bpo-39796: Fix _warnings module initialization (GH-18739)

* Add _PyWarnings_InitState() which only initializes the _warnings
  module state (tstate->interp->warnings) without creating a module
  object
* Py_InitializeFromConfig() now calls _PyWarnings_InitState() instead
  of _PyWarnings_Init()
* Rename also private functions of _warnings.c to avoid confusion
  between the public C API and the private C API.

Include/internal/pycore_warnings.h

@@ -17,6 +17,8 @@ struct _warnings_runtime_state {
     long filters_version;
 };
 
+extern PyStatus _PyWarnings_InitState(PyThreadState *tstate);
+
 #ifdef __cplusplus
 }
 #endif

Python/_warnings.c

@@ -1,4 +1,5 @@
 #include "Python.h"
+#include "pycore_initconfig.h"
 #include "pycore_pyerrors.h"
 #include "pycore_pystate.h"
 #include "frameobject.h"
@@ -28,12 +29,12 @@ _Py_IDENTIFIER(__name__);
 
 /* Given a module object, get its per-module state. */
 static WarningsState *
-_Warnings_GetState()
+warnings_get_state(void)
 {
     PyThreadState *tstate = _PyThreadState_GET();
     if (tstate == NULL) {
         _PyErr_SetString(tstate, PyExc_RuntimeError,
-                          "_Warnings_GetState: could not identify "
+                          "warnings_get_state: could not identify "
                           "current interpreter");
         return NULL;
     }
@@ -42,7 +43,7 @@ _Warnings_GetState()
 
 /* Clear the given warnings module state. */
 static void
-_Warnings_ClearState(WarningsState *st)
+warnings_clear_state(WarningsState *st)
 {
     Py_CLEAR(st->filters);
     Py_CLEAR(st->once_registry);
@@ -112,7 +113,7 @@ init_filters(void)
 
 /* Initialize the given warnings module state. */
 static int
-_Warnings_InitState(WarningsState *st)
+warnings_init_state(WarningsState *st)
 {
     if (st->filters == NULL) {
         st->filters = init_filters();
@@ -140,7 +141,7 @@ _Warnings_InitState(WarningsState *st)
     return 0;
 
 error:
-    _Warnings_ClearState(st);
+    warnings_clear_state(st);
     return -1;
 }
 
@@ -286,7 +287,7 @@ get_filter(PyObject *category, PyObject *text, Py_ssize_t lineno,
     Py_ssize_t i;
     PyObject *warnings_filters;
     _Py_IDENTIFIER(filters);
-    WarningsState *st = _Warnings_GetState();
+    WarningsState *st = warnings_get_state();
     if (st == NULL) {
         return NULL;
     }
@@ -388,7 +389,7 @@ already_warned(PyObject *registry, PyObject *key, int should_set)
     if (key == NULL)
         return -1;
 
-    WarningsState *st = _Warnings_GetState();
+    WarningsState *st = warnings_get_state();
     if (st == NULL) {
         return -1;
     }
@@ -706,7 +707,7 @@ warn_explicit(PyObject *category, PyObject *message,
 
         if (_PyUnicode_EqualToASCIIString(action, "once")) {
             if (registry == NULL || registry == Py_None) {
-                WarningsState *st = _Warnings_GetState();
+                WarningsState *st = warnings_get_state();
                 if (st == NULL) {
                     goto cleanup;
                 }
@@ -1066,7 +1067,7 @@ warnings_warn_explicit(PyObject *self, PyObject *args, PyObject *kwds)
 static PyObject *
 warnings_filters_mutated(PyObject *self, PyObject *args)
 {
-    WarningsState *st = _Warnings_GetState();
+    WarningsState *st = warnings_get_state();
     if (st == NULL) {
         return NULL;
     }
@@ -1333,6 +1334,16 @@ static struct PyModuleDef warningsmodule = {
 };
 
 
+PyStatus
+_PyWarnings_InitState(PyThreadState *tstate)
+{
+    if (warnings_init_state(&tstate->interp->warnings) < 0) {
+        return _PyStatus_ERR("can't initialize warnings");
+    }
+    return _PyStatus_OK();
+}
+
+
 PyMODINIT_FUNC
 _PyWarnings_Init(void)
 {
@@ -1343,11 +1354,11 @@ _PyWarnings_Init(void)
         return NULL;
     }
 
-    WarningsState *st = _Warnings_GetState();
+    WarningsState *st = warnings_get_state();
     if (st == NULL) {
         goto error;
     }
-    if (_Warnings_InitState(st) < 0) {
+    if (warnings_init_state(st) < 0) {
         goto error;
     }
 
@@ -1370,7 +1381,7 @@ _PyWarnings_Init(void)
 
 error:
     if (st != NULL) {
-        _Warnings_ClearState(st);
+        warnings_clear_state(st);
     }
     Py_DECREF(m);
     return NULL;
@@ -1380,5 +1391,5 @@ _PyWarnings_Init(void)
 void
 _PyWarnings_Fini(PyInterpreterState *interp)
 {
-    _Warnings_ClearState(&interp->warnings);
+    warnings_clear_state(&interp->warnings);
 }

Python/pylifecycle.c

@@ -677,8 +677,9 @@ pycore_init_import_warnings(PyThreadState *tstate, PyObject *sysmod)
     const PyConfig *config = &tstate->interp->config;
     if (_Py_IsMainInterpreter(tstate)) {
         /* Initialize _warnings. */
-        if (_PyWarnings_Init() == NULL) {
-            return _PyStatus_ERR("can't initialize warnings");
+        status = _PyWarnings_InitState(tstate);
+        if (_PyStatus_EXCEPTION(status)) {
+            return status;
         }
 
         if (config->_install_importlib) {