bpo-47000: Make `io.text_encoding()` respects UTF-8 mode (GH-32003)

Co-authored-by: Eric Snow <ericsnowcurrently@gmail.com>

1 files changed, 12 insertions, 4 deletions

diff --git a/Modules/_io/_iomodule.c b/Modules/_io/_iomodule.c
index 7f029f2..065f5e2 100644
--- a/Modules/_io/_iomodule.c
+++ b/Modules/_io/_iomodule.c
@@ -457,8 +457,9 @@ _io.text_encoding
 
 A helper function to choose the text encoding.
 
-When encoding is not None, just return it.
-Otherwise, return the default text encoding (i.e. "locale").
+When encoding is not None, this function returns it.
+Otherwise, this function returns the default text encoding
+(i.e. "locale" or "utf-8" depends on UTF-8 mode).
 
 This function emits an EncodingWarning if encoding is None and
 sys.flags.warn_default_encoding is true.
@@ -469,7 +470,7 @@ However, please consider using encoding="utf-8" for new APIs.
 
 static PyObject *
 _io_text_encoding_impl(PyObject *module, PyObject *encoding, int stacklevel)
-/*[clinic end generated code: output=91b2cfea6934cc0c input=bf70231213e2a7b4]*/
+/*[clinic end generated code: output=91b2cfea6934cc0c input=4999aa8b3d90f3d4]*/
 {
     if (encoding == NULL || encoding == Py_None) {
         PyInterpreterState *interp = _PyInterpreterState_GET();
@@ -479,7 +480,14 @@ _io_text_encoding_impl(PyObject *module, PyObject *encoding, int stacklevel)
                 return NULL;
             }
         }
-        return &_Py_ID(locale);
+        const PyPreConfig *preconfig = &_PyRuntime.preconfig;
+        if (preconfig->utf8_mode) {
+            _Py_DECLARE_STR(utf_8, "utf-8");
+            encoding = &_Py_STR(utf_8);
+        }
+        else {
+            encoding = &_Py_ID(locale);
+        }
     }
     Py_INCREF(encoding);
     return encoding;