Mypy 2.X periodically and inconsistently throws an error

Crash Report

Mypy 2.X periodically and inconsistently throws an error

Traceback

Exception in thread Thread-7 (write_bytes):
Exception in thread Thread-8 (write_bytes):
Exception in thread Thread-9 (write_bytes):
Exception in thread Thread-10 (write_bytes):
Exception in thread Thread-11 (write_bytes):
Exception in thread Thread-12 (write_bytes):
Traceback (most recent call last):
Traceback (most recent call last):
  File "mypy\ipc.py", line 158, in write_bytes
Traceback (most recent call last):
Traceback (most recent call last):
OSError: [WinError 233] С обоих концов канала отсутствуют процессы
  File "mypy\ipc.py", line 158, in write_bytes
Traceback (most recent call last):
  File "mypy\ipc.py", line 158, in write_bytes
Traceback (most recent call last):
  File "mypy\ipc.py", line 158, in write_bytes

During handling of the above exception, another exception occurred:

OSError: [WinError 233] С обоих концов канала отсутствуют процессы
  File "mypy\ipc.py", line 158, in write_bytes
    ov, err = _winapi.WriteFile(self.connection, encoded_data, overlapped=True)
OSError: [WinError 233] С обоих концов канала отсутствуют процессы
  File "mypy\ipc.py", line 158, in write_bytes
    ov, err = _winapi.WriteFile(self.connection, encoded_data, overlapped=True)
OSError: [WinError 233] С обоих концов канала отсутствуют процессы
Traceback (most recent call last):

During handling of the above exception, another exception occurred:

OSError: [WinError 233] С обоих концов канала отсутствуют процессы

During handling of the above exception, another exception occurred:

OSError: [WinError 233] С обоих концов канала отсутствуют процессы

During handling of the above exception, another exception occurred:

  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
Traceback (most recent call last):

During handling of the above exception, another exception occurred:

Traceback (most recent call last):

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
Traceback (most recent call last):
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
Traceback (most recent call last):
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "mypy\ipc.py", line 174, in write_bytes
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1082, in _bootstrap_inner
    self._context.run(self.run)
    ~~~~~~~~~~~~~~~~~^^^^^^^^^^
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
mypy.ipc.IPCException: Failed to write with error: 233
  File "mypy\ipc.py", line 174, in write_bytes
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "mypy\ipc.py", line 174, in write_bytes
  File "C:\Users\user\AppData\Local\Programs\Python\Python314\Lib\threading.py", line 1024, in run
    self._target(*self._args, **self._kwargs)
    ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "mypy\ipc.py", line 174, in write_bytes
mypy.ipc.IPCException: Failed to write with error: 233
  File "mypy\ipc.py", line 174, in write_bytes
    raise IPCException(f"Failed to write with error: {e.winerror}") from e
mypy.ipc.IPCException: Failed to write with error: 233
mypy.ipc.IPCException: Failed to write with error: 233
mypy.ipc.IPCException: Failed to write with error: 233
  File "mypy\ipc.py", line 174, in write_bytes
    raise IPCException(f"Failed to write with error: {e.winerror}") from e
mypy.ipc.IPCException: Failed to write with error: 233
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: 2.1.0
Traceback (most recent call last):
  File "mypy\build.py", line 1392, in receive_worker_message
    return receive(self.workers[idx].conn)
  File "mypy\ipc.py", line 479, in receive
    bdata = connection.read_bytes()
  File "mypy\ipc.py", line 101, in read_bytes
    ov, err = _winapi.ReadFile(self.connection, size, overlapped=True)
OSError: [WinError 233] С обоих концов канала отсутствуют процессы

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "<frozen runpy>", line 203, in _run_module_as_main
  File "<frozen runpy>", line 88, in _run_code
  File "D:\Dev\strana\contracts-backend\.venv\Lib\site-packages\mypy\__main__.py", line 16, in console_entry
    main()
    ~~~~^^
  File "mypy\main.py", line 154, in main
  File "mypy\main.py", line 244, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "mypy\build.py", line 422, in build
  File "mypy\build.py", line 537, in build_inner
    graph = dispatch(sources, manager, stdout, connect_threads)
  File "mypy\build.py", line 4150, in dispatch
    process_graph(graph, manager)
  File "mypy\build.py", line 4587, in process_graph
    manager.wait_ack()
  File "mypy\build.py", line 1386, in wait_ack
    buf = self.receive_worker_message(idx)
  File "mypy\build.py", line 1400, in receive_worker_message
    raise OSError(
OSError: Worker 0 disconnected before sending data (exit code 0)

note: use --pdb to drop into pdb

To Reproduce
Idk how reproduce it :( It's random

Your Environment

• Mypy version used: 2.1.0
• Mypy command-line flags: mypy src tests main.py --num-workers=6 --show-traceback
• Mypy configuration options from mypy.ini (and other config files): pyproject.toml

[tool.mypy]
allow_redefinition = false
disallow_any_explicit = false
exclude = "(alembic)|(src/ignored)|src/t.py|(_entrypoints)|(tests/factories)|src/core/docx_templating/docx_templating.py"
follow_imports = "silent"
ignore_errors = false
ignore_missing_imports = true
local_partial_types = true
mypy_path = "src ."
no_implicit_optional = true
plugins = [
  "pydantic.mypy",
]
python_version = 3.14
strict = true
strict_optional = true
warn_no_return = true
warn_return_any = true
warn_unreachable = false

pretty = true
show_column_numbers = true
show_error_codes = true

[[tool.mypy.overrides]]
disable_error_code = ["name-defined", "misc", "var-annotated", "attr-defined", "no-untyped-call"]
module = "tests.factories.*"

[[tool.mypy.overrides]]
disable_error_code = ["assignment", "misc", "var-annotated", "attr-defined", "arg-type"]
ignore_errors = true
module = [
  "core.docx_templating.*",
]

• Python version used: 3.14.5
• Operating system and version: Windows 10 Pro, build 19043

Start by reading mypy/ipc.py around read_bytes and write_bytes, then follow mypy/build.py through receive_worker_message and wait_ack. Run the reported command with --num-workers=6 on Windows and the provided Python 3.14.5 configuration; done means the intermittent worker disconnect and IPCException can be reproduced and no longer occurs, with coverage for the failure if a test location is identified.