Stubtest crashes if an `@overload` is decorated

Crash Report

I tried running stubtest on the numpy codebase using the compiled mypy 1.18.2 version + the patch from #20063. This triggered an assertion failure in hypothesis.extra.numpy.arrays (huh?). The relevant code contains code like

@overload
@defines_strategy(force_reusable_values=True)
def arrays(
   # --snip--

which I believe is what is triggering this asserion to fail. See HypothesisWorks/hypothesis#4564 for the relevant code.

Traceback

Traceback (most recent call last):
  File "/home/joren/Workspace/numpy/.venv/bin/stubtest", line 10, in <module>
    sys.exit(main())
             ~~~~^^
  File "/home/joren/Workspace/numpy/.venv/lib/python3.14/site-packages/mypy/stubtest.py", line 2448, in main
    return test_stubs(parse_options(sys.argv[1:]))
  File "/home/joren/Workspace/numpy/.venv/lib/python3.14/site-packages/mypy/stubtest.py", line 2296, in test_stubs
    for error in test_module(module):
                 ~~~~~~~~~~~^^^^^^^^
  File "/home/joren/Workspace/numpy/.venv/lib/python3.14/site-packages/mypy/stubtest.py", line 257, in test_module
    yield from verify(stub, runtime, [module_name])
  File "/home/joren/Workspace/numpy/.venv/lib/python3.14/site-packages/mypy/stubtest.py", line 436, in verify_mypyfile
    yield from verify(stub_entry, runtime_entry, object_path + [entry])
  File "/home/joren/Workspace/numpy/.venv/lib/python3.14/site-packages/mypy/stubtest.py", line 1347, in verify_overloadedfuncdef
    stub_sig = Signature.from_overloadedfuncdef(stub)
  File "/home/joren/Workspace/numpy/.venv/lib/python3.14/site-packages/mypy/stubtest.py", line 971, in from_overloadedfuncdef
    assert func is not None, f"Failed to resolve decorated overload of {stub.fullname!r}"
           ^^^^^^^^^^^^^^^^
AssertionError: Failed to resolve decorated overload of 'hypothesis.extra.numpy.arrays'

To Reproduce

• clone https://github.com/numpy/numpy
• uv venv .venv
• source .venv/bin/activate
• uv pip install -r requirements/build_requirements.txt -r requirements/test_requirements.txt
• spin build
• create mypy.ini:

  [mypy]
  ignore_errors = True
  

• create allowlist.txt:

  numpy\._typing.*
  numpy\.typing\.mypy_plugin
  numpy\.conftest.*
  numpy\.random\._generator\.__test__
  numpy(\.\w+)?\.tests.*
  numpy\._core\.cversions
  numpy\.f2py\.__main__
  numpy\.distutils.*
  numpy\.f2py\._backends\._distutils
  numpy\._build_utils.*
  numpy\._pyinstaller.*
  

• stubtest --mypy-config-file=mypy.ini --allowlist=allowlist.txt --concise --tb numpy

Your Environment

• Mypy version used: 1.18.2 (compiled: yes)
• Mypy command-line flags: see above
• Mypy configuration options from mypy.ini (and other config files): see above
• Python version used: 3.14.0
• Operating system and version: Ubuntu 22.04

BTW, adding hypothesis.* to the allowlist doesn't seem to help.

mypy/stubtest.py の Signature.from_overloadedfuncdef と verify_overloadedfuncdef から始め、traceback を使ってデコレートされた @overload 関数がどのように解決されるかを追跡します。提供されている NumPy のセットアップと stubtest コマンドで再現します。このデコレートされた overload が assertion failure を引き起こさなくなれば完了です。