osutil: fix excessive decref on tuple creation failure in listdir()

The stat object would be freed on error for the same reason as the previous
patch. makestat() can be inlined, but this patch doesn't change it.

https://github.com/python/cpython/blob/2.7/Python/modsupport.c#L292

The __APPLE__ code is untested.

mercurial/cext/osutil.c

@@ -336,7 +336,7 b' static PyObject *makestat(const struct s'
 static PyObject *_listdir_stat(char *path, int pathlen, int keepstat,
 			       char *skip)
 {
-	PyObject *list, *elem, *stat = NULL, *ret = NULL;
+	PyObject *list, *elem, *ret = NULL;
 	char fullpath[PATH_MAX + 10];
 	int kind, err;
 	struct stat st;
@@ -409,7 +409,7 b' static PyObject *_listdir_stat(char *pat'
 		}
 
 		if (keepstat) {
-			stat = makestat(&st);
+			PyObject *stat = makestat(&st);
 			if (!stat)
 				goto error;
 			elem = Py_BuildValue(PY23("siN", "yiN"), ent->d_name,
@@ -419,7 +419,6 b' static PyObject *_listdir_stat(char *pat'
 					     kind);
 		if (!elem)
 			goto error;
-		stat = NULL;
 
 		PyList_Append(list, elem);
 		Py_DECREF(elem);
@@ -430,7 +429,6 b' static PyObject *_listdir_stat(char *pat'
 
 error:
 	Py_DECREF(list);
-	Py_XDECREF(stat);
 error_list:
 	closedir(dir);
 	/* closedir also closes its dirfd */
@@ -480,7 +478,7 b' int attrkind(attrbuf_entry *entry)'
 static PyObject *_listdir_batch(char *path, int pathlen, int keepstat,
 				char *skip, bool *fallback)
 {
-	PyObject *list, *elem, *stat = NULL, *ret = NULL;
+	PyObject *list, *elem, *ret = NULL;
 	int kind, err;
 	unsigned long index;
 	unsigned int count, old_state, new_state;
@@ -586,6 +584,7 b' static PyObject *_listdir_batch(char *pa'
 			}
 
 			if (keepstat) {
+				PyObject *stat = NULL;
 				/* from the getattrlist(2) man page: "Only the
 				   permission bits ... are valid". */
 				st.st_mode = (entry->access_mask & ~S_IFMT) | kind;
@@ -601,7 +600,6 b' static PyObject *_listdir_batch(char *pa'
 						     filename, kind);
 			if (!elem)
 				goto error;
-			stat = NULL;
 
 			PyList_Append(list, elem);
 			Py_DECREF(elem);
@@ -615,7 +613,6 b' static PyObject *_listdir_batch(char *pa'
 
 error:
 	Py_DECREF(list);
-	Py_XDECREF(stat);
 error_dir:
 	close(dfd);
 error_value: