Fixed on PyPy

Author: YannickJadoul

include/pybind11/cast.h

@@ -1020,23 +1020,32 @@ struct type_caster<T, enable_if_t<std::is_arithmetic<T>::value && !is_std_char_t
         if (!src)
             return false;
 
+#if !defined(PYPY_VERSION)
+        auto index_check = [](PyObject *o) { return PyIndex_Check(o); };
+#else
+        // In PyPy 7.3.3, `PyIndex_Check` is implemented by calling `__index__`,
+        // while CPython only considers the existence of `nb_index`/`__index__`.
+        auto index_check = [](PyObject *o) { return hasattr(o, "__index__"); };
+#endif
+
         if (std::is_floating_point<T>::value) {
             if (convert || PyFloat_Check(src.ptr()))
                 py_value = (py_type) PyFloat_AsDouble(src.ptr());
             else
                 return false;
         } else if (PyFloat_Check(src.ptr())) {
             return false;
-        } else if (!convert && !PyIndex_Check(src.ptr()) && !PYBIND11_LONG_CHECK(src.ptr())) {
+        } else if (!convert && !index_check(src.ptr()) && !PYBIND11_LONG_CHECK(src.ptr())) {
             return false;
         } else {
             handle obj = src;
 #if PY_VERSION_HEX < 0x03080000
             bool do_decref = false;
-            if (PyIndex_Check(src.ptr())) {
+            if (index_check(src.ptr())) {
                 PyObject *tmp = PyNumber_Index(src.ptr());
                 if (!tmp) {
-                    py_value = (py_type) -1;
+                    PyErr_Clear();
+                    return false;
                 }
                 do_decref = true;
                 obj = tmp;