[Java.Interop.Tools.JavaCallableWrappers] Collect overriden methods (#985)

We are prototyping a new marshal method generator in xamarin-android
which emits native functions with [JNI native method names][0].
This would remove the need for `Runtime.register()` invocations from
Java Callable Wrappers and all the related Reflection-heavy marshal
method registration code; see 4787e01 for some details for how the
current Reflection approach works.

In order to emit native functions which have the correct names, we
need to know additional information, such as the package name and
type name of the Java `native` method, method signature, etc.

Update `JavaCallableWrapperGenerator` to collect this additional
information, making it available via a new
`JavaCallableWrapperGenerator.OverriddenMethods` property.

[0]: https://docs.oracle.com/javase/8/docs/technotes/guides/jni/spec/design.html#resolving_native_method_names

Author: grendello

src/Java.Interop.Tools.JavaCallableWrappers/Java.Interop.Tools.JavaCallableWrappers/JavaCallableWrapperGenerator.cs

@@ -25,6 +25,36 @@ public enum JavaPeerStyle {
 		JavaInterop1,
 	}
 
+	public class OverriddenMethodDescriptor
+	{
+		static readonly char[] methodDescSplitChars = new char[] { ':' };
+
+		public string JavaPackageName { get; }
+		public string NativeName      { get; }
+		public string JniSignature    { get; }
+		public string Connector       { get; }
+		public string ManagedTypeName { get; }
+
+		public OverriddenMethodDescriptor (string javaPackageName, string methodDescription)
+		{
+			JavaPackageName = javaPackageName;
+			string[] parts = methodDescription.Split (methodDescSplitChars, 4);
+
+			if (parts.Length < 2) {
+				throw new InvalidOperationException ($"Unexpected format for method description. Expected at least 2 parts, got {parts.Length} from: '{methodDescription}'");
+			}
+
+			NativeName = parts[0];
+			JniSignature = parts[1];
+			if (parts.Length > 2) {
+				Connector = parts[2];
+				if (parts.Length > 3) {
+					ManagedTypeName = parts[3];
+				}
+			}
+		}
+	}
+
 	 public class JavaCallableWrapperGenerator {
 
 		class JavaFieldInfo {
@@ -59,6 +89,7 @@ public string GetJavaAccess ()
 		List<Signature> methods = new List<Signature> ();
 		List<Signature> ctors   = new List<Signature> ();
 		List<JavaCallableWrapperGenerator> children;
+		List<OverriddenMethodDescriptor> overriddenMethodDescriptors;
 		readonly IMetadataResolver cache;
 
 		[Obsolete ("Use the TypeDefinitionCache overload for better performance.")]
@@ -80,6 +111,7 @@ public JavaCallableWrapperGenerator (TypeDefinition type, Action<string, object[
 			}
 		}
 
+		public  IList<OverriddenMethodDescriptor> OverriddenMethodDescriptors => overriddenMethodDescriptors;
 		public  string          ApplicationJavaClass            { get; set; }
 		public  JavaPeerStyle   CodeGenerationTarget            { get; set; }
 
@@ -89,7 +121,7 @@ public JavaCallableWrapperGenerator (TypeDefinition type, Action<string, object[
 
 		/// <summary>
 		/// The Java source code to be included in Instrumentation.onCreate
-		/// 
+		///
 		/// Originally came from MonoRuntimeProvider.java delimited by:
 		/// // Mono Runtime Initialization {{{
 		/// // }}}
@@ -497,6 +529,7 @@ string GetManagedParameters (MethodDefinition ctor, string outerType)
 
 		public void Generate (TextWriter writer)
 		{
+			overriddenMethodDescriptors = new List<OverriddenMethodDescriptor> ();
 			if (!string.IsNullOrEmpty (package)) {
 				writer.WriteLine ("package " + package + ";");
 				writer.WriteLine ();
@@ -530,6 +563,17 @@ public void Generate (TextWriter writer)
 				}
 
 			GenerateFooter (writer);
+
+			string javaTypeName = $"{package}.{name}";
+			AddOverridenMethods (methods);
+			AddOverridenMethods (ctors);
+
+			void AddOverridenMethods (List<Signature> list)
+			{
+				foreach (Signature sig in list) {
+					overriddenMethodDescriptors.Add (new OverriddenMethodDescriptor (javaTypeName, sig.Method));
+				}
+			}
 		}
 
 		public void Generate (string outputPath)
@@ -958,5 +1002,3 @@ public string GetDestinationPath (string outputPath)
 		}
 	}
 }
-
-