Issue 24237: Raise PendingDeprecationWarning per PEP 479

Raise PendingDeprecationWarning when generator raises StopIteration
and no __future__ import is used.  Fix offenders in the stdlib
and tests.

See also issue 22906.
Thanks to Nick Coghlan and Berker Peksag for reviews.

1 files changed, 20 insertions, 3 deletions

diff --git a/Objects/genobject.c b/Objects/genobject.c
index 555e4fd76e..8e5624d460 100644
--- a/Objects/genobject.c
+++ b/Objects/genobject.c
@@ -143,13 +143,12 @@ gen_send_ex(PyGenObject *gen, PyObject *arg, int exc)
         }
         Py_CLEAR(result);
     }
-    else if (!result) {
+    else if (!result && PyErr_ExceptionMatches(PyExc_StopIteration)) {
         /* Check for __future__ generator_stop and conditionally turn
          * a leaking StopIteration into RuntimeError (with its cause
          * set appropriately). */
-        if ((((PyCodeObject *)gen->gi_code)->co_flags &
+        if (((PyCodeObject *)gen->gi_code)->co_flags &
               (CO_FUTURE_GENERATOR_STOP | CO_COROUTINE | CO_ITERABLE_COROUTINE))
-            && PyErr_ExceptionMatches(PyExc_StopIteration))
         {
             PyObject *exc, *val, *val2, *tb;
             PyErr_Fetch(&exc, &val, &tb);
@@ -167,6 +166,24 @@ gen_send_ex(PyGenObject *gen, PyObject *arg, int exc)
             PyException_SetContext(val2, val);
             PyErr_Restore(exc, val2, tb);
         }
+        else {
+            PyObject *exc, *val, *tb;
+
+            /* Pop the exception before issuing a warning. */
+            PyErr_Fetch(&exc, &val, &tb);
+
+            if (PyErr_WarnFormat(PyExc_PendingDeprecationWarning, 1,
+                                 "generator '%.50S' raised StopIteration",
+                                 gen->gi_qualname)) {
+                /* Warning was converted to an error. */
+                Py_XDECREF(exc);
+                Py_XDECREF(val);
+                Py_XDECREF(tb);
+            }
+            else {
+                PyErr_Restore(exc, val, tb);
+            }
+        }
     }
 
     if (!result || f->f_stacktop == NULL) {