Fix false positive for ``undefined-variable`` when using class attribute in decorator (#511)

4 files changed, 53 insertions, 12 deletions

diff --git a/CONTRIBUTORS.txt b/CONTRIBUTORS.txt
index cd15199a8..420c62417 100644
--- a/CONTRIBUTORS.txt
+++ b/CONTRIBUTORS.txt
@@ -379,3 +379,5 @@ contributors:
 * Matthew Beckers (mattlbeck): contributor
 
 * Yang Yang: contributor
+
+* Andrew J. Simmons (anjsimmo): contributor
diff --git a/ChangeLog b/ChangeLog
index b794688b5..5f2306f94 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,10 @@ What's New in Pylint 2.5.0?
 
 Release date: TBA
 
+* Fix a false positive for ``undefined-variable`` when using class attribute in decorator
+
+  Close #511
+
 * Remove HTML quoting of messages in JSON output.
 
   Close #2769
diff --git a/pylint/checkers/variables.py b/pylint/checkers/variables.py
index e93e1b3d0..ac1d176ee 100644
--- a/pylint/checkers/variables.py
+++ b/pylint/checkers/variables.py
@@ -1249,16 +1249,20 @@ class VariablesChecker(BaseChecker):
 
     @staticmethod
     def _defined_in_function_definition(node, frame):
-        in_annotation_or_default = False
+        in_annotation_or_default_or_decorator = False
         if isinstance(frame, astroid.FunctionDef) and node.statement() is frame:
-            in_annotation_or_default = (
-                node in frame.args.annotations
-                or node in frame.args.posonlyargs_annotations
-                or node in frame.args.kwonlyargs_annotations
-                or node is frame.args.varargannotation
-                or node is frame.args.kwargannotation
-            ) or frame.args.parent_of(node)
-        return in_annotation_or_default
+            in_annotation_or_default_or_decorator = (
+                (
+                    node in frame.args.annotations
+                    or node in frame.args.posonlyargs_annotations
+                    or node in frame.args.kwonlyargs_annotations
+                    or node is frame.args.varargannotation
+                    or node is frame.args.kwargannotation
+                )
+                or frame.args.parent_of(node)
+                or (frame.decorators and frame.decorators.parent_of(node))
+            )
+        return in_annotation_or_default_or_decorator
 
     @staticmethod
     def _is_variable_violation(
@@ -1419,13 +1423,18 @@ class VariablesChecker(BaseChecker):
 
         name = node.name
         frame = node.statement().scope()
-        in_annotation_or_default = self._defined_in_function_definition(node, frame)
-        if in_annotation_or_default:
+        in_annotation_or_default_or_decorator = self._defined_in_function_definition(
+            node, frame
+        )
+        if in_annotation_or_default_or_decorator:
             frame_locals = frame.parent.scope().locals
         else:
             frame_locals = frame.locals
         return not (
-            (isinstance(frame, astroid.ClassDef) or in_annotation_or_default)
+            (
+                isinstance(frame, astroid.ClassDef)
+                or in_annotation_or_default_or_decorator
+            )
             and name in frame_locals
         )
 
diff --git a/tests/unittest_checker_variables.py b/tests/unittest_checker_variables.py
index b594e7d18..f33dbf8af 100644
--- a/tests/unittest_checker_variables.py
+++ b/tests/unittest_checker_variables.py
@@ -119,6 +119,32 @@ class TestVariablesChecker(CheckerTestCase):
         with self.assertAddsMessages(msg):
             self.checker.visit_global(node)
 
+    def test_listcomp_in_decorator(self):
+        """ Make sure class attributes in scope for listcomp in decorator.
+
+        https://github.com/PyCQA/pylint/issues/511
+        """
+        module = astroid.parse(
+            """
+        def dec(inp):
+            def inner(func):
+                print(inp)
+                return func
+            return inner
+
+
+        class Cls:
+
+            DATA = "foo"
+
+            @dec([x for x in DATA])
+            def fun(self):
+                pass
+        """
+        )
+        with self.assertNoMessages():
+            self.walk(module)
+
 
 class TestVariablesCheckerWithTearDown(CheckerTestCase):