Don't consider ``Union`` to always be a type alias (#8489)

Co-authored-by: Pierre Sassoulas <pierre.sassoulas@gmail.com>

1 files changed, 7 insertions, 1 deletions

diff --git a/pylint/checkers/base/name_checker/checker.py b/pylint/checkers/base/name_checker/checker.py
index 1341edc96..616067d1f 100644
--- a/pylint/checkers/base/name_checker/checker.py
+++ b/pylint/checkers/base/name_checker/checker.py
@@ -597,7 +597,13 @@ class NameChecker(_BasicChecker):
         inferred = utils.safe_infer(node)
         if isinstance(inferred, nodes.ClassDef):
             if inferred.qname() == ".Union":
-                return True
+                # Union is a special case because it can be used as a type alias
+                # or as a type annotation. We only want to check the former.
+                assert node is not None
+                return not (
+                    isinstance(node.parent, nodes.AnnAssign)
+                    and node.parent.value is not None
+                )
         elif isinstance(inferred, nodes.FunctionDef):
             if inferred.qname() == "typing.TypeAlias":
                 return True