[generator] Support using DIM to nest interface types. (#589)

Context: #509

Consider the following Java code:

	package example;
	public interface Parent {
	    public interface Child {
	    }
	}

Before C#8, interfaces could not contain types.  To bind
`example.Parent.Child`, we had to "un-nest" the interface, *prefixing*
the interface name with the name of the enclosing type:

	namespace Example {
	    public interface IParent {
	    }
	    public interface IParentChild {
	    }
	}

With C#8, interfaces can now contain types.  We can now emit:

	namespace Example {
	    public interface IParent {
	        public interface IChild {
		}
	    }
	}

Enable this new style of binding when
`generator --lang-features=nested-interface-types` is used.  This is
*disabled* by default.

However, even when `nested-interface-types` is enabled, not all
interfaces should follow this new strategy.  In the case of
`Mono.Android.dll`, nested interface types should *only* be used for
types added in API-R/API-30.

Add support for a new `unnest` Metadata attribute which can be placed
on nested types to explicitly emit the C#7-compatible bindings:

	<attr path="/api/package[@name='example']/interface[@name='Parent.Child']" name="unnest">true</attr>

In a future integration with xamarin-android,
[`src/Mono.Android/metadata`][0] can be updated so that all APIs
prior to API-30 are unnested, and all APIs starting with API-30 are
nested:

	<!-- Handle everything that has always existed -->
	<attr api-since="30" path="/api/package/interface[not(@merge.SourceFile)]" name="unnest">true</attr>
	<attr api-since="30" path="/api/package/class[not(@merge.SourceFile)]" name="unnest">true</attr>

	<!-- Need these 2 for each platform prior to 30 -->
	<attr api-since="30" path="/api/package/interface[contains(@merge.SourceFile,'api-29.xml.in')]" 	name="unnest">true</attr>
	<attr api-since="30" path="/api/package/class[contains(@merge.SourceFile,'api-29.xml.in')]" name="unnest">true</attr>

This will ensure we preserve API compatibility.

[0]: https://github.com/xamarin/xamarin-android/blob/b366ac1e6d411dc052dc8711d881d71b7e967685/src/Mono.Android/metadata

