Our list format is the same as CPython's

well, except that two fields were swapped, and there is an
extra struct wrapper in there.  But with some small changes
we can now let capi code use the list macros for faster list
manipulation.

from_cpython/Include/listobject.h

@@ -20,8 +20,6 @@ returned item's reference count.
 extern "C" {
 #endif
 
-// Pyston change: comment this out since this is not the format we're using
-#if 0
 typedef struct {
     PyObject_VAR_HEAD
     /* Vector of pointers to list elements.  list[0] is ob_item[0], etc. */
@@ -40,9 +38,6 @@ typedef struct {
      */
     Py_ssize_t allocated;
 } PyListObject;
-#endif
-struct _PyListObject;
-typedef struct _PyListObject PyListObject;
 
 // Pyston change: this is no longer a static object
 PyAPI_DATA(PyTypeObject*) list_cls;
@@ -69,13 +64,9 @@ PyAPI_FUNC(PyObject *) _PyList_Extend(PyListObject *, PyObject *) PYSTON_NOEXCEP
 PyAPI_FUNC(PyObject **) PyList_Items(PyObject *) PYSTON_NOEXCEPT;
 
 /* Macro, trading safety for speed */
-// Pyston changes: these aren't direct macros any more [they potentially could be though]
-#define PyList_GET_ITEM(op, i) PyList_GetItem((PyObject*)(op), (i))
-#define PyList_SET_ITEM(op, i, v) PyList_SetItem((PyObject*)(op), (i), (v))
-#define PyList_GET_SIZE(op)    PyList_Size((PyObject*)(op))
-//#define PyList_GET_ITEM(op, i) (((PyListObject *)(op))->ob_item[i])
-//#define PyList_SET_ITEM(op, i, v) (((PyListObject *)(op))->ob_item[i] = (v))
-//#define PyList_GET_SIZE(op)    Py_SIZE(op)
+#define PyList_GET_ITEM(op, i) (((PyListObject *)(op))->ob_item[i])
+#define PyList_SET_ITEM(op, i, v) (((PyListObject *)(op))->ob_item[i] = (v))
+#define PyList_GET_SIZE(op)    Py_SIZE(op)
 
 #ifdef __cplusplus
 }

src/runtime/list.cpp

@@ -257,12 +257,22 @@ extern "C" Box* listSetitemInt(BoxedList* self, BoxedInt* slice, Box* v) {
 }
 
 extern "C" int PyList_SetItem(PyObject* op, Py_ssize_t i, PyObject* newitem) noexcept {
-    assert(isSubclass(op->cls, list_cls));
-    try {
-        listSetitemUnboxed(static_cast<BoxedList*>(op), i, newitem);
-    } catch (ExcInfo e) {
-        abort();
+    PyObject* olditem;
+    PyObject** p;
+    if (!PyList_Check(op)) {
+        Py_XDECREF(newitem);
+        PyErr_BadInternalCall();
+        return -1;
+    }
+    if (i < 0 || i >= Py_SIZE(op)) {
+        Py_XDECREF(newitem);
+        PyErr_SetString(PyExc_IndexError, "list assignment index out of range");
+        return -1;
     }
+    p = ((PyListObject*)op)->ob_item + i;
+    olditem = *p;
+    *p = newitem;
+    Py_XDECREF(olditem);
     return 0;
 }
 

src/runtime/types.h

@@ -602,6 +602,12 @@ public:
 
     DEFAULT_CLASS_SIMPLE(list_cls);
 };
+static_assert(sizeof(BoxedList) <= sizeof(PyListObject), "");
+static_assert(sizeof(BoxedList) >= sizeof(PyListObject), "");
+static_assert(offsetof(BoxedList, size) == offsetof(PyListObject, ob_size), "");
+static_assert(offsetof(BoxedList, elts) == offsetof(PyListObject, ob_item), "");
+static_assert(offsetof(GCdArray, elts) == 0, "");
+static_assert(offsetof(BoxedList, capacity) == offsetof(PyListObject, allocated), "");
 
 class BoxedTuple : public BoxVar {
 public: