bpo-38304: Remove PyConfig.struct_size (GH-16500)

For now, we'll rely on the fact that the config structures aren't covered by the stable ABI.

We may revisit this in the future if we further explore the idea of offering a stable embedding API.

Author: vstinner

Doc/c-api/init_config.rst

@@ -194,25 +194,18 @@ PyPreConfig
    * Configure the LC_CTYPE locale
    * Set the UTF-8 mode
 
-   The :c:member:`struct_size` field must be explicitly initialized to
-   ``sizeof(PyPreConfig)``.
-
    Function to initialize a preconfiguration:
 
-   .. c:function:: PyStatus PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)
+   .. c:function:: void PyPreConfig_InitIsolatedConfig(PyPreConfig *preconfig)
 
       Initialize the preconfiguration with :ref:`Python Configuration
       <init-python-config>`.
 
-   .. c:function:: PyStatus PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)
+   .. c:function:: void PyPreConfig_InitPythonConfig(PyPreConfig *preconfig)
 
       Initialize the preconfiguration with :ref:`Isolated Configuration
       <init-isolated-conf>`.
 
-   The caller of these functions is responsible to handle exceptions (error or
-   exit) using :c:func:`PyStatus_Exception` and
-   :c:func:`Py_ExitStatusException`.
-
    Structure fields:
 
    .. c:member:: int allocator
@@ -274,13 +267,6 @@ PyPreConfig
       same way the regular Python parses command line arguments: see
       :ref:`Command Line Arguments <using-on-cmdline>`.
 
-   .. c:member:: size_t struct_size
-
-      Size of the structure in bytes: must be initialized to
-      ``sizeof(PyPreConfig)``.
-
-      Field used for API and ABI compatibility.
-
    .. c:member:: int use_environment
 
       See :c:member:`PyConfig.use_environment`.
@@ -332,12 +318,7 @@ Example using the preinitialization to enable the UTF-8 Mode::
 
     PyStatus status;
     PyPreConfig preconfig;
-    preconfig.struct_size = sizeof(PyPreConfig);
-
-    status = PyPreConfig_InitPythonConfig(&preconfig);
-    if (PyStatus_Exception(status)) {
-        Py_ExitStatusException(status);
-    }
+    PyPreConfig_InitPythonConfig(&preconfig);
 
     preconfig.utf8_mode = 1;
 
@@ -360,9 +341,6 @@ PyConfig
 
    Structure containing most parameters to configure Python.
 
-   The :c:member:`struct_size` field must be explicitly initialized to
-   ``sizeof(PyConfig)``.
-
    Structure methods:
 
    .. c:function:: PyStatus PyConfig_InitPythonConfig(PyConfig *config)
@@ -679,13 +657,6 @@ PyConfig
       Encoding and encoding errors of :data:`sys.stdin`, :data:`sys.stdout` and
       :data:`sys.stderr`.
 
-   .. c:member:: size_t struct_size
-
-      Size of the structure in bytes: must be initialized to
-      ``sizeof(PyConfig)``.
-
-      Field used for API and ABI compatibility.
-
    .. c:member:: int tracemalloc
 
       If non-zero, call :func:`tracemalloc.start` at startup.
@@ -754,7 +725,6 @@ Example setting the program name::
     {
         PyStatus status;
         PyConfig config;
-        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
@@ -787,7 +757,6 @@ configuration, and then override some parameters::
     {
         PyStatus status;
         PyConfig config;
-        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
@@ -875,7 +844,6 @@ Example of customized Python always running in isolated mode::
     {
         PyStatus status;
         PyConfig config;
-        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {
@@ -1067,7 +1035,6 @@ phases::
     {
         PyStatus status;
         PyConfig config;
-        config.struct_size = sizeof(PyConfig);
 
         status = PyConfig_InitPythonConfig(&config);
         if (PyStatus_Exception(status)) {

Include/cpython/initconfig.h

@@ -45,10 +45,6 @@ PyAPI_FUNC(PyStatus) PyWideStringList_Insert(PyWideStringList *list,
 /* --- PyPreConfig ----------------------------------------------- */
 
 typedef struct {
-    /* Size of the structure in bytes: must be initialized to
-       sizeof(PyPreConfig). Field used for API and ABI compatibility. */
-    size_t struct_size;
-
     int _config_init;     /* _PyConfigInitEnum value */
 
