VariableChecker now accounts for attribute lookups in type comments

Prior to this commit VariableChecker did not recurse into attribute lookups
in type comments. This lead to false positive unused-import messages in e.g.

    import collections
    d = ...  # type: collections.OrderedDict

Fixes pylint-dev#4603.

CONTRIBUTORS.txt

@@ -503,3 +503,5 @@ contributors:
 * Markus Siebenhaar: contributor
 
 * Lorena Buciu (lorena-b): contributor
+
+* Sergei Lebedev (superbobry): contributor

ChangeLog

@@ -171,6 +171,11 @@ Closes #4555
 
   Closes #4023
 
+* Fix ``unused-import`` false positive for imported modules referenced in
+  attribute lookups in type comments.
+
+  Closes #4603
+
 
 What's New in Pylint 2.8.3?
 ===========================

pylint/checkers/variables.py

@@ -1826,6 +1826,10 @@ def _store_type_annotation_node(self, type_annotation):
             self._type_annotation_names.append(type_annotation.name)
             return
 
+        if isinstance(type_annotation, astroid.Attribute):
+            self._store_type_annotation_node(type_annotation.expr)
+            return
+
         if not isinstance(type_annotation, astroid.Subscript):
             return
 

pylint/constants.py

@@ -1,6 +1,7 @@
 # Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
 # For details: https://github.com/PyCQA/pylint/blob/master/LICENSE
 
+import platform
 import sys
 
 import astroid
@@ -11,6 +12,7 @@
 PY39_PLUS = sys.version_info[:2] >= (3, 9)
 PY310_PLUS = sys.version_info[:2] >= (3, 10)
 
+IS_PYPY = platform.python_implementation() == "PyPy"
 
 PY_EXTS = (".py", ".pyc", ".pyo", ".pyw", ".so", ".dll")
 

tests/checkers/unittest_variables.py

@@ -21,11 +21,14 @@
 import os
 import re
 import sys
+import unittest
+import platform
 from pathlib import Path
 
 import astroid
 
 from pylint.checkers import variables
+from pylint.constants import IS_PYPY
 from pylint.interfaces import UNDEFINED
 from pylint.testutils import CheckerTestCase, Message, linter, set_config
 
@@ -191,6 +194,23 @@ def my_method(self) -> MyType:
         with self.assertNoMessages():
             self.walk(module)
 
+    @unittest.skipIf(IS_PYPY, "PyPy does not parse type comments")
+    def test_attribute_in_type_comment(self):
+        """Ensure attribute lookups in type comments are accounted for.
+
+        https://github.com/PyCQA/pylint/issues/4603
+        """
+        module = astroid.parse(
+            """
+        import foo
+        from foo import Bar, Boo
+        a = ... # type: foo.Bar
+        b = ... # type: foo.Bar[Boo]
+        c = ... # type: Bar.Boo
+        """)
+        with self.assertNoMessages():
+            self.walk(module)
+
 
 class TestVariablesCheckerWithTearDown(CheckerTestCase):