[runtime] Report which element failed to convert when marshalling an array between Objective-C and managed code.

docs/website/mmp-errors.md

@@ -796,4 +796,10 @@ This exception will have an inner exception which gives the reason for the failu
 
 ### MM8035: Failed to get the 'this' instance in a method call to {method}.
 
-This exception will have an inner exception which gives the reason for the failure.
+This exception will have an inner exception which gives the reason for the failure.
+
+<a name="MM8036" />
+
+### MM8036: Failed to marshal the value at index {index}.
+
+This exception will have an inner exception which gives the reason for the failure.

docs/website/mtouch-errors.md

@@ -3586,3 +3586,9 @@ This exception will have an inner exception which gives the reason for the failu
 ### MT8035: Failed to get the 'this' instance in a method call to {method}.
 
 This exception will have an inner exception which gives the reason for the failure.
+
+<a name="MT8036" />
+
+### MT8036: Failed to convert the value at index {index} from {type} to {type}.
+
+This exception will have an inner exception which gives the reason for the failure.

runtime/trampolines.m

@@ -1197,8 +1197,10 @@ xamarin_convert_managed_to_nsarray_with_func (MonoArray *array, xamarin_managed_
 	for (int i = 0; i < length; i++) {
 		MonoObject *value = mono_value_box (mono_domain_get (), element_class, ptr + element_size * i);
 		buf [i] = convert (value, context, exception_gchandle);
-		if (*exception_gchandle != 0)
+		if (*exception_gchandle != 0) {
+			*exception_gchandle = xamarin_get_exception_for_element_conversion_failure (*exception_gchandle, i);
 			goto exception_handling;
+		}
 	}
 	rv = [NSArray arrayWithObjects: buf count: length];
 
@@ -1225,8 +1227,10 @@ xamarin_convert_nsarray_to_managed_with_func (NSArray *array, MonoClass *managed
 	char *ptr = (char *) mono_array_addr_with_size (rv, element_size, 0);
 	for (int i = 0; i < length; i++) {
 		valueptr = convert ([array objectAtIndex: i], valueptr, managedElementType, context, exception_gchandle);
-		if (*exception_gchandle != 0)
+		if (*exception_gchandle != 0) {
+			*exception_gchandle = xamarin_get_exception_for_element_conversion_failure (*exception_gchandle, i);
 			goto exception_handling;
+		}
 		memcpy (ptr, valueptr, element_size);
 		ptr += element_size;
 	}