Fix undefined-loop-variable from walrus in comprehension test

doc/whatsnew/fragments/7222.bugfix

@@ -0,0 +1,3 @@
+Fix `undefined-loop-variable` from walrus in comprehension test.
+
+Closes #7222

pylint/checkers/variables.py

@@ -2249,6 +2249,24 @@ def _loopvar_name(self, node: astroid.Name) -> None:
         ):
             return
 
+        maybe_walrus = utils.get_node_first_ancestor_of_type(node, nodes.NamedExpr)
+        if maybe_walrus:
+            maybe_comprehension = utils.get_node_first_ancestor_of_type(
+                maybe_walrus, nodes.Comprehension
+            )
+            if maybe_comprehension:
+                comprehension_scope = utils.get_node_first_ancestor_of_type(
+                    maybe_comprehension, nodes.ComprehensionScope
+                )
+                if comprehension_scope is None:
+                    # Should not be possible.
+                    pass
+                elif (
+                    comprehension_scope.parent.scope() is scope
+                    and node.name in comprehension_scope.locals
+                ):
+                    return
+
         # For functions we can do more by inferring the length of the itered object
         try:
             inferred = next(assign.iter.infer())

tests/functional/u/undefined/undefined_loop_variable_py38.py

@@ -0,0 +1,8 @@
+"""Tests for undefined-loop-variable with assignment expressions"""
+
+
+def walrus_in_comprehension_test(container):
+    """https://github.com/PyCQA/pylint/issues/7222"""
+    for something in container:
+        print(something)
+    print([my_test for something in container if (my_test := something)])

tests/functional/u/undefined/undefined_loop_variable_py38.rc

@@ -0,0 +1,2 @@
+[testoptions]
+min_pyver=3.8