[python] Fix inheriting from multiple director classes

Fix mishandling of a Python class inheriting from multiple SWIG-wrapped
director classes.

Fixes #422
Fixes https://sourceforge.net/p/swig/bugs/1379/

CHANGES.current

@@ -7,6 +7,10 @@ the issue number to the end of the URL: https://github.com/swig/swig/issues/
 Version 4.1.0 (in progress)
 ===========================
 
+2022-07-20: jicks, Ingener74, olly
+	    #422 [Python] Fix mishandling of a Python class inheriting from
+	    multiple SWIG-wrapped director classes.
+
 2022-07-19: wsfulton
             #692 [C#, Java, Perl, Python, Ruby] std::unique_ptr and std::auto_ptr typemaps
             provided for inputs types in std_unique_ptr.i and std_auto_ptr.i.

Examples/test-suite/director_multiple_inheritance.i

@@ -0,0 +1,71 @@
+//%module(ruby_minherit="1") multiple_inheritance
+%module(directors="1") director_multiple_inheritance
+
+%feature("director") A;
+%feature("director") B;
+%feature("director") C;
+%feature("director") D;
+
+%inline %{
+
+class A {
+public:
+    virtual ~A() { }
+    virtual int testA();
+};
+
+class B: virtual public A {
+public:
+    virtual ~B() { }
+    virtual int testB();
+};
+
+class C: virtual public A {
+public:
+    virtual ~C() { }
+    virtual int testC();
+};
+
+class D: virtual public A {
+public:
+    virtual ~D() { }
+    virtual int testD();
+};
+
+class E {
+public:
+    virtual ~E() { }
+    virtual int testE(B*);
+};
+
+class F {
+public:
+    virtual ~F() { }
+    virtual int testF(C*);
+};
+
+class T {
+public:
+    virtual ~T() { }
+    virtual int testT(D*);
+};
+
+%}
+
+%{
+
+int A::testA() { return 1; }
+
+int B::testB() { return 2; }
+
+int C::testC() { return 3; }
+
+int D::testD() { return 4; }
+
+int E::testE(B*) { return 5; }
+
+int F::testF(C*) { return 6; }
+
+int T::testT(D*) { return 20; }
+
+%}

Examples/test-suite/python/director_multiple_inheritance_runme.py

@@ -0,0 +1,36 @@
+import director_multiple_inheritance as st
+
+class TestBCD(st.B, st.C, st.D):
+    def __init__(self):
+        st.B.__init__(self)
+        st.C.__init__(self)
+        st.D.__init__(self)
+
+class TestBDC(st.B, st.C, st.D):
+    def __init__(self):
+        st.B.__init__(self)
+        st.D.__init__(self)
+        st.C.__init__(self)
+
+class TestCBD(st.B, st.C, st.D):
+    def __init__(self):
+        st.C.__init__(self)
+        st.B.__init__(self)
+        st.D.__init__(self)
+
+def dotest(test):
+    e = st.E()
+    if e.testE(test) != 5:
+        raise RuntimeError(e.testE(test))
+
+    f = st.F()
+    if f.testF(test) != 6:
+        raise RuntimeError(f.testF(test))
+
+    t = st.T()
+    if t.testT(test) != 20:
+        raise RuntimeError(t.testT(test))
+
+dotest(TestBCD())
+dotest(TestCBD())
+dotest(TestBDC())

Lib/python/pyrun.swg

@@ -792,6 +792,7 @@ SwigPyObject_append(PyObject* v, PyObject* next)
     PyErr_SetString(PyExc_TypeError, "Attempt to append a non SwigPyObject");
     return NULL;
   }
+  ((SwigPyObject *)next)->next = sobj->next;
   sobj->next = next;
   Py_INCREF(next);
   return SWIG_Py_Void();