     /* Parse Py_PreInitializeFromBytesArgs() arguments?
@@ -124,17 +120,13 @@ typedef struct {
     int allocator;
 } PyPreConfig;
 
-PyAPI_FUNC(PyStatus) PyPreConfig_InitPythonConfig(PyPreConfig *config);
-PyAPI_FUNC(PyStatus) PyPreConfig_InitIsolatedConfig(PyPreConfig *config);
+PyAPI_FUNC(void) PyPreConfig_InitPythonConfig(PyPreConfig *config);
+PyAPI_FUNC(void) PyPreConfig_InitIsolatedConfig(PyPreConfig *config);
 
 
 /* --- PyConfig ---------------------------------------------- */
 
 typedef struct {
-    /* Size of the structure in bytes: must be initialized to
-       sizeof(PyConfig). Field used for API and ABI compatibility. */
-    size_t struct_size;
-
     int _config_init;     /* _PyConfigInitEnum value */
 
     int isolated;         /* Isolated mode? see PyPreConfig.isolated */

Include/internal/pycore_initconfig.h

@@ -120,8 +120,8 @@ extern PyStatus _PyPreCmdline_Read(_PyPreCmdline *cmdline,
 
 /* --- PyPreConfig ----------------------------------------------- */
 
-PyAPI_FUNC(PyStatus) _PyPreConfig_InitCompatConfig(PyPreConfig *preconfig);
-extern PyStatus _PyPreConfig_InitFromConfig(
+PyAPI_FUNC(void) _PyPreConfig_InitCompatConfig(PyPreConfig *preconfig);
+extern void _PyPreConfig_InitFromConfig(
     PyPreConfig *preconfig,
     const PyConfig *config);
 extern PyStatus _PyPreConfig_InitFromPreConfig(

Misc/NEWS.d/next/C API/2019-09-28-03-43-27.bpo-38304.RqHAwd.rst

@@ -53,20 +53,15 @@ pymain_init(const _PyArgv *args)
 #endif
 
     PyPreConfig preconfig;
-    preconfig.struct_size = sizeof(PyPreConfig);
-
-    status = PyPreConfig_InitPythonConfig(&preconfig);
-    if (_PyStatus_EXCEPTION(status)) {
-        return status;
-    }
+    PyPreConfig_InitPythonConfig(&preconfig);
 
     status = _Py_PreInitializeFromPyArgv(&preconfig, args);
     if (_PyStatus_EXCEPTION(status)) {
         return status;
     }
 
     PyConfig config;
-    config.struct_size = sizeof(PyConfig);
+
     status = PyConfig_InitPythonConfig(&config);
     if (_PyStatus_EXCEPTION(status)) {
         goto done;

Modules/main.c

@@ -165,12 +165,8 @@ int
 wmain(int argc, wchar_t **argv)
 {
     PyStatus status;
-
     PyPreConfig preconfig;
-    preconfig.struct_size = sizeof(PyPreConfig);
-
     PyConfig config;
-    config.struct_size = sizeof(PyConfig);
 
     const wchar_t *moduleName = NULL;
     const wchar_t *p = wcsrchr(argv[0], L'\\');
@@ -189,10 +185,7 @@ wmain(int argc, wchar_t **argv)
         }
     }
 
-    status = PyPreConfig_InitPythonConfig(&preconfig);
-    if (PyStatus_Exception(status)) {
-        goto fail_without_config;
-    }
+    PyPreConfig_InitPythonConfig(&preconfig);
     if (!moduleName) {
         status = Py_PreInitializeFromArgs(&preconfig, argc, argv);
         if (PyStatus_Exception(status)) {

PC/python_uwp.cpp

@@ -78,7 +78,6 @@ main(int argc, char *argv[])
 
     PyStatus status;
     PyConfig config;
-    config.struct_size = sizeof(PyConfig);
 
     status = PyConfig_InitIsolatedConfig(&config);
     if (PyStatus_Exception(status)) {