[bgen] Preserve all public methods supporting protocol methos as events. Fixes #24236.

src/bgen/Generator.cs

@@ -6720,6 +6720,13 @@ public void Generate (Type type)
 					} else
 						print ("public _{0} () {{ IsDirectBinding = false; }}\n", dtype.Name);
 
+					// Tell the trimmer to not remove any of our protocol implementations, they might be called from native
+					// code even if we don't have any event handlers listening for them.
+					print ($"[DynamicDependency (DynamicallyAccessedMemberTypes.PublicMethods, typeof (_{dtype.Name}))]");
+					print ($"static _{dtype.Name} ()");
+					print ("{");
+					print ("\tGC.KeepAlive (null);"); // need to do _something_ (doesn't seem to matter what), otherwise the static cctor (and the DynamicDependency attributes) are trimmed away.
+					print ("}");
 
 					string shouldOverrideDelegateString = isProtocolEventBacked ? "" : "override ";
 
@@ -6748,8 +6755,6 @@ public void Generate (Type type)
 						} else
 							previous_miname = miname;
 
-						// Tell the trimmer to not remove the delegate's method if someone is listening for the event
-						print ($"[DynamicDependency (nameof ({mi.Name}))]");
 						if (mi.ReturnType == TypeCache.System_Void) {
 							if (bta.Singleton || mi.GetParameters ().Length == 1)
 								print ("internal EventHandler? {0};", miname);

tests/bindings-test/ApiDefinition.cs

@@ -853,6 +853,14 @@ interface HitchhikerDelegate {
 		[EventArgs ("")]
 		[Export ("buildIntergalacticHighway:")]
 		void BuildIntergalacticHighway (Hitchhiker sender);
+
+		[EventArgs ("")]
+		[Export ("byeByeDolphins:")]
+		void ByeByeDolphins (Hitchhiker sender);
+
+		[EventArgs ("")]
+		[Export ("hitchhikeWithVogons:")]
+		void HitchhikeWithVogons (Hitchhiker sender);
 	}
 
 	[BaseType (typeof (NSObject), Delegates = new string [] { "Delegate" }, Events = new Type [] { typeof (HitchhikerDelegate) })]
@@ -862,5 +870,8 @@ interface Hitchhiker {
 
 		[Export ("destroyEarth")]
 		void DestroyEarth ();
+
+		[Export ("buildHighway")]
+		void BuildHighway ();
 	}
 }

tests/monotouch-test/ObjCRuntime/RegistrarTest.cs

@@ -21,6 +21,7 @@
 using PlatformException = ObjCRuntime.RuntimeException;
 using NativeException = ObjCRuntime.ObjCException;
 using CoreAnimation;
+using CoreBluetooth;
 using CoreGraphics;
 using CoreLocation;
 #if !__TVOS__
@@ -56,15 +57,31 @@ public static Registrars CurrentRegistrar {
 		[Test]
 		public void EventTestCustomType ()
 		{
-			var earthDestroyed = false;
+			var earthDestroyed = 0;
 			using var vogons = new Hitchhiker ();
 			vogons.BuildIntergalacticHighway += (object sender, EventArgs ea) => {
-				earthDestroyed = true;
+				earthDestroyed++;
 			};
 			vogons.DestroyEarth ();
-			Assert.That (earthDestroyed, Is.True, "Event raised");
+			Assert.That (earthDestroyed, Is.EqualTo (1), "Event raised");
+
+			vogons.BuildHighway ();
+			Assert.That (earthDestroyed, Is.EqualTo (2), "Event raised");
 		}
 
+		[Test]
+		public void EventTestOSType ()
+		{
+			using var mgr = new CBCentralManager (new DispatchQueue ("com.xamarin.tests.ios-plain"));
+			// The bug happens when there's no event listener for 'UpdatedState', which is a required protocol method.
+			// mgr.UpdatedState += (sender, e) => { };
+
+			// attach at least one event handler, to create an instance of the internal class that transforms protocol callbacks into events
+			mgr.DiscoveredPeripheral += (sender, e) => { };
+
+			// mimic what CBCentralManager does, instead of having to spin up the entire Bluetooth stack.
+			Messaging.void_objc_msgSend_IntPtr (mgr.Delegate.Handle, Selector.GetHandle ("centralManagerDidUpdateState:"), IntPtr.Zero);
+		}
 
 		[Test]
 		public void EventTestSdkType ()

tests/test-libraries/libtest.h

@@ -367,14 +367,18 @@ typedef void (^outerBlock) (innerBlock callback);
 
 @class Hitchhiker;
 @protocol HitchhikerDelegate <NSObject>
+@required
+	-(void) byeByeDolphins: (Hitchhiker *) sender;
 @optional
 	-(void) buildIntergalacticHighway: (Hitchhiker *) sender;
+	-(void) hitchhikeWithVogons: (Hitchhiker *) sender;
 @end
 
 @interface Hitchhiker : NSObject {
 }
 @property (retain) id<HitchhikerDelegate> delegate;
 -(void) destroyEarth;
+-(void) buildHighway;
 @end
 
 #pragma clang diagnostic pop

tests/test-libraries/libtest.m

@@ -1542,6 +1542,12 @@ @implementation ClassWithNoDefaultCtor : NSObject {
 @implementation Hitchhiker : NSObject {
 }
 -(void) destroyEarth
+{
+	[self.delegate byeByeDolphins: self];
+	[self.delegate buildIntergalacticHighway: self];
+	[self.delegate hitchhikeWithVogons: self];
+}
+-(void) buildHighway
 {
 	[self.delegate buildIntergalacticHighway: self];
 }