[Java.Interop] remove Type.GetTypeInfo() calls (#557)

Java.Interop used to be a PCL, but is now a netstandard 2.0 library.

We make use of `IntrospectionExtensions.GetTypeInfo()`:

  * https://github.com/mono/mono/blob/c5b88ec4f323f2bdb7c7d0a595ece28dae66579c/mcs/class/referencesource/mscorlib/system/reflection/introspectionextensions.cs#L24
  * https://github.com/mono/mono/blob/c5b88ec4f323f2bdb7c7d0a595ece28dae66579c/mcs/class/corlib/ReferenceSources/RuntimeType.cs

This is a "compat layer", because some of the System.Reflection APIs
are different for PCLs and netstandard 1.x.

If we remove these calls and just use the regular `System.Type` APIs,
the code is simpler and makes fewer method calls.

API differences to mention:

  * `TypeInfo.GetDeclaredNestedType()` is equivalent to
    `Type.GetNestedTypes(BindingFlags.Public | BindingFlags.NonPublic)`
  * `TypeInfo.DeclaredConstructors()` is equivalent to
    `Type.GetConstructors(BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance | BindingFlags.Static)`
    Places checking `IsStatic` can drop `BindingFlags.Static`.

~~ Results ~~

Testing a Release build of the Xamarin.Forms integration project in
xamarin-android:

  * Before:

        01-09 16:21:41.904  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +756ms
        01-09 16:21:45.886  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +749ms
        01-09 16:21:49.851  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +758ms
        01-09 16:21:53.818  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +757ms
        01-09 16:21:57.785  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +747ms
        01-09 16:22:01.783  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +763ms
        01-09 16:22:05.832  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +756ms
        01-09 16:22:09.782  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +754ms
        01-09 16:22:13.798  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +757ms
        01-09 16:22:17.798  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +757ms

      * Average(ms): 755.4
      * Std Err(ms): 1.43913554299486
      * Std Dev(ms): 4.55094617756694

  * After:

        01-09 17:07:41.164  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +757ms
        01-09 17:07:45.148  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +758ms
        01-09 17:07:49.113  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +747ms
        01-09 17:07:53.096  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +748ms
        01-09 17:07:57.062  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +747ms
        01-09 17:08:01.045  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +756ms
        01-09 17:08:05.012  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +745ms
        01-09 17:08:08.994  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +753ms
        01-09 17:08:13.011  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +765ms
        01-09 17:08:17.026  1473  1503 I ActivityTaskManager: Displayed Xamarin.Forms_Performance_Integration/xamarin.forms.performance.integration.MainActivity: +752ms

      * Average(ms): 752.8
      * Std Err(ms): 1.98774020211674
      * Std Dev(ms): 6.28578643537236

This might save ~3ms on startup?

Comparing the number of calls:

	Method call summary
	Total(ms) Self(ms)      Calls Method name
	-      4        3       3457 System.Reflection.IntrospectionExtensions:GetTypeInfo (System.Type)
	+      3        2       3020 System.Reflection.IntrospectionExtensions:GetTypeInfo (System.Type)

`GetTypeInfo()` is reduced by ~437 calls.  Xamarin.Forms still
supports netstandard 1.x, so that is where some of the remaining
calls are coming from.

Author: jonathanpeppers

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

@@ -102,7 +102,7 @@ internal IList<T> ToTargetType (Type targetType, bool dispose)
 		{
 			if (TargetTypeIsCurrentType (targetType))
 				return this;
-			if (targetType == typeof (T[]) || targetType.GetTypeInfo ().IsAssignableFrom (typeof (IList<T>).GetTypeInfo ())) {
+			if (targetType == typeof (T[]) || targetType.IsAssignableFrom (typeof (IList<T>))) {
 				try {
 					return ToArray ();
 				} finally {

src/Java.Interop/Java.Interop/JniPeerMembers.cs

@@ -19,7 +19,7 @@ public JniPeerMembers (string jniPeerTypeName, Type managedPeerType)
 		{
 			if (managedPeerType == null)
 				throw new ArgumentNullException (nameof (managedPeerType));
-			if (!typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (managedPeerType.GetTypeInfo ()))
+			if (!typeof (IJavaPeerable).IsAssignableFrom (managedPeerType))
 				throw new ArgumentException ("'managedPeerType' must implement the IJavaPeerable interface.", nameof (managedPeerType));
 
