0.990 internal error "IsADirectoryError" when not having __init__.py files

[osteenbergen]

Crash Report

MyPy 0.981 was working fine, since update to latest 0.990 it crashes. Adding __init__.py to folders seems to solve it

Traceback

version: 0.990
Traceback (most recent call last):
  File "/home/osteenbergen/Documents/semiotic-iot/.tox/mypy/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "mypy/build.py", line 2067, in wrap_context
  File "mypy/build.py", line 2393, in finish_passes
  File "mypy/build.py", line 876, in report_file
  File "mypy/report.py", line 91, in file
  File "mypy/report.py", line 640, in on_file
  File "/usr/lib/python3.8/tokenize.py", line 392, in open
    buffer = _builtin_open(filename, 'rb')
IsADirectoryError: [Errno 21] Is a directory: 'tests/testresources/monitor'

To Reproduce

Folder structure

tests/example.py

example.py

print("Hello World!")

Your Environment

• Mypy version used: 0.990
• Mypy command-line flags: --config-file mypy.ini -p tests
• Mypy configuration options from mypy.ini (and other config files):

[mypy]
check_untyped_defs = True
disallow_any_generics = True
disallow_incomplete_defs = True
disallow_subclassing_any = True
disallow_untyped_calls = True
disallow_untyped_decorators = True
disallow_untyped_defs = True
ignore_missing_imports = True
no_implicit_optional = True
no_implicit_reexport = True
show_error_codes = True
strict_equality = True
warn_redundant_casts = True
warn_return_any = True
warn_unused_configs = True
warn_unused_ignores = True

cobertura_xml_report = mypy_report
html_report = mypy_report

• Python version used: 3.8.13
• Operating system and version: Ubuntu 20.04

[osteenbergen]

If i remove the report generation from the mypy.ini it works.

[hauntsaninja]

Thanks, similar to #13733

[hauntsaninja]

--no-namespace-packages is an alternative way to get unblocked