cpython/Python/coreconfig.c

#include "Python.h"
#include "internal/pystate.h"


#define DECODE_LOCALE_ERR(NAME, LEN) \
    (((LEN) == -2) \
     ? _Py_INIT_USER_ERR("cannot decode " NAME) \
     : _Py_INIT_NO_MEMORY())


/* Global configuration variables */

/* The default encoding used by the platform file system APIs
   Can remain NULL for all platforms that don't have such a concept

   Don't forget to modify PyUnicode_DecodeFSDefault() if you touch any of the
   values for Py_FileSystemDefaultEncoding!
*/
#if defined(__APPLE__)
const char *Py_FileSystemDefaultEncoding = "utf-8";
int Py_HasFileSystemDefaultEncoding = 1;
#elif defined(MS_WINDOWS)
/* may be changed by initfsencoding(), but should never be free()d */
const char *Py_FileSystemDefaultEncoding = "utf-8";
int Py_HasFileSystemDefaultEncoding = 1;
#else
const char *Py_FileSystemDefaultEncoding = NULL; /* set by initfsencoding() */
int Py_HasFileSystemDefaultEncoding = 0;
#endif
const char *Py_FileSystemDefaultEncodeErrors = "surrogateescape";
/* UTF-8 mode (PEP 540): if equals to 1, use the UTF-8 encoding, and change
   stdin and stdout error handler to "surrogateescape". It is equal to
   -1 by default: unknown, will be set by Py_Main() */
int Py_UTF8Mode = -1;
int Py_DebugFlag = 0; /* Needed by parser.c */
int Py_VerboseFlag = 0; /* Needed by import.c */
int Py_QuietFlag = 0; /* Needed by sysmodule.c */
int Py_InteractiveFlag = 0; /* Needed by Py_FdIsInteractive() below */
int Py_InspectFlag = 0; /* Needed to determine whether to exit at SystemExit */
int Py_OptimizeFlag = 0; /* Needed by compile.c */
int Py_NoSiteFlag = 0; /* Suppress 'import site' */
int Py_BytesWarningFlag = 0; /* Warn on str(bytes) and str(buffer) */
int Py_FrozenFlag = 0; /* Needed by getpath.c */
int Py_IgnoreEnvironmentFlag = 0; /* e.g. PYTHONPATH, PYTHONHOME */
int Py_DontWriteBytecodeFlag = 0; /* Suppress writing bytecode files (*.pyc) */
int Py_NoUserSiteDirectory = 0; /* for -s and site.py */
int Py_UnbufferedStdioFlag = 0; /* Unbuffered binary std{in,out,err} */
int Py_HashRandomizationFlag = 0; /* for -R and PYTHONHASHSEED */
int Py_IsolatedFlag = 0; /* for -I, isolate from user's env */
#ifdef MS_WINDOWS
int Py_LegacyWindowsFSEncodingFlag = 0; /* Uses mbcs instead of utf-8 */
int Py_LegacyWindowsStdioFlag = 0; /* Uses FileIO instead of WindowsConsoleIO */
#endif


void
_Py_wstrlist_clear(int len, wchar_t **list)
{
    for (int i=0; i < len; i++) {
        PyMem_RawFree(list[i]);
    }
    PyMem_RawFree(list);
}


wchar_t**
_Py_wstrlist_copy(int len, wchar_t **list)
{
    assert((len > 0 && list != NULL) || len == 0);
    size_t size = len * sizeof(list[0]);
    wchar_t **list_copy = PyMem_RawMalloc(size);
    for (int i=0; i < len; i++) {
        wchar_t* arg = _PyMem_RawWcsdup(list[i]);
        if (arg == NULL) {
            _Py_wstrlist_clear(i, list);
            return NULL;
        }
        list_copy[i] = arg;
    }
    return list_copy;
}


/* Free memory allocated in config, but don't clear all attributes */
void
_PyCoreConfig_Clear(_PyCoreConfig *config)
{
#define CLEAR(ATTR) \
    do { \
        PyMem_RawFree(ATTR); \
        ATTR = NULL; \
    } while (0)
#define CLEAR_WSTRLIST(LEN, LIST) \
    do { \
        _Py_wstrlist_clear(LEN, LIST); \
        LEN = 0; \
        LIST = NULL; \
    } while (0)

    CLEAR(config->pycache_prefix);
    CLEAR(config->module_search_path_env);
    CLEAR(config->home);
    CLEAR(config->program_name);
    CLEAR(config->program);

