Crash when __lt__ has a second argument

[srittau]

Please consider the following stub file:

class Foo:
    def __lt__(self, other: object, context: str = ...) -> bool: ...

Checking it with either mypy 0.610 or current HEAD (0.620+dev-b07f8f5bdaeb25fc4111c2a01276635123f1a293) with Python 3.7.0 (and other versions) results in the following crash:

srittau@moby:~$ mypy --show-traceback test.pyi 
test.pyi:2: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.620+dev-b07f8f5bdaeb25fc4111c2a01276635123f1a293
Traceback (most recent call last):
  File "/home/srittau/.local/bin/mypy", line 11, in <module>
    load_entry_point('mypy==0.620+dev.b07f8f5bdaeb25fc4111c2a01276635123f1a293', 'console_scripts', 'mypy')()
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/__main__.py", line 7, in console_entry
    main(None)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/main.py", line 91, in main
    res = type_check_only(sources, bin_dir, options, flush_errors, fscache)  # noqa
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/main.py", line 148, in type_check_only
    fscache=fscache)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/build.py", line 177, in build
    flush_errors, fscache)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/build.py", line 350, in _build
    graph = dispatch(sources, manager)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/build.py", line 2560, in dispatch
    process_graph(graph, manager)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/build.py", line 2853, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/build.py", line 2976, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/build.py", line 2151, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 253, in check_first_pass
    self.accept(d)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 352, in accept
    stmt.accept(self)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/nodes.py", line 808, in accept
    return visitor.visit_class_def(self)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 1368, in visit_class_def
    self.accept(defn.defs)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 352, in accept
    stmt.accept(self)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/nodes.py", line 873, in accept
    return visitor.visit_block(self)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 1514, in visit_block
    self.accept(s)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 352, in accept
    stmt.accept(self)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/nodes.py", line 591, in accept
    return visitor.visit_func_def(self)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 663, in visit_func_def
    self._visit_func_def(defn)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 667, in _visit_func_def
    self.check_func_item(defn, name=defn.name())
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 729, in check_func_item
    self.check_func_def(defn, typ, name)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 779, in check_func_def
    self.check_reverse_op_method(item, typ, name, defn)
  File "/home/srittau/.local/lib/python3.7/site-packages/mypy/checker.py", line 1006, in check_reverse_op_method
    assert len(reverse_type.arg_types) == 2
AssertionError: 
test.pyi:2: : note: use --pdb to drop into pdb

[emmatyping]

Closing as a duplicate of #5337. The current check is too strict.