Mypy crashes with pydantic plugin enabled: Must not defer during final iteration

[SoptikHa2]

Crash Report

When I run mypy on our codebase, it works fine. When I enable pydantic plugin, it crashes.

Pyproject:

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

python_version = "3.10"
follow_imports = "silent"
# Start off with these
warn_unused_configs = false
warn_redundant_casts = false
warn_unused_ignores = false

# Getting these passing should be easy
strict_equality = false
strict_concatenate = false

# Strongly recommend enabling this one as soon as you can
check_untyped_defs = false

# These shouldn't be too much additional work, but may be tricky to
# get passing if you use a lot of untyped libraries
disallow_subclassing_any = false
disallow_untyped_decorators = false
disallow_any_generics = false

# These next few are various gradations of forcing use of type annotations
disallow_untyped_calls = false
disallow_incomplete_defs = false
disallow_untyped_defs = false

# This one isn't too hard to get passing, but return on investment is lower
no_implicit_reexport = false

# This one can be tricky to get passing if you use a lot of untyped libraries
warn_return_any = false

Traceback

version: 1.6.0+dev.7141d6bcff9e26e774e88712015ca6bbe8307c9e
Traceback (most recent call last):
 File "/Users/foobar/Library/Caches/pypoetry/virtualenvs/foobar-py3.10/bin/mypy", line 8, in <module>
 sys.exit(console_entry())
 File "/private/tmp/mypy/mypy/__main__.py", line 15, in console_entry
 main()
 File "/private/tmp/mypy/mypy/main.py", line 99, in main
 res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
 File "/private/tmp/mypy/mypy/main.py", line 178, in run_build
 res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
 File "/private/tmp/mypy/mypy/build.py", line 189, in build
 result = _build(
 File "/private/tmp/mypy/mypy/build.py", line 262, in _build
 graph = dispatch(sources, manager, stdout)
 File "/private/tmp/mypy/mypy/build.py", line 2938, in dispatch
 process_graph(graph, manager)
 File "/private/tmp/mypy/mypy/build.py", line 3336, in process_graph
 process_stale_scc(graph, scc, manager)
 File "/private/tmp/mypy/mypy/build.py", line 3431, in process_stale_scc
 mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
 File "/private/tmp/mypy/mypy/semanal_main.py", line 94, in semantic_analysis_for_scc
 process_functions(graph, scc, patches)
 File "/private/tmp/mypy/mypy/semanal_main.py", line 252, in process_functions
 process_top_level_function(
 File "/private/tmp/mypy/mypy/semanal_main.py", line 291, in process_top_level_function
 deferred, incomplete, progress = semantic_analyze_target(
 File "/private/tmp/mypy/mypy/semanal_main.py", line 349, in semantic_analyze_target
 analyzer.refresh_partial(
 File "/private/tmp/mypy/mypy/semanal.py", line 603, in refresh_partial
 self.accept(node)
 File "/private/tmp/mypy/mypy/semanal.py", line 6477, in accept
 node.accept(self)
 File "/private/tmp/mypy/mypy/nodes.py", line 790, in accept
 return visitor.visit_func_def(self)
 File "/private/tmp/mypy/mypy/semanal.py", line 833, in visit_func_def
 self.analyze_func_def(defn)
 File "/private/tmp/mypy/mypy/semanal.py", line 868, in analyze_func_def
 self.defer(defn)
 File "/private/tmp/mypy/mypy/semanal.py", line 6149, in defer
 assert not self.final_iteration, "Must not defer during final iteration"
AssertionError: Must not defer during final iteration

To Reproduce

from typing import *
from pydantic import BaseModel

AnyBaseFoo = TypeVar("AnyBaseFoo", bound="BaseFoo")

class BaseFoo:
 pass

class Foo(BaseModel, Generic[AnyBaseFoo]):
 pass

Your Environment

• Mypy version used: 1.6.0+dev.7141d6bcff9e26e774e88712015ca6bbe8307c9e
• Mypy command-line flags: mypy foobar/baz --show-traceback
• Python version used: 3.10.10
• Operating system and version: Darwin mac 22.6.0, rosetta was used

[SoptikHa2]

A workaround has been found:

from typing import *
from pydantic import BaseModel

class BaseFoo:
 pass

AnyBaseFoo = TypeVar("AnyBaseFoo", bound="BaseFoo")

class Foo(BaseModel, Generic[AnyBaseFoo]):
 pass

Declaring the TypeVar anywhere after its bound avoids the crash.

[jp-u]

A workaround has been found:

from typing import *
from pydantic import BaseModel

class BaseFoo:
 pass

AnyBaseFoo = TypeVar("AnyBaseFoo", bound="BaseFoo")

class Foo(BaseModel, Generic[AnyBaseFoo]):
 pass

Declaring the TypeVar anywhere after its bound avoids the crash.

This isn't a great/complete answer IMO because you sometimes need the TypeVar in class methods and such defined on the class.

[patrys]

I have the same code (a TypeVar bound to a deferred definition) crash mypy 1.11.2 with the django plugin enabled.

[ilevkivskyi]

It looks like same (or similar) problem affects multiple plugins. I am going to close this as a duplicate of #18579 to consolidate discussion, please continue there.