AssertionError on version 0.960

[Apakottur]

Bug Report

We are using the ddtrace Python package.
Consider the following file:

# test.py
import ddtrace

Running mypy test.py passes without issues on version 0.950 but when run on version 0.960 the following is printed:

Traceback (most recent call last):
  File ".../bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File ".../python3.10/site-packages/mypy/__main__.py", line 12, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "mypy/main.py", line 96, in main
  File "mypy/main.py", line 173, in run_build
  File "mypy/build.py", line 154, in build
  File "mypy/build.py", line 230, in _build
  File "mypy/build.py", line 2729, in dispatch
  File "mypy/build.py", line 3087, in process_graph
  File "mypy/build.py", line 3179, in process_stale_scc
  File "mypy/semanal_main.py", line 88, in semantic_analysis_for_scc
  File "mypy/semanal_main.py", line 414, in apply_class_plugin_hooks
  File "mypy/semanal_main.py", line 434, in apply_hooks_to_class
  File "mypy/plugins/attrs.py", line 309, in attr_class_maker_callback
  File "mypy/plugins/attrs.py", line 372, in _analyze_class
  File "mypy/plugins/attrs.py", line 498, in _attributes_from_assignment
  File "mypy/plugins/attrs.py", line 594, in _attribute_from_attrib_maker
  File "mypy/semanal.py", line 5450, in anal_type
  File "mypy/types.py", line 765, in accept
  File "mypy/typeanal.py", line 172, in visit_unbound_type
  File "mypy/typeanal.py", line 263, in visit_unbound_type_nonoptional
  File "mypy/typeanal.py", line 1168, in anal_array
  File "mypy/typeanal.py", line 1177, in anal_type
  File "mypy/types.py", line 765, in accept
  File "mypy/typeanal.py", line 172, in visit_unbound_type
  File "mypy/typeanal.py", line 180, in visit_unbound_type_nonoptional
  File "mypy/semanal.py", line 4563, in lookup_qualified
  File "mypy/semanal.py", line 4458, in lookup
  File "mypy/semanal.py", line 4508, in is_active_symbol_in_class_body
AssertionError

I tried using the --pdb and --tb flags to get the traceback, or see which part of the library is causing this but was unable to do so.
I tried clearing the mypy cache, which didn't help as well.

Is this an issue with mypy, the library or both?

Your Environment

• Mypy version used: 0.960
• Python version used: 3.10
• Operating system and version: Ubuntu 22.04

[AlexWaygood]

Thanks for the report! I can reproduce this on the master branch, if I create a new virtual environment with just mypy's dependencies and ddtrace installed, and then run mypy on a file that only has import ddtrace inside it.

The crash bisects to 50a653e (PR #12772). Cc. @JukkaL.

[P403n1x87]

I don't know if this could be related, but there seems to be issues with how dataclasses are handled too:

https://github.com/DataDog/riot/runs/6594827098?check_suite_focus=true

The logs show that the latest version of mypy has started complaining about attributes that are defined on the dataclass

https://github.com/DataDog/riot/blob/2f6ea2e7a128239c45d4771245f572095651436e/riot/riot.py#L177-L231

[gitpushdashf]

Thanks for reporting this! Getting this as well.

[JukkaL]

Here is a small reproducer for the attrs crash:

import attr

@attr.s
class C:
    @attr.s
    class D:
        pass
    x = attr.ib(type=list[D])

As a workaround, moving the nested class to the module top level should fix the crash. I'm working on a fix.

[JukkaL]

@P403n1x87 That's a separate issue, and it looks like it's related to #12798. Here's a skeleton of a workaround for the issue:

from dataclasses import dataclass, InitVar, field

@dataclass
class D:
    _x: InitVar[int]
    x: str = field(init=False)

    def __post_init__(self, _x: int) -> None:
        self.x = str(_x)

Feel free to create a separate issue if this isn't sufficient to resolve your issue.

[P403n1x87]

@JukkaL ah this makes a lot of sense, thanks! I guess this is an actual improvement from mypy that has just highlighted a misuse of InitVar from our side!