Crash in latest master with new semantics analyzer

[reinhrst]

As requested on #6960, I'm sharing the trace from the crash of the new semantics analyzer.

It crashes in directory with just 1 file (test.py):

import dataclasses


@dataclasses.dataclass(frozen=True)
class Test():
    def __init__(self, **kwargs) -> None:
        super().__init__(**kwargs)

> mypy . --new-semantic-analyzer --show-traceback
./test.py: error: INTERNAL ERROR -- Please try using mypy master on Github:
https://mypy.rtfd.io/en/latest/common_issues.html#using-development-mypy-build
Please report a bug at https://github.com/python/mypy/issues
version: 0.710+dev.16ade15bcd2a5b6b02ad2c76b6b13efa6c2ddf0a
Traceback (most recent call last):
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/bin/mypy", line 10, in <module>
    sys.exit(console_entry())
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/__main__.py", line 8, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/main.py", line 88, in main
    res = build.build(sources, options, None, flush_errors, fscache, stdout, stderr)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/build.py", line 168, in build
    result = _build(sources, options, alt_lib_path, flush_errors, fscache, stdout, stderr)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/build.py", line 228, in _build
    graph = dispatch(sources, manager, stdout)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/build.py", line 2574, in dispatch
    process_graph(graph, manager)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/build.py", line 2887, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/build.py", line 2985, in process_stale_scc
    semantic_analysis_for_scc(graph, scc, manager.errors)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_main.py", line 80, in semantic_analysis_for_scc
    check_type_arguments(graph, scc, errors)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_main.py", line 338, in check_type_arguments
    state.tree.accept(analyzer)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/contextlib.py", line 130, in __exit__
    self.gen.throw(type, value, traceback)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/build.py", line 1832, in wrap_context
    yield
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_main.py", line 338, in check_type_arguments
    state.tree.accept(analyzer)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/nodes.py", line 281, in accept
    return visitor.visit_mypy_file(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_typeargs.py", line 33, in visit_mypy_file
    super().visit_mypy_file(o)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/traverser.py", line 33, in visit_mypy_file
    d.accept(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/nodes.py", line 913, in accept
    return visitor.visit_class_def(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_typeargs.py", line 44, in visit_class_def
    super().visit_class_def(defn)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/mixedtraverser.py", line 28, in visit_class_def
    super().visit_class_def(o)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/traverser.py", line 65, in visit_class_def
    o.defs.accept(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/nodes.py", line 978, in accept
    return visitor.visit_block(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_typeargs.py", line 48, in visit_block
    super().visit_block(o)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/traverser.py", line 37, in visit_block
    s.accept(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/nodes.py", line 655, in accept
    return visitor.visit_func_def(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/traverser.py", line 52, in visit_func_def
    self.visit_func(o)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_typeargs.py", line 40, in visit_func
    super().visit_func(defn)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/mixedtraverser.py", line 23, in visit_func
    self.visit_optional_type(o.type)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/mixedtraverser.py", line 91, in visit_optional_type
    t.accept(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/types.py", line 975, in accept
    return visitor.visit_callable_type(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/typetraverser.py", line 52, in visit_callable_type
    t.fallback.accept(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/types.py", line 666, in accept
    return visitor.visit_instance(self)
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/newsemanal/semanal_typeargs.py", line 54, in visit_instance
    for (i, arg), tvar in zip(enumerate(t.args), info.defn.type_vars):
  File "/Users/reinoud/Envs/tmp-4caf160a3041c9e/lib/python3.7/site-packages/mypy/nodes.py", line 2600, in __getattribute__
    raise AssertionError(object.__getattribute__(self, 'msg'))
AssertionError: fallback can't be filled out until semanal
./test.py: : note: use --pdb to drop into pdb

[ilevkivskyi]

Oh, this will be fixed by #6972.