[generator] Add @managedOverride values none and reabstract. (#1000)

Fixes: #981

Context: 5a0e37e

Add support for `//class/method[@managedOverride = 'none']` and
`//interface/method[@managedOverride = 'reabstract']`.

Setting `@managedOverride` to `none` ensures that the member is not
marked with `virtual` or `override`.  This is useful for `sealed`
classes, to avoid a [CS0549 error][0].  Previously, given the Java:

	// Java
	public final class MyClass {
	    public void doThing() {/* … */ }
	}

The `class-parse` XML would specify that `MyClass.doThing()` was
"virtual" -- `@abstract` is false, `@final` is false:

	<class name="MyClass …>
	  <method
	      abstract="false"
	      final="false"
	      name="doThing"
	      return="void"
	      … />
	</class>

This would result in the C# binding:

	// C#
	public sealed partial class MyClass {
	    public virtual void DoThing() => …
	}

which would error out with a CS0549:

	error CS0549: 'MyClass.DoThing()' is a new virtual member in sealed type 'MyClass'

This can now be resolved by setting `@managedOverride` to `none`:

	<attr path="//class[@name='MyClass']/method[@name='doThing']"
	    name="managedOverride">none</attr>

which will result in the compilable binding:

	// C#
	public sealed partial class MyClass {
	    public void DoThing() => …
	}

Setting `@managedOverride` to `reabstract` is part of support for
re-abstracting interface members; see also a65d6fb.  Currently in
`src/Java.Base`, we have Java:

	// Java
	public interface AnnotatedType {
	    default AnnotatedType getAnnotatedOwnerType() {…}
	}
	public interface AnnotatedArrayType implements AnnotatedType {
	    AnnotatedType getAnnotatedOwnerType(); // re-abstract interface default method
	}

which results in the C# binding:

	// C#
	public partial interface IAnnotatedType {
	    virtual IAnnotatedType? AnnotatedOwnerType {
	        get => …
	    }
	}
	public partial interface IAnnotatedArrayType : IAnnotatedType {
	    IAnnotatedType? AnnotatedOwnerType { get; }     // CS0108
	}

which results in a [warning CS0108][1]:

	warning CS0108: 'IAnnotatedArrayType.AnnotatedOwnerType' hides inherited member
	'IAnnotatedType.AnnotatedOwnerType'. Use the new keyword if hiding was intended.

Fixing this requires two steps.  First, we can now set
`//interface/method/@managedOverride` to `reabstract`:

	<attr path="//interface[@name='AnnotatedArrayType']/method[@name='getAnnotatedOwnerType']"
	    name="managedOverride">reabstract</attr>

What we *also* need to do is make the member *explicitly qualified*.
This can be "forced" for *properties* by setting `@propertyName`:

	<attr path="//interface[@name='AnnotatedArrayType']/method[@name='getAnnotatedOwnerType']"
	    name="propertyName">IAnnotatedType.AnnotatedOwnerType</attr>

`@managedOverride` and `@propertyName` work together to emit:

	public partial interface IAnnotatedArrayType : IAnnotatedType {
	    abstract IAnnotatedType? IAnnotatedType.AnnotatedOwnerType {get;}
	}

The problem is that this combination probably breaks Android output,
and it can't be used for *method* overrides, e.g. having
`java.io.Closeable.close()` re-abstract `java.lang.AutoCloseable.close()`.

TODO: complete the "interface reabstract" case, possibly via
`//interface/method[@explicitInterface='ManagedInterfaceName']`:

	<attr path="//interface[@name='AnnotatedArrayType']/method[@name='getAnnotatedOwnerType']"
	    name="explicitInterface">IAnnotatedType</attr>

[0]: https://docs.microsoft.com/en-us/dotnet/csharp/misc/cs0549
[1]: https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/compiler-messages/cs0108

Author: jpobst

tests/generator-Tests/Unit-Tests/CodeGeneratorTests.cs

@@ -147,6 +147,56 @@ public void ManagedOverrideMethod_Override ()
 			Assert.True (writer.ToString ().Contains ("public override unsafe int DoStuff ()"), $"was: `{writer.ToString ()}`");
 		}
 
