[generator] fix C# compiler warning in every Invoker (#217)

Context: https://github.com/xamarin/AndroidSupportComponents

When compiling the Xamarin support libraries from source, its binding
projects generate thousands of warnings. Most of these warnings are
noise that could be fixed, and `generator` is just overdue for some
improvement.

My first steps to improve this:

  - By default `generator-Tests` should fail if there is a C#
    compiler warning
  - Add an `AllowWarnings` option for `BaseGeneratorTest`, since
    there are a few tests that generate C# compiler warnings that
    aren’t addressed yet. The hope is this feature could be dropped
    from the tests eventually.
  - Fix the most common warning: `Invoker` types have a warning of a
    missing `new` keyword on the generated `class_ref` field

Since `Java.Lang.Object` has a static `class_ref` property, all
`Invoker` types will produce this warning. An `Invoker` is generated
for any `interface` or `abstract` class, so you can see how a large
binding project could run into this warning many times.

Author: jonathanpeppers

tools/generator/InterfaceGen.cs

@@ -224,7 +224,7 @@ void GenerateInvoker (StreamWriter sw, string indent, CodeGenerationOptions opt)
 			sw.WriteLine ("{0}internal class {1}Invoker : global::Java.Lang.Object, {1} {{", indent, Name);
 			sw.WriteLine ();
 			opt.CodeGenerator.WriteInterfaceInvokerHandle (this, sw, indent + "\t", opt, Name + "Invoker");
-			sw.WriteLine ("{0}\tIntPtr class_ref;", indent);
+			sw.WriteLine ("{0}\tnew IntPtr class_ref;", indent);
 			sw.WriteLine ();
 			sw.WriteLine ("{0}\tpublic static {1} GetObject (IntPtr handle, JniHandleOwnership transfer)", indent, Name);
 			sw.WriteLine ("{0}\t{{", indent);

tools/generator/Tests/BaseGeneratorTest.cs

@@ -30,6 +30,7 @@ public void Setup ()
 		protected CodeGeneratorOptions Options = null;
 		protected Assembly BuiltAssembly = null;
 		protected List<string> AdditionalSourceDirectories;
+		protected bool AllowWarnings;
 
 		public void Execute ()
 		{
@@ -41,7 +42,7 @@ public void Execute ()
 			bool    hasErrors;
 			string  compilerOutput;
 			BuiltAssembly = Compiler.Compile (Options, "Mono.Android", AdditionalSourceDirectories,
-				out hasErrors, out compilerOutput);
+				out hasErrors, out compilerOutput, AllowWarnings);
 			Assert.AreEqual (false, hasErrors, compilerOutput);
 			Assert.IsNotNull (BuiltAssembly);
 		}

tools/generator/Tests/Compiler.cs

@@ -33,7 +33,7 @@ static CodeDomProvider GetCodeDomProvider ()
 
 		public static Assembly Compile (Xamarin.Android.Binder.CodeGeneratorOptions options,
 			string assemblyFileName, IEnumerable<string> AdditionalSourceDirectories,
-			out bool hasErrors, out string output)
+			out bool hasErrors, out string output, bool allowWarnings)
 		{
 			var generatedCodePath = options.ManagedCallableWrapperSourceOutputDirectory;
 			var sourceFiles = Directory.EnumerateFiles (generatedCodePath, "*.cs",
@@ -73,7 +73,7 @@ public static Assembly Compile (Xamarin.Android.Binder.CodeGeneratorOptions opti
 				hasErrors = false;
 
 				foreach (CompilerError message in results.Errors) {
-					hasErrors = hasErrors || (!message.IsWarning);
+					hasErrors |= !message.IsWarning || !allowWarnings;
 				}
 				output = string.Join (Environment.NewLine, results.Output.Cast<string> ());
 

tools/generator/Tests/Interfaces.cs

@@ -9,6 +9,7 @@ public class Interfaces : BaseGeneratorTest
 		[Test]
 		public void Generated_OK ()
 		{
+			AllowWarnings = true;
 			RunAllTargets (
 					outputRelativePath:     "TestInterface",
 					apiDescriptionFile:     "expected/TestInterface/TestInterface.xml",

tools/generator/Tests/NormalMethods.cs

@@ -9,6 +9,7 @@ public class NormalMethods : BaseGeneratorTest
 		[Test]
 		public void GeneratedOK ()
 		{
+			AllowWarnings = true;
 			RunAllTargets (
 					outputRelativePath:     "NormalMethods",
 					apiDescriptionFile:     "expected/NormalMethods/NormalMethods.xml",

tools/generator/Tests/expected.ji/Adapters/Xamarin.Test.IAdapter.cs

@@ -32,7 +32,7 @@ protected override IntPtr ThresholdClass {
 			get { return _members.ManagedPeerType; }
 		}
 
-		IntPtr class_ref;
+		new IntPtr class_ref;
 
 		public static IAdapter GetObject (IntPtr handle, JniHandleOwnership transfer)
 		{

tools/generator/Tests/expected.ji/Adapters/Xamarin.Test.ISpinnerAdapter.cs

@@ -32,7 +32,7 @@ protected override IntPtr ThresholdClass {
 			get { return _members.ManagedPeerType; }
 		}
 
-		IntPtr class_ref;
+		new IntPtr class_ref;
 
 		public static ISpinnerAdapter GetObject (IntPtr handle, JniHandleOwnership transfer)
 		{

tools/generator/Tests/expected.ji/GenericArguments/Com.Google.Android.Exoplayer.Drm.IExoMediaDrm.cs

@@ -37,7 +37,7 @@ protected override IntPtr ThresholdClass {
 			get { return _members.ManagedPeerType; }
 		}
 
-		IntPtr class_ref;
+		new IntPtr class_ref;
 
 		public static IExoMediaDrmOnEventListener GetObject (IntPtr handle, JniHandleOwnership transfer)
 		{
@@ -217,7 +217,7 @@ protected override IntPtr ThresholdClass {
 			get { return _members.ManagedPeerType; }
 		}
 
-		IntPtr class_ref;
+		new IntPtr class_ref;
 
 		public static IExoMediaDrm GetObject (IntPtr handle, JniHandleOwnership transfer)
 		{

tools/generator/Tests/expected.ji/NestedTypes/Xamarin.Test.NotificationCompatBase.cs

@@ -44,7 +44,7 @@ protected override IntPtr ThresholdClass {
 					get { return _members.ManagedPeerType; }
 				}
 
-				IntPtr class_ref;
+				new IntPtr class_ref;
 
 				public static IFactory GetObject (IntPtr handle, JniHandleOwnership transfer)
 				{

tools/generator/Tests/expected.ji/TestInterface/Test.ME.IGenericInterface.cs

@@ -37,7 +37,7 @@ protected override IntPtr ThresholdClass {
 			get { return _members.ManagedPeerType; }
 		}
 
-		IntPtr class_ref;
+		new IntPtr class_ref;
 
 		public static IGenericInterface GetObject (IntPtr handle, JniHandleOwnership transfer)
 		{