Change in behavior regarding __getattr__ and @no_type_check

[PhilReinhold]

Bug Report

In #6251 it was recommended to use @no_type_check on __getattr__ if you wanted errors to still be raised for missing attributes. However this appears to no longer work since v0.930

To Reproduce

# test.py
from typing import no_type_check

# Using no_type_check decorator on __getattr__
class Base:
    @no_type_check
    def __getattr__(self, name):
        pass

class Model(Base):
    age: int


m = Model()
reveal_type(m.foo)

# Without no_type_check decorator on __getattr__
class Base2:
    def __getattr__(self, name):
        pass

class Model2(Base2):
    age: int


m2 = Model2()
reveal_type(m2.foo)

Expected Behavior

Following the discussion on #6251, I expected that adding a @no_type_check decorator would restore errors on missing attributes. I see this behavior on several versions <= 0.921

When running mypy test.py on version 0.921 I get the expected output

test.py:13: error: "Model" has no attribute "foo"
test.py:13: note: Revealed type is "Any"
test.py:24: note: Revealed type is "Any"

Actual Behavior

When running on versions 0.930-0.971 I do not see the (expected) first error indicating the missing attribute,

test.py:13: note: Revealed type is "Any"
test.py:24: note: Revealed type is "Any"

Your Environment

• Mypy version used: Multiple, error appears on at least v0.930 v0.931 v0.941 v0.971 and not before
• Mypy command-line flags: None
• Mypy configuration options from mypy.ini (and other config files): None
• Python version used: 3.10.4
• Operating system and version: OSX 11.6.7

[hauntsaninja]

A workaround is to use:

if not TYPE_CHECKING:
    def __getattr__(self): ...

I'm not sure that no_type_check should work for this, let's see what others say. Would also be interesting to bisect and see what changed — will do this later with mypy_primer.

[JelleZijlstra]

I don't think @no_type_check should work for this use case. PEP 484 says a function with that decorator should be treated as having no annotations, not that a type checker should ignore its existence.

[hauntsaninja]

Okay yeah, I'm going to close this as won't fix then.

For the record, mypy_primer -p ~/dev/mypy_primer/nogetattr.py --bisect --new v0.930 --old v0.920 --debug bisects it to:

4e34fecfe59d83aa3b9e04cbde1834aff7a47e5d is the first bad commit
commit 4e34fecfe59d83aa3b9e04cbde1834aff7a47e5d
Author: Nikita Sobolev <mail@sobolevn.me>
Date:   Fri Dec 3 16:20:30 2021 +0300

    Now `TypeInfo.get_method` also returns `Decorator` nodes (#11150)
    
    Support decorators properly in additional contexts.
    
    Closes #10409

This makes sense, previously mypy struggled to understand decorators on __getattr__