Crash due to unresolved forward reference to decorated method

[JukkaL]

Mypy crashes when type checking this program:

from typing import NewType

N = NewType('N', XXX)

b = C.g()

class C:
    @staticmethod
    def g() -> N:
        pass

If I replace @staticmethod with another decorator the crash persists.

Here's the traceback:

$ mypy --show-traceback t/t2.py
t/t2.py:3: error: Argument 2 to NewType(...) must be subclassable (got "Any")
t/t2.py:3: error: Name 'XXX' is not defined
t/t2.py:9: error: Invalid type "t2.N"
t/t2.py:5: error: INTERNAL ERROR -- please report a bug at https://github.com/python/mypy/issues version: 0.560-dev-ba615b74f07c92221f264f7a6a5375be0a41ebed
Traceback (most recent call last):
  File "/Users/jukka/src/mypy/scripts/mypy", line 6, in <module>
    main(__file__)
  File "/Users/jukka/src/mypy/mypy/main.py", line 66, in main
    res = type_check_only(sources, bin_dir, options)
  File "/Users/jukka/src/mypy/mypy/main.py", line 119, in type_check_only
    options=options)
  File "/Users/jukka/src/mypy/mypy/build.py", line 218, in build
    graph = dispatch(sources, manager)
  File "/Users/jukka/src/mypy/mypy/build.py", line 2001, in dispatch
    process_graph(graph, manager)
  File "/Users/jukka/src/mypy/mypy/build.py", line 2305, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/Users/jukka/src/mypy/mypy/build.py", line 2481, in process_stale_scc
    graph[id].type_check_first_pass()
  File "/Users/jukka/src/mypy/mypy/build.py", line 1880, in type_check_first_pass
    self.type_checker().check_first_pass()
  File "/Users/jukka/src/mypy/mypy/checker.py", line 200, in check_first_pass
    self.accept(d)
  File "/Users/jukka/src/mypy/mypy/checker.py", line 295, in accept
    stmt.accept(self)
  File "/Users/jukka/src/mypy/mypy/nodes.py", line 805, in accept
    return visitor.visit_assignment_stmt(self)
  File "/Users/jukka/src/mypy/mypy/checker.py", line 1350, in visit_assignment_stmt
    self.check_assignment(s.lvalues[-1], s.rvalue, s.type is None, s.new_syntax)
  File "/Users/jukka/src/mypy/mypy/checker.py", line 1445, in check_assignment
    rvalue)
  File "/Users/jukka/src/mypy/mypy/checker.py", line 1909, in infer_variable_type
    elif not is_valid_inferred_type(init_type) and not self.no_partial_types:
  File "/Users/jukka/src/mypy/mypy/checker.py", line 3441, in is_valid_inferred_type
    return is_valid_inferred_type_component(typ)
  File "/Users/jukka/src/mypy/mypy/checker.py", line 3450, in is_valid_inferred_type_component
    if is_same_type(typ, UninhabitedType()):
  File "/Users/jukka/src/mypy/mypy/sametypes.py", line 28, in is_same_type
    return left.accept(SameTypeVisitor(right))
  File "/Users/jukka/src/mypy/mypy/types.py", line 1415, in accept
    return visitor.visit_forwardref_type(self)
  File "/Users/jukka/src/mypy/mypy/types.py", line 1500, in visit_forwardref_type
    raise RuntimeError('Internal error: unresolved forward reference')
RuntimeError: Internal error: unresolved forward reference
t/t2.py:5: : note: use --pdb to drop into pdb

This seems related to #4200 but the same fix doesn't seem to work.

[JukkaL]

Actually this doesn't happen on master .. it must be caused by my local changes.

[ilevkivskyi]

Yes, this was fixed by #4375

[JukkaL]

Yes, I hadn't rebased in a few days.