crash on decorated method redefinition + circular imports

[dmoisset]

Mypy crashes with an internal crash on this multi-file package. The example code doesn't make much sense (I arrived to it by trimming a much larger project that's crashing mypy), but I should probably just get errors. If I have the following three files:

# foo/__init__.py
from .derived import *

# foo/base.py
from . import *

class Base:
    @decorator
    def method(self) -> None:
        pass

# foo/derived.py
from .base import Base

class Derived(Base):
    def method(self) -> None:
        pass

And then I run mypy foo/base.py, I get the following

Traceback (most recent call last):
  File ".../bin/mypy", line 6, in <module>
    main(__file__)
  File ".../mypy/main.py", line 40, in main
    res = type_check_only(sources, bin_dir, options)
  File ".../mypy/main.py", line 81, in type_check_only
    options=options)
  File ".../mypy/build.py", line 177, in build
    dispatch(sources, manager)
  File ".../mypy/build.py", line 1323, in dispatch
    process_graph(graph, manager)
  File ".../mypy/build.py", line 1461, in process_graph
    process_stale_scc(graph, scc)
  File ".../mypy/build.py", line 1538, in process_stale_scc
    graph[id].type_check()
  File ".../mypy/build.py", line 1301, in type_check
    manager.type_checker.visit_file(self.tree, self.xpath)
  File ".../mypy/checker.py", line 152, in visit_file
    self.accept(d)
  File ".../mypy/checker.py", line 201, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 660, in accept
    return visitor.visit_class_def(self)
  File ".../mypy/checker.py", line 802, in visit_class_def
    self.accept(defn.defs)
  File ".../mypy/checker.py", line 201, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 723, in accept
    return visitor.visit_block(self)
  File ".../mypy/checker.py", line 897, in visit_block
    self.accept(s)
  File ".../mypy/checker.py", line 201, in accept
    typ = node.accept(self)
  File ".../mypy/nodes.py", line 475, in accept
    return visitor.visit_func_def(self)
  File ".../mypy/checker.py", line 325, in visit_func_def
    self.check_method_override(defn)
  File ".../mypy/checker.py", line 681, in check_method_override
    self.check_method_or_accessor_override_for_base(defn, base)
  File ".../mypy/checker.py", line 690, in check_method_or_accessor_override_for_base
    self.check_method_override_for_base_with_name(defn, name, base)
  File ".../mypy/checker.py", line 728, in check_method_override_for_base_with_name
    assert original_type is not None
AssertionError: 

*** INTERNAL ERROR ***

/home/machinalis/0/foo/derived.py:4: error: Internal error -- please report a bug at https://github.com/python/mypy/issues

[dmoisset]

Got it down to a 2 file version

# foo/__init__.py
import foo.base

class Derived(foo.base.Base):
    def method(self) -> None:
        pass

# foo/base.py
import foo

class Base:

    @decorator
    def method(self) -> None:
        pass

[gvanrossum]

Where is @decorator defined? Or is its undefined-ness necessary to repro this case? Also, does it not repro if Derived and Base live in the same file?

[dmoisset]

On the original code it was imported from yet another module (which was unannotated), but it wasn't required to reproduce the crash (as I mentioned the code is silly and doesn't run). If I define a dummy implementation, the crash goes away.

I couldn't reproduce in a single file scenario, or even removing the (unused) import foo in base.py

[gvanrossum]

I'm sorry, maybe I'm being dense, but I still don't understand whether the crash repro requires a definition of decorator or not. Unless I am reading your code wrong it is not defined so it would be flagged as an undefined name by mypy, right?

[dmoisset]

Let me clarify my previous message, it might have been confusing

• Yes, the definition for "decorator" is intentionally missing in the code snippet, mypy crashes on the code as shown (i.e. with the missing definition)
• If I add a decorator definition to the snippet and re-run mypy on that, mypy doesn't crash (it shows some type errors which are actual errors).

To clarify: I expect mypy here to just tell me that "decorator isn't defined" but the observed behaviour is the "*** INTERNAL ERROR ***" shown.

[gvanrossum]

OK, I can repro, and I have one simplification: in foo/__init__.py it is sufficient to write from derived import Derived -- there's no import * needed here to repro the crash. But the rest is all needed. I suspect it's one of the many cases where due to a previous error message something is not fully initialized.