Work around missing features in Python < 3.9

Author: tiran

.github/workflows/main.yml

@@ -147,7 +147,8 @@ jobs:
         env:
             WRAPT_INSTALL_EXTENSIONS: true  # Require extensions.
             CIBW_SKIP: pp*                  # Skip wheels for PyPy.
-            CIBW_BUILD: cp36-*              # only build on 3.6 for stable cp36-abi3
+            # build on 3.6 to 3.9. cp39 provides stable abi cp39-abi3
+            CIBW_BUILD: cp36-* cp37-* cp38-* cp39-*
       - uses: actions/upload-artifact@v2
         with:
           name: dist

setup.cfg

@@ -44,7 +44,6 @@ where=src
 
 [bdist_wheel]
 universal = false
-py_limited_api=cp36
 
 # --- Test and coverage configuration ------------------------------------------
 

setup.py

@@ -1,7 +1,14 @@
 import os
 import platform
+
+import sys
 import setuptools
 
+try:
+    from wheel.bdist_wheel import bdist_wheel
+except ImportError:
+    bdist_wheel = None
+
 
 # # --- Detect if extensions should be disabled ------------------------------
 
@@ -17,20 +24,43 @@
 if platform.python_implementation() != "CPython":
     disable_extensions = True
 
+# # --- stable ABI / limited API hacks ---------------------------------------
+# Python < 3.9 is missing some features to build wheels with stable ABI
+
+define_macros = []
+cmdclass = {}
+
+if sys.version_info >= (3, 9, 0) and platform.python_implementation() == "CPython":
+    py_limited_api = True
+    define_macros.append(("Py_LIMITED_API", "0x03090000"))
+
+    if bdist_wheel is not None:
+        class LimitedAPIWheel(bdist_wheel):
+            def finalize_options(self):
+                self.py_limited_api = "cp39"
+                bdist_wheel.finalize_options(self)
+
+        cmdclass["bdist_wheel"] = LimitedAPIWheel
+else:
+    py_limited_api = False
+
+
 # --- C extension ------------------------------------------------------------
 
 extensions = [
     setuptools.Extension(
         "wrapt._wrappers",
         sources=["src/wrapt/_wrappers.c"],
         optional=not force_extensions,
-        py_limited_api=True,
+        py_limited_api=py_limited_api,
+        define_macros=define_macros,
     )
 ]
 
 
 # --- Setup ------------------------------------------------------------------
 
 setuptools.setup(
-    ext_modules=[] if disable_extensions else extensions
+    ext_modules=[] if disable_extensions else extensions,
+    cmdclass=cmdclass
 )

src/wrapt/_wrappers.c

@@ -1,10 +1,5 @@
 /* ------------------------------------------------------------------------- */
 
-#ifndef Py_LIMITED_API
-/* stable ABI Python >= 3.6, keep in sync with setup.cfg py_limited_api */
-#define Py_LIMITED_API 0x03060000
-#endif
-
 #include "Python.h"
 
 #include "structmember.h"
@@ -13,6 +8,20 @@
 #define PyVarObject_HEAD_INIT(type, size) PyObject_HEAD_INIT(type) size,
 #endif
 
+/* Heap types in Python < 3.9 don't support __weaklistoffset__ and
+ * __dictoffset__ in PyMemberDef.
+ */
+#if PY_VERSION_HEX >= 0x03090000
+#define WRAPT_HEAPTYPE_SUPPORT_OFFSET 1
+#endif
+
+/* Instanes of heap types in Python < 3.8 don't hold strong ref to their
+ * type object.
+ */
+#if PY_VERSION_HEX >= 0x03080000
+#define WRAPT_HEAPTYPE_STRONG_TYPEREF 1
+#endif
+
 /* ------------------------------------------------------------------------- */
 
 typedef struct {
@@ -147,6 +156,7 @@ static int WraptObjectProxy_init(WraptObjectProxyObject *self,
 static int WraptObjectProxy_traverse(WraptObjectProxyObject *self,
         visitproc visit, void *arg)
 {
+    Py_VISIT(Py_TYPE(self));
     Py_VISIT(self->dict);
     Py_VISIT(self->wrapped);
 
@@ -167,7 +177,10 @@ static int WraptObjectProxy_clear(WraptObjectProxyObject *self)
 
 static void WraptObjectProxy_dealloc(WraptObjectProxyObject *self)
 {
+#ifdef WRAPT_HEAPTYPE_STRONG_TYPEREF
+    /* Type decref causes segfaults in <= 3.7 */
     PyTypeObject *tp = Py_TYPE(self);
+#endif
 
     PyObject_GC_UnTrack(self);
 
@@ -179,7 +192,9 @@ static void WraptObjectProxy_dealloc(WraptObjectProxyObject *self)
     freefunc free_func = PyType_GetSlot(Py_TYPE(self), Py_tp_free);
     free_func(self);
 
+#ifdef WRAPT_HEAPTYPE_STRONG_TYPEREF
     Py_DECREF(tp);
+#endif
 }
 
 /* ------------------------------------------------------------------------- */
@@ -1589,8 +1604,10 @@ static PyGetSetDef WraptObjectProxy_getset[] = {
 };
 
 static struct PyMemberDef WraptObjectProxy_Type_members[] = {
+#ifdef WRAPT_HEAPTYPE_SUPPORT_OFFSET
     {"__weaklistoffset__", T_PYSSIZET, offsetof(WraptObjectProxyObject, weakreflist), READONLY},
     {"__dictoffset__", T_PYSSIZET, offsetof(WraptObjectProxyObject, dict), READONLY},
+#endif
     {NULL},
 };
 
@@ -1697,6 +1714,7 @@ static PyType_Spec WraptCallableObjectProxy_Type_spec = {
     "CallableObjectProxy",
     sizeof(WraptObjectProxyObject),
     0,
+    /* Only define HAVE_GC if the object defines custom traverse and clear */
     Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE,
     WraptCallableObjectProxy_Type_slots
 };
@@ -2778,6 +2796,11 @@ init_type(PyObject *module, PyObject **newtype, PyType_Spec *spec,
             return -1;
         }
         assert(((PyTypeObject *)*newtype)->tp_traverse != NULL);
+#ifndef WRAPT_HEAPTYPE_SUPPORT_OFFSET
+        /* hack for Python <= 3.8 */
+        ((PyTypeObject *)*newtype)->tp_weaklistoffset = offsetof(WraptObjectProxyObject, weakreflist);
+        ((PyTypeObject *)*newtype)->tp_dictoffset = offsetof(WraptObjectProxyObject, dict);
+#endif
     }
 
     if (PyModule_AddObject(module, attrname, *newtype) < 0) {