bpo-32230: Set sys.warnoptions with -X dev (#4820)

Rather than supporting dev mode directly in the warnings module, this
instead adjusts the initialisation code to add an extra 'default'
entry to sys.warnoptions when dev mode is enabled.

This ensures that dev mode behaves *exactly* as if `-Wdefault` had
been passed on the command line, including in the way it interacts
with `sys.warnoptions`, and with other command line flags like `-bb`.

Fix also bpo-20361: have -b & -bb options take precedence over any
other warnings options.

Patch written by Nick Coghlan, with minor modifications of Victor Stinner.

1 files changed, 22 insertions, 51 deletions

diff --git a/Python/_warnings.c b/Python/_warnings.c
index 29370369e2..7b2bdd5462 100644
--- a/Python/_warnings.c
+++ b/Python/_warnings.c
@@ -11,9 +11,9 @@ MODULE_NAME " provides basic warning filtering support.\n"
 
 _Py_IDENTIFIER(argv);
 _Py_IDENTIFIER(stderr);
+#ifndef Py_DEBUG
 _Py_IDENTIFIER(ignore);
-_Py_IDENTIFIER(error);
-_Py_static_string(PyId_default, "default");
+#endif
 
 static int
 check_matched(PyObject *obj, PyObject *arg)
@@ -1156,6 +1156,7 @@ static PyMethodDef warnings_functions[] = {
 };
 
 
+#ifndef Py_DEBUG
 static PyObject *
 create_filter(PyObject *category, _Py_Identifier *id)
 {
@@ -1168,70 +1169,40 @@ create_filter(PyObject *category, _Py_Identifier *id)
     return PyTuple_Pack(5, action_str, Py_None,
                         category, Py_None, _PyLong_Zero);
 }
+#endif
+
 
 static PyObject *
 init_filters(const _PyCoreConfig *config)
 {
-    int dev_mode = config->dev_mode;
-
-    Py_ssize_t count = 2;
-    if (dev_mode) {
-        count++;
-    }
-#ifndef Py_DEBUG
-    if (!dev_mode) {
-        count += 3;
-    }
-#endif
-    PyObject *filters = PyList_New(count);
-    if (filters == NULL)
-        return NULL;
-
-    size_t pos = 0;  /* Post-incremented in each use. */
-#ifndef Py_DEBUG
-    if (!dev_mode) {
-        PyList_SET_ITEM(filters, pos++,
-                        create_filter(PyExc_DeprecationWarning, &PyId_ignore));
-        PyList_SET_ITEM(filters, pos++,
-                        create_filter(PyExc_PendingDeprecationWarning, &PyId_ignore));
-        PyList_SET_ITEM(filters, pos++,
-                        create_filter(PyExc_ImportWarning, &PyId_ignore));
-    }
-#endif
-
-    _Py_Identifier *bytes_action;
-    if (Py_BytesWarningFlag > 1)
-        bytes_action = &PyId_error;
-    else if (Py_BytesWarningFlag)
-        bytes_action = &PyId_default;
-    else
-        bytes_action = &PyId_ignore;
-    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_BytesWarning,
-                    bytes_action));
-
-    _Py_Identifier *resource_action;
-    /* resource usage warnings are enabled by default in pydebug mode */
 #ifdef Py_DEBUG
-    resource_action = &PyId_default;
+    /* Py_DEBUG builds show all warnings by default */
+    return PyList_New(0);
 #else
-    resource_action = (dev_mode ? &PyId_default: &PyId_ignore);
-#endif
-    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_ResourceWarning,
-                    resource_action));
-
-    if (dev_mode) {
-        PyList_SET_ITEM(filters, pos++,
-                        create_filter(PyExc_Warning, &PyId_default));
+    /* Other builds ignore a number of warning categories by default */
+    PyObject *filters = PyList_New(4);
+    if (filters == NULL) {
+        return NULL;
     }
 
+    size_t pos = 0;  /* Post-incremented in each use. */
+    PyList_SET_ITEM(filters, pos++,
+                    create_filter(PyExc_DeprecationWarning, &PyId_ignore));
+    PyList_SET_ITEM(filters, pos++,
+                    create_filter(PyExc_PendingDeprecationWarning, &PyId_ignore));
+    PyList_SET_ITEM(filters, pos++,
+                    create_filter(PyExc_ImportWarning, &PyId_ignore));
+    PyList_SET_ITEM(filters, pos++,
+                    create_filter(PyExc_ResourceWarning, &PyId_ignore));
+
     for (size_t x = 0; x < pos; x++) {
         if (PyList_GET_ITEM(filters, x) == NULL) {
             Py_DECREF(filters);
             return NULL;
         }
     }
-
     return filters;
+#endif
 }
 
 static struct PyModuleDef warningsmodule = {