Suppress locale warning for PYTHONCOERCECLOCALE=0

Lib/test/support/script_helper.py

@@ -14,13 +14,6 @@
 from test.support import make_legacy_pyc, strip_python_stderr
 
 
-RUNTIME_C_LOCALE_WARNING = (
-    "Python runtime initialized with LC_CTYPE=C (a locale with default ASCII "
-    "encoding), which may cause Unicode compatibility problems. Using C.UTF-8, "
-    "C.utf8, or UTF-8 (if available) as alternative Unicode-compatible "
-    "locales is recommended."
-)
-
 # Cached result of the expensive test performed in the function below.
 __cached_interp_requires_environment = None
 

Lib/test/test_cmd_line.py

@@ -9,8 +9,7 @@
 import tempfile
 from test.support import script_helper, is_android
 from test.support.script_helper import (
-    spawn_python, kill_python, assert_python_ok, assert_python_failure,
-    RUNTIME_C_LOCALE_WARNING
+    spawn_python, kill_python, assert_python_ok, assert_python_failure
 )
 
 
@@ -162,18 +161,17 @@ def test_undecodable_code(self):
             stdout=subprocess.PIPE, stderr=subprocess.STDOUT,
             env=env)
         stdout, stderr = p.communicate()
-        pattern = RUNTIME_C_LOCALE_WARNING.encode() + b'\n'
         if p.returncode == 1:
             # _Py_char2wchar() decoded b'\xff' as '\udcff' (b'\xff' is not
             # decodable from ASCII) and run_command() failed on
             # PyUnicode_AsUTF8String(). This is the expected behaviour on
             # Linux.
-            pattern += b"Unable to decode the command from the command line:"
+            pattern = b"Unable to decode the command from the command line:"
         elif p.returncode == 0:
             # _Py_char2wchar() decoded b'\xff' as '\xff' even if the locale is
             # C and the locale encoding is ASCII. It occurs on FreeBSD, Solaris
             # and Mac OS X.
-            pattern += b"'\\xff' "
+            pattern = b"'\\xff' "
             # The output is followed by the encoding name, an alias to ASCII.
             # Examples: "US-ASCII" or "646" (ISO 646, on Solaris).
         else:

Lib/test/test_locale_coercion.py

@@ -8,7 +8,6 @@
 from test.support.script_helper import (
     run_python_until_end,
     interpreter_requires_environment,
-    RUNTIME_C_LOCALE_WARNING
 )
 
 # In order to get the warning messages to match up as expected, the candidate
@@ -30,6 +29,14 @@ def _set_locale_in_subprocess(locale_name, category):
     result, py_cmd = run_python_until_end("-c", cmd, __isolated=True)
     return result.rc == 0
 
+# Details of the shared library warning emitted at runtime
+LIBRARY_C_LOCALE_WARNING = (
+    "Python runtime initialized with LC_CTYPE=C (a locale with default ASCII "
+    "encoding), which may cause Unicode compatibility problems. Using C.UTF-8, "
+    "C.utf8, or UTF-8 (if available) as alternative Unicode-compatible "
+    "locales is recommended."
+)
+
 # Details of the CLI warning emitted at runtime
 CLI_COERCION_WARNING_FMT = (
     "Python detected LC_CTYPE=C: {} coerced to {} (set another locale "
@@ -100,16 +107,10 @@ def _check_c_locale_coercion(self, expected_fsencoding, coerce_c_locale):
               None: don't set the variable at all
               str: the value set in the child's environment
         """
-        if coerce_c_locale == "0":
-            # Check the library emits a warning
-            expected_warning = [
-                RUNTIME_C_LOCALE_WARNING,
-            ]
-        else:
+        expected_warning = []
+        if coerce_c_locale != "0":
             # Check C locale is coerced with a warning on stderr
-            expected_warning = [
-                self.EXPECTED_COERCION_WARNING,
-            ]
+            expected_warning.append(self.EXPECTED_COERCION_WARNING)
         base_var_dict = {
             "LANG": "",
             "LC_CTYPE": "",

Lib/test/test_sys.py

@@ -1,8 +1,5 @@
 import unittest, test.support
-from test.support.script_helper import (
-    assert_python_ok, assert_python_failure,
-    RUNTIME_C_LOCALE_WARNING
-)
+from test.support.script_helper import assert_python_ok, assert_python_failure
 import sys, io, os
 import struct
 import subprocess
@@ -679,8 +676,6 @@ def test_getfilesystemencoding(self):
             expected = None
         self.check_fsencoding(fs_encoding, expected)
 
-    _SKIP_RUNTIME_C_LOCALE_WARNING = len(RUNTIME_C_LOCALE_WARNING + "\n")
-
     def c_locale_get_error_handler(self, isolated=False, encoding=None):
         # Force the POSIX locale
         env = os.environ.copy()
@@ -708,7 +703,7 @@ def c_locale_get_error_handler(self, isolated=False, encoding=None):
                               env=env,
                               universal_newlines=True)
         stdout, stderr = p.communicate()
-        return stdout[self._SKIP_RUNTIME_C_LOCALE_WARNING:]
+        return stdout
 
     def test_c_locale_surrogateescape(self):
         out = self.c_locale_get_error_handler(isolated=True)

Python/pylifecycle.c

@@ -311,9 +311,17 @@ static const char *_C_LOCALE_WARNING =
 static void
 _emit_stderr_warning_for_c_locale(void)
 {
-    const char *ctype_loc = setlocale(LC_CTYPE, NULL);
-    if (ctype_loc != NULL && strcmp(ctype_loc, "C") == 0) {
-        fprintf(stderr, "%s", _C_LOCALE_WARNING);
+    const char *coerce_c_locale = getenv("PYTHONCOERCECLOCALE");
+    /* We don't emit a warning if locale coercion has been explicitly disabled.
+     *
+     * For consistency with the corresponding check in Programs/python.c
+     * we ignore the Python -E and -I flags here.
+     */
+    if (coerce_c_locale == NULL || strncmp(coerce_c_locale, "0", 2) != 0) {
+        const char *ctype_loc = setlocale(LC_CTYPE, NULL);
+        if (ctype_loc != NULL && strcmp(ctype_loc, "C") == 0) {
+            fprintf(stderr, "%s", _C_LOCALE_WARNING);
+        }
     }
 }