mypyc assertion error when generating `__ne__` from inherited `__eq__` in package import cycle

[rheard]

Bug Report

mypyc can fail with an internal AssertionError when it tries to generate __ne__ from an inherited __eq__.

This happens when the inherited method's declaration is available before its FuncIR body has been generated. One way to trigger this is with a package import cycle where __init__.py imports a child module before importing the subpackage that defines the base class.

To Reproduce

Add this test case to mypyc/test-data/run-multimodule.test:

[case testPackageCycleInheritedEq]
from other.other_child import Child

def make_child() -> Child:
    return Child()

[file other/__init__.py]
from other.other_child import Child as Child
from other.other_subpkg import Base as Base

[file other/other_child.py]
from other.other_subpkg import Base

class Child(Base):
    pass

[file other/other_subpkg/__init__.py]
from other.other_subpkg.other_base import Base as Base

[file other/other_subpkg/other_base.py]
class Base:
    def __eq__(self, other: object) -> bool:
        return True

[file driver.py]
from native import make_child
left = make_child()
right = make_child()
assert left == right
assert not (left != right)

Run:

python -m pytest -q mypyc/test/test_run.py -k testPackageCycleInheritedEq

Expected Behavior

mypyc should compile this successfully.

Since Child inherits Base.__eq__ but does not define __ne__, mypyc should be able to synthesize Child.__ne__ from the inherited __eq__ declaration.

Actual Behavior

mypyc fails with an internal assertion error while generating __ne__:

mypyc/irbuild/classdef.py:...: in gen_glue_ne_method
    assert func_ir
AssertionError

[rheard]

Cause

create_ne_from_eq() checks whether the class has an __eq__ method using cls.has_method("__eq__"), but gen_glue_ne_method() then requires cls.get_method("__eq__") to return a concrete FuncIR.

In this package-cycle case, the inherited method declaration exists, but the concrete FuncIR body is not available yet. This makes cls.has_method("__eq__") true while cls.get_method("__eq__") returns None.