Crash with mypy plugin on mypy 0.961

まず returns/contrib/mypy/_typeops/analtype.py の analyze_call traceback の箇所から始め、次に呼び出し元である returns/contrib/mypy/_features/partial.py を調べます。mypy 0.961 と Python 3.9 で再現し、削除された MessageBuilder.clean_copy メソッドに依存せずに partial 関数を解析しても mypy プラグインがクラッシュしなくなったことを確認します。

Bug report

What's wrong

Traceback (most recent call last):
  File "mypy/checkexpr.py", line 3991, in accept
  File "mypy/nodes.py", line 1760, in accept
  File "mypy/checkexpr.py", line 305, in visit_call_expr
  File "mypy/checkexpr.py", line 383, in visit_call_expr_inner
  File "mypy/checkexpr.py", line 892, in check_call_expr_with_callee_type
  File "mypy/checkexpr.py", line 957, in check_call
  File "mypy/checkexpr.py", line 1085, in check_callable_call
  File "mypy/checkexpr.py", line 763, in apply_function_plugin
  File ".pyenv/versions/3.9.7/envs/venv/lib/python3.9/site-packages/returns/contrib/mypy/_features/partial.py", line 62, in analyze
    return _PartialFunctionReducer(
  File ".pyenv/versions/3.9.7/envs/venv/lib/python3.9/site-packages/returns/contrib/mypy/_features/partial.py", line 131, in new_partial
    fallback, intermediate = self._create_intermediate(case_function)
  File ".pyenv/versions/3.9.7/envs/venv/lib/python3.9/site-packages/returns/contrib/mypy/_features/partial.py", line 150, in _create_intermediate
    return intermediate, analyze_call(
  File ".pyenv/versions/3.9.7/envs/venv/lib/python3.9/site-packages/returns/contrib/mypy/_typeops/analtype.py", line 55, in analyze_call
    messages = checker.msg if show_errors else checker.msg.clean_copy()
AttributeError: 'MessageBuilder' object has no attribute 'clean_copy'

How is that should be

Don't use MessageBuilder.clean_copy (removed in https://github.com/python/mypy/pull/12631)

System information

• python version: 3.9

• returns version: 0.19

• mypy version: 0.961

• hypothesis version (if any):

• pytest version (if any):