Incompletely defining a TypeAliasType causes mypy to crash #18307
Description
Crash Report, Reproduction, & Traceback
See mypy Playground. This causes usability issues with the mypy daemon, as the session would need to be relaunched with a long startup wait.
from typing_extensions import TypeAliasType
MyType = TypeAliasType("MyType")Traceback (most recent call last):
File "<frozen runpy>", line 198, in _run_module_as_main
File "<frozen runpy>", line 88, in _run_code
File "mypy/semanal.py", line 7113, in accept
File "mypy/nodes.py", line 1351, in accept
File "mypy/semanal.py", line 3119, in visit_assignment_stmt
File "mypy/semanal.py", line 3863, in check_and_set_up_type_alias
IndexError: list index out of range
main.py:3: error: INTERNAL ERROR -- Please try using mypy master on GitHub:
https://mypy.readthedocs.io/en/stable/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 1.13.0
main.py:3: : note: use --pdb to drop into pdb
Your Environment
- Mypy version used: 1.13
- Mypy command-line flags:
--show-traceback - Mypy configuration options from
mypy.ini(and other config files): None