Internal error with unresolved forward reference

[mitar]

I am getting an internal error even with current master, version 0.570-dev-38337a8900052c40992d39bb09b1fcbb53a15d59.

RuntimeError: Internal error: unresolved forward reference

Traceback (most recent call last):
  File "/<redacted>/bin/mypy", line 11, in <module>
    load_entry_point('mypy===0.570-dev-38337a8900052c40992d39bb09b1fcbb53a15d59', 'console_scripts', 'mypy')()
  File "/<redacted>/lib/python3.6/site-packages/mypy/__main__.py", line 7, in console_entry
    main(None)
  File "/<redacted>/lib/python3.6/site-packages/mypy/main.py", line 66, in main
    res = type_check_only(sources, bin_dir, options)
  File "/<redacted>/lib/python3.6/site-packages/mypy/main.py", line 119, in type_check_only
    options=options)
  File "/<redacted>/lib/python3.6/site-packages/mypy/build.py", line 218, in build
    graph = dispatch(sources, manager)
  File "/<redacted>/lib/python3.6/site-packages/mypy/build.py", line 2000, in dispatch
    process_graph(graph, manager)
  File "/<redacted>/lib/python3.6/site-packages/mypy/build.py", line 2304, in process_graph
    process_stale_scc(graph, scc, manager)
  File "/<redacted>/lib/python3.6/site-packages/mypy/build.py", line 2474, in process_stale_scc
    graph[id].semantic_analysis_pass_three()
  File "/<redacted>/lib/python3.6/site-packages/mypy/build.py", line 1866, in semantic_analysis_pass_three
    self.options, patches)
  File "/<redacted>/lib/python3.6/site-packages/mypy/semanal_pass3.py", line 61, in visit_file
    self.accept(file_node)
  File "/<redacted>/lib/python3.6/site-packages/mypy/semanal_pass3.py", line 79, in accept
    node.accept(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/nodes.py", line 228, in accept
    return visitor.visit_mypy_file(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/traverser.py", line 30, in visit_mypy_file
    d.accept(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/nodes.py", line 699, in accept
    return visitor.visit_class_def(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/semanal_pass3.py", line 134, in visit_class_def
    super().visit_class_def(tdef)
  File "/<redacted>/lib/python3.6/site-packages/mypy/traverser.py", line 61, in visit_class_def
    o.defs.accept(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/nodes.py", line 759, in accept
    return visitor.visit_block(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/semanal_pass3.py", line 86, in visit_block
    super().visit_block(b)
  File "/<redacted>/lib/python3.6/site-packages/mypy/traverser.py", line 34, in visit_block
    s.accept(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/nodes.py", line 497, in accept
    return visitor.visit_func_def(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/semanal_pass3.py", line 92, in visit_func_def
    self.analyze(fdef.type, fdef)
  File "/<redacted>/lib/python3.6/site-packages/mypy/semanal_pass3.py", line 350, in analyze
    type.accept(analyzer)
  File "/<redacted>/lib/python3.6/site-packages/mypy/types.py", line 739, in accept
    return visitor.visit_callable_type(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/typeanal.py", line 771, in visit_callable_type
    arg_type.accept(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/types.py", line 475, in accept
    return visitor.visit_instance(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/typeanal.py", line 727, in visit_instance
    if not is_subtype(arg, bound):
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 83, in is_subtype
    ignore_declared_variance=ignore_declared_variance))
  File "/<redacted>/lib/python3.6/site-packages/mypy/types.py", line 543, in accept
    return visitor.visit_type_var(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 204, in visit_type_var
    return is_subtype(left.upper_bound, self.right)
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 83, in is_subtype
    ignore_declared_variance=ignore_declared_variance))
  File "/<redacted>/lib/python3.6/site-packages/mypy/types.py", line 475, in accept
    return visitor.visit_instance(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 169, in visit_instance
    zip(t.args, right.args, right.type.defn.type_vars))
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 168, in <genexpr>
    for lefta, righta, tvar in
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 38, in check_type_parameter
    return is_subtype(lefta, righta, check_type_parameter)
  File "/<redacted>/lib/python3.6/site-packages/mypy/subtypes.py", line 83, in is_subtype
    ignore_declared_variance=ignore_declared_variance))
  File "/<redacted>/lib/python3.6/site-packages/mypy/types.py", line 1415, in accept
    return visitor.visit_forwardref_type(self)
  File "/<redacted>/lib/python3.6/site-packages/mypy/types.py", line 1500, in visit_forwardref_type
    raise RuntimeError('Internal error: unresolved forward reference')
RuntimeError: Internal error: unresolved forward reference

I made a reproduction here: https://github.com/mitar/forward-reference-test

Run mypy bar.

[ilevkivskyi]

This is a duplicate of #4200

[mitar]

I am not sure. For me things work until I define the compute method:

class Bary(typing.Generic[Container]):
    def compute(self) -> Container:
        pass

[ilevkivskyi]

You can check that #4384 will fix your repro as well.

[mitar]

It does. Perfect!