INTERNAL ERROR: AssertionError: ClassDef is lacking info

[martinky24]

Crash Report

I am seeing a Mypy INTERNAL ERROR on both 1.4.1 and 1.6.0+dev.54bc37ccade0476a1738b33cd34b6eb35d7124e1.

I don't see it on first run of mypy immedaitely after clearing .mypy_cache, but I see it on all runs after that first one.

Relatively minimal info to reproduce, at least for me:

This python file, config.py:

from typing import Any, Optional

from pydantic import PostgresDsn, field_validator
from pydantic_settings import BaseSettings


class Settings(BaseSettings):

    SQLALCHEMY_DATABASE_URI: Optional[PostgresDsn] = None

    @field_validator("SQLALCHEMY_DATABASE_URI", mode="before")
    def assemble_db_connection(cls, v: Optional[str], values: dict[str, Any]) -> Any:
        return v

This mypy configs file:

[tool.mypy]
python_version = "3.11"
plugins = ["pydantic.mypy"]

With these dependencies:

$ pip freeze
annotated-types==0.5.0
mypy @ file:///Users/kyle/open-source/mypy
mypy-extensions==1.0.0
pydantic==2.1.1
pydantic-settings==2.0.2
pydantic_core==2.4.0
python-dotenv==1.0.0
typing_extensions==4.7.1

This command:

mypy --config pyproject.toml --show-traceback config.py

Traceback

$ mypy --config pyproject.toml --show-traceback config.py
config.py:7: 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: 1.6.0+dev.54bc37ccade0476a1738b33cd34b6eb35d7124e1
Traceback (most recent call last):
  File "/Users/kyle/open-source/mypy-crash/.venv/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/__main__.py", line 15, in console_entry
    main()
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/main.py", line 94, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/main.py", line 173, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/build.py", line 195, in build
    result = _build(
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/build.py", line 268, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/build.py", line 2927, in dispatch
    process_graph(graph, manager)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/build.py", line 3325, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/build.py", line 3420, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal_main.py", line 93, in semantic_analysis_for_scc
    process_top_levels(graph, scc, patches)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal_main.py", line 220, in process_top_levels
    deferred, incomplete, progress = semantic_analyze_target(
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal_main.py", line 349, in semantic_analyze_target
    analyzer.refresh_partial(
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 600, in refresh_partial
    self.refresh_top_level(node)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 611, in refresh_top_level
    self.accept(d)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 6465, in accept
    node.accept(self)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/nodes.py", line 1141, in accept
    return visitor.visit_class_def(self)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 1600, in visit_class_def
    self.analyze_class(defn)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 1685, in analyze_class
    self.analyze_class_body_common(defn)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 1714, in analyze_class_body_common
    self.apply_class_plugin_hooks(defn)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/semanal.py", line 1801, in apply_class_plugin_hooks
    hook(ClassDefContext(defn, base_expr, self))
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/pydantic/mypy.py", line 182, in _pydantic_model_class_maker_callback
    return transformer.transform()
           ^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/pydantic/mypy.py", line 443, in transform
    self.add_initializer(fields, config, is_settings)
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/pydantic/mypy.py", line 804, in add_initializer
    base_settings_init_arguments = base_settings_info.names['__init__'].node.arguments
                                   ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/Users/kyle/open-source/mypy-crash/.venv/lib/python3.11/site-packages/mypy/nodes.py", line 3409, in __getattribute__
    raise AssertionError(object.__getattribute__(self, "msg"))
AssertionError: ClassDef is lacking info
config.py:7: : note: use --pdb to drop into pdb

To Reproduce

Above setup, with

mypy --config pyproject.toml --show-traceback config.py

Your Environment

• Mypy version used: 1.6.0+dev.54bc37ccade0476a1738b33cd34b6eb35d7124e1 AND 1.4.1
• Mypy command-line flags: mypy --config pyproject.toml --show-traceback config.py
• Mypy configuration options:

[tool.mypy]
python_version = "3.11"
plugins = ["pydantic.mypy"]

• Python version used: Python 3.11.4
• Operating system and version: macOS Ventura 13.4.1

[martinky24]

Appreciate all the work from the mypy team, if there's anything else I can provide let me know! Sorry if this is a dup.

[martinky24]

I think this has something to do with Pydantic 2.0's field_validator

[JelleZijlstra]

Chances are this is a bug in pydantic's mypy plugin, which is maintained by the Pydantic project, not by mypy itself.

[A5rocks]

Hi, maybe this is an instance of pydantic/pydantic#6985? While the manifested error is different it's the exact same code path in the pydantic plugin...?

[martinky24]

I think the MR linked in that issue (pydantic/pydantic#7002) does fix this, from some local testing I did.

[JelleZijlstra]

Closing as this is a bug in pydantic, not mypy.