gh-125196: Use PyUnicodeWriter for repr(list) (#125202)

Replace the private _PyUnicodeWriter with the public PyUnicodeWriter.

Replace PyObject_Repr() + _PyUnicodeWriter_WriteStr()
with PyUnicodeWriter_WriteRepr().

Objects/listobject.c

@@ -522,49 +522,50 @@ list_dealloc(PyObject *self)
 static PyObject *
 list_repr_impl(PyListObject *v)
 {
- PyObject *s;
- _PyUnicodeWriter writer;
- Py_ssize_t i = Py_ReprEnter((PyObject*)v);
- if (i != 0) {
- return i > 0 ? PyUnicode_FromString("[...]") : NULL;
+ int res = Py_ReprEnter((PyObject*)v);
+ if (res != 0) {
+ return (res > 0 ? PyUnicode_FromString("[...]") : NULL);
  }
 
- _PyUnicodeWriter_Init(&writer);
- writer.overallocate = 1;
  /* "[" + "1" + ", 2" * (len - 1) + "]" */
- writer.min_length = 1 + 1 + (2 + 1) * (Py_SIZE(v) - 1) + 1;
+ Py_ssize_t prealloc = 1 + 1 + (2 + 1) * (Py_SIZE(v) - 1) + 1;
+ PyUnicodeWriter *writer = PyUnicodeWriter_Create(prealloc);
+ if (writer == NULL) {
+ goto error;
+ }
 
- if (_PyUnicodeWriter_WriteChar(&writer, '[') < 0)
+ if (PyUnicodeWriter_WriteChar(writer, '[') < 0) {
  goto error;
+ }
 
  /* Do repr() on each element. Note that this may mutate the list,
  so must refetch the list size on each iteration. */
- for (i = 0; i < Py_SIZE(v); ++i) {
+ for (Py_ssize_t i = 0; i < Py_SIZE(v); ++i) {
  if (i > 0) {
- if (_PyUnicodeWriter_WriteASCIIString(&writer, ", ", 2) < 0)
+ if (PyUnicodeWriter_WriteChar(writer, ',') < 0) {
+ goto error;
+ }
+ if (PyUnicodeWriter_WriteChar(writer, ' ') < 0) {
  goto error;
+ }
  }
 
- s = PyObject_Repr(v->ob_item[i]);
- if (s == NULL)
- goto error;
-
- if (_PyUnicodeWriter_WriteStr(&writer, s) < 0) {
- Py_DECREF(s);
+ if (PyUnicodeWriter_WriteRepr(writer, v->ob_item[i]) < 0) {
  goto error;
  }
- Py_DECREF(s);
  }
 
- writer.overallocate = 0;
- if (_PyUnicodeWriter_WriteChar(&writer, ']') < 0)
+ if (PyUnicodeWriter_WriteChar(writer, ']') < 0) {
  goto error;
+ }
 
  Py_ReprLeave((PyObject *)v);
- return _PyUnicodeWriter_Finish(&writer);
+ return PyUnicodeWriter_Finish(writer);
 
 error:
- _PyUnicodeWriter_Dealloc(&writer);
+ if (writer != NULL) {
+ PyUnicodeWriter_Discard(writer);
+ }
  Py_ReprLeave((PyObject *)v);
  return NULL;
 }