[generator] Eliminate usage of JNINativeWrapper.CreateDelegate in b…

…indings.

tools/generator/SourceWriters/Attributes/DebuggerDisableUserUnhandledExceptionsAttributeAttr.cs

@@ -0,0 +1,17 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Xamarin.SourceWriter;
+
+namespace generator.SourceWriters
+{
+	public class DebuggerDisableUserUnhandledExceptionsAttributeAttr : AttributeWriter
+	{
+		public override void WriteAttribute (CodeWriter writer)
+		{
+			writer.WriteLine ("[global::System.Diagnostics.DebuggerDisableUserUnhandledExceptionsAttribute]");
+		}
+	}
+}

tools/generator/SourceWriters/MethodCallback.cs

@@ -47,6 +47,8 @@ public MethodCallback (GenBase type, Method method, CodeGenerationOptions option
 
 			SourceWriterExtensions.AddSupportedOSPlatform (Attributes, method, opt);
 
+			Attributes.Add (new DebuggerDisableUserUnhandledExceptionsAttributeAttr ());
+
 			Parameters.Add (new MethodParameterWriter ("jnienv", TypeReferenceWriter.IntPtr));
 			Parameters.Add (new MethodParameterWriter ("native__this", TypeReferenceWriter.IntPtr));
 
@@ -56,6 +58,11 @@ public MethodCallback (GenBase type, Method method, CodeGenerationOptions option
 
 		protected override void WriteBody (CodeWriter writer)
 		{
+			writer.WriteLine ("var __envp = new global::Java.Interop.JniTransition (jnienv);");
+			writer.WriteLine ();
+			writer.WriteLine ("try {");
+
+			writer.Indent ();
 			writer.WriteLine ($"var __this = global::Java.Lang.Object.GetObject<{opt.GetOutputName (type.FullName)}> (jnienv, native__this, JniHandleOwnership.DoNotTransfer){opt.NullForgivingOperator};");
 
 			foreach (var s in method.Parameters.GetCallbackPrep (opt))
@@ -79,6 +86,25 @@ protected override void WriteBody (CodeWriter writer)
 
 			if (!method.IsVoid && method.Parameters.HasCleanup)
 				writer.WriteLine ("return __ret;");
+
+			writer.Unindent ();
+
+			writer.WriteLine ("} catch (global::System.Exception __e) {");
+			writer.Indent ();
+			writer.WriteLine ("__envp.SetPendingException (__e);");
+			writer.WriteLine ("global::System.Diagnostics.Debugger.BreakForUserUnhandledException (__e);");
+
+			if (!method.IsVoid)
+				writer.WriteLine ("return default;");
+
+			writer.Unindent ();
+			writer.WriteLine ("} finally {");
+			writer.Indent ();
+			writer.WriteLine ("__envp.Dispose ();");
+			writer.Unindent ();
+			writer.WriteLine ("}");
+
+
 		}
 
 		public override void Write (CodeWriter writer)
@@ -143,10 +169,7 @@ public GetDelegateHandlerMethod (Method method, CodeGenerationOptions opt)
 		protected override void WriteBody (CodeWriter writer)
 		{
 			var callback_name = method.EscapedCallbackName;
-
-			writer.WriteLine ($"if ({callback_name} == null)");
-			writer.WriteLine ($"\t{callback_name} = JNINativeWrapper.CreateDelegate (new {method.GetDelegateType (opt)} (n_{method.Name + method.IDSignature}));");
-			writer.WriteLine ($"return {callback_name};");
+			writer.WriteLine ($"return {callback_name} ??= new {method.GetDelegateType (opt)} (n_{method.Name + method.IDSignature});");
 		}
 	}
 }