1776 Generic Virtual Method Causes Invalid Program: Fix + test

- If a method is virtual AND generic, it cannot be overridden by the python class. Hence the method call is deferred to the base class. - Added a unit test which verifies this behavior is now working.
pythonnet · lostmsu · Nov 30, 2022 · Nov 29, 2022 · Nov 30, 2022 · Nov 29, 2022
commit d4e3c18a824b8e957c04b8a569e8ff857f71094e
diff --git a/CHANGELOG.md b/CHANGELOG.md
@@ -13,6 +13,8 @@ This document follows the conventions laid out in [Keep a CHANGELOG][].
 
 ### Fixed
 
+- Fixed error occuring when inheriting a class containing a virtual generic method.
+
 ## [3.0.1](https://github.com/pythonnet/pythonnet/releases/tag/v3.0.1) - 2022-11-03
 
 ### Added

diff --git a/src/python_tests_runner/PythonTestRunner.cs b/src/python_tests_runner/PythonTestRunner.cs
@@ -35,6 +35,7 @@ static IEnumerable<string[]> PythonTestCases()
             // Add the test that you want to debug here.
             yield return new[] { "test_indexer", "test_boolean_indexer" };
             yield return new[] { "test_delegate", "test_bool_delegate" };
+            yield return new[] { "test_subclass", "test_virtual_generic_method" };
         }
 
         /// <summary>

diff --git a/src/runtime/Types/ClassDerived.cs b/src/runtime/Types/ClassDerived.cs
@@ -220,7 +220,10 @@ internal static Type CreateDerivedType(string name,
             foreach (MethodInfo method in methods)
             {
                 if (!method.Attributes.HasFlag(MethodAttributes.Virtual) |
-                    method.Attributes.HasFlag(MethodAttributes.Final))
+                    method.Attributes.HasFlag(MethodAttributes.Final)
+                    // overriding generic virtual methods is not supported
+                    // so a call to that should be deferred to the base class method.
+                    || method.IsGenericMethod)
                 {
                     continue;
                 }

diff --git a/src/testing/generictest.cs b/src/testing/generictest.cs
@@ -136,4 +136,12 @@ public static T[] EchoRange<T>(T[] items)
             return items;
         }
     }
+
+    public abstract class GenericVirtualMethodTest
+    {
+        public virtual Q VirtMethod<Q>(Q arg1)
+        {
+            return arg1;
+        }
+    }
 }
diff --git a/tests/test_subclass.py b/tests/test_subclass.py
@@ -9,7 +9,7 @@
 import System
 import pytest
 from Python.Test import (IInterfaceTest, SubClassTest, EventArgsTest,
-                         FunctionsTest, IGenericInterface)
+                         FunctionsTest, IGenericInterface, GenericVirtualMethodTest)
 from System.Collections.Generic import List
 
 
@@ -327,3 +327,15 @@ def test_generic_interface():
     obj = GenericInterfaceImpl()
     SpecificInterfaceUser(obj, Int32(0))
     GenericInterfaceUser[Int32](obj, Int32(0))
+
+def test_virtual_generic_method():
+    class OverloadingSubclass(GenericVirtualMethodTest):
+        __namespace__ = "test_virtual_generic_method_cls"
+    class OverloadingSubclass2(OverloadingSubclass):
+        __namespace__ = "test_virtual_generic_method_cls"
+    obj = OverloadingSubclass()
+    assert obj.VirtMethod[int](5) == 5
+    obj = OverloadingSubclass2()
+    assert obj.VirtMethod[int](5) == 5
+
+