Type hints persist module usage between independent modules (unused-import)

[skeeto]

When a module is used in a type hint in a certain way it will count as using the module in all source files analyzed afterwards. This leads to a false negative for unused-import depending on the order that sources were scanned.

Steps to reproduce

Given two files, a.py:

"x"
import uuid
from typing import Optional
ID = None  # type: Optional[uuid.UUID]

And b.py:

"x"
import uuid

Current behavior

When analyzing a.py then b.py it misses the unused-import:

$ pylint a.py b.py

----------------------------------------------------------------------
Your code has been rated at 10.00/10

But swap the order and unused-import appears:

$ pylint b.py a.py
************* Module b
b.py:2:0: W0611: Unused import uuid (unused-import)

-----------------------------------
Your code has been rated at 7.50/10

Expected behavior

The outputs should be identical and both report unused-import.

pylint --version output

Result of pylint --version output:

pylint 2.7.1
astroid 2.5
Python 3.7.3 (default, Jul 25 2020, 13:03:44) 
[GCC 8.3.0]

[hippo91]

@skeeto thanks for the report.