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Add checking for a number of metaclass error conditions.

Browse source 
We add some new rules that are required for preserving internal
invariants of types.

1.  If type (or a subclass of type) appears in bases, it must appear
    before any non-type bases.  If a non-type base (like a regular
    new-style class) occurred first, it could trick type into
    allocating the new class an __dict__ which must be impossible.

2. There are several checks that are made of bases when creating a
   type.  Those checks are now repeated when assigning to __bases__.
   We also add the restriction that assignment to __bases__ may not
   change the metaclass of the type.

Add new tests for these cases and for a few other oddball errors that
were no previously tested.  Remove a crasher test that was fixed.

Also some internal refactoring:  Extract the code to find the most
derived metaclass of a type and its bases.  It is now needed in two
places.  Rewrite the TypeError checks in test_descr to use doctest.
The tests now clearly show what exception they expect to see.
This commit is contained in:
Jeremy Hylton 2007-02-27 18:29:45 +00:00
parent 2d1f5c93bb
commit fa955697fa
3 changed files with 192 additions and 91 deletions
Download patch file Download diff file Expand all files Collapse all files

126
Objects/typeobject.c
View file

@ -127,6 +127,7 @@ type_get_bases(PyTypeObject *type, void *context)
return type->tp_bases;
}
static PyTypeObject *most_derived_metaclass(PyTypeObject *, PyObject *);
static PyTypeObject *best_base(PyObject *);
static int mro_internal(PyTypeObject *);
static int compatible_for_assignment(PyTypeObject *, PyTypeObject *, char *);
@ -187,7 +188,7 @@ type_set_bases(PyTypeObject *type, PyObject *value, void *context)
Py_ssize_t i;
int r = 0;
PyObject *ob, *temp;
PyTypeObject *new_base, *old_base;
PyTypeObject *new_base, *old_base, *metatype;
PyObject *old_bases, *old_mro;
if (!(type->tp_flags & Py_TPFLAGS_HEAPTYPE)) {
@ -230,6 +231,17 @@ type_set_bases(PyTypeObject *type, PyObject *value, void *context)
}
}
metatype = most_derived_metaclass(type->ob_type, value);
if (metatype == NULL)
return -1;
if (metatype != type->ob_type) {
PyErr_SetString(PyExc_TypeError,
"assignment to __bases__ may not change "
"metatype");
return -1;
}
new_base = best_base(value);
if (!new_base) {
@ -1355,7 +1367,14 @@ mro_internal(PyTypeObject *type)
/* Calculate the best base amongst multiple base classes.
This is the first one that's on the path to the "solid base". */
This is the first one that's on the path to the "solid base".
Requires that all base classes be types or classic classes.
Will return NULL with TypeError set if
1) the base classes have conflicting layout instances, or
2) all the bases are classic classes.
*/
static PyTypeObject *
best_base(PyObject *bases)
@ -1373,12 +1392,7 @@ best_base(PyObject *bases)
base_proto = PyTuple_GET_ITEM(bases, i);
if (PyClass_Check(base_proto))
continue;
if (!PyType_Check(base_proto)) {
PyErr_SetString(
PyExc_TypeError,
"bases must be types");
return NULL;
}
assert(PyType_Check(base_proto));
base_i = (PyTypeObject *)base_proto;
if (base_i->tp_dict == NULL) {
if (PyType_Ready(base_i) < 0)
@ -1431,6 +1445,8 @@ extra_ivars(PyTypeObject *type, PyTypeObject *base)
return t_size != b_size;
}
/* Return the type object that will determine the layout of the instance. */
static PyTypeObject *
solid_base(PyTypeObject *type)
{
@ -1446,6 +1462,71 @@ solid_base(PyTypeObject *type)
return base;
}
/* Determine the proper metatype to deal with this, and check some
error cases while we're at it. Note that if some other metatype
wins to contract, it's possible that its instances are not types.
Error cases of interest: 1. The metaclass is not a subclass of a
base class. 2. A non-type, non-classic base class appears before
type.
*/
static PyTypeObject *
most_derived_metaclass(PyTypeObject *metatype, PyObject *bases)
{
Py_ssize_t nbases, i;
PyTypeObject *winner;
/* types_ordered: One of three states possible:
0 type is in bases
1 non-types also in bases
2 type follows non-type in bases (error)
*/
int types_ordered = 0;
nbases = PyTuple_GET_SIZE(bases);
winner = metatype;
for (i = 0; i < nbases; i++) {
PyObject *tmp = PyTuple_GET_ITEM(bases, i);
PyTypeObject *tmptype = tmp->ob_type;
if (tmptype == &PyClass_Type)
continue; /* Special case classic classes */
if (!PyType_Check(tmp)) {
PyErr_SetString(PyExc_TypeError,
"bases must be types");
return NULL;
}
if (PyObject_IsSubclass(tmp, (PyObject*)&PyType_Type)) {
if (types_ordered == 1) {
types_ordered = 2;
}
}
else if (!types_ordered)
types_ordered = 1;
if (winner == tmptype)
continue;
if (PyType_IsSubtype(winner, tmptype))
continue;
if (PyType_IsSubtype(tmptype, winner)) {
winner = tmptype;
continue;
}
PyErr_SetString(PyExc_TypeError,
"metaclass conflict: "
"the metaclass of a derived class "
"must be a (non-strict) subclass "
"of the metaclasses of all its bases");
return NULL;
}
if (types_ordered == 2) {
PyErr_SetString(PyExc_TypeError,
"metaclass conflict: "
"type must occur in bases before other "
"non-classic base classes");
return NULL;
}
return winner;
}
static void object_dealloc(PyObject *);
static int object_init(PyObject *, PyObject *, PyObject *);
static int update_slot(PyTypeObject *, PyObject *);
@ -1642,37 +1723,18 @@ type_new(PyTypeObject *metatype, PyObject *args, PyObject *kwds)
&PyDict_Type, &dict))
return NULL;
/* Determine the proper metatype to deal with this,
and check for metatype conflicts while we're at it.
Note that if some other metatype wins to contract,
it's possible that its instances are not types. */
nbases = PyTuple_GET_SIZE(bases);
winner = metatype;
for (i = 0; i < nbases; i++) {
tmp = PyTuple_GET_ITEM(bases, i);
tmptype = tmp->ob_type;
if (tmptype == &PyClass_Type)
continue; /* Special case classic classes */
if (PyType_IsSubtype(winner, tmptype))
continue;
if (PyType_IsSubtype(tmptype, winner)) {
winner = tmptype;
continue;
}
PyErr_SetString(PyExc_TypeError,
"metaclass conflict: "
"the metaclass of a derived class "
"must be a (non-strict) subclass "
"of the metaclasses of all its bases");
winner = most_derived_metaclass(metatype, bases);
if (winner == NULL)
return NULL;
}
if (winner != metatype) {
if (winner->tp_new != type_new) /* Pass it to the winner */
if (winner->tp_new != type_new) /* Pass it to the winner */ {
return winner->tp_new(winner, args, kwds);
}
metatype = winner;
}
/* Adjust for empty tuple bases */
nbases = PyTuple_GET_SIZE(bases);
if (nbases == 0) {
bases = PyTuple_Pack(1, &PyBaseObject_Type);
if (bases == NULL)