    CLEAR_WSTRLIST(config->argc, config->argv);
    config->argc = -1;

    CLEAR_WSTRLIST(config->nwarnoption, config->warnoptions);
    CLEAR_WSTRLIST(config->nxoption, config->xoptions);
    CLEAR_WSTRLIST(config->nmodule_search_path, config->module_search_paths);
    config->nmodule_search_path = -1;

    CLEAR(config->executable);
    CLEAR(config->prefix);
    CLEAR(config->base_prefix);
    CLEAR(config->exec_prefix);
#ifdef MS_WINDOWS
    CLEAR(config->dll_path);
#endif
    CLEAR(config->base_exec_prefix);
#undef CLEAR
#undef CLEAR_WSTRLIST
}


int
_PyCoreConfig_Copy(_PyCoreConfig *config, const _PyCoreConfig *config2)
{
    _PyCoreConfig_Clear(config);

#define COPY_ATTR(ATTR) config->ATTR = config2->ATTR
#define COPY_STR_ATTR(ATTR) \
    do { \
        if (config2->ATTR != NULL) { \
            config->ATTR = _PyMem_RawWcsdup(config2->ATTR); \
            if (config->ATTR == NULL) { \
                return -1; \
            } \
        } \
    } while (0)
#define COPY_WSTRLIST(LEN, LIST) \
    do { \
        if (config2->LIST != NULL) { \
            config->LIST = _Py_wstrlist_copy(config2->LEN, config2->LIST); \
            if (config->LIST == NULL) { \
                return -1; \
            } \
        } \
        config->LEN = config2->LEN; \
    } while (0)

    COPY_ATTR(install_signal_handlers);
    COPY_ATTR(use_environment);
    COPY_ATTR(use_hash_seed);
    COPY_ATTR(hash_seed);
    COPY_ATTR(_install_importlib);
    COPY_ATTR(allocator);
    COPY_ATTR(dev_mode);
    COPY_ATTR(faulthandler);
    COPY_ATTR(tracemalloc);
    COPY_ATTR(import_time);
    COPY_ATTR(show_ref_count);
    COPY_ATTR(show_alloc_count);
    COPY_ATTR(dump_refs);
    COPY_ATTR(malloc_stats);

    COPY_ATTR(coerce_c_locale);
    COPY_ATTR(coerce_c_locale_warn);
    COPY_ATTR(utf8_mode);

    COPY_STR_ATTR(pycache_prefix);
    COPY_STR_ATTR(module_search_path_env);
    COPY_STR_ATTR(home);
    COPY_STR_ATTR(program_name);
    COPY_STR_ATTR(program);

    COPY_WSTRLIST(argc, argv);
    COPY_WSTRLIST(nwarnoption, warnoptions);
    COPY_WSTRLIST(nxoption, xoptions);
    COPY_WSTRLIST(nmodule_search_path, module_search_paths);

    COPY_STR_ATTR(executable);
    COPY_STR_ATTR(prefix);
    COPY_STR_ATTR(base_prefix);
    COPY_STR_ATTR(exec_prefix);
#ifdef MS_WINDOWS
    COPY_STR_ATTR(dll_path);
#endif
    COPY_STR_ATTR(base_exec_prefix);

    COPY_ATTR(isolated);
    COPY_ATTR(site_import);
    COPY_ATTR(bytes_warning);
    COPY_ATTR(inspect);
    COPY_ATTR(interactive);
    COPY_ATTR(optimization_level);
    COPY_ATTR(parser_debug);
    COPY_ATTR(write_bytecode);
    COPY_ATTR(verbose);
    COPY_ATTR(quiet);
    COPY_ATTR(user_site_directory);
    COPY_ATTR(buffered_stdio);
#ifdef MS_WINDOWS
    COPY_ATTR(legacy_windows_fs_encoding);
    COPY_ATTR(legacy_windows_stdio);
#endif
    COPY_ATTR(_check_hash_pycs_mode);
    COPY_ATTR(_frozen);

#undef COPY_ATTR
#undef COPY_STR_ATTR
#undef COPY_WSTRLIST
    return 0;
}


const char*
_PyCoreConfig_GetEnv(const _PyCoreConfig *config, const char *name)
{
    assert(config->use_environment >= 0);

    if (!config->use_environment) {
        return NULL;
    }

    const char *var = getenv(name);
    if (var && var[0] != '\0') {
        return var;
    }
    else {
        return NULL;
    }
}


int
_PyCoreConfig_GetEnvDup(const _PyCoreConfig *config,
                        wchar_t **dest,
                        wchar_t *wname, char *name)
{
    assert(config->use_environment >= 0);

    if (!config->use_environment) {
        *dest = NULL;
        return 0;
    }

#ifdef MS_WINDOWS
    const wchar_t *var = _wgetenv(wname);
    if (!var || var[0] == '\0') {
        *dest = NULL;
        return 0;
    }

    wchar_t *copy = _PyMem_RawWcsdup(var);
    if (copy == NULL) {
        return -1;
    }

    *dest = copy;
#else
    const char *var = getenv(name);
    if (!var || var[0] == '\0') {
        *dest = NULL;
        return 0;
    }

    size_t len;
    wchar_t *wvar = Py_DecodeLocale(var, &len);
    if (!wvar) {
        if (len == (size_t)-2) {
            return -2;
        }
        else {
            return -1;
        }
    }
    *dest = wvar;
#endif
    return 0;
}


void
_PyCoreConfig_GetGlobalConfig(_PyCoreConfig *config)
{
#define COPY_FLAG(ATTR, VALUE) \
        if (config->ATTR == -1) { \
            config->ATTR = VALUE; \
        }
#define COPY_NOT_FLAG(ATTR, VALUE) \
        if (config->ATTR == -1) { \
            config->ATTR = !(VALUE); \
        }

    COPY_FLAG(utf8_mode, Py_UTF8Mode);
    COPY_FLAG(isolated, Py_IsolatedFlag);
    COPY_FLAG(bytes_warning, Py_BytesWarningFlag);
    COPY_FLAG(inspect, Py_InspectFlag);
    COPY_FLAG(interactive, Py_InteractiveFlag);
    COPY_FLAG(optimization_level, Py_OptimizeFlag);
    COPY_FLAG(parser_debug, Py_DebugFlag);
    COPY_FLAG(verbose, Py_VerboseFlag);
    COPY_FLAG(quiet, Py_QuietFlag);
#ifdef MS_WINDOWS
    COPY_FLAG(legacy_windows_fs_encoding, Py_LegacyWindowsFSEncodingFlag);
    COPY_FLAG(legacy_windows_stdio, Py_LegacyWindowsStdioFlag);
#endif
    COPY_FLAG(_frozen, Py_FrozenFlag);

    COPY_NOT_FLAG(use_environment, Py_IgnoreEnvironmentFlag);
    COPY_NOT_FLAG(buffered_stdio, Py_UnbufferedStdioFlag);
    COPY_NOT_FLAG(site_import, Py_NoSiteFlag);
    COPY_NOT_FLAG(write_bytecode, Py_DontWriteBytecodeFlag);
    COPY_NOT_FLAG(user_site_directory, Py_NoUserSiteDirectory);

#undef COPY_FLAG
#undef COPY_NOT_FLAG
}


/* Set Py_xxx global configuration variables from 'config' configuration. */
void
_PyCoreConfig_SetGlobalConfig(const _PyCoreConfig *config)
{
#define COPY_FLAG(ATTR, VAR) \
        if (config->ATTR != -1) { \
            VAR = config->ATTR; \
        }
#define COPY_NOT_FLAG(ATTR, VAR) \
        if (config->ATTR != -1) { \
            VAR = !config->ATTR; \
        }

    COPY_FLAG(utf8_mode, Py_UTF8Mode);
    COPY_FLAG(isolated, Py_IsolatedFlag);
    COPY_FLAG(bytes_warning, Py_BytesWarningFlag);
    COPY_FLAG(inspect, Py_InspectFlag);
    COPY_FLAG(interactive, Py_InteractiveFlag);
    COPY_FLAG(optimization_level, Py_OptimizeFlag);
    COPY_FLAG(parser_debug, Py_DebugFlag);
    COPY_FLAG(verbose, Py_VerboseFlag);
    COPY_FLAG(quiet, Py_QuietFlag);
#ifdef MS_WINDOWS
    COPY_FLAG(legacy_windows_fs_encoding, Py_LegacyWindowsFSEncodingFlag);
    COPY_FLAG(legacy_windows_stdio, Py_LegacyWindowsStdioFlag);
#endif

