Description
Ok -- this is a weird one, but I think I've got it down to the smallest possible repro.
I first noticed this issue with the aiohttp
library as of version 3.4.0
(when they introduced type-hinting), but I'm cross-posting this issue to both projects since the issue seems to run deeper than just a library issue. Importing the aiohttp
library, even if it is unused, causes the mypy
cache to occasionally get poisoned.
Here's the repro case:
import aiohttp
def trigger() -> dict:
return 'foo'
Running python -m mypy repro.py
against this file works as expected (eg. returns an incompatible return type error). Replacing the -> dict
with -> str
throws the following assertion (attached at bottom of report) on re-running the type check. Note that this holds true in the opposite direction -- if we begin with -> str
, the first typecheck is successful, but replacing -> str
with -> dict
causes the same assertion error. Either way, the situation can only be resolved by clearing the .mypy_cache
folder, at which point mypy
acts as expected once more.
Interestingly, removing the aiohttp
import prevents this poisoning from occurring. In addition, removing the import once the cache is poisoned also fixes the issue.
I speculate there are two issues here, one with aiohttp
and one with mypy
:
aiohttp
seems to have some weirdness going on in their type hinting- regardless of what a library does, the above repro case should not cause
mypy
issues when dealing only with stdlib types.
Error Trace:
Traceback (most recent call last):
File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 193, in _run_module_as_main
"__main__", mod_spec)
File "/usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/runpy.py", line 85, in _run_code
exec(code, run_globals)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/__main__.py", line 11, in <module>
main(None)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/main.py", line 91, in main
res = type_check_only(sources, bin_dir, options, flush_errors, fscache) # noqa
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/main.py", line 148, in type_check_only
fscache=fscache)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/build.py", line 177, in build
flush_errors, fscache)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/build.py", line 350, in _build
graph = dispatch(sources, manager)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/build.py", line 2560, in dispatch
process_graph(graph, manager)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/build.py", line 2846, in process_graph
process_fresh_modules(graph, prev_scc, manager)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/build.py", line 2932, in process_fresh_modules
graph[id].fix_cross_refs()
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/build.py", line 1975, in fix_cross_refs
self.options.use_fine_grained_cache)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/fixup.py", line 24, in fixup_module
node_fixer.visit_symbol_table(tree.names)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/fixup.py", line 89, in visit_symbol_table
value.node.accept(self)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/nodes.py", line 2539, in accept
return visitor.visit_type_alias(self)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/fixup.py", line 135, in visit_type_alias
a.target.accept(self.type_fixer)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/types.py", line 511, in accept
return visitor.visit_instance(self)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/fixup.py", line 149, in visit_instance
inst.type = lookup_qualified_typeinfo(self.modules, type_ref, self.quick_and_dirty)
File "/Users/kevin/coding/mypy-bug/venv/lib/python3.7/site-packages/mypy/fixup.py", line 239, in lookup_qualified_typeinfo
assert quick_and_dirty, "Should never get here in normal mode"
AssertionError: Should never get here in normal mode
Versions:
(venv) kevin@box ~/c/mypy-bug » python --version
Python 3.7.0
(venv) kevin@box ~/c/mypy-bug » python -m mypy --version
mypy 0.620
(venv) kevin@box ~/c/mypy-bug » python -m pip freeze | grep aiohttp
aiohttp==3.4.0