gh-90716: bugfixes and more tests for _pylong. (#99073)

* Properly decref on _pylong import error.
* Improve the error message on _pylong TypeError.
* Fix the assertion error in pydebug builds to be a TypeError.
* Tie the return value comments together.

These are minor followups to issues not caught among the reviewers on
https://github.com/python/cpython/pull/96673.

1 files changed, 11 insertions, 4 deletions

diff --git a/Objects/longobject.c b/Objects/longobject.c
index cf859cc..a872938 100644
--- a/Objects/longobject.c
+++ b/Objects/longobject.c
@@ -1753,7 +1753,11 @@ pylong_int_to_decimal_string(PyObject *aa,
     if (s == NULL) {
         goto error;
     }
-    assert(PyUnicode_Check(s));
+    if (!PyUnicode_Check(s)) {
+        PyErr_SetString(PyExc_TypeError,
+                        "_pylong.int_to_decimal_string did not return a str");
+        goto error;
+    }
     if (writer) {
         Py_ssize_t size = PyUnicode_GET_LENGTH(s);
         if (_PyUnicodeWriter_Prepare(writer, size, '9') == -1) {
@@ -2362,6 +2366,7 @@ pylong_int_from_string(const char *start, const char *end, PyLongObject **res)
     }
     PyObject *s = PyUnicode_FromStringAndSize(start, end-start);
     if (s == NULL) {
+        Py_DECREF(mod);
         goto error;
     }
     PyObject *result = PyObject_CallMethod(mod, "int_from_string", "O", s);
@@ -2371,14 +2376,15 @@ pylong_int_from_string(const char *start, const char *end, PyLongObject **res)
         goto error;
     }
     if (!PyLong_Check(result)) {
-        PyErr_SetString(PyExc_TypeError, "an integer is required");
+        PyErr_SetString(PyExc_TypeError,
+                        "_pylong.int_from_string did not return an int");
         goto error;
     }
     *res = (PyLongObject *)result;
     return 0;
 error:
     *res = NULL;
-    return 0;
+    return 0;  // See the long_from_string_base() API comment.
 }
 #endif /* WITH_PYLONG_MODULE */
 
@@ -2617,7 +2623,8 @@ long_from_non_binary_base(const char *start, const char *end, Py_ssize_t digits,
  * Return values:
  *
  *   - Returns -1 on syntax error (exception needs to be set, *res is untouched)
- *   - Returns 0 and sets *res to NULL for MemoryError/OverflowError.
+ *   - Returns 0 and sets *res to NULL for MemoryError, OverflowError, or
+ *     _pylong.int_from_string() errors.
  *   - Returns 0 and sets *res to an unsigned, unnormalized PyLong (success!).
  *
  * Afterwards *str is set to point to the first non-digit (which may be *str!).