Crash with alembic 1.7.0

[nicoddemus]

Crash Report

Running mypy in a simple file which uses type annotations from alembic 1.7.0 gives a crash. Works fine with `1.6.5 .

Traceback

Traceback (most recent call last):
  File "C:\Python39\lib\runpy.py", line 197, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "C:\Python39\lib\runpy.py", line 87, in _run_code
    exec(code, run_globals)
  File "E:\projects\temp\.env39-alembic-mypy\Scripts\mypy.exe\__main__.py", line 7, in <module>
  File "e:\projects\temp\.env39-alembic-mypy\lib\site-packages\mypy\__main__.py", line 11, in console_entry
    main(None, sys.stdout, sys.stderr)
  File "mypy\main.py", line 87, in main
  File "mypy\main.py", line 165, in run_build
  File "mypy\build.py", line 179, in build
  File "mypy\build.py", line 254, in _build
  File "mypy\build.py", line 2697, in dispatch
  File "mypy\build.py", line 3021, in process_graph
  File "mypy\build.py", line 3138, in process_stale_scc
  File "mypy\build.py", line 2288, in write_cache
  File "mypy\build.py", line 1475, in write_cache
  File "mypy\nodes.py", line 313, in serialize
  File "mypy\nodes.py", line 3149, in serialize
  File "mypy\nodes.py", line 3083, in serialize
AssertionError: Definition of alembic.runtime.migration.EnvironmentContext is unexpectedly incomplete

To Reproduce

File:

from alembic.operations import Operations

def update(op: Operations) -> None:
    ...

Command-line:

λ mypy foo.py --no-implicit-reexport --show-traceback --ignore-missing-imports

Relevant information:

• Crash only happens with alembic 1.7.0, works fine with 1.6.5.

Your Environment

λ pip list
Package           Version
----------------- --------
alembic           1.7.0
greenlet          1.1.1
Mako              1.1.5
MarkupSafe        2.0.1
mypy              0.910
mypy-extensions   0.4.3
pip               21.1.2
setuptools        57.4.0
SQLAlchemy        1.4.23
toml              0.10.2
typing-extensions 3.10.0.2
wheel             0.36.2

OS: Windows 10
Python: 3.9.6

---

I was wondering if I should report this in alembic's repository, but given this generates an internal error I figured I should post here first.

[elpablete]

Having the same issue on my code, I really don't understand where and why, can someone shed some light?

[elpablete]

mentioned in alembics repo: sqlalchemy/alembic#897

[CaselIT]

I've tried to debug this a bit on alembic side: sqlalchemy/alembic#897 (comment)

It seems a circular import issue. If I comment some of the import that are guarded by TYPE_CHECKING the crash disappears. This is of course not feasible, since it defeats the purpose of TYPE_CHECKING

[Morikko]

It looks like this could be closed as sqlalchemy/alembic#897 is closed and I confirm that with an upgrade to alembic==1.7.4 the crash disappeared.

[CaselIT]

Well the fix in alembic was a workaround for this issue of mypy.

The issue seems a circular import or something related to the import resolution, since the error was triggered by an import of a class from a module that re-exported it instead of the module defining it.

It may be worth looking into it from the mypy side, but I have no idea of how common this may be, so maybe it's not worth the effort, especially if there is a reliable way of fixing the issue