mypy crash when .mypy_cache is present

[danifus]

What's wrong

Under certain circumstances, a project with a typing error will produce correct mypy errors and hints when .mypy_cache is not present but a stack trace if it is.

Here is a simplified reproduction repo demonstrating this behaviour: https://github.com/danifus/djstubs-reproduce2

• pip install django and django-stubs
• cd to directory containing mypy.ini
• run mypy . --tb
• run mypy . --tb

The first mypy . --tb produces:

second_app/models.py:10: error: Incompatible types in assignment (expression has type "str", variable has type "int")
Found 1 error in 1 file (checked 28 source files)

The second run produces:

./test_app/models.py:6: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-a-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.770
Traceback (most recent call last):
  File "mypy/semanal.py", line 4679, in accept
  File "mypy/nodes.py", line 939, in accept
  File "mypy/semanal.py", line 1001, in visit_class_def
  File "mypy/semanal.py", line 1078, in analyze_class
  File "mypy/semanal.py", line 1087, in analyze_class_body_common
  File "mypy/semanal.py", line 1147, in apply_class_plugin_hooks
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/main.py", line 37, in transform_model_class
    process_model_class(ctx, django_context)
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/transformers/models.py", line 357, in process_model_class
    initializer_cls(ctx, django_context).run()
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/transformers/models.py", line 71, in run
    self.run_with_model_cls(model_cls)
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/transformers/models.py", line 231, in run_with_model_cls
    base_manager_info=manager_info)
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/transformers/models.py", line 186, in create_new_model_parametrized_manager
    method_node=sym.node)
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/lib/helpers.py", line 329, in copy_method_to_another_class
    arguments, return_type = build_unannotated_method_args(method_node)
  File "<venv>/mypytest/lib/python3.7/site-packages/mypy_django_plugin/lib/helpers.py", line 314, in build_unannotated_method_args
    for argument in method_node.arguments[1:]:
AttributeError: attribute 'arguments' of 'FuncItem' undefined
./test_app/models.py:6: : note: use --pdb to drop into pdb

This behaviour occurs if the error is in either test_app/models.py or second_app/models.py (it currently is only in second_app/models.py).

How is that should be

Every run should produce the same (initial) output

System information

• OS: mac
• python version: 3.7
• django version: 3.0.8
• mypy version: 0.770
• django-stubs version: 1.5

[kszmigiel]

@danifus I've encountered the same problem, reinstalling both django-stubs and mypy worked for me, but I'll check your repo tomorrow and try to reproduce this bug.

[kszmigiel]

@danifus fixed, sorry for the delay, I'm a bit busy with GSoC stuff at the moment

[danifus]

Thanks! That was actually super quick! It's great to be able to use incremental mode again :D

[javulticat]

Any news on a new release containing this fix? Even if 1.6.0 isn't close to being ready, a minor hotfix (1.5.1?) containing this change would be incredibly appreciated - it's a significant impediment to development on large typed Django code bases to have to run mypy with no caching.