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteNestedInterfaceTypes.txt

@@ -0,0 +1,179 @@
+// Metadata.xml XPath interface reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent']"
+[Register ("com/xamarin/android/Parent", "", "Com.Xamarin.Android.IParentInvoker")]
+public partial interface IParent : IJavaObject, IJavaPeerable {
+
+	int Bar {
+		// Metadata.xml XPath method reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent']/method[@name='getBar' and count(parameter)=0]"
+		[Register ("getBar", "()I", "GetGetBarHandler:Com.Xamarin.Android.IParentInvoker, MyAssembly")] get;
+	}
+
+	// Metadata.xml XPath interface reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent.Child']"
+	[Register ("com/xamarin/android/Parent$Child", "", "Com.Xamarin.Android.IParent/IChildInvoker")]
+	public partial interface IChild : IJavaObject, IJavaPeerable {
+
+		int Bar {
+			// Metadata.xml XPath method reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent.Child']/method[@name='getBar' and count(parameter)=0]"
+			[Register ("getBar", "()I", "GetGetBarHandler:Com.Xamarin.Android.IParent/IChildInvoker, MyAssembly")] get;
+		}
+
+	}
+
+	[global::Android.Runtime.Register ("com/xamarin/android/Parent$Child", DoNotGenerateAcw=true)]
+	internal partial class IChildInvoker : global::Java.Lang.Object, IChild {
+
+		static readonly JniPeerMembers _members = new JniPeerMembers ("com/xamarin/android/Parent$Child", typeof (IChildInvoker));
+
+		static IntPtr java_class_ref {
+			get { return _members.JniPeerType.PeerReference.Handle; }
+		}
+
+		public override global::Java.Interop.JniPeerMembers JniPeerMembers {
+			get { return _members; }
+		}
+
+		protected override IntPtr ThresholdClass {
+			get { return class_ref; }
+		}
+
+		protected override global::System.Type ThresholdType {
+			get { return _members.ManagedPeerType; }
+		}
+
+		new IntPtr class_ref;
+
+		public static IChild GetObject (IntPtr handle, JniHandleOwnership transfer)
+		{
+			return global::Java.Lang.Object.GetObject<IChild> (handle, transfer);
+		}
+
+		static IntPtr Validate (IntPtr handle)
+		{
+			if (!JNIEnv.IsInstanceOf (handle, java_class_ref))
+				throw new InvalidCastException (string.Format ("Unable to convert instance of type '{0}' to type '{1}'.",
+							JNIEnv.GetClassNameFromInstance (handle), "com.xamarin.android.Parent.Child"));
+			return handle;
+		}
+
+		protected override void Dispose (bool disposing)
+		{
+			if (this.class_ref != IntPtr.Zero)
+				JNIEnv.DeleteGlobalRef (this.class_ref);
+			this.class_ref = IntPtr.Zero;
+			base.Dispose (disposing);
+		}
+
+		public IChildInvoker (IntPtr handle, JniHandleOwnership transfer) : base (Validate (handle), transfer)
+		{
+			IntPtr local_ref = JNIEnv.GetObjectClass (((global::Java.Lang.Object) this).Handle);
+			this.class_ref = JNIEnv.NewGlobalRef (local_ref);
+			JNIEnv.DeleteLocalRef (local_ref);
+		}
+
+		static Delegate cb_getBar;
+#pragma warning disable 0169
+		static Delegate GetGetBarHandler ()
+		{
+			if (cb_getBar == null)
+				cb_getBar = JNINativeWrapper.CreateDelegate ((Func<IntPtr, IntPtr, int>) n_GetBar);
+			return cb_getBar;
+		}
+
+		static int n_GetBar (IntPtr jnienv, IntPtr native__this)
+		{
+			Com.Xamarin.Android.IParent.IChild __this = global::Java.Lang.Object.GetObject<Com.Xamarin.Android.IParent.IChild> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
+			return __this.Bar;
+		}
+#pragma warning restore 0169
+
+		IntPtr id_getBar;
+		public unsafe int Bar {
+			get {
+				if (id_getBar == IntPtr.Zero)
+					id_getBar = JNIEnv.GetMethodID (class_ref, "getBar", "()I");
+				return JNIEnv.CallIntMethod (((global::Java.Lang.Object) this).Handle, id_getBar);
+			}
+		}
+
+	}
+
+
+}
+
+[global::Android.Runtime.Register ("com/xamarin/android/Parent", DoNotGenerateAcw=true)]
+internal partial class IParentInvoker : global::Java.Lang.Object, IParent {
+
+	static readonly JniPeerMembers _members = new JniPeerMembers ("com/xamarin/android/Parent", typeof (IParentInvoker));
+
+	static IntPtr java_class_ref {
+		get { return _members.JniPeerType.PeerReference.Handle; }
+	}
+
+	public override global::Java.Interop.JniPeerMembers JniPeerMembers {
+		get { return _members; }
+	}
+
+	protected override IntPtr ThresholdClass {
+		get { return class_ref; }
+	}
+
+	protected override global::System.Type ThresholdType {
+		get { return _members.ManagedPeerType; }
+	}
+
+	new IntPtr class_ref;
+
+	public static IParent GetObject (IntPtr handle, JniHandleOwnership transfer)
+	{
+		return global::Java.Lang.Object.GetObject<IParent> (handle, transfer);
+	}
+
+	static IntPtr Validate (IntPtr handle)
+	{
+		if (!JNIEnv.IsInstanceOf (handle, java_class_ref))
+			throw new InvalidCastException (string.Format ("Unable to convert instance of type '{0}' to type '{1}'.",
+						JNIEnv.GetClassNameFromInstance (handle), "com.xamarin.android.Parent"));
+		return handle;
+	}
+
+	protected override void Dispose (bool disposing)
+	{
+		if (this.class_ref != IntPtr.Zero)
+			JNIEnv.DeleteGlobalRef (this.class_ref);
+		this.class_ref = IntPtr.Zero;
+		base.Dispose (disposing);
+	}
+
+	public IParentInvoker (IntPtr handle, JniHandleOwnership transfer) : base (Validate (handle), transfer)
+	{
+		IntPtr local_ref = JNIEnv.GetObjectClass (((global::Java.Lang.Object) this).Handle);
+		this.class_ref = JNIEnv.NewGlobalRef (local_ref);
+		JNIEnv.DeleteLocalRef (local_ref);
+	}
+
+	static Delegate cb_getBar;
+#pragma warning disable 0169
+	static Delegate GetGetBarHandler ()
+	{
+		if (cb_getBar == null)
+			cb_getBar = JNINativeWrapper.CreateDelegate ((Func<IntPtr, IntPtr, int>) n_GetBar);
+		return cb_getBar;
+	}
+
+	static int n_GetBar (IntPtr jnienv, IntPtr native__this)
+	{
+		Com.Xamarin.Android.IParent __this = global::Java.Lang.Object.GetObject<Com.Xamarin.Android.IParent> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
+		return __this.Bar;
+	}
+#pragma warning restore 0169
+
+	IntPtr id_getBar;
+	public unsafe int Bar {
+		get {
+			if (id_getBar == IntPtr.Zero)
+				id_getBar = JNIEnv.GetMethodID (class_ref, "getBar", "()I");
+			return JNIEnv.CallIntMethod (((global::Java.Lang.Object) this).Handle, id_getBar);
+		}
+	}
+
+}
+

tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteUnnestedInterfaceTypes.txt

@@ -0,0 +1,179 @@
+// Metadata.xml XPath interface reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent.Child']"
+[Register ("com/xamarin/android/Parent$Child", "", "Com.Xamarin.Android.IParentChildInvoker")]
+public partial interface IParentChild : IJavaObject, IJavaPeerable {
+
+	int Bar {
+		// Metadata.xml XPath method reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent.Child']/method[@name='getBar' and count(parameter)=0]"
+		[Register ("getBar", "()I", "GetGetBarHandler:Com.Xamarin.Android.IParentChildInvoker, MyAssembly")] get;
+	}
+
+}
+
+[global::Android.Runtime.Register ("com/xamarin/android/Parent$Child", DoNotGenerateAcw=true)]
+internal partial class IParentChildInvoker : global::Java.Lang.Object, IParentChild {
+
+	static readonly JniPeerMembers _members = new JniPeerMembers ("com/xamarin/android/Parent$Child", typeof (IParentChildInvoker));
+
+	static IntPtr java_class_ref {
+		get { return _members.JniPeerType.PeerReference.Handle; }
+	}
+
+	public override global::Java.Interop.JniPeerMembers JniPeerMembers {
+		get { return _members; }
+	}
+
+	protected override IntPtr ThresholdClass {
+		get { return class_ref; }
+	}
+
+	protected override global::System.Type ThresholdType {
+		get { return _members.ManagedPeerType; }
+	}
+
+	new IntPtr class_ref;
+
+	public static IParentChild GetObject (IntPtr handle, JniHandleOwnership transfer)
+	{
+		return global::Java.Lang.Object.GetObject<IParentChild> (handle, transfer);
+	}
+
+	static IntPtr Validate (IntPtr handle)
+	{
+		if (!JNIEnv.IsInstanceOf (handle, java_class_ref))
+			throw new InvalidCastException (string.Format ("Unable to convert instance of type '{0}' to type '{1}'.",
+						JNIEnv.GetClassNameFromInstance (handle), "com.xamarin.android.Parent.Child"));
+		return handle;
+	}
+
+	protected override void Dispose (bool disposing)
+	{
+		if (this.class_ref != IntPtr.Zero)
+			JNIEnv.DeleteGlobalRef (this.class_ref);
+		this.class_ref = IntPtr.Zero;
+		base.Dispose (disposing);
+	}
+
+	public IParentChildInvoker (IntPtr handle, JniHandleOwnership transfer) : base (Validate (handle), transfer)
+	{
+		IntPtr local_ref = JNIEnv.GetObjectClass (((global::Java.Lang.Object) this).Handle);
+		this.class_ref = JNIEnv.NewGlobalRef (local_ref);
+		JNIEnv.DeleteLocalRef (local_ref);
+	}
+
+	static Delegate cb_getBar;
+#pragma warning disable 0169
+	static Delegate GetGetBarHandler ()
+	{
+		if (cb_getBar == null)
+			cb_getBar = JNINativeWrapper.CreateDelegate ((Func<IntPtr, IntPtr, int>) n_GetBar);
+		return cb_getBar;
+	}
+
+	static int n_GetBar (IntPtr jnienv, IntPtr native__this)
+	{
+		Com.Xamarin.Android.IParentChild __this = global::Java.Lang.Object.GetObject<Com.Xamarin.Android.IParentChild> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
+		return __this.Bar;
+	}
+#pragma warning restore 0169
+
+	IntPtr id_getBar;
+	public unsafe int Bar {
+		get {
+			if (id_getBar == IntPtr.Zero)
+				id_getBar = JNIEnv.GetMethodID (class_ref, "getBar", "()I");
