gh-94526: getpath_dirname() no longer encodes the path (#97645)

Fix the Python path configuration used to initialized sys.path at Python startup. Paths are no longer encoded to UTF-8/strict to avoid encoding errors if it contains surrogate characters (bytes paths are decoded with the surrogateescape error handler). getpath_basename() and getpath_dirname() functions no longer encode the path to UTF-8/strict, but work directly on Unicode strings. These functions now use PyUnicode_FindChar() and PyUnicode_Substring() on the Unicode path, rather than strrchr() on the encoded bytes string.

Author: vstinner

Misc/NEWS.d/next/Core and Builtins/2022-09-29-15-19-29.gh-issue-94526.wq5m6T.rst

@@ -0,0 +1,4 @@
+Fix the Python path configuration used to initialized :data:`sys.path` at
+Python startup. Paths are no longer encoded to UTF-8/strict to avoid encoding
+errors if it contains surrogate characters (bytes paths are decoded with the
+surrogateescape error handler). Patch by Victor Stinner.

Modules/getpath.c

@@ -82,27 +82,32 @@ getpath_abspath(PyObject *Py_UNUSED(self), PyObject *args)
 static PyObject *
 getpath_basename(PyObject *Py_UNUSED(self), PyObject *args)
 {
- const char *path;
- if (!PyArg_ParseTuple(args, "s", &path)) {
+ PyObject *path;
+ if (!PyArg_ParseTuple(args, "U", &path)) {
  return NULL;
  }
- const char *name = strrchr(path, SEP);
- return PyUnicode_FromString(name ? name + 1 : path);
+ Py_ssize_t end = PyUnicode_GET_LENGTH(path);
+ Py_ssize_t pos = PyUnicode_FindChar(path, SEP, 0, end, -1);
+ if (pos < 0) {
+ return Py_NewRef(path);
+ }
+ return PyUnicode_Substring(path, pos + 1, end);
 }
 
 
 static PyObject *
 getpath_dirname(PyObject *Py_UNUSED(self), PyObject *args)
 {
- const char *path;
- if (!PyArg_ParseTuple(args, "s", &path)) {
+ PyObject *path;
+ if (!PyArg_ParseTuple(args, "U", &path)) {
  return NULL;
  }
- const char *name = strrchr(path, SEP);
- if (!name) {
+ Py_ssize_t end = PyUnicode_GET_LENGTH(path);
+ Py_ssize_t pos = PyUnicode_FindChar(path, SEP, 0, end, -1);
+ if (pos < 0) {
  return PyUnicode_FromStringAndSize(NULL, 0);
  }
- return PyUnicode_FromStringAndSize(path, (name - path));
+ return PyUnicode_Substring(path, 0, pos);
 }