 #if !XA_INTEGRATION
@@ -42,7 +42,7 @@ public JniPeerMembers (string jniPeerTypeName, Type managedPeerType)
 			if (checkManagedPeerType) {
 				if (managedPeerType == null)
 					throw new ArgumentNullException (nameof (managedPeerType));
-				if (!typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (managedPeerType.GetTypeInfo ()))
+				if (!typeof (IJavaPeerable).IsAssignableFrom (managedPeerType))
 					throw new ArgumentException ("'managedPeerType' must implement the IJavaPeerable interface.", nameof (managedPeerType));
 
 #if !XA_INTEGRATION

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

@@ -226,8 +226,8 @@ protected bool TryRegisterNativeMembers (JniType nativeClass, Type type, string
 
 			static bool TryLoadJniMarshalMethods (JniType nativeClass, Type type, string methods)
 			{
-				var marshalType = type.GetTypeInfo ()?.GetDeclaredNestedType ("__<$>_jni_marshal_methods")?.AsType ();
-				if (marshalType == null || !(marshalType is Type))
+				var marshalType = type?.GetNestedType ("__<$>_jni_marshal_methods", BindingFlags.NonPublic);
+				if (marshalType == null)
 					return false;
 
 				var registerMethod = marshalType.GetRuntimeMethod ("__RegisterNativeMembers", registerMethodParameters);

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Linq.Expressions;
@@ -260,7 +260,7 @@ public virtual IJavaPeerable CreatePeer (ref JniObjectReference reference, JniOb
 				targetType  = targetType ?? typeof (JavaObject);
 				targetType  = GetPeerType (targetType);
 
-				if (!typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ()))
+				if (!typeof (IJavaPeerable).IsAssignableFrom (targetType))
 					throw new ArgumentException ($"targetType `{targetType.AssemblyQualifiedName}` must implement IJavaPeerable!", nameof (targetType));
 
 				var ctor = GetPeerConstructor (reference, targetType);
@@ -321,7 +321,7 @@ ConstructorInfo GetPeerConstructor (JniObjectReference instance, Type fallbackTy
 			static ConstructorInfo GetActivationConstructor (Type type)
 			{
 				return
-					(from c in type.GetTypeInfo ().DeclaredConstructors
+					(from c in type.GetConstructors (BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
 					 let p = c.GetParameters ()
 					 where p.Length == 2 && p [0].ParameterType == ByRefJniObjectReference && p [1].ParameterType == typeof (JniObjectReferenceOptions)
 					 select c)
@@ -337,7 +337,7 @@ public object CreateValue (ref JniObjectReference reference, JniObjectReferenceO
 				if (!reference.IsValid)
 					return null;
 
-				if (targetType != null && typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ())) {
+				if (targetType != null && typeof (IJavaPeerable).IsAssignableFrom (targetType)) {
 					return JavaPeerableValueMarshaler.Instance.CreateGenericValue (ref reference, options, targetType);
 				}
 
@@ -366,7 +366,7 @@ public T CreateValue<T> (ref JniObjectReference reference, JniObjectReferenceOpt
 				if (!reference.IsValid)
 					return default (T);
 
-				if (targetType != null && !typeof (T).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ()))
+				if (targetType != null && !typeof (T).IsAssignableFrom (targetType))
 					throw new ArgumentException (
 							string.Format ("Requested runtime '{0}' value of '{1}' is not compatible with requested compile-time type T of '{2}'.",
 								nameof (targetType),
@@ -382,7 +382,7 @@ public T CreateValue<T> (ref JniObjectReference reference, JniObjectReferenceOpt
 
 				targetType  = targetType ?? typeof (T);
 
-				if (typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ())) {
+				if (typeof (IJavaPeerable).IsAssignableFrom (targetType)) {
 					return (T) JavaPeerableValueMarshaler.Instance.CreateGenericValue (ref reference, options, targetType);
 				}
 
@@ -407,12 +407,12 @@ public object GetValue (ref JniObjectReference reference, JniObjectReferenceOpti
 					return null;
 
 				var existing = PeekValue (reference);
-				if (existing != null && (targetType == null || targetType.GetTypeInfo ().IsAssignableFrom (existing.GetType ().GetTypeInfo ()))) {
+				if (existing != null && (targetType == null || targetType.IsAssignableFrom (existing.GetType ()))) {
 					JniObjectReference.Dispose (ref reference, options);
 					return existing;
 				}
 
-				if (targetType != null && typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ())) {
+				if (targetType != null && typeof (IJavaPeerable).IsAssignableFrom (targetType)) {
 					return JavaPeerableValueMarshaler.Instance.CreateGenericValue (ref reference, options, targetType);
 				}
 
@@ -436,7 +436,7 @@ public T GetValue<T> (ref JniObjectReference reference, JniObjectReferenceOption
 				if (!reference.IsValid)
 					return default (T);
 
-				if (targetType != null && !typeof (T).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ()))
+				if (targetType != null && !typeof (T).IsAssignableFrom (targetType))
 					throw new ArgumentException (
 							string.Format ("Requested runtime '{0}' value of '{1}' is not compatible with requested compile-time type T of '{2}'.",
 								nameof (targetType),
@@ -447,12 +447,12 @@ public T GetValue<T> (ref JniObjectReference reference, JniObjectReferenceOption
 				targetType  = targetType ?? typeof (T);
 
 				var existing = PeekValue (reference);
-				if (existing != null && (targetType == null || targetType.GetTypeInfo ().IsAssignableFrom (existing.GetType ().GetTypeInfo ()))) {
+				if (existing != null && (targetType == null || targetType.IsAssignableFrom (existing.GetType ()))) {
 					JniObjectReference.Dispose (ref reference, options);
 					return (T) existing;
 				}
 
-				if (typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (targetType.GetTypeInfo ())) {
+				if (typeof (IJavaPeerable).IsAssignableFrom (targetType)) {
 					return (T) JavaPeerableValueMarshaler.Instance.CreateGenericValue (ref reference, options, targetType);
 				}
 
@@ -486,11 +486,10 @@ public JniValueMarshaler GetValueMarshaler (Type type)
 
 				if (type == null)
 					throw new ArgumentNullException (nameof (type));
-				var info = type.GetTypeInfo ();
-				if (info.ContainsGenericParameters)
+				if (type.ContainsGenericParameters)
 					throw new ArgumentException ("Generic type definitions are not supported.", nameof (type));
 
-				var marshalerAttr   = info.GetCustomAttribute<JniValueMarshalerAttribute> ();
+				var marshalerAttr   = type.GetCustomAttribute<JniValueMarshalerAttribute> ();
 				if (marshalerAttr != null)
 					return (JniValueMarshaler) Activator.CreateInstance (marshalerAttr.MarshalerType);
 
@@ -505,32 +504,31 @@ public JniValueMarshaler GetValueMarshaler (Type type)
 						return marshaler.Value;
 				}
 
