Fix kwargs handling in ast node constructors

Author: Rémi Lapeyre

Lib/ast.py

@@ -443,6 +443,14 @@ def __instancecheck__(cls, inst):
         return type.__instancecheck__(cls, inst)
 
 def _new(cls, *args, **kwargs):
+    for key in kwargs:
+        try:
+            pos = cls._fields.index(key)
+            if pos < len(args):
+                raise TypeError(f"{cls.__name__} got multiple values for argument {key!r}")
+        except ValueError:
+            # arbitrary keywork arguments are accepted
+            pass
     if cls in _const_types:
         return Constant(*args, **kwargs)
     return Constant.__new__(cls, *args, **kwargs)

Misc/NEWS.d/next/Library/2019-03-17-19-01-53.bpo-36290.7VXo_K.rst

@@ -0,0 +1,2 @@
+_ast.ast_type_init now raises TypeError on conflicting keyword arguments.
+Patch contributed by Rémi Lapeyre.

Parser/asdl_c.py

@@ -625,6 +625,7 @@ def visitModule(self, mod):
         self.emit("""
 _Py_IDENTIFIER(_fields);
 _Py_IDENTIFIER(_attributes);
+_Py_IDENTIFIER(index);
 
 typedef struct {
     PyObject_HEAD
@@ -660,13 +661,15 @@ def visitModule(self, mod):
     Py_ssize_t i, numfields = 0;
     int res = -1;
     PyObject *key, *value, *fields;
+    PyObject *index = NULL;
     if (_PyObject_LookupAttrId((PyObject*)Py_TYPE(self), &PyId__fields, &fields) < 0) {
         goto cleanup;
     }
     if (fields) {
         numfields = PySequence_Size(fields);
-        if (numfields == -1)
+        if (numfields == -1) {
             goto cleanup;
+        }
     }
 
     res = 0; /* if no error occurs, this stays 0 to the end */
@@ -687,19 +690,50 @@ def visitModule(self, mod):
         }
         res = PyObject_SetAttr(self, name, PyTuple_GET_ITEM(args, i));
         Py_DECREF(name);
-        if (res < 0)
+        if (res < 0) {
             goto cleanup;
+        }
     }
     if (kw) {
         i = 0;  /* needed by PyDict_Next */
+        if (_PyObject_LookupAttrId(fields, &PyId_index, &index) < 0) {
+            goto cleanup;
+        }
         while (PyDict_Next(kw, &i, &key, &value)) {
+            PyObject* pos = _PyObject_FastCallDict(index, &key, 1, NULL);
+            PyObject* err = PyErr_Occurred();
+            if (pos == NULL || err != NULL) {
+                // arbitrary keyword arguments are accepted
+                if (!PyErr_GivenExceptionMatches(err, PyExc_ValueError)) {
+                    res = -1;
+                    goto cleanup;
+                }
+                PyErr_Clear();
+            }
+            else {
+                Py_ssize_t p = PyNumber_AsSsize_t(pos, NULL);
+                Py_DECREF(pos);
+                if (p == -1 && PyErr_Occurred()) {
+                    res = -1;
+                    goto cleanup;
+                }
+                if (p < PyTuple_GET_SIZE(args)) {
+                    PyErr_Format(PyExc_TypeError,
+                        "%.400s got multiple values for argument '%U'",
+                        Py_TYPE(self)->tp_name, key);
+                    res = -1;
+                    goto cleanup;
+                }
+            }
             res = PyObject_SetAttr(self, key, value);
-            if (res < 0)
+            if (res < 0) {
                 goto cleanup;
+            }
         }
     }
   cleanup:
     Py_XDECREF(fields);
+    Py_XDECREF(index);
     return res;
 }