    COPY_NOT_FLAG(use_environment, Py_IgnoreEnvironmentFlag);
    COPY_NOT_FLAG(buffered_stdio, Py_UnbufferedStdioFlag);
    COPY_NOT_FLAG(site_import, Py_NoSiteFlag);
    COPY_NOT_FLAG(write_bytecode, Py_DontWriteBytecodeFlag);
    COPY_NOT_FLAG(user_site_directory, Py_NoUserSiteDirectory);

    /* Random or non-zero hash seed */
    Py_HashRandomizationFlag = (config->use_hash_seed == 0 ||
                                config->hash_seed != 0);

#undef COPY_FLAG
#undef COPY_NOT_FLAG
}


/* Get the program name: use PYTHONEXECUTABLE and __PYVENV_LAUNCHER__
   environment variables on macOS if available. */
static _PyInitError
config_init_program_name(_PyCoreConfig *config)
{
    /* If Py_SetProgramName() was called, use its value */
    const wchar_t *program_name = _Py_path_config.program_name;
    if (program_name != NULL) {
        config->program_name = _PyMem_RawWcsdup(program_name);
        if (config->program_name == NULL) {
            return _Py_INIT_NO_MEMORY();
        }
        return _Py_INIT_OK();
    }

#ifdef __APPLE__
    /* On MacOS X, when the Python interpreter is embedded in an
       application bundle, it gets executed by a bootstrapping script
       that does os.execve() with an argv[0] that's different from the
       actual Python executable. This is needed to keep the Finder happy,
       or rather, to work around Apple's overly strict requirements of
       the process name. However, we still need a usable sys.executable,
       so the actual executable path is passed in an environment variable.
       See Lib/plat-mac/bundlebuiler.py for details about the bootstrap
       script. */
    const char *p = _PyCoreConfig_GetEnv(config, "PYTHONEXECUTABLE");
    if (p != NULL) {
        size_t len;
        wchar_t* program_name = Py_DecodeLocale(p, &len);
        if (program_name == NULL) {
            return DECODE_LOCALE_ERR("PYTHONEXECUTABLE environment "
                                     "variable", (Py_ssize_t)len);
        }
        config->program_name = program_name;
        return _Py_INIT_OK();
    }
#ifdef WITH_NEXT_FRAMEWORK
    else {
        const char* pyvenv_launcher = getenv("__PYVENV_LAUNCHER__");
        if (pyvenv_launcher && *pyvenv_launcher) {
            /* Used by Mac/Tools/pythonw.c to forward
             * the argv0 of the stub executable
             */
            size_t len;
            wchar_t* program_name = Py_DecodeLocale(pyvenv_launcher, &len);
            if (program_name == NULL) {
                return DECODE_LOCALE_ERR("__PYVENV_LAUNCHER__ environment "
                                         "variable", (Py_ssize_t)len);
            }
            config->program_name = program_name;
            return _Py_INIT_OK();
        }
    }
#endif   /* WITH_NEXT_FRAMEWORK */
#endif   /* __APPLE__ */

    /* Use argv[0] by default, if available */
    if (config->program != NULL) {
        config->program_name = _PyMem_RawWcsdup(config->program);
        if (config->program_name == NULL) {
            return _Py_INIT_NO_MEMORY();
        }
        return _Py_INIT_OK();
    }

    /* Last fall back: hardcoded string */
#ifdef MS_WINDOWS
    const wchar_t *default_program_name = L"python";
#else
    const wchar_t *default_program_name = L"python3";
#endif
    config->program_name = _PyMem_RawWcsdup(default_program_name);
    if (config->program_name == NULL) {
        return _Py_INIT_NO_MEMORY();
    }
    return _Py_INIT_OK();
}


static const wchar_t*
config_get_xoption(const _PyCoreConfig *config, wchar_t *name)
{
    int nxoption = config->nxoption;
    wchar_t **xoptions = config->xoptions;
    for (int i=0; i < nxoption; i++) {
        wchar_t *option = xoptions[i];
        size_t len;
        wchar_t *sep = wcschr(option, L'=');
        if (sep != NULL) {
            len = (sep - option);
        }
        else {
            len = wcslen(option);
        }
        if (wcsncmp(option, name, len) == 0 && name[len] == L'\0') {
            return option;
        }
    }
    return NULL;
}


static _PyInitError
config_init_home(_PyCoreConfig *config)
{
    wchar_t *home;