+		[Test]
+		public void ManagedOverrideMethod_None ()
+		{
+			var xml = @"<api>
+			  <package name='java.lang' jni-name='java/lang'>
+			    <class abstract='false' deprecated='not deprecated' final='false' name='Object' static='false' visibility='public' jni-signature='Ljava/lang/Object;' />
+			  </package>
+			  <package name='com.xamarin.android' jni-name='com/xamarin/android'>
+			    <class abstract='false' deprecated='not deprecated' extends='java.lang.Object' extends-generic-aware='java.lang.Object' jni-extends='Ljava/lang/Object;' final='false' name='MyClass' static='false' visibility='public' jni-signature='Lcom/xamarin/android/MyClass;'>
+			      <method abstract='false' deprecated='not deprecated' final='false' name='DoStuff' jni-signature='()I' bridge='false' native='false' return='int' jni-return='I' static='false' synchronized='false' synthetic='false' visibility='public' managedOverride='none'></method>
+			    </class>
+			  </package>
+			</api>";
+
+			var gens = ParseApiDefinition (xml);
+			var klass = gens.Single (g => g.Name == "MyClass");
+
+			generator.Context.ContextTypes.Push (klass);
+			generator.WriteType (klass, string.Empty, new GenerationInfo ("", "", "MyAssembly"));
+			generator.Context.ContextTypes.Pop ();
+
+			// This would contain 'virtual' if the 'managedOverride' was not working
+			Assert.True (writer.ToString ().Contains ("public unsafe int DoStuff ()"), $"was: `{writer}`");
+		}
+
+		[Test]
+		public void ManagedOverrideInterfaceMethod_Reabstract ()
+		{
+			var xml = @"<api>
+			  <package name='java.lang' jni-name='java/lang'>
+			    <class abstract='false' deprecated='not deprecated' final='false' name='Object' static='false' visibility='public' jni-signature='Ljava/lang/Object;' />
+			  </package>
+			  <package name='com.xamarin.android' jni-name='com/xamarin/android'>
+			    <interface abstract='false' deprecated='not deprecated' extends='java.lang.Object' extends-generic-aware='java.lang.Object' jni-extends='Ljava/lang/Object;' final='false' name='MyInterface' static='false' visibility='public' jni-signature='Lcom/xamarin/android/MyInterface;'>
+			      <method abstract='true' deprecated='not deprecated' final='false' name='DoStuff' jni-signature='()I' bridge='false' native='false' return='int' jni-return='I' static='false' synchronized='false' synthetic='false' visibility='public' managedOverride='reabstract'></method>
+			    </interface>
+			  </package>
+			</api>";
+
+			var gens = ParseApiDefinition (xml);
+			var iface = gens.Single (g => g.Name == "IMyInterface");
+
+			generator.Context.ContextTypes.Push (iface);
+			generator.WriteType (iface, string.Empty, new GenerationInfo ("", "", "MyAssembly"));
+			generator.Context.ContextTypes.Pop ();
+
+			// This would not contain 'abstract' if the 'managedOverride' was not working
+			Assert.True (writer.ToString ().Contains ("abstract int DoStuff ()"), $"was: `{writer}`");
+		}
+
 		[Test]
 		public void ManagedOverrideProperty_Virtual ()
 		{
@@ -195,6 +245,56 @@ public void ManagedOverrideProperty_Override ()
 			Assert.True (writer.ToString ().Contains ("public override unsafe int Name {"), $"was: `{writer.ToString ()}`");
 		}
 
