dirs._addpath: reinstate use of Py_CLEAR

I changed this to an explicit Py_DECREF + set to null in 6f0e6fa9fdd7. This was
a silly misunderstanding on my part -- for some reason I thought Py_CLEAR set
its argument to null only if its refcount reached 0. Turns out that's not
actually the case -- Py_CLEAR is just Py_DECREF + set to null with some
additional precautions around destructors that aren't relevant here.

The real bug that 6f0e6fa9fdd7 fixed was the fact that we were mutating the
string after setting it in the Python dictionary.

mercurial/dirs.c

@@ -1,307 +1,305 b''
 /*
  dirs.c - dynamic directory diddling for dirstates
 
  Copyright 2013 Facebook
 
  This software may be used and distributed according to the terms of
  the GNU General Public License, incorporated herein by reference.
 */
 
 #define PY_SSIZE_T_CLEAN
 #include <Python.h>
 #include <string.h>
 #include "util.h"
 
 /*
  * This is a multiset of directory names, built from the files that
  * appear in a dirstate or manifest.
  *
  * A few implementation notes:
  *
  * We modify Python integers for refcounting, but those integers are
  * never visible to Python code.
  *
  * We mutate strings in-place, but leave them immutable once they can
  * be seen by Python code.
  */
 typedef struct {
 	PyObject_HEAD
 	PyObject *dict;
 } dirsObject;
 
 static inline Py_ssize_t _finddir(PyObject *path, Py_ssize_t pos)
 {
 	const char *s = PyString_AS_STRING(path);
 
 	const char *ret = strchr(s + pos, '/');
 	return (ret != NULL) ? (ret - s) : -1;
 }
 
 static int _addpath(PyObject *dirs, PyObject *path)
 {
 	char *cpath = PyString_AS_STRING(path);
 	Py_ssize_t len = PyString_GET_SIZE(path);
 	Py_ssize_t pos = -1;
 	PyObject *key = NULL;
 	int ret = -1;
 
 	while ((pos = _finddir(path, pos + 1)) != -1) {
 		PyObject *val;
 
 		/* It's likely that every prefix already has an entry
 		   in our dict. Try to avoid allocating and
 		   deallocating a string for each prefix we check. */
 		if (key != NULL)
 			((PyStringObject *)key)->ob_shash = -1;
 		else if (pos != 0) {
 			/* pos >= 1, which means that len >= 2. This is
 			   guaranteed to produce a non-interned string. */
 			key = PyString_FromStringAndSize(cpath, len);
 			if (key == NULL)
 				goto bail;
 		} else {
 			/* pos == 0, which means we need to increment the dir
 			   count for the empty string. We need to make sure we
 			   don't muck around with interned strings, so throw it
 			   away later. */
 			key = PyString_FromString("");
 			if (key == NULL)
 				goto bail;
 		}
 		PyString_GET_SIZE(key) = pos;
 		PyString_AS_STRING(key)[pos] = '\0';
 
 		val = PyDict_GetItem(dirs, key);
 		if (val != NULL) {
 			PyInt_AS_LONG(val) += 1;
 			if (pos != 0)
 				PyString_AS_STRING(key)[pos] = '/';
 			else
 				key = NULL;
 			continue;
 		}
 
 		/* Force Python to not reuse a small shared int. */
 		val = PyInt_FromLong(0x1eadbeef);
 
 		if (val == NULL)
 			goto bail;
 
 		PyInt_AS_LONG(val) = 1;
 		ret = PyDict_SetItem(dirs, key, val);
 		Py_DECREF(val);
 		if (ret == -1)
 			goto bail;
 
 		/* Clear the key out since we've already exposed it to Python
-		   and can't mutate it further. key's refcount is currently 2 so
-		   we can't just use Py_CLEAR. */
-		Py_DECREF(key);
-		key = NULL;
+		   and can't mutate it further. */
+		Py_CLEAR(key);
 	}
 	ret = 0;
 
 bail:
 	Py_XDECREF(key);
 
 	return ret;
 }
 
 static int _delpath(PyObject *dirs, PyObject *path)
 {
 	Py_ssize_t pos = -1;
 	PyObject *key = NULL;
 	int ret = -1;
 
 	while ((pos = _finddir(path, pos + 1)) != -1) {
 		PyObject *val;
 
 		key = PyString_FromStringAndSize(PyString_AS_STRING(path), pos);
 
 		if (key == NULL)
 			goto bail;
 
 		val = PyDict_GetItem(dirs, key);
 		if (val == NULL) {
 			PyErr_SetString(PyExc_ValueError,
 					"expected a value, found none");
 			goto bail;
 		}
 
 		if (--PyInt_AS_LONG(val) <= 0 &&
 		    PyDict_DelItem(dirs, key) == -1)
 			goto bail;
 		Py_CLEAR(key);
 	}
 	ret = 0;
 
 bail:
 	Py_XDECREF(key);
 
 	return ret;
 }
 
 static int dirs_fromdict(PyObject *dirs, PyObject *source, char skipchar)
 {
 	PyObject *key, *value;
 	Py_ssize_t pos = 0;
 
