Fix [ 771097 ] frozen programs fail due to implicit import of "warnings".

If the initial import of warnings fails, clear the error.  When the module
is actually needed, if the original import failed, see if it has managed
to find its way to sys.modules yet and if so, remember it.

Python/errors.c

@@ -599,16 +599,17 @@ PyErr_WriteUnraisable(PyObject *obj)
 	Py_XDECREF(tb);
 }
 
-extern PyObject *PyModule_WarningsModule;
+extern PyObject *PyModule_GetWarningsModule();
 
 /* Function to issue a warning message; may raise an exception. */
 int
 PyErr_Warn(PyObject *category, char *message)
 {
 	PyObject *dict, *func = NULL;
+	PyObject *warnings_module = PyModule_GetWarningsModule();
 
-	if (PyModule_WarningsModule != NULL) {
-		dict = PyModule_GetDict(PyModule_WarningsModule);
+	if (warnings_module != NULL) {
+		dict = PyModule_GetDict(warnings_module);
 		func = PyDict_GetItemString(dict, "warn");
 	}
 	if (func == NULL) {

Python/pythonrun.c

@@ -69,9 +69,38 @@ int Py_IgnoreEnvironmentFlag; /* e.g. PYTHONPATH, PYTHONHOME */
 int _Py_QnewFlag = 0;
 
 /* Reference to 'warnings' module, to avoid importing it
-   on the fly when the import lock may be held.  See 683658
+   on the fly when the import lock may be held.  See 683658/771097
 */
-PyObject *PyModule_WarningsModule = NULL;
+static PyObject *warnings_module = NULL;
+
+/* Returns a borrowed reference to the 'warnings' module, or NULL.
+   If the module is returned, it is guaranteed to have been obtained
+   without acquiring the import lock
+*/
+PyObject *PyModule_GetWarningsModule()
+{
+	PyObject *typ, *val, *tb;
+	PyObject *all_modules;
+	/* If we managed to get the module at init time, just use it */
+	if (warnings_module)
+		return warnings_module;
+	/* If it wasn't available at init time, it may be available
+	   now in sys.modules (common scenario is frozen apps: import
+	   at init time fails, but the frozen init code sets up sys.path
+	   correctly, then does an implicit import of warnings for us
+	*/
+	/* Save and restore any exceptions */
+	PyErr_Fetch(&typ, &val, &tb);
+
+	all_modules = PySys_GetObject("__modules__");
+	if (all_modules) {
+		warnings_module = PyDict_GetItemString(all_modules, "warnings");
+		/* We keep a ref in the global */
+		Py_XINCREF(warnings_module);
+	}
+	PyErr_Restore(typ, val, tb);
+	return warnings_module;
+}
 
 static int initialized = 0;
 
@@ -190,7 +219,9 @@ Py_Initialize(void)
 	_PyGILState_Init(interp, tstate);
 #endif /* WITH_THREAD */
 
-	PyModule_WarningsModule = PyImport_ImportModule("warnings");
+	warnings_module = PyImport_ImportModule("warnings");
+	if (!warnings_module)
+		PyErr_Clear();
 
 #if defined(Py_USING_UNICODE) && defined(HAVE_LANGINFO_H) && defined(CODESET)
 	/* On Unix, set the file system encoding according to the
@@ -262,8 +293,8 @@ Py_Finalize(void)
 	PyOS_FiniInterrupts();
 
 	/* drop module references we saved */
-	Py_XDECREF(PyModule_WarningsModule);
-	PyModule_WarningsModule = NULL;
+	Py_XDECREF(warnings_module);
+	warnings_module = NULL;
 
 	/* Collect garbage.  This may call finalizers; it's nice to call these
 	   before all modules are destroyed. */