clear weak reference list when an extension type is destroyed

According to official documentation for defining extension types, if they are to support weak references, they must clear weak reference list associated with the instance in tp_clear. Extension types were missed in #1758 ( 50da522 )
filmor · Apr 10, 2022 · Apr 9, 2022 · Apr 9, 2022 · 7fa3e8e3b5de6e77c9a0e5467952867df953cd37
commit 7fa3e8e3b5de6e77c9a0e5467952867df953cd37
diff --git a/src/embed_tests/ExtensionTypes.cs b/src/embed_tests/ExtensionTypes.cs
@@ -0,0 +1,32 @@
+using System;
+
+using NUnit.Framework;
+
+using Python.Runtime;
+
+namespace Python.EmbeddingTest;
+
+public class ExtensionTypes
+{
+    [OneTimeSetUp]
+    public void SetUp()
+    {
+        PythonEngine.Initialize();
+    }
+
+    [OneTimeTearDown]
+    public void Dispose()
+    {
+        PythonEngine.Shutdown();
+    }
+
+    [Test]
+    public void WeakrefIsNone_AfterBoundMethodIsGone()
+    {
+        using var makeref = Py.Import("weakref").GetAttr("ref");
+        var boundMethod = new UriBuilder().ToPython().GetAttr(nameof(UriBuilder.GetHashCode));
+        var weakref = makeref.Invoke(boundMethod);
+        boundMethod.Dispose();
+        Assert.IsTrue(weakref.Invoke().IsNone());
+    }
+}
diff --git a/src/runtime/Types/ExtensionType.cs b/src/runtime/Types/ExtensionType.cs
@@ -86,6 +86,12 @@ public unsafe static void tp_dealloc(NewReference lastRef)
 
         public static int tp_clear(BorrowedReference ob)
         {
+            var weakrefs = Runtime.PyObject_GetWeakRefList(ob);
+            if (weakrefs != null)
+            {
+                Runtime.PyObject_ClearWeakRefs(ob);
+            }
+
             if (TryFreeGCHandle(ob))
             {
                 bool deleted = loadedExtensions.Remove(ob.DangerousGetAddress());

diff --git a/src/runtime/Types/MetaType.cs b/src/runtime/Types/MetaType.cs
@@ -273,6 +273,12 @@ public static NewReference mp_subscript(BorrowedReference tp, BorrowedReference
         /// </summary>
         public static void tp_dealloc(NewReference lastRef)
         {
+            var weakrefs = Runtime.PyObject_GetWeakRefList(lastRef.Borrow());
+            if (weakrefs != null)
+            {
+                Runtime.PyObject_ClearWeakRefs(lastRef.Borrow());
+            }
+
             // Fix this when we dont cheat on the handle for subclasses!
 
             var flags = PyType.GetFlags(lastRef.Borrow());