[release/10.0.1xx] [src] Fix calling ConformsToProtocol on native instances that don't have a managed peer yet. Fixes #24111. (#24190)

Say we have:

1. A native type with an init method.
2. A managed binding for that native type, but the init method isn't bound.
3. A managed subclass of the managed binding (also without an implementation for the init method).

In this case, native code can create a native instance of the subclass, but no
managed code is executed, which means there won't be a corresponding managed
peer either.

This became a problem in our ConformsToProtocol override/implementation,
because recently it changed to just return 'false' if we couldn't find a
managed peer for a native instance.

The fix is to create the managed instance in that case (by doing what we
did before: call "Runtime.GetNSObject" on the native handle).

Fixes #24111.

---------

Backport of #24189.

Author: rolfbjarne

src/ObjCRuntime/Runtime.cs

@@ -2704,8 +2704,13 @@ public static string? OriginalWorkingDirectory {
 		static nint InvokeConformsToProtocol (IntPtr gchandle, IntPtr handle, IntPtr protocol)
 		{
 			var obj = GetGCHandleTarget (gchandle) as NSObject;
-			if (obj is null)
-				return 0;
+			if (obj is null) {
+				// conformsToProtocol is special, we might get here before a managed instance has been created
+				// for a native instance, in which case we need to create the managed instance (which GetNSObject will do)
+				obj = GetNSObject (handle);
+				if (obj is null)
+					return 0;
+			}
 			var rv = obj.ConformsToProtocol (protocol);
 			return rv ? 1 : 0;
 		}

tests/bindings-test/ApiDefinition.cs

@@ -840,4 +840,8 @@ interface WrappedNSDictionary {
 		UIEdgeInsets UIEdgeInsetsField { get; set; }
 #endif // !__MACOS____MACOS__
 	}
+
+	[BaseType (typeof (NSObject))]
+	[DisableDefaultCtor]
+	interface ClassWithNoDefaultCtor { }
 }

tests/monotouch-test/ObjCRuntime/RuntimeTest.cs

@@ -9,6 +9,7 @@
 using UIKit;
 #endif
 
+using Bindings.Test;
 using MonoTests.System.Net.Http;
 using Xamarin.Utils;
 
@@ -912,6 +913,27 @@ class IntPtrBoolConstructor : DisposableObject {
 			{
 			}
 		}
+
+		[Test]
+		public void ConformsToProtocolCreatesManagedInstance ()
+		{
+			// The point of this test is to verify what happens if an instance of a subclassed type is created
+			// through an Objective-C initializer that is not bound in managed code. In this case, no managed
+			// code will be executed when the native instance is created, which means there won't be a managed
+			// instance either.
+			// At some point this caused trouble for our conformsToProtocol: override/implementation: we'd just
+			// return 'false' if there was no managed instance for a native object.
+			var cls = new Class (typeof (ConformsToProtocolCreatesManagedInstanceTestClass));
+			var handle = Messaging.IntPtr_objc_msgSend (cls.Handle, Selector.GetHandle ("alloc"));
+			handle = Messaging.IntPtr_objc_msgSend (handle, Selector.GetHandle ("init"));
+			var conforms = Messaging.bool_objc_msgSend_IntPtr (handle, Selector.GetHandle ("conformsToProtocol:"), Runtime.GetProtocol ("NSObject"));
+			Messaging.void_objc_msgSend (handle, Selector.GetHandle ("release"));
+			Assert.That (conforms, Is.EqualTo (true), "Conforms");
+		}
+
+		class ConformsToProtocolCreatesManagedInstanceTestClass : ClassWithNoDefaultCtor {
+			protected ConformsToProtocolCreatesManagedInstanceTestClass (NativeHandle handle) : base (handle) { }
+		}
 	}
 
 	[TestFixture]

tests/test-libraries/libtest.h

@@ -361,6 +361,10 @@ typedef void (^outerBlock) (innerBlock callback);
 @property (retain) NSPointerArray* array;
 @end
 
+@interface ClassWithNoDefaultCtor : NSObject {
+}
+@end
+
 #pragma clang diagnostic pop
 // NS_ASSUME_NONNULL_END
 

tests/test-libraries/libtest.m

@@ -1535,4 +1535,8 @@ -(void) callDoSomething: (int*) nilObjectCount nonNilObjectCount: (int *) nonNil
 
 @end
 
+@implementation ClassWithNoDefaultCtor : NSObject {
+}
+@end
+
 #include "libtest.decompile.m"