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Bug involving Python 2, incremental mode, partial cache invalidation, and possibly nested folders #1967
Description
I recently ran into a bug that manifests when running Python 2 with incremental mode. Here is the shortest repro I was able to create so far:
File structure
parent/
__init__.py
a.py
b.py
subfolder/
__init__.py
child_a/
__init__.py
c.py
child_b/
__init__.py
d.py
e.py
parent/a.py
import e
a_const = 0parent/b.py
b_const = 0parent/subfolder/child_a/__init__.py
from .c import c_constparent/subfolder/child_a/c.py
from parent.b import b_const
c_const = 0parent/subfolder/child_b/d.py
from parent.a import a_const
from ..child_a import ce.py
from types import FunctionTypeAll of the other __init__.py files are empty.
When you try running mypy in incremental mode with Python 2, you get a spurious error in the second run (note that I update the timestamp of parent/b.py to force mypy to recheck that file):
$ rm -rf .mypy_cache
$ python3 -m mypy --py2 --incremental parent
$ touch parent/b.py
$ python3 -m mypy --py2 --incremental parent
experiments/parent/subfolder/child_b/d.py:2: error: Module has no attribute 'c'
However, mypy works as expected when running in Python 3 mode. I'm not entirely sure why that is.
I'm planning on continuing to try and make a shorter/more enlightening repro, but I figured I should file an issue now to get this on the record.
Activity
[-]Bug involving Python 2, incremental mode, and possibly nested folders[/-][+]Bug involving Python 2, incremental mode, partial cache invalidation, and possibly nested folders[/+]gvanrossum commentedon Aug 1, 2016
gnprice commentedon Aug 4, 2016
Apparently this triggers frequently when using
--incrementalon some of our larger internal codebases at Dropbox.gvanrossum commentedon Oct 10, 2016
I cannot repro this any more. According to
git bisectit was fixed on August 18 by revision 95a0186, "Make incremental not propagate staleness if the public interface of a module is unchanged (v2) (#2014)". That's good enough for me!