Py_LIMITED_API support in SwigPyObject_Check for -builtin

Simplify implementation for -builtin, which does not need a fallback to
use strcmp as PyType_IsSubtype() 'just works' even when using multiple
modules (I think perhaps because SwigPyObject_stype->clientdata->pytype is
common across modules due to the implementation in SwigPyObject_Type()).

In the non-builtin case SwigPyObject is not a base type and usage is
different and when multiple modules are being used, SwigPyObject_Type()
returns two implementations of SwigPyObject which is solved in a hacky
way by comparing the types as strings when the pointer comparison fails.

Add import_callback test - tests %import and %callback to exercise
all of SwigPyPacked_Check(). Python only - the main callback example is
not widely tested and needs work in most of the other languages.

Examples/test-suite/import_callback.list

@@ -0,0 +1,2 @@
+import_callback_x
+import_callback_y

Examples/test-suite/import_callback_x.h

@@ -0,0 +1,16 @@
+class X {
+  int val;
+public:
+
+  X(int val = 0) : val(val) {}
+  int xmethod(int a) {
+    return -a;
+  }
+  int call_xmethod(int a) {
+    return xmethod(a);
+  }
+};
+
+extern "C" int go_for_it_x(int a, X x, int (X::*pf)(int a)) {
+  return (x.*pf)(a) + 11;
+}

Examples/test-suite/import_callback_x.i

@@ -0,0 +1,11 @@
+%module import_callback_x
+
+%{
+#include "import_callback_x.h"
+%}
+
+%callback("%s_cb_ptr") X::xmethod;
+
+%import "import_callback_y.i"
+
+%include "import_callback_x.h"

Examples/test-suite/import_callback_y.h

@@ -0,0 +1,5 @@
+#include "import_callback_x.h"
+
+extern "C" int go_for_it_y(int a, X x, int (X::*pf)(int a)) {
+  return (x.*pf)(a) + 111;
+}

Examples/test-suite/import_callback_y.i

@@ -0,0 +1,7 @@
+%module import_callback_y
+
+%{
+#include "import_callback_y.h"
+%}
+
+%include "import_callback_y.h"

Examples/test-suite/python/Makefile.in

@@ -113,6 +113,7 @@ C_TEST_CASES += \
 	python_varargs_typemap \
 
 MULTI_CPP_TEST_CASES += \
+	import_callback \
 	python_runtime_data \
 
 include $(srcdir)/../common.mk
@@ -183,6 +184,7 @@ clean:
 	rm -f imports_a.py imports_b.py mod_a.py mod_b.py multi_import_a.py
 	rm -f multi_import_b.py multi_import_d.py packageoption_a.py packageoption_b.py packageoption_c.py
 	rm -f template_typedef_cplx2.py python_runtime_data_builtin.py python_runtime_data_nobuiltin.py
+	rm -f import_callback_x.py import_callback_y.py
 
 hugemod_runme = $(SCRIPTPREFIX)hugemod$(SCRIPTSUFFIX)
 

Examples/test-suite/python/import_callback_runme.py

@@ -0,0 +1,20 @@
+import import_callback_x
+import import_callback_y
+
+x = import_callback_x.X()
+
+# Sanity check
+aa = x.call_xmethod(5)
+if aa != -5:
+    raise RuntimeError("Bad aa {}".format(aa))
+
+# Callback within import_callback_x module
+res = import_callback_x.go_for_it_x(3, x, import_callback_x.X.xmethod_cb_ptr) - 11
+if res != x.call_xmethod(3):
+    raise RuntimeError("Bad res {}".format(res))
+
+# Callback across modules
+# This uses the fallback string comparison in SwigPyPacked_Check()
+res = import_callback_y.go_for_it_y(3, x, import_callback_x.X.xmethod_cb_ptr) - 111
+if res != x.call_xmethod(3):
+    raise RuntimeError("Bad res {}".format(res))

Lib/python/pyrun.swg

@@ -780,10 +780,10 @@ SwigPyObject_Check(PyObject *op) {
   PyTypeObject *target_tp = SwigPyObject_Type();
   PyTypeObject *op_type = Py_TYPE(op);
 #ifdef SWIGPYTHON_BUILTIN
-  if (PyType_IsSubtype(op_type, target_tp))
-    return 1;
-  return (strcmp(op_type->tp_name, SWIG_RUNTIME_MODULE ".SwigPyObject") == 0);
+  /* Only builtin types have SwigPyObject as a base type */
+  return PyType_IsSubtype(op_type, target_tp);
 #else
+  /* Check for an exact match to SwigPyObject */
 # ifdef Py_LIMITED_API
   int cmp;
   PyObject *tp_name;
@@ -791,6 +791,7 @@ SwigPyObject_Check(PyObject *op) {
   if (op_type == target_tp)
     return 1;
 # ifdef Py_LIMITED_API
+  /* Fallback for multiple modules */
   tp_name = PyObject_GetAttrString((PyObject *)op_type, "__name__");
   if (!tp_name)
     return 0;
@@ -1184,14 +1185,17 @@ SwigPyPacked_Type(void) {
 
 SWIGRUNTIMEINLINE int
 SwigPyPacked_Check(PyObject *op) {
+  PyTypeObject *target_tp = SwigPyPacked_Type();
+  PyTypeObject *op_type = Py_TYPE(op);
+  /* Check for an exact match to SwigPyPacked */
 #ifdef Py_LIMITED_API
   int cmp;
   PyObject *tp_name;
 #endif
-  PyTypeObject* op_type = Py_TYPE(op);
-  if (op_type == SwigPyPacked_Type())
+  if (op_type == target_tp)
     return 1;
 #ifdef Py_LIMITED_API
+  /* Fallback for multiple modules */
   tp_name = PyObject_GetAttrString((PyObject *)op_type, "__name__");
   if (!tp_name)
     return 0;