+		[Test]
+		public void ManagedOverrideProperty_None ()
+		{
+			var xml = @"<api>
+			  <package name='java.lang' jni-name='java/lang'>
+			    <class abstract='false' deprecated='not deprecated' final='false' name='Object' static='false' visibility='public' jni-signature='Ljava/lang/Object;' />
+			  </package>
+			  <package name='com.xamarin.android' jni-name='com/xamarin/android'>
+			    <class abstract='false' deprecated='not deprecated' extends='java.lang.Object' extends-generic-aware='java.lang.Object' jni-extends='Ljava/lang/Object;' final='false' name='MyClass' static='false' visibility='public' jni-signature='Lcom/xamarin/android/MyClass;'>
+			      <method abstract='false' deprecated='not deprecated' final='false' name='getName' jni-signature='()I' bridge='false' native='false' return='int' jni-return='I' static='false' synchronized='false' synthetic='false' visibility='public' managedOverride='none'></method>
+			    </class>
+			  </package>
+			</api>";
+
+			var gens = ParseApiDefinition (xml);
+			var klass = gens.Single (g => g.Name == "MyClass");
+
+			generator.Context.ContextTypes.Push (klass);
+			generator.WriteType (klass, string.Empty, new GenerationInfo ("", "", "MyAssembly"));
+			generator.Context.ContextTypes.Pop ();
+
+			// This would contain 'virtual' if the 'managedOverride' was not working
+			Assert.True (writer.ToString ().Contains ("public unsafe int Name {"), $"was: `{writer}`");
+		}
+
+		[Test]
+		public void ManagedOverrideInterfaceProperty_Reabstract ()
+		{
+			var xml = @"<api>
+			  <package name='java.lang' jni-name='java/lang'>
+			    <class abstract='false' deprecated='not deprecated' final='false' name='Object' static='false' visibility='public' jni-signature='Ljava/lang/Object;' />
+			  </package>
+			  <package name='com.xamarin.android' jni-name='com/xamarin/android'>
+			    <interface abstract='false' deprecated='not deprecated' extends='java.lang.Object' extends-generic-aware='java.lang.Object' jni-extends='Ljava/lang/Object;' final='false' name='MyInterface' static='false' visibility='public' jni-signature='Lcom/xamarin/android/MyInterface;'>
+			      <method abstract='true' deprecated='not deprecated' final='false' name='getName' jni-signature='()I' bridge='false' native='false' return='int' jni-return='I' static='false' synchronized='false' synthetic='false' visibility='public' managedOverride='reabstract'></method>
+			    </interface>
+			  </package>
+			</api>";
+
+			var gens = ParseApiDefinition (xml);
+			var iface = gens.Single (g => g.Name == "IMyInterface");
+
+			generator.Context.ContextTypes.Push (iface);
+			generator.WriteType (iface, string.Empty, new GenerationInfo ("", "", "MyAssembly"));
+			generator.Context.ContextTypes.Pop ();
+
+			// This would not contain 'abstract' if the 'managedOverride' was not working
+			Assert.True (writer.ToString ().Contains ("abstract int Name {"), $"was: `{writer}`");
+		}
+
 		[Test]
 		public void WriteDuplicateInterfaceEventArgs ()
 		{

tools/generator/SourceWriters/BoundInterfaceMethodDeclaration.cs

@@ -25,6 +25,10 @@ public BoundInterfaceMethodDeclaration (Method method, string adapter, CodeGener
 			ReturnType = new TypeReferenceWriter (opt.GetTypeReferenceName (method.RetVal));
 			IsDeclaration = true;
 
+			// Allow user to force adding the 'abstract' keyword for "reabstraction"
+			if (method.ManagedOverride?.ToLowerInvariant () == "reabstract")
+				IsAbstract = true;
+
 			if (method.DeclaringType.IsGeneratable)
 				Comments.Add ($"// Metadata.xml XPath method reference: path=\"{method.GetMetadataXPathReference (method.DeclaringType)}\"");
 			if (method.Deprecated != null)

tools/generator/SourceWriters/BoundInterfacePropertyDeclaration.cs

@@ -20,6 +20,10 @@ public BoundInterfacePropertyDeclaration (GenBase gen, Property property, string
 			PropertyType = new TypeReferenceWriter (opt.GetTypeReferenceName (property));
 			IsAutoProperty = true;
 
+			// Allow user to force adding the 'abstract' keyword for "reabstraction"
+			if ((property.Getter ?? property.Setter).ManagedOverride?.ToLowerInvariant () == "reabstract")
+				IsAbstract = true;
+
 			if (property.Getter != null) {
 				HasGet = true;
 

tools/generator/SourceWriters/BoundMethod.cs

@@ -58,6 +58,9 @@ public BoundMethod (GenBase type, Method method, CodeGenerationOptions opt, bool
 			} else if (method.ManagedOverride?.ToLowerInvariant () == "override") {
 				IsVirtual = false;
 				IsOverride = true;
+			} else if (method.ManagedOverride?.ToLowerInvariant () == "none") {
+				IsVirtual = false;
+				IsOverride = false;
 			}
 
 			ReturnType = new TypeReferenceWriter (opt.GetTypeReferenceName (method.RetVal));

tools/generator/SourceWriters/BoundProperty.cs

@@ -66,6 +66,9 @@ public BoundProperty (GenBase gen, Property property, CodeGenerationOptions opt,
 			} else if (!forceOverride && (property.Getter ?? property.Setter).ManagedOverride?.ToLowerInvariant () == "override") {
 				IsVirtual = false;
 				IsOverride = true;
+			} else if (!forceOverride && (property.Getter ?? property.Setter).ManagedOverride?.ToLowerInvariant () == "none") {
+				IsVirtual = false;
+				IsOverride = false;
 			}
 
 			// Unlike [Register], [Obsolete] cannot be put on property accessors, so we can apply them only under limited condition...