patch 9.1.0726: not using correct python3 API with dynamic linking

Problem:  not using correct python3 API with dynamic linking
Solution: Use stable IncRef / DecRef in Python 3 dynamic bindings
          (Yee Cheng Chin)

Previously, we were using the Py_DECREF macros even when using dynamic
linking of Python 3. This caused issues because Python's headers contain
references to internal APIs like `_Py_Dealloc` and in v8.1.2201 and
v8.2.1225 we simply hacked around the issue by manually copying the
Python header implementation to Vim and linking in the private APIs.
This is fragile and prone to break. In fact, the Py_DECREF
implementation is different in newer versions of Python meaning that
this could potentially cause memory issues.

Instead, simply use the API versions (`Py_DECREF` and `Py_INCREF`) which
are functions exposed by the Python library. They could be slightly
slower since they require a function call instead of a macro, but are
much more reliable and we should only be calling these when the Python
Vim plugins are crossing the language boundary anyway which are always
going to be slow.

Note that this only affects dynamically linked Python builds that are
not using stable ABI.

Also see #15648

closes: #15653

Signed-off-by: Yee Cheng Chin <ychin.git@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/if_python3.c

@@ -219,7 +219,7 @@ static HINSTANCE hinstPy3 = 0; // Instance of python.dll
 # define PyObject_GetItem py3_PyObject_GetItem
 # define PyObject_IsTrue py3_PyObject_IsTrue
 # define PyModule_GetDict py3_PyModule_GetDict
-# ifdef USE_LIMITED_API
+# if defined(USE_LIMITED_API) || PY_VERSION_HEX >= 0x03080000
 #  define Py_IncRef py3_Py_IncRef
 #  define Py_DecRef py3_Py_DecRef
 # endif
@@ -293,9 +293,6 @@ static HINSTANCE hinstPy3 = 0; // Instance of python.dll
 # define PyBytes_FromString py3_PyBytes_FromString
 # undef PyBytes_FromStringAndSize
 # define PyBytes_FromStringAndSize py3_PyBytes_FromStringAndSize
-# if defined(Py_DEBUG) || PY_VERSION_HEX >= 0x030900b0 || defined(USE_LIMITED_API)
-#  define _Py_Dealloc py3__Py_Dealloc
-# endif
 # define PyFloat_FromDouble py3_PyFloat_FromDouble
 # define PyFloat_AsDouble py3_PyFloat_AsDouble
 # define PyObject_GenericGetAttr py3_PyObject_GenericGetAttr
@@ -396,7 +393,7 @@ static void (*py3_Py_Finalize)(void);
 static void (*py3_PyErr_SetString)(PyObject *, const char *);
 static void (*py3_PyErr_SetObject)(PyObject *, PyObject *);
 static int (*py3_PyErr_ExceptionMatches)(PyObject *);
-# ifdef USE_LIMITED_API
+# if defined(USE_LIMITED_API) || PY_VERSION_HEX >= 0x03080000
 static void (*py3_Py_IncRef)(PyObject *);
 static void (*py3_Py_DecRef)(PyObject *);
 # endif
@@ -497,9 +494,6 @@ static char* (*py3_PyBytes_AsString)(PyObject *bytes);
 static int (*py3_PyBytes_AsStringAndSize)(PyObject *bytes, char **buffer, Py_ssize_t *length);
 static PyObject* (*py3_PyBytes_FromString)(char *str);
 static PyObject* (*py3_PyBytes_FromStringAndSize)(char *str, Py_ssize_t length);
-# if defined(Py_DEBUG) || PY_VERSION_HEX >= 0x030900b0 || defined(USE_LIMITED_API)
-static void (*py3__Py_Dealloc)(PyObject *obj);
-# endif
 # if PY_VERSION_HEX >= 0x030900b0
 static PyObject* (*py3__PyObject_New)(PyTypeObject *);
 # endif
@@ -607,7 +601,7 @@ static struct
     {"PyErr_SetString", (PYTHON_PROC*)&py3_PyErr_SetString},
     {"PyErr_SetObject", (PYTHON_PROC*)&py3_PyErr_SetObject},
     {"PyErr_ExceptionMatches", (PYTHON_PROC*)&py3_PyErr_ExceptionMatches},
-# ifdef USE_LIMITED_API
+# if defined(USE_LIMITED_API) || PY_VERSION_HEX >= 0x03080000
     {"Py_IncRef", (PYTHON_PROC*)&py3_Py_IncRef},
     {"Py_DecRef", (PYTHON_PROC*)&py3_Py_DecRef},
 # endif
@@ -702,9 +696,6 @@ static struct
     {"PyBytes_AsStringAndSize", (PYTHON_PROC*)&py3_PyBytes_AsStringAndSize},
     {"PyBytes_FromString", (PYTHON_PROC*)&py3_PyBytes_FromString},
     {"PyBytes_FromStringAndSize", (PYTHON_PROC*)&py3_PyBytes_FromStringAndSize},
-# if defined(Py_DEBUG) || PY_VERSION_HEX >= 0x030900b0 || defined(USE_LIMITED_API)
-    {"_Py_Dealloc", (PYTHON_PROC*)&py3__Py_Dealloc},
-# endif
 # if PY_VERSION_HEX >= 0x030900b0
     {"_PyObject_New", (PYTHON_PROC*)&py3__PyObject_New},
 # endif
@@ -752,44 +743,15 @@ static struct
     {"", NULL},
 };
 
-# if PY_VERSION_HEX >= 0x030800f0
+# if defined(USE_LIMITED_API) || PY_VERSION_HEX >= 0x03080000
-    static inline void
-py3__Py_DECREF(const char *filename UNUSED, int lineno UNUSED, PyObject *op)
-{
-    if (--op->ob_refcnt != 0)
-    {
-#  ifdef Py_REF_DEBUG
-	if (op->ob_refcnt < 0)
-	{
-	    _Py_NegativeRefcount(filename, lineno, op);
-	}
-#  endif
-    }
-    else
-    {
-	_Py_Dealloc(op);
-    }
-}
-
-#  undef Py_DECREF
-#  define Py_DECREF(op) py3__Py_DECREF(__FILE__, __LINE__, _PyObject_CAST(op))
-
-    static inline void
-py3__Py_XDECREF(PyObject *op)
-{
-    if (op != NULL)
-    {
-	Py_DECREF(op);
-    }
-}
-
-#  undef Py_XDECREF
-#  define Py_XDECREF(op) py3__Py_XDECREF(_PyObject_CAST(op))
-# endif
-
-# ifdef USE_LIMITED_API
 // Use stable versions of inc/dec ref. Note that these always null-check and
 // therefore there's no difference between XINCREF and INCREF.
+//
+// For 3.8 or above, we also use this version even if not using limited API.
+// The Py_DECREF macros in 3.8+ include references to internal functions which
+// cause link errors when building Vim. The stable versions are exposed as API
+// functions and don't have these problems (albeit slightly slower as they
+// require function calls rather than an inlined macro).
 #  undef Py_INCREF
 #  define Py_INCREF(obj) Py_IncRef((PyObject *)obj)
 #  undef Py_XINCREF

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    726,
 /**/
     725,
 /**/