Issue #28410: Added _PyErr_FormatFromCause() -- the helper for raising

new exception with setting current exception as __cause__.

_PyErr_FormatFromCause(exception, format, args...) is equivalent to Python

    raise exception(format % args) from sys.exc_info()[1]

1 files changed, 41 insertions, 0 deletions

diff --git a/Python/errors.c b/Python/errors.c
index 12bde28..918f4df 100644
--- a/Python/errors.c
+++ b/Python/errors.c
@@ -401,6 +401,47 @@ _PyErr_ChainExceptions(PyObject *exc, PyObject *val, PyObject *tb)
     }
 }
 
+static PyObject *
+_PyErr_FormatVFromCause(PyObject *exception, const char *format, va_list vargs)
+{
+    PyObject *exc, *val, *val2, *tb;
+
+    assert(PyErr_Occurred());
+    PyErr_Fetch(&exc, &val, &tb);
+    PyErr_NormalizeException(&exc, &val, &tb);
+    if (tb != NULL) {
+        PyException_SetTraceback(val, tb);
+        Py_DECREF(tb);
+    }
+    Py_DECREF(exc);
+    assert(!PyErr_Occurred());
+
+    PyErr_FormatV(exception, format, vargs);
+
+    PyErr_Fetch(&exc, &val2, &tb);
+    PyErr_NormalizeException(&exc, &val2, &tb);
+    Py_INCREF(val);
+    PyException_SetCause(val2, val);
+    PyException_SetContext(val2, val);
+    PyErr_Restore(exc, val2, tb);
+
+    return NULL;
+}
+
+PyObject *
+_PyErr_FormatFromCause(PyObject *exception, const char *format, ...)
+{
+    va_list vargs;
+#ifdef HAVE_STDARG_PROTOTYPES
+    va_start(vargs, format);
+#else
+    va_start(vargs);
+#endif
+    _PyErr_FormatVFromCause(exception, format, vargs);
+    va_end(vargs);
+    return NULL;
+}
+
 /* Convenience functions to set a type error exception and return 0 */
 
 int