Mypy plugin crashes with `explicit_package_bases` set as true

[marcelopgc]

Initial Checks

• I have searched GitHub for a duplicate issue and I'm sure this is something new
• I have searched Google & StackOverflow for a solution and couldn't find anything
• I have read and followed the docs and still think this is a bug
• I am confident that the issue is with pydantic (not my code, or another library in the ecosystem like FastAPI or mypy)

Description

After updating mypy to v1.1.1, I added the following pyproject.toml config, as descripted in the documentation, to prevent mypy errors on classes with Optional attributes:

[tool.mypy]
strict = true
files = "src/app"
mypy_path = "src/"
namespace_packages = true
explicit_package_bases = true
follow_imports = "silent"
ignore_missing_imports = true
exclude = "(resources/.*)"

plugins = [
    "pydantic.mypy"
]

warn_redundant_casts = true
warn_unused_ignores = true
disallow_any_generics = true
check_untyped_defs = true
no_implicit_reexport = true

# for strict mypy: (this is the tricky one :-))
disallow_untyped_defs = true

[tool.pydantic-mypy]
init_forbid_extra = true
init_typed = true
warn_required_dynamic_aliases = true
warn_untyped_fields = true

Using that config, I found an internal error while running mypy

src/app/models/stages.py:152: 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: 1.1.1
Traceback (most recent call last):
  File "mypy/semanal.py", line 6261, in accept
  File "mypy/nodes.py", line 1123, in accept
  File "mypy/semanal.py", line 1561, in visit_class_def
  File "mypy/semanal.py", line 1641, in analyze_class
  File "mypy/semanal.py", line 1668, in analyze_class_body_common
  File "mypy/semanal.py", line 1751, in apply_class_plugin_hooks
  File "pydantic/mypy.py", line 150, in pydantic.mypy.PydanticPlugin._pydantic_model_class_maker_callback
  File "pydantic/mypy.py", line 315, in pydantic.mypy.PydanticModelTransformer.transform
  File "pydantic/mypy.py", line 524, in pydantic.mypy.PydanticModelTransformer.set_frozen
AssertionError: 
src/app/models/stages.py:152: : note: use --pdb to drop into pdb

If remove the explicit_package_bases configuration, mypy is able to run without this setting.

mypy version:

 name         : mypy                              
 version      : 1.1.1                             
 description  : Optional static typing for Python 

dependencies
 - mypy-extensions >=1.0.0
 - tomli >=1.1.0
 - typing-extensions >=3.10

Example Code

No response

Python, Pydantic & OS Version

pydantic version: 1.10.6
pydantic compiled: True
install path: /workspace/.venv/lib/python3.9/site-packages/pydantic
python version: 3.9.16 (main, Jan 11 2023, 15:55:30)  [GCC 10.2.1 20210110]
platform: Linux-5.10.102.1-microsoft-standard-WSL2-x86_64-with-glibc2.31
optional deps. installed: ['typing-extensions']

Affected Components

• Compatibility between releases
• Data validation/parsing
• Data serialization - .dict() and .json()
• JSON Schema
• Dataclasses
• Model Config
• Field Types - adding or changing a particular data type
• Function validation decorator
• Generic Models
• Other Model behaviour - construct(), pickling, private attributes, ORM mode
• Plugins and integration with other tools - mypy, FastAPI, python-devtools, Hypothesis, VS Code, PyCharm, etc.

[samuelcolvin]

See #5192

[dmontagu]

@marcelopgc I'm looking at this now — do you have example code you can share that causes this issue when you run mypy on it? At the very least I will make it produce an error that we can debug as opposed to crashing mypy, but if I can reproduce the issue I should be able to resolve it.

[dmontagu]

@marcelopgc if you can't easily share code that I could use to reproduce the failure — if you checkout the branch in the pull request #5208 and install it locally (pip install .) and run mypy with the plugin, and can share the error message you get, it may provide some insight.

[marcelopgc]

@dmontagu here it is the link to the code that we were able to reproduce this error: https://github.com/marcelopgc/pydantic1.10.6_debug

[dmontagu]

@marcelopgc thank you — I was able to figure out what was going on by analyzing that codebase. Turns out the circular imports were causing something called a PlaceholderNode to be produced which I hadn't seen before. #5208 should resolve this issue for you.

[dmontagu]

The fix for this will be released in 1.10.7 today.