke = method.IsStatic
 				? Expression.Call (method, invokeParameters)
 				: Expression.Call (self, method, invokeParameters);
-			ParameterExpression ret = null;
+			Expression ret = null;
 			if (method.ReturnType == typeof (void)) {
+				envpVars.AddRange (marshalerContext.LocalVariables);
+
 				marshalBody.Add (invoke);
 				envpBody.Add (
 						Expression.TryCatchFinally (
-							Expression.Block (variables, marshalBody),
-							CreateDisposeJniEnvironment (envp),
+							Expression.Block (marshalBody),
+							CreateDisposeJniEnvironment (envp, marshalerContext.CleanupStatements),
 							CreateMarshalException (envp, null)));
 			} else {
-				var jniRType    = GetMarshalToJniReturnType (method.ReturnType);
+				var rmarshaler  = Runtime.ValueManager.GetValueMarshaler (method.ReturnType);
+				var jniRType    = rmarshaler.MarshalType;
 				var exit        = Expression.Label (jniRType, "__exit");
-				ret             = Expression.Variable (jniRType, "__jret");
 				var mret        = Expression.Variable (method.ReturnType, "__mret");
-				envpVars.Add (ret);
-				variables.Add (mret);
+				envpVars.Add (mret);
 				marshalBody.Add (Expression.Assign (mret, invoke));
-				if (jniRType == method.ReturnType)
-					marshalBody.Add (Expression.Assign (ret, mret));
-				else {
-					var marshalExpr = GetMarshalToJniExpression (method.ReturnType, mret);
-					if (marshalExpr == null)
-						throw new NotSupportedException (string.Format ("Don't know how to marshal '{0}' to '{1}'.",
-								method.ReturnType, jniRType));
-					marshalBody.Add (Expression.Assign (ret, marshalExpr));
-				}
+				marshalerContext.CreationStatements.Clear ();
+				ret = rmarshaler.CreateReturnValueFromManagedExpression (marshalerContext, mret);
+				marshalBody.AddRange (marshalerContext.CreationStatements);
 				marshalBody.Add (Expression.Return (exit, ret));
 
+				envpVars.AddRange (marshalerContext.LocalVariables);
+
 				envpBody.Add (
 						Expression.TryCatchFinally (
-						Expression.Block (variables, marshalBody),
-							CreateDisposeJniEnvironment (envp),
+							Expression.Block (marshalBody),
+							CreateDisposeJniEnvironment (envp, marshalerContext.CleanupStatements),
 							CreateMarshalException (envp, exit)));
 
 				envpBody.Add (Expression.Label (exit, Expression.Default (jniRType)));
@@ -222,7 +208,8 @@ void CheckMarshalTypesMatch (MethodInfo method, string signature, ParameterInfo[
 			var mptypes = JniSignature.GetMarshalParameterTypes (signature).ToList ();
 			int len     = Math.Min (methodParameters.Length, mptypes.Count);
 			for (int i = 0; i < len; ++i) {
-				var jni = GetMarshalFromJniParameterType (methodParameters [i].ParameterType);
+				var vm  = Runtime.ValueManager.GetValueMarshaler (methodParameters [i].ParameterType);
+				var jni = vm.MarshalType;
 				if (mptypes [i] != jni)
 					throw new ArgumentException (
 							string.Format ("JNI parameter type mismatch. Type '{0}' != '{1}.", jni, mptypes [i]),
@@ -236,63 +223,14 @@ void CheckMarshalTypesMatch (MethodInfo method, string signature, ParameterInfo[
 						"signature");
 
 			var jrinfo = JniSignature.GetMarshalReturnType (signature);
-			var mrinfo = GetMarshalToJniReturnType (method.ReturnType);
+			var mrvm   = Runtime.ValueManager.GetValueMarshaler (method.ReturnType);
+			var mrinfo = mrvm.MarshalType;
 			if (mrinfo != jrinfo)
 				throw new ArgumentException (
-						string.Format ("JNI return type mismatch. Type '{0}' != '{1}.", jrinfo, mrinfo),
+						string.Format ("JNI return type mismatch. Type '{0}' != '{1}'.", jrinfo, mrinfo),
 						"signature");
 		}
 