-				var listIface   = typeof(IList<>).GetTypeInfo ();
+				var listIface   = typeof (IList<>);
 				var listType    =
-					(from iface in info.ImplementedInterfaces.Concat (new[]{type})
-					 let iinfo = iface.GetTypeInfo ()
-					 where (listIface).IsAssignableFrom (iinfo.IsGenericType ? iinfo.GetGenericTypeDefinition ().GetTypeInfo () : iinfo)
-					 select iinfo)
+					(from iface in type.GetInterfaces ().Concat (new[]{type})
+					 where (listIface).IsAssignableFrom (iface.IsGenericType ? iface.GetGenericTypeDefinition () : iface)
+					 select iface)
 					.FirstOrDefault ();
 				if (listType != null) {
 					var elementType = listType.GenericTypeArguments [0];
-					if (elementType.GetTypeInfo ().IsValueType) {
+					if (elementType.IsValueType) {
 						foreach (var marshaler in JniPrimitiveArrayMarshalers.Value) {
-							if (info.IsAssignableFrom (marshaler.Key.GetTypeInfo ()))
+							if (type.IsAssignableFrom (marshaler.Key))
 								return marshaler.Value;
 						}
 					}
 
 					return GetObjectArrayMarshaler (elementType);
 				}
 
-				if (typeof (IJavaPeerable).GetTypeInfo ().IsAssignableFrom (info)) {
+				if (typeof (IJavaPeerable).IsAssignableFrom (type)) {
 					return JavaPeerableValueMarshaler.Instance;
 				}
 
 				JniValueMarshalerAttribute ifaceAttribute = null;
-				foreach (var iface in info.ImplementedInterfaces) {
-					marshalerAttr = iface.GetTypeInfo ().GetCustomAttribute<JniValueMarshalerAttribute> ();
+				foreach (var iface in type.GetInterfaces ()) {
+					marshalerAttr = iface.GetCustomAttribute<JniValueMarshalerAttribute> ();
 					if (marshalerAttr != null) {
 						if (ifaceAttribute != null)
 							throw new NotSupportedException ($"There is more than one interface with custom marshaler for type {type}.");

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

@@ -277,8 +277,7 @@ public virtual string GetCurrentManagedThreadStackTrace (int skipFrames = 0, boo
 
 		public virtual void FailFast (string message)
 		{
-			var t = typeof (Environment).GetTypeInfo ();
-			var m = t.DeclaredMethods.FirstOrDefault (x => x.Name == "FailFast");
+			var m = typeof (Environment).GetMethod ("FailFast");
 			m.Invoke (null, new object[]{ message });
 		}
 

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Reflection;
 
 namespace Java.Interop {
@@ -15,7 +15,7 @@ public JniValueMarshalerAttribute (Type marshalerType)
 		{
 			if (marshalerType == null)
 				throw new ArgumentNullException (nameof (marshalerType));
-			if (!typeof (JniValueMarshaler).GetTypeInfo ().IsAssignableFrom (marshalerType.GetTypeInfo ()))
+			if (!typeof (JniValueMarshaler).IsAssignableFrom (marshalerType))
 				throw new ArgumentException (
 						string.Format ("`{0}` must inherit from JniValueMarshaler!", marshalerType.FullName),
 						nameof (marshalerType));

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

@@ -1,4 +1,4 @@
-using System;
+using System;
 using System.Diagnostics;
 using System.Linq;
 using System.Linq.Expressions;
@@ -83,17 +83,16 @@ static void Construct (
 				}
 
 				var type    = Type.GetType (JniEnvironment.Strings.ToString (n_assemblyQualifiedName), throwOnError: true);
-				var info    = type.GetTypeInfo ();
-				if (info.IsGenericTypeDefinition) {
+				if (type.IsGenericTypeDefinition) {
 					throw new NotSupportedException (
 							"Constructing instances of generic types from Java is not supported, as the type parameters cannot be determined.",
 							CreateJniLocationException ());
 				}
 
 				var ptypes  = GetParameterTypes (JniEnvironment.Strings.ToString (n_constructorSignature));
 				var pvalues = GetValues (runtime, new JniObjectReference (n_constructorArguments), ptypes);
-				var ctor    = info.DeclaredConstructors
-					.FirstOrDefault (c => !c.IsStatic &&
+				var ctor    = type.GetConstructors (BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance)
+					.FirstOrDefault (c =>
 						c.GetParameters ().Select (p => p.ParameterType).SequenceEqual (ptypes));
 				if (ctor == null) {
 					throw CreateMissingConstructorException (type, ptypes);