 	while (PyDict_Next(source, &pos, &key, &value)) {
 		if (!PyString_Check(key)) {
 			PyErr_SetString(PyExc_TypeError, "expected string key");
 			return -1;
 		}
 		if (skipchar) {
 			if (!dirstate_tuple_check(value)) {
 				PyErr_SetString(PyExc_TypeError,
 						"expected a dirstate tuple");
 				return -1;
 			}
 			if (((dirstateTupleObject *)value)->state == skipchar)
 				continue;
 		}
 
 		if (_addpath(dirs, key) == -1)
 			return -1;
 	}
 
 	return 0;
 }
 
 static int dirs_fromiter(PyObject *dirs, PyObject *source)
 {
 	PyObject *iter, *item = NULL;
 	int ret;
 
 	iter = PyObject_GetIter(source);
 	if (iter == NULL)
 		return -1;
 
 	while ((item = PyIter_Next(iter)) != NULL) {
 		if (!PyString_Check(item)) {
 			PyErr_SetString(PyExc_TypeError, "expected string");
 			break;
 		}
 
 		if (_addpath(dirs, item) == -1)
 			break;
 		Py_CLEAR(item);
 	}
 
 	ret = PyErr_Occurred() ? -1 : 0;
 	Py_DECREF(iter);
 	Py_XDECREF(item);
 	return ret;
 }
 
 /*
  * Calculate a refcounted set of directory names for the files in a
  * dirstate.
  */
 static int dirs_init(dirsObject *self, PyObject *args)
 {
 	PyObject *dirs = NULL, *source = NULL;
 	char skipchar = 0;
 	int ret = -1;
 
 	self->dict = NULL;
 
 	if (!PyArg_ParseTuple(args, "|Oc:__init__", &source, &skipchar))
 		return -1;
 
 	dirs = PyDict_New();
 
 	if (dirs == NULL)
 		return -1;
 
 	if (source == NULL)
 		ret = 0;
 	else if (PyDict_Check(source))
 		ret = dirs_fromdict(dirs, source, skipchar);
 	else if (skipchar)
 		PyErr_SetString(PyExc_ValueError,
 				"skip character is only supported "
 				"with a dict source");
 	else
 		ret = dirs_fromiter(dirs, source);
 
 	if (ret == -1)
 		Py_XDECREF(dirs);
 	else
 		self->dict = dirs;
 
 	return ret;
 }
 
 PyObject *dirs_addpath(dirsObject *self, PyObject *args)
 {
 	PyObject *path;
 
 	if (!PyArg_ParseTuple(args, "O!:addpath", &PyString_Type, &path))
 		return NULL;
 
 	if (_addpath(self->dict, path) == -1)
 		return NULL;
 
 	Py_RETURN_NONE;
 }
 
 static PyObject *dirs_delpath(dirsObject *self, PyObject *args)
 {
 	PyObject *path;
 
 	if (!PyArg_ParseTuple(args, "O!:delpath", &PyString_Type, &path))
 		return NULL;
 
 	if (_delpath(self->dict, path) == -1)
 		return NULL;
 
 	Py_RETURN_NONE;
 }
 
 static int dirs_contains(dirsObject *self, PyObject *value)
 {
 	return PyString_Check(value) ? PyDict_Contains(self->dict, value) : 0;
 }
 
 static void dirs_dealloc(dirsObject *self)
 {
 	Py_XDECREF(self->dict);
 	PyObject_Del(self);
 }
 
 static PyObject *dirs_iter(dirsObject *self)
 {
 	return PyObject_GetIter(self->dict);
 }
 
 static PySequenceMethods dirs_sequence_methods;
 
 static PyMethodDef dirs_methods[] = {
 	{"addpath", (PyCFunction)dirs_addpath, METH_VARARGS, "add a path"},
 	{"delpath", (PyCFunction)dirs_delpath, METH_VARARGS, "remove a path"},
 	{NULL} /* Sentinel */
 };
 
 static PyTypeObject dirsType = { PyObject_HEAD_INIT(NULL) };
 
 void dirs_module_init(PyObject *mod)
 {
 	dirs_sequence_methods.sq_contains = (objobjproc)dirs_contains;
 	dirsType.tp_name = "parsers.dirs";
 	dirsType.tp_new = PyType_GenericNew;
 	dirsType.tp_basicsize = sizeof(dirsObject);
 	dirsType.tp_dealloc = (destructor)dirs_dealloc;
 	dirsType.tp_as_sequence = &dirs_sequence_methods;
 	dirsType.tp_flags = Py_TPFLAGS_DEFAULT;
 	dirsType.tp_doc = "dirs";
 	dirsType.tp_iter = (getiterfunc)dirs_iter;
 	dirsType.tp_methods = dirs_methods;
 	dirsType.tp_init = (initproc)dirs_init;
 
 	if (PyType_Ready(&dirsType) < 0)
 		return;
 	Py_INCREF(&dirsType);
 
 	PyModule_AddObject(mod, "dirs", (PyObject *)&dirsType);
 }