-		protected virtual Type GetMarshalFromJniParameterType (Type type)
-		{
-			if (JniBuiltinTypes.Contains (type))
-				return type;
-			return typeof (IntPtr);
-		}
-
-		protected virtual Type GetMarshalToJniReturnType (Type type)
-		{
-			if (JniBuiltinTypes.Contains (type))
-				return type;
-			return typeof (IntPtr);
-		}
-
-		protected virtual Expression GetMarshalFromJniExpression (Expression jvm, Type targetType, Expression jniParameter)
-		{
-			MarshalInfo v;
-			if (Marshalers.TryGetValue (targetType, out v))
-				return v.FromJni (jvm, targetType, jniParameter);
-			if (typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ()))
-				return Marshalers [typeof (IJavaPeerable)].FromJni (jvm, targetType, jniParameter);
-			return null;
-		}
-
-		protected virtual Expression GetMarshalToJniExpression (Type sourceType, Expression managedParameter)
-		{
-			MarshalInfo v;
-			if (Marshalers.TryGetValue (sourceType, out v))
-				return v.ToJni (managedParameter);
-			if (typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (sourceType.GetTypeInfo ()))
-				return Marshalers [typeof (IJavaPeerable)].ToJni (managedParameter);
-			return null;
-		}
-
-		static readonly Dictionary<Type, MarshalInfo> Marshalers = new Dictionary<Type, MarshalInfo> () {
-			{ typeof (string), new MarshalInfo {
-					FromJni = (vm, t, p) => Expression.Call (F<IntPtr, string> (JniEnvironment.Strings.ToString).GetMethodInfo (), p),
-					ToJni   = p => Expression.Call (F<string, JniObjectReference> (JniEnvironment.Strings.NewString).GetMethodInfo (), p)
-			} },
-			{ typeof (IJavaPeerable), new MarshalInfo {
-					FromJni = (vm, t, p) => GetThis (vm, t, p),
-					ToJni   = p => Expression.Call (F<IJavaPeerable, IntPtr> (JniEnvironment.References.NewReturnToJniRef).GetMethodInfo (), p)
-			} },
-		};
-
-		static Func<T, TRet> F<T, TRet> (Func<T, TRet> func)
-		{
-			return func;
-		}
-
 		static Expression CreateJniTransition (ParameterExpression jnienv)
 		{
 			var ctor =
@@ -319,18 +257,11 @@ static CatchBlock CreateMarshalException  (ParameterExpression envp, LabelTarget
 			return Expression.Catch (ex, Expression.Block (body));
 		}
 
-		static Expression CreateDisposeJniEnvironment (ParameterExpression envp)
+		static Expression CreateDisposeJniEnvironment (ParameterExpression envp, IList<Expression> cleanup)
 		{
-			return Expression.Call (envp, typeof (JniTransition).GetTypeInfo ().GetDeclaredMethod ("Dispose"));
-		}
-
-		static Expression GetThis (Expression vm, Type targetType, Expression context)
-		{
-			return Expression.Call (
-					Expression.Property (vm, "ValueManager"),
-					"GetValue",
-					new[]{targetType},
-					context);
+			var disposeTransition   = Expression.Call (envp, typeof(JniTransition).GetTypeInfo ().GetDeclaredMethod ("Dispose"));
+			return Expression.Block (
+					cleanup.Reverse ().Concat (new[]{ disposeTransition }));;
 		}
 
 		static Expression GetRuntime ()
@@ -339,26 +270,6 @@ static Expression GetRuntime ()
 			var runtime = Expression.Property (null, env, "Runtime");
 			return runtime;
 		}
-
-		static readonly ISet<Type> JniBuiltinTypes = new HashSet<Type> {
-			typeof (IntPtr),
-			typeof (void),
-			typeof (bool),
-			typeof (sbyte),
-			typeof (char),
-			typeof (short),
-			typeof (int),
-			typeof (long),
-			typeof (float),
-			typeof (double),
-		};
-
-	}
-
-	class MarshalInfo {
-
-		public Func<Expression /* vm */, Type /* targetType */, Expression /* value */, Expression /* managed rep */>    FromJni;
-		public Func<Expression /* managed rep */, Expression /* jni rep */>    ToJni;
 	}
 
 	static class JniSignature {