Check dict item accesses where it isn't already checked (#2863)

* Convert PyDict_GetXXX to internal error checking variant

* Check unlikely error return from PyDict_DelItemString

Author: virtuald

include/pybind11/pybind11.h

@@ -636,7 +636,7 @@ class cpp_function : public function {
                 bool bad_arg = false;
                 for (; args_copied < args_to_copy; ++args_copied) {
                     const argument_record *arg_rec = args_copied < func.args.size() ? &func.args[args_copied] : nullptr;
-                    if (kwargs_in && arg_rec && arg_rec->name && PyDict_GetItemString(kwargs_in, arg_rec->name)) {
+                    if (kwargs_in && arg_rec && arg_rec->name && dict_getitemstring(kwargs_in, arg_rec->name)) {
                         bad_arg = true;
                         break;
                     }
@@ -684,15 +684,17 @@ class cpp_function : public function {
 
                         handle value;
                         if (kwargs_in && arg_rec.name)
-                            value = PyDict_GetItemString(kwargs.ptr(), arg_rec.name);
+                            value = dict_getitemstring(kwargs.ptr(), arg_rec.name);
 
                         if (value) {
                             // Consume a kwargs value
                             if (!copied_kwargs) {
                                 kwargs = reinterpret_steal<dict>(PyDict_Copy(kwargs.ptr()));
                                 copied_kwargs = true;
                             }
-                            PyDict_DelItemString(kwargs.ptr(), arg_rec.name);
+                            if (PyDict_DelItemString(kwargs.ptr(), arg_rec.name) == -1) {
+                                throw error_already_set();
+                            }
                         } else if (arg_rec.value) {
                             value = arg_rec.value;
                         }
@@ -2139,7 +2141,7 @@ inline function get_type_override(const void *this_ptr, const type_info *this_ty
     if (frame && (std::string) str(frame->f_code->co_name) == name &&
         frame->f_code->co_argcount > 0) {
         PyFrame_FastToLocals(frame);
-        PyObject *self_caller = PyDict_GetItem(
+        PyObject *self_caller = dict_getitem(
             frame->f_locals, PyTuple_GET_ITEM(frame->f_code->co_varnames, 0));
         if (self_caller == self.ptr())
             return function();

include/pybind11/pytypes.h

@@ -485,6 +485,43 @@ inline handle get_function(handle value) {
     return value;
 }
 
+// Reimplementation of python's dict helper functions to ensure that exceptions
+// aren't swallowed (see #2862)
+
+// copied from cpython _PyDict_GetItemStringWithError
+inline PyObject * dict_getitemstring(PyObject *v, const char *key)
+{
+#if PY_MAJOR_VERSION >= 3
+    PyObject *kv, *rv;
+    kv = PyUnicode_FromString(key);
+    if (kv == NULL) {
+        throw error_already_set();
+    }
+
+    rv = PyDict_GetItemWithError(v, kv);
+    Py_DECREF(kv);
+    if (rv == NULL && PyErr_Occurred()) {
+        throw error_already_set();
+    }
+    return rv;
+#else
+    return PyDict_GetItemString(v, key);
+#endif
+}
+
+inline PyObject * dict_getitem(PyObject *v, PyObject *key)
+{
+#if PY_MAJOR_VERSION >= 3
+    PyObject *rv = PyDict_GetItemWithError(v, key);
+    if (rv == NULL && PyErr_Occurred()) {
+        throw error_already_set();
+    }
+    return rv;
+#else
+    return PyDict_GetItem(v, key);
+#endif
+}
+
 // Helper aliases/functions to support implicit casting of values given to python accessors/methods.
 // When given a pyobject, this simply returns the pyobject as-is; for other C++ type, the value goes
 // through pybind11::cast(obj) to convert it to an `object`.