    /* If Py_SetPythonHome() was called, use its value */
    home = _Py_path_config.home;
    if (home) {
        config->home = _PyMem_RawWcsdup(home);
        if (config->home == NULL) {
            return _Py_INIT_NO_MEMORY();
        }
        return _Py_INIT_OK();
    }

    int res = _PyCoreConfig_GetEnvDup(config, &home,
                                      L"PYTHONHOME", "PYTHONHOME");
    if (res < 0) {
        return DECODE_LOCALE_ERR("PYTHONHOME", res);
    }
    config->home = home;
    return _Py_INIT_OK();
}


static _PyInitError
config_init_hash_seed(_PyCoreConfig *config)
{
    const char *seed_text = _PyCoreConfig_GetEnv(config, "PYTHONHASHSEED");

    Py_BUILD_ASSERT(sizeof(_Py_HashSecret_t) == sizeof(_Py_HashSecret.uc));
    /* Convert a text seed to a numeric one */
    if (seed_text && strcmp(seed_text, "random") != 0) {
        const char *endptr = seed_text;
        unsigned long seed;
        errno = 0;
        seed = strtoul(seed_text, (char **)&endptr, 10);
        if (*endptr != '\0'
            || seed > 4294967295UL
            || (errno == ERANGE && seed == ULONG_MAX))
        {
            return _Py_INIT_USER_ERR("PYTHONHASHSEED must be \"random\" "
                                     "or an integer in range [0; 4294967295]");
        }
        /* Use a specific hash */
        config->use_hash_seed = 1;
        config->hash_seed = seed;
    }
    else {
        /* Use a random hash */
        config->use_hash_seed = 0;
        config->hash_seed = 0;
    }
    return _Py_INIT_OK();
}


static _PyInitError
config_init_utf8_mode(_PyCoreConfig *config)
{
    const wchar_t *xopt = config_get_xoption(config, L"utf8");
    if (xopt) {
        wchar_t *sep = wcschr(xopt, L'=');
        if (sep) {
            xopt = sep + 1;
            if (wcscmp(xopt, L"1") == 0) {
                config->utf8_mode = 1;
            }
            else if (wcscmp(xopt, L"0") == 0) {
                config->utf8_mode = 0;
            }
            else {
                return _Py_INIT_USER_ERR("invalid -X utf8 option value");
            }
        }
        else {
            config->utf8_mode = 1;
        }
        return _Py_INIT_OK();
    }

    const char *opt = _PyCoreConfig_GetEnv(config, "PYTHONUTF8");
    if (opt) {
        if (strcmp(opt, "1") == 0) {
            config->utf8_mode = 1;
        }
        else if (strcmp(opt, "0") == 0) {
            config->utf8_mode = 0;
        }
        else {
            return _Py_INIT_USER_ERR("invalid PYTHONUTF8 environment "
                                     "variable value");
        }
        return _Py_INIT_OK();
    }

    return _Py_INIT_OK();
}


static int
config_str_to_int(const char *str, int *result)
{
    const char *endptr = str;
    errno = 0;
    long value = strtol(str, (char **)&endptr, 10);
    if (*endptr != '\0' || errno == ERANGE) {
        return -1;
    }
    if (value < INT_MIN || value > INT_MAX) {
        return -1;
    }

    *result = (int)value;
    return 0;
}


static int
config_wstr_to_int(const wchar_t *wstr, int *result)
{
    const wchar_t *endptr = wstr;
    errno = 0;
    long value = wcstol(wstr, (wchar_t **)&endptr, 10);
    if (*endptr != '\0' || errno == ERANGE) {
        return -1;
    }
    if (value < INT_MIN || value > INT_MAX) {
        return -1;
    }

    *result = (int)value;
    return 0;
}


static void
get_env_flag(_PyCoreConfig *config, int *flag, const char *name)
{
    const char *var = _PyCoreConfig_GetEnv(config, name);
    if (!var) {
        return;
    }
    int value;
    if (config_str_to_int(var, &value) < 0 || value < 0) {
        /* PYTHONDEBUG=text and PYTHONDEBUG=-2 behave as PYTHONDEBUG=1 */
        value = 1;
    }
    if (*flag < value) {
        *flag = value;
    }
}


static _PyInitError
config_read_env_vars(_PyCoreConfig *config)
{
    assert(config->use_environment > 0);

