gh-140576: Fixed crash produced by lexer in case of dedented zero byte (#140583)

Author: efimov-mikhail

Lib/test/test_tokenize.py

@@ -3183,6 +3183,7 @@ def get_tokens(string):
             f'__{
                 x:d
             }__'""",
+            " a\n\x00",
         ]:
             with self.subTest(case=case):
                 self.assertRaises(tokenize.TokenError, get_tokens, case)

Misc/NEWS.d/next/Core_and_Builtins/2025-10-25-17-36-46.gh-issue-140576.kj0SCY.rst

@@ -0,0 +1,2 @@
+Fixed crash in :func:`tokenize.generate_tokens` in case of
+specific incorrect input. Patch by Mikhail Efimov.

Parser/lexer/lexer.c

@@ -539,6 +539,9 @@ tok_get_normal_mode(struct tok_state *tok, tokenizer_mode* current_tok, struct t
                     return MAKE_TOKEN(ERRORTOKEN);
                 }
             }
+            else if (c == EOF && PyErr_Occurred()) {
+                return MAKE_TOKEN(ERRORTOKEN);
+            }
             else {
                 break;
             }