AssertionError: Must not defer during final iteration

[mostrows2]

Crash Report

Running myyp produces: AssertionError: Must not defer during final iteration

Traceback

> mypy . --show-traceback
./mypybug.py:18: 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: 0.940+dev.c0e49abcf27ff59e761f3ec06a24ee94e700464d
Traceback (most recent call last):
  File "/Users/mostrows/.pyenv/versions/3.10.1/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/__main__.py", line 12, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/main.py", line 96, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/main.py", line 173, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/build.py", line 180, in build
    result = _build(
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/build.py", line 256, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/build.py", line 2715, in dispatch
    process_graph(graph, manager)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/build.py", line 3046, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/build.py", line 3138, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal_main.py", line 79, in semantic_analysis_for_scc
    process_functions(graph, scc, patches)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal_main.py", line 233, in process_functions
    process_top_level_function(analyzer,
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal_main.py", line 274, in process_top_level_function
    deferred, incomplete, progress = semantic_analyze_target(target, state, node, active_type,
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal_main.py", line 326, in semantic_analyze_target
    analyzer.refresh_partial(refresh_node,
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal.py", line 415, in refresh_partial
    self.accept(node)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal.py", line 5171, in accept
    node.accept(self)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/nodes.py", line 730, in accept
    return visitor.visit_func_def(self)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal.py", line 628, in visit_func_def
    self.analyze_func_def(defn)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal.py", line 660, in analyze_func_def
    self.defer(defn)
  File "/Users/mostrows/.pyenv/versions/3.10.1/lib/python3.10/site-packages/mypy/semanal.py", line 4871, in defer
    assert not self.final_iteration, 'Must not defer during final iteration'
AssertionError: Must not defer during final iteration
./mypybug.py:18: : note: use --pdb to drop into pdb

To Reproduce

source of mypybug.py:

import dataclasses
import typing

if typing.TYPE_CHECKING:
    import classb as b
    
ItemType = typing.TypeVar('ItemType', bound='b.ClassB')

class Item(typing.Protocol):
    name: str

class ItemBase(typing.Generic[ItemType]):
    pass

# dataclasses required to trigger bug.
@dataclasses.dataclass(kw_only=True)
class ItemBaseX(ItemBase[ItemType]):
    name: str

Source of classb.py:

import typing

# This import is required to trigger bug.
import mypybug as eitem

class ClassB(typing.Protocol):
    field: str

Executed:

mypy mypybug.py

Your Environment

• Mypy version used: 0.940+dev.c0e49abcf27ff59e761f3ec06a24ee94e700464d (and others)
• Mypy command-line flags: none
• Mypy configuration options from mypy.ini (and other config files): none
• Python version used: 3.10.1
• Operating system and version: mac os 12.1

[felixmeziere]

Same issue here!

[AlexWaygood]

Same assertion is hit in #12252, #11728, #12112, #10672 and #10140

[JukkaL]

This was fixed in #12762.