    /* Get environment variables */
    get_env_flag(config, &config->parser_debug, "PYTHONDEBUG");
    get_env_flag(config, &config->verbose, "PYTHONVERBOSE");
    get_env_flag(config, &config->optimization_level, "PYTHONOPTIMIZE");
    get_env_flag(config, &config->inspect, "PYTHONINSPECT");

    int dont_write_bytecode = 0;
    get_env_flag(config, &dont_write_bytecode, "PYTHONDONTWRITEBYTECODE");
    if (dont_write_bytecode) {
        config->write_bytecode = 0;
    }

    int no_user_site_directory = 0;
    get_env_flag(config, &no_user_site_directory, "PYTHONNOUSERSITE");
    if (no_user_site_directory) {
        config->user_site_directory = 0;
    }

    int unbuffered_stdio = 0;
    get_env_flag(config, &unbuffered_stdio, "PYTHONUNBUFFERED");
    if (unbuffered_stdio) {
        config->buffered_stdio = 0;
    }

#ifdef MS_WINDOWS
    get_env_flag(config, &config->legacy_windows_fs_encoding,
                 "PYTHONLEGACYWINDOWSFSENCODING");
    get_env_flag(config, &config->legacy_windows_stdio,
                 "PYTHONLEGACYWINDOWSSTDIO");
#endif

    if (config->allocator == NULL) {
        config->allocator = _PyCoreConfig_GetEnv(config, "PYTHONMALLOC");
    }

    if (_PyCoreConfig_GetEnv(config, "PYTHONDUMPREFS")) {
        config->dump_refs = 1;
    }
    if (_PyCoreConfig_GetEnv(config, "PYTHONMALLOCSTATS")) {
        config->malloc_stats = 1;
    }

    const char *env = _PyCoreConfig_GetEnv(config, "PYTHONCOERCECLOCALE");
    if (env) {
        if (strcmp(env, "0") == 0) {
            config->coerce_c_locale = 0;
        }
        else if (strcmp(env, "warn") == 0) {
            config->coerce_c_locale_warn = 1;
        }
        else {
            config->coerce_c_locale = 1;
        }
    }

    wchar_t *path;
    int res = _PyCoreConfig_GetEnvDup(config, &path,
                                      L"PYTHONPATH", "PYTHONPATH");
    if (res < 0) {
        return DECODE_LOCALE_ERR("PYTHONPATH", res);
    }
    config->module_search_path_env = path;

    if (config->use_hash_seed < 0) {
        _PyInitError err = config_init_hash_seed(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    return _Py_INIT_OK();
}


static _PyInitError
config_init_tracemalloc(_PyCoreConfig *config)
{
    int nframe;
    int valid;

    const char *env = _PyCoreConfig_GetEnv(config, "PYTHONTRACEMALLOC");
    if (env) {
        if (!config_str_to_int(env, &nframe)) {
            valid = (nframe >= 0);
        }
        else {
            valid = 0;
        }
        if (!valid) {
            return _Py_INIT_USER_ERR("PYTHONTRACEMALLOC: invalid number "
                                     "of frames");
        }
        config->tracemalloc = nframe;
    }

    const wchar_t *xoption = config_get_xoption(config, L"tracemalloc");
    if (xoption) {
        const wchar_t *sep = wcschr(xoption, L'=');
        if (sep) {
            if (!config_wstr_to_int(sep + 1, &nframe)) {
                valid = (nframe >= 0);
            }
            else {
                valid = 0;
            }
            if (!valid) {
                return _Py_INIT_USER_ERR("-X tracemalloc=NFRAME: "
                                         "invalid number of frames");
            }
        }
        else {
            /* -X tracemalloc behaves as -X tracemalloc=1 */
            nframe = 1;
        }
        config->tracemalloc = nframe;
    }
    return _Py_INIT_OK();
}


static _PyInitError
config_init_pycache_prefix(_PyCoreConfig *config)
{
    assert(config->pycache_prefix == NULL);

    const wchar_t *xoption = config_get_xoption(config, L"pycache_prefix");
    if (xoption) {
        const wchar_t *sep = wcschr(xoption, L'=');
        if (sep && wcslen(sep) > 1) {
            config->pycache_prefix = _PyMem_RawWcsdup(sep + 1);
            if (config->pycache_prefix == NULL) {
                return _Py_INIT_NO_MEMORY();
            }
        }
        else {
            // -X pycache_prefix= can cancel the env var
            config->pycache_prefix = NULL;
        }
    }
    else {
        wchar_t *env;
        int res = _PyCoreConfig_GetEnvDup(config, &env,
                                          L"PYTHONPYCACHEPREFIX",
                                          "PYTHONPYCACHEPREFIX");
        if (res < 0) {
            return DECODE_LOCALE_ERR("PYTHONPYCACHEPREFIX", res);
        }

