[3.12] gh-105375: Improve PyErr_WarnExplicit() error handling (GH-105610

) (#105659)

Bail on first error to prevent exceptions from possibly being
overwritten.
(cherry picked from commit 567d6ae)

Co-authored-by: Erlend E. Aasland <erlend.aasland@protonmail.com>

Misc/NEWS.d/next/C API/2023-06-09-23-34-25.gh-issue-105375.n7amiF.rst

@@ -0,0 +1,2 @@
+Fix a bug in :c:func:`PyErr_WarnExplicit` where an exception could end up
+being overwritten if the API failed internally.

Python/_warnings.c

@@ -1301,25 +1301,29 @@ PyErr_WarnExplicit(PyObject *category, const char *text,
  const char *module_str, PyObject *registry)
 {
  PyObject *message = PyUnicode_FromString(text);
+ if (message == NULL) {
+ return -1;
+ }
  PyObject *filename = PyUnicode_DecodeFSDefault(filename_str);
+ if (filename == NULL) {
+ Py_DECREF(message);
+ return -1;
+ }
  PyObject *module = NULL;
- int ret = -1;
-
- if (message == NULL || filename == NULL)
- goto exit;
  if (module_str != NULL) {
  module = PyUnicode_FromString(module_str);
- if (module == NULL)
- goto exit;
+ if (module == NULL) {
+ Py_DECREF(filename);
+ Py_DECREF(message);
+ return -1;
+ }
  }
 
- ret = PyErr_WarnExplicitObject(category, message, filename, lineno,
- module, registry);
-
- exit:
- Py_XDECREF(message);
+ int ret = PyErr_WarnExplicitObject(category, message, filename, lineno,
+ module, registry);
  Py_XDECREF(module);
- Py_XDECREF(filename);
+ Py_DECREF(filename);
+ Py_DECREF(message);
  return ret;
 }