ncoghlan · Dec 6, 2017 · Dec 6, 2017 · Dec 6, 2017 · Dec 6, 2017 · Dec 6, 2017
diff --git a/Lib/subprocess.py b/Lib/subprocess.py
@@ -241,7 +241,7 @@ def _optim_args_from_interpreter_flags():
 
 def _args_from_interpreter_flags():
     """Return a list of command-line arguments reproducing the current
-    settings in sys.flags and sys.warnoptions."""
+    settings in sys.flags, sys.warnoptions and sys._xoptions."""
     flag_opt_map = {
         'debug': 'd',
         # 'inspect': 'i',
@@ -268,6 +268,7 @@ def _args_from_interpreter_flags():
     # -X options
     xoptions = getattr(sys, '_xoptions', {})
     if 'dev' in xoptions:
+        args.remove('-Wdefault')
         args.extend(('-X', 'dev'))
     for opt in ('faulthandler', 'tracemalloc', 'importtime',
                 'showalloccount', 'showrefcount'):

diff --git a/Lib/test/test_cmd_line.py b/Lib/test/test_cmd_line.py
@@ -541,31 +541,47 @@ def test_xdev(self):
         code = ("import sys, warnings; "
                 "print(' '.join('%s::%s' % (f[0], f[2].__name__) "
                                 "for f in warnings.filters))")
+        if sys.flags.debug:
+            resource_action = "default"
+        else:
+            resource_action = "ignore"
 
         out = self.run_xdev("-c", code)
         self.assertEqual(out,
+                         "default::Warning "
+                         "ignore::DeprecationWarning "
+                         "ignore::PendingDeprecationWarning "
+                         "ignore::ImportWarning "
                          "ignore::BytesWarning "
-                         "default::ResourceWarning "
-                         "default::Warning")
+                         f"{resource_action}::ResourceWarning")
 
         out = self.run_xdev("-b", "-c", code)
         self.assertEqual(out,
+                         "default::Warning "
+                         "ignore::DeprecationWarning "
+                         "ignore::PendingDeprecationWarning "
+                         "ignore::ImportWarning "
                          "default::BytesWarning "
-                         "default::ResourceWarning "
-                         "default::Warning")
+                         f"{resource_action}::ResourceWarning")
 
         out = self.run_xdev("-bb", "-c", code)
         self.assertEqual(out,
+                         "default::Warning "
+                         "ignore::DeprecationWarning "
+                         "ignore::PendingDeprecationWarning "
+                         "ignore::ImportWarning "
                          "error::BytesWarning "
-                         "default::ResourceWarning "
-                         "default::Warning")
+                         f"{resource_action}::ResourceWarning")
 
         out = self.run_xdev("-Werror", "-c", code)
         self.assertEqual(out,
                          "error::Warning "
+                         "default::Warning "
+                         "ignore::DeprecationWarning "
+                         "ignore::PendingDeprecationWarning "
+                         "ignore::ImportWarning "
                          "ignore::BytesWarning "
-                         "default::ResourceWarning "
-                         "default::Warning")
+                         f"{resource_action}::ResourceWarning")
 
         # Memory allocator debug hooks
         try:

diff --git a/Lib/warnings.py b/Lib/warnings.py
@@ -519,14 +519,11 @@ def _filters_mutated():
 # Module initialization
 _processoptions(sys.warnoptions)
 if not _warnings_defaults:
-    dev_mode = ('dev' in getattr(sys, '_xoptions', {}))
-    py_debug = hasattr(sys, 'gettotalrefcount')
-
-    if not(dev_mode or py_debug):
-        silence = [ImportWarning, PendingDeprecationWarning]
-        silence.append(DeprecationWarning)
-        for cls in silence:
-            simplefilter("ignore", category=cls)
+    # TODO: Define a test case that ensures this fallback code always remains
+    #       consistent with init_filters() in _warnings.c
+    simplefilter("ignore", category=DeprecationWarning, append=1)
+    simplefilter("ignore", category=PendingDeprecationWarning, append=1)
+    simplefilter("ignore", category=ImportWarning, append=1)
 
     bytes_warning = sys.flags.bytes_warning
     if bytes_warning > 1:
@@ -538,15 +535,10 @@ def _filters_mutated():
     simplefilter(bytes_action, category=BytesWarning, append=1)
 
     # resource usage warnings are enabled by default in pydebug mode
-    if dev_mode or py_debug:
+    if sys.flags.debug:
         resource_action = "default"
     else:
         resource_action = "ignore"
     simplefilter(resource_action, category=ResourceWarning, append=1)
 
-    if dev_mode:
-        simplefilter("default", category=Warning, append=1)
-
-    del py_debug, dev_mode
-
 del _warnings_defaults
diff --git a/Misc/NEWS.d/next/Core and Builtins/2017-12-06-20-18-34.bpo-32230.PgGQaB.rst b/Misc/NEWS.d/next/Core and Builtins/2017-12-06-20-18-34.bpo-32230.PgGQaB.rst
@@ -0,0 +1,3 @@
+`-X dev` now injects a ``'default'`` entry into sys.warnoptions, ensuring
+that it behaves identically to actually passing ``-Wdefault`` at the command
+line.
diff --git a/Modules/main.c b/Modules/main.c
@@ -740,11 +740,33 @@ pymain_add_warnings_optlist(_Py_OptList *warnings)
     return 0;
 }
 
+static int
+pymain_add_warnings_dev_mode(_PyCoreConfig *core_config)
+{
+    if (core_config->dev_mode) {
+        PyObject *option = PyUnicode_FromString("default");
+        if (option == NULL) {
+            return -1;
+        }
+        if (_PySys_AddWarnOptionWithError(option)) {
+            Py_DECREF(option);
+            return -1;
+        }
+        Py_DECREF(option);
+    }
+    return 0;
+}
+
 static int
 pymain_add_warnings_options(_PyMain *pymain)
 {
     PySys_ResetWarnOptions();
 
+    if (pymain_add_warnings_dev_mode(&pymain->core_config) < 0) {
+        pymain->err = _Py_INIT_NO_MEMORY();
+        return -1;
+    }
+
     if (pymain_add_warnings_optlist(&pymain->env_warning_options) < 0) {
         pymain->err = _Py_INIT_NO_MEMORY();
         return -1;

diff --git a/Python/_warnings.c b/Python/_warnings.c
@@ -1172,32 +1172,18 @@ create_filter(PyObject *category, _Py_Identifier *id)
 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
+    Py_ssize_t count = 5;
     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
+    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));
 
     _Py_Identifier *bytes_action;
     if (Py_BytesWarningFlag > 1)
@@ -1206,23 +1192,19 @@ init_filters(const _PyCoreConfig *config)
         bytes_action = &PyId_default;
     else
         bytes_action = &PyId_ignore;
-    PyList_SET_ITEM(filters, pos++, create_filter(PyExc_BytesWarning,
-                    bytes_action));
+    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;
 #else
-    resource_action = (dev_mode ? &PyId_default: &PyId_ignore);
+    resource_action = &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));
-    }
+    PyList_SET_ITEM(filters, pos++,
+                    create_filter(PyExc_ResourceWarning, resource_action));
 
     for (size_t x = 0; x < pos; x++) {
         if (PyList_GET_ITEM(filters, x) == NULL) {