        if (env) {
            config->pycache_prefix = env;
        }
    }
    return _Py_INIT_OK();
}


static _PyInitError
config_read_complex_options(_PyCoreConfig *config)
{
    /* More complex options configured by env var and -X option */
    if (config->faulthandler < 0) {
        if (_PyCoreConfig_GetEnv(config, "PYTHONFAULTHANDLER")
           || config_get_xoption(config, L"faulthandler")) {
            config->faulthandler = 1;
        }
    }
    if (_PyCoreConfig_GetEnv(config, "PYTHONPROFILEIMPORTTIME")
       || config_get_xoption(config, L"importtime")) {
        config->import_time = 1;
    }
    if (config_get_xoption(config, L"dev" ) ||
        _PyCoreConfig_GetEnv(config, "PYTHONDEVMODE"))
    {
        config->dev_mode = 1;
    }

    _PyInitError err;
    if (config->tracemalloc < 0) {
        err = config_init_tracemalloc(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    if (config->pycache_prefix == NULL) {
        err = config_init_pycache_prefix(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }
    return _Py_INIT_OK();
}


static void
config_init_locale(_PyCoreConfig *config)
{
    if (config->utf8_mode >= 0 && config->coerce_c_locale >= 0) {
        return;
    }

    if (_Py_LegacyLocaleDetected()) {
        /* POSIX locale: enable C locale coercion and UTF-8 Mode */
        if (config->utf8_mode < 0) {
            config->utf8_mode = 1;
        }
        if (config->coerce_c_locale < 0) {
            config->coerce_c_locale = 1;
        }
        return;
    }
}


/* Read configuration settings from standard locations
 *
 * This function doesn't make any changes to the interpreter state - it
 * merely populates any missing configuration settings. This allows an
 * embedding application to completely override a config option by
 * setting it before calling this function, or else modify the default
 * setting before passing the fully populated config to Py_EndInitialization.
 *
 * More advanced selective initialization tricks are possible by calling
 * this function multiple times with various preconfigured settings.
 */

_PyInitError
_PyCoreConfig_Read(_PyCoreConfig *config)
{
    _PyInitError err;

    _PyCoreConfig_GetGlobalConfig(config);

    if (config->isolated > 0) {
        config->use_environment = 0;
        config->user_site_directory = 0;
    }

#ifdef MS_WINDOWS
    if (config->legacy_windows_fs_encoding) {
        config->utf8_mode = 0;
    }
#endif

    assert(config->use_environment >= 0);
    if (config->use_environment) {
        err = config_read_env_vars(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    /* -X options */
    if (config_get_xoption(config, L"showrefcount")) {
        config->show_ref_count = 1;
    }
    if (config_get_xoption(config, L"showalloccount")) {
        config->show_alloc_count = 1;
    }

    err = config_read_complex_options(config);
    if (_Py_INIT_FAILED(err)) {
        return err;
    }

    if (config->utf8_mode < 0) {
        err = config_init_utf8_mode(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    if (config->home == NULL) {
        err = config_init_home(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    if (config->program_name == NULL) {
        err = config_init_program_name(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    config_init_locale(config);

    if (config->_install_importlib) {
        err = _PyCoreConfig_InitPathConfig(config);
        if (_Py_INIT_FAILED(err)) {
            return err;
        }
    }

    /* default values */
    if (config->dev_mode) {
        if (config->faulthandler < 0) {
            config->faulthandler = 1;
        }
        if (config->allocator == NULL) {
            config->allocator = "debug";
        }
    }
    if (config->use_hash_seed < 0) {
        config->use_hash_seed = 0;
        config->hash_seed = 0;
    }
    if (config->faulthandler < 0) {
        config->faulthandler = 0;
    }
    if (config->tracemalloc < 0) {
        config->tracemalloc = 0;
    }
    if (config->coerce_c_locale < 0) {
        config->coerce_c_locale = 0;
    }
    if (config->utf8_mode < 0) {
        config->utf8_mode = 0;
    }
    if (config->_frozen < 0) {
        config->_frozen = 0;
    }
    if (config->argc < 0) {
        config->argc = 0;
    }

    return _Py_INIT_OK();
}