+			return JNIEnv.CallIntMethod (((global::Java.Lang.Object) this).Handle, id_getBar);
+		}
+	}
+
+}
+
+
+// Metadata.xml XPath interface reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent']"
+[Register ("com/xamarin/android/Parent", "", "Com.Xamarin.Android.IParentInvoker")]
+public partial interface IParent : IJavaObject, IJavaPeerable {
+
+	int Bar {
+		// Metadata.xml XPath method reference: path="/api/package[@name='com.xamarin.android']/interface[@name='Parent']/method[@name='getBar' and count(parameter)=0]"
+		[Register ("getBar", "()I", "GetGetBarHandler:Com.Xamarin.Android.IParentInvoker, MyAssembly")] get;
+	}
+
+}
+
+[global::Android.Runtime.Register ("com/xamarin/android/Parent", DoNotGenerateAcw=true)]
+internal partial class IParentInvoker : global::Java.Lang.Object, IParent {
+
+	static readonly JniPeerMembers _members = new JniPeerMembers ("com/xamarin/android/Parent", typeof (IParentInvoker));
+
+	static IntPtr java_class_ref {
+		get { return _members.JniPeerType.PeerReference.Handle; }
+	}
+
+	public override global::Java.Interop.JniPeerMembers JniPeerMembers {
+		get { return _members; }
+	}
+
+	protected override IntPtr ThresholdClass {
+		get { return class_ref; }
+	}
+
+	protected override global::System.Type ThresholdType {
+		get { return _members.ManagedPeerType; }
+	}
+
+	new IntPtr class_ref;
+
+	public static IParent GetObject (IntPtr handle, JniHandleOwnership transfer)
+	{
+		return global::Java.Lang.Object.GetObject<IParent> (handle, transfer);
+	}
+
+	static IntPtr Validate (IntPtr handle)
+	{
+		if (!JNIEnv.IsInstanceOf (handle, java_class_ref))
+			throw new InvalidCastException (string.Format ("Unable to convert instance of type '{0}' to type '{1}'.",
+						JNIEnv.GetClassNameFromInstance (handle), "com.xamarin.android.Parent"));
+		return handle;
+	}
+
+	protected override void Dispose (bool disposing)
+	{
+		if (this.class_ref != IntPtr.Zero)
+			JNIEnv.DeleteGlobalRef (this.class_ref);
+		this.class_ref = IntPtr.Zero;
+		base.Dispose (disposing);
+	}
+
+	public IParentInvoker (IntPtr handle, JniHandleOwnership transfer) : base (Validate (handle), transfer)
+	{
+		IntPtr local_ref = JNIEnv.GetObjectClass (((global::Java.Lang.Object) this).Handle);
+		this.class_ref = JNIEnv.NewGlobalRef (local_ref);
+		JNIEnv.DeleteLocalRef (local_ref);
+	}
+
+	static Delegate cb_getBar;
+#pragma warning disable 0169
+	static Delegate GetGetBarHandler ()
+	{
+		if (cb_getBar == null)
+			cb_getBar = JNINativeWrapper.CreateDelegate ((Func<IntPtr, IntPtr, int>) n_GetBar);
+		return cb_getBar;
+	}
+
+	static int n_GetBar (IntPtr jnienv, IntPtr native__this)
+	{
+		Com.Xamarin.Android.IParent __this = global::Java.Lang.Object.GetObject<Com.Xamarin.Android.IParent> (jnienv, native__this, JniHandleOwnership.DoNotTransfer);
+		return __this.Bar;
+	}
+#pragma warning restore 0169
+
+	IntPtr id_getBar;
+	public unsafe int Bar {
+		get {
+			if (id_getBar == IntPtr.Zero)
+				id_getBar = JNIEnv.GetMethodID (class_ref, "getBar", "()I");
+			return JNIEnv.CallIntMethod (((global::Java.Lang.Object) this).Handle, id_getBar);
+		}
+	}
+
+}
+