generalization of nb::chain_error

docs/api_core.rst

@@ -1217,8 +1217,9 @@ the reference section on :ref:`class binding <class_binding>`.
    Raise a Python error of type ``type`` using the format string ``fmt``
    interpreted by ``PyErr_FormatV``.
 
-   This newly created error is chained on top of an already existing error
-   status that must be set before calling the function.
+   If a Python error state was already set prior to calling this method, then
+   the new error is *chained* on top of the existing one. Otherwise, the
+   function creates a new error without initializing its ``__cause__`` field.
 
 .. cpp:function:: void raise_from(python_error &e, handle type, const char * fmt, ...)
 

include/nanobind/nb_error.h

@@ -148,6 +148,6 @@ class exception : public object {
 };
 
 NB_CORE void chain_error(handle type, const char *fmt, ...) noexcept;
-NB_CORE void raise_from(python_error &e, handle type, const char *fmt, ...);
+[[noreturn]] NB_CORE void raise_from(python_error &e, handle type, const char *fmt, ...);
 
 NAMESPACE_END(NB_NAMESPACE)

src/error.cpp

@@ -253,20 +253,21 @@ NAMESPACE_END(detail)
 static void chain_error_v(handle type, const char *fmt, va_list args) noexcept {
 #if PY_VERSION_HEX >= 0x030C0000
     PyObject *value = PyErr_GetRaisedException();
-    check(value, "nanobind::detail::raise_from(): error status is not set!");
 #else
     PyObject *tp = nullptr, *value = nullptr, *traceback = nullptr;
 
     PyErr_Fetch(&tp, &value, &traceback);
-    check(tp, "nanobind::detail::raise_from(): error status is not set!");
 
-    PyErr_NormalizeException(&tp, &value, &traceback);
-    if (traceback) {
-        PyException_SetTraceback(value, traceback);
-        Py_DECREF(traceback);
-    }
+    if (tp) {
+        PyErr_NormalizeException(&tp, &value, &traceback);
+        if (traceback) {
+            PyException_SetTraceback(value, traceback);
+            Py_DECREF(traceback);
+        }
 
-    Py_DECREF(tp);
+        Py_DECREF(tp);
+        tp = traceback = nullptr;
+    }
 #endif
 
 #if !defined(PYPY_VERSION)
@@ -278,6 +279,9 @@ static void chain_error_v(handle type, const char *fmt, va_list args) noexcept {
     Py_DECREF(exc_str);
 #endif
 
+    if (!value)
+        return;
+
     PyObject *value_2 = nullptr;
 #if PY_VERSION_HEX >= 0x030C0000
     value_2 = PyErr_GetRaisedException();