bpo-34485: Fix _Py_InitializeCore() for C locale coercion (GH-8979)

* _Py_InitializeCore() now sets the LC_CTYPE locale to the user
  preferred locale before checking if the C locale should be coerced
  or not in _PyCoreConfig_Read().
* Fix pymain_read_conf(): remember if the C locale has been coerced
  when the configuration should be read again if the encoding has
  changed.

2 files changed, 16 insertions, 12 deletions

diff --git a/Python/coreconfig.c b/Python/coreconfig.c
index d08d75b..8724681 100644
--- a/Python/coreconfig.c
+++ b/Python/coreconfig.c
@@ -671,16 +671,18 @@ config_read_env_vars(_PyCoreConfig *config)
         config->malloc_stats = 1;
     }
 
-    if (config->coerce_c_locale < 0) {
-        const char *env = _PyCoreConfig_GetEnv(config, "PYTHONCOERCECLOCALE");
-        if (env) {
-            if (strcmp(env, "0") == 0) {
+    const char *env = _PyCoreConfig_GetEnv(config, "PYTHONCOERCECLOCALE");
+    if (env) {
+        if (strcmp(env, "0") == 0) {
+            if (config->coerce_c_locale < 0) {
                 config->coerce_c_locale = 0;
             }
-            else if (strcmp(env, "warn") == 0) {
-                config->coerce_c_locale_warn = 1;
-            }
-            else {
+        }
+        else if (strcmp(env, "warn") == 0) {
+            config->coerce_c_locale_warn = 1;
+        }
+        else {
+            if (config->coerce_c_locale < 0) {
                 config->coerce_c_locale = 1;
             }
         }
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 29711df..4d248ed 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -659,10 +659,6 @@ _Py_InitializeCore_impl(PyInterpreterState **interp_p,
     _PyRuntime.finalizing = NULL;
 
 #ifndef MS_WINDOWS
-    /* Set up the LC_CTYPE locale, so we can obtain
-       the locale's charset without having to switch
-       locales. */
-    _Py_SetLocaleFromEnv(LC_CTYPE);
     _emit_stderr_warning_for_legacy_locale(core_config);
 #endif
 
@@ -815,6 +811,12 @@ _Py_InitializeCore(PyInterpreterState **interp_p,
        (and the input configuration is read only). */
     _PyCoreConfig config = _PyCoreConfig_INIT;
 
+#ifndef MS_WINDOWS
+    /* Set up the LC_CTYPE locale, so we can obtain the locale's charset
+       without having to switch locales. */
+    _Py_SetLocaleFromEnv(LC_CTYPE);
+#endif
+
     _PyMem_SetDefaultAllocator(PYMEM_DOMAIN_RAW, &old_alloc);
     if (_PyCoreConfig_Copy(&config, src_config) >= 0) {
         err = _PyCoreConfig_Read(&config);