Issue #10779: PyErr_WarnExplicit() decodes the filename from the filesystem

encoding instead of UTF-8.

Doc/c-api/exceptions.rst

@@ -297,8 +297,9 @@ in various ways.  There is a separate error indicator for each thread.
    is a straightforward wrapper around the Python function
    :func:`warnings.warn_explicit`, see there for more information.  The *module*
    and *registry* arguments may be set to *NULL* to get the default effect
-   described there. *message*, *filename* and *module* are UTF-8 encoded
+   described there. *message* and *module* are UTF-8 encoded strings,
-   strings.
+   *filename* is decoded from the filesystem encoding
+   (:func:`sys.getfilesystemencoding`).
 
 
 .. c:function:: int PyErr_WarnFormat(PyObject *category, Py_ssize_t stack_level, const char *format, ...)

Include/warnings.h

@@ -20,7 +20,7 @@ PyAPI_FUNC(int) PyErr_WarnFormat(
 PyAPI_FUNC(int) PyErr_WarnExplicit(
     PyObject *category,
     const char *message,        /* UTF-8 encoded string */
-    const char *filename,       /* UTF-8 encoded string */
+    const char *filename,       /* decoded from the filesystem encoding */
     int lineno,
     const char *module,         /* UTF-8 encoded string */
     PyObject *registry);

Misc/NEWS

@@ -8,6 +8,9 @@ What's New in Python 3.2 Release Candidate 1
 Core and Builtins
 -----------------
 
+- Issue #10779: PyErr_WarnExplicit() decodes the filename from the filesystem
+  encoding instead of UTF-8.
+
 Library
 -------
 

Python/_warnings.c

@@ -783,7 +783,7 @@ PyErr_WarnExplicit(PyObject *category, const char *text,
 {
     PyObject *res;
     PyObject *message = PyUnicode_FromString(text);
-    PyObject *filename = PyUnicode_FromString(filename_str);
+    PyObject *filename = PyUnicode_DecodeFSDefault(filename_str);
     PyObject *module = NULL;
     int ret = -1;