gh-94526: getpath_dirname() no longer encodes the path (GH-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.
(cherry picked from commit 9f2f1dd131b912e224cd0269adde8879799686c4)

Co-authored-by: Victor Stinner <vstinner@python.org>

1 files changed, 14 insertions, 9 deletions

diff --git a/Modules/getpath.c b/Modules/getpath.c
index 9447988..be704ad 100644
--- a/Modules/getpath.c
+++ b/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);
 }