Internal error when providing a def with type hints in a TypedDict class

[sami-evangelista]

Input file:

from typing import Any, TypedDict
dict_t = TypedDict('dict_t', {
    'i': int,
    's': str,
    'b': bool
}, total=False)
class D(dict_t):
    def __setitem__(self, key: str, val: Any) -> None:
        pass

Internal error:

$ mypy --show-traceback d.py

d.py:8: error: Invalid statement in TypedDict definition; expected "field_name: field_type"
d.py: 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: 0.920+dev.bbea3b56297d3d966b9a98900c218df6616fec85
d.py: : note: use --pdb to drop into pdb
d.py:8: error: Invalid statement in TypedDict definition; expected "field_name: field_type"
Traceback (most recent call last):
  File "/home/user/.local/bin/mypy", line 8, in <module>
    sys.exit(console_entry())
  File "/home/user/.local/lib/python3.9/site-packages/mypy/__main__.py", line 11, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/main.py", line 87, in main
    res, messages, blockers = run_build(sources, options, fscache, t0, stdout, stderr)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/main.py", line 165, in run_build
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/build.py", line 179, in build
    result = _build(
  File "/home/user/.local/lib/python3.9/site-packages/mypy/build.py", line 254, in _build
    graph = dispatch(sources, manager, stdout)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/build.py", line 2707, in dispatch
    process_graph(graph, manager)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/build.py", line 3031, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/build.py", line 3123, in process_stale_scc
    mypy.semanal_main.semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_main.py", line 84, in semantic_analysis_for_scc
    check_type_arguments(graph, scc, errors)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_main.py", line 360, in check_type_arguments
    state.tree.accept(analyzer)
  File "/usr/lib64/python3.9/contextlib.py", line 135, in __exit__
    self.gen.throw(type, value, traceback)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/build.py", line 1962, in wrap_context
    yield
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_main.py", line 360, in check_type_arguments
    state.tree.accept(analyzer)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/nodes.py", line 310, in accept
    return visitor.visit_mypy_file(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_typeargs.py", line 39, in visit_mypy_file
    super().visit_mypy_file(o)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/traverser.py", line 37, in visit_mypy_file
    d.accept(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/nodes.py", line 959, in accept
    return visitor.visit_class_def(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_typeargs.py", line 49, in visit_class_def
    super().visit_class_def(defn)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/mixedtraverser.py", line 28, in visit_class_def
    super().visit_class_def(o)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/traverser.py", line 73, in visit_class_def
    o.defs.accept(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/nodes.py", line 1024, in accept
    return visitor.visit_block(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_typeargs.py", line 53, in visit_block
    super().visit_block(o)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/traverser.py", line 41, in visit_block
    s.accept(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/nodes.py", line 696, in accept
    return visitor.visit_func_def(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/traverser.py", line 56, in visit_func_def
    self.visit_func(o)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_typeargs.py", line 45, in visit_func
    super().visit_func(defn)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/mixedtraverser.py", line 23, in visit_func
    self.visit_optional_type(o.type)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/mixedtraverser.py", line 91, in visit_optional_type
    t.accept(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/types.py", line 1114, in accept
    return visitor.visit_callable_type(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/typetraverser.py", line 52, in visit_callable_type
    t.fallback.accept(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/types.py", line 858, in accept
    return visitor.visit_instance(self)
  File "/home/user/.local/lib/python3.9/site-packages/mypy/semanal_typeargs.py", line 69, in visit_instance
    for (i, arg), tvar in zip(enumerate(t.args), info.defn.type_vars):
  File "/home/user/.local/lib/python3.9/site-packages/mypy/nodes.py", line 2656, in __getattribute__
    raise AssertionError(object.__getattribute__(self, 'msg'))
AssertionError: fallback can't be filled out until semanal

[sami-evangelista]

Actually, it suffices to put a def with a type hint in the class for mypy to crash. This code also make mypy crash:

from typing import Any, TypedDict
class D(TypeDict):
    def x(self, key: int):
        pass

[sobolevn]

Thanks a lot for the report!

Yes, I can reproduce it on the latest master. I thing that I might know that the problem is.
PR is incomming 🚀