bpo-27535: Fix memory leak with warnings ignore (#4489)

The warnings module doesn't leak memory anymore in the hidden
warnings registry for the "ignore" action of warnings filters.

The warn_explicit() function doesn't add the warning key to the
registry anymore for the "ignore" action.

1 files changed, 9 insertions, 4 deletions

diff --git a/Python/_warnings.c b/Python/_warnings.c
index 27f5b813a7..29370369e2 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -528,16 +528,21 @@ warn_explicit(PyObject *category, PyObject *message,
         goto cleanup;
     }
 
+    if (_PyUnicode_EqualToASCIIString(action, "ignore")) {
+        goto return_none;
+    }
+
     /* Store in the registry that we've been here, *except* when the action
        is "always". */
     rc = 0;
     if (!_PyUnicode_EqualToASCIIString(action, "always")) {
         if (registry != NULL && registry != Py_None &&
-                PyDict_SetItem(registry, key, Py_True) < 0)
+            PyDict_SetItem(registry, key, Py_True) < 0)
+        {
             goto cleanup;
-        else if (_PyUnicode_EqualToASCIIString(action, "ignore"))
-            goto return_none;
-        else if (_PyUnicode_EqualToASCIIString(action, "once")) {
+        }
+
+        if (_PyUnicode_EqualToASCIIString(action, "once")) {
             if (registry == NULL || registry == Py_None) {
                 registry = get_once_registry();
                 if (registry == NULL)