fix: handle for-loop variable shadowing correctly (#10569)

Signed-off-by: Emmanuel Ferdman <emmanuelferdman@gmail.com>

Author: emmanuel-ferdman

doc/whatsnew/fragments/10562.bugfix

@@ -0,0 +1,3 @@
+Fix false positive ``undefined-variable`` (E0602) for for-loop variable shadowing patterns like ``for item in item:`` when the variable was previously defined.
+
+Closes #10562

pylint/checkers/variables.py

@@ -585,7 +585,12 @@ def get_next_to_consume(self, node: nodes.Name) -> list[nodes.NodeNG] | None:
             and parent_node.iter == node
             and parent_node.target in found_nodes
         ):
-            found_nodes = None
+            # Only filter out the for-loop target if there are other definitions besides the target
+            other_definitions = [fn for fn in found_nodes if fn != parent_node.target]
+            if other_definitions:
+                found_nodes = other_definitions
+            else:
+                found_nodes = None
 
         # Before filtering, check that this node's name is not a nonlocal
         if _is_nonlocal_name(node, node.frame()):

tests/functional/f/for_loop_variable_shadowing.py

@@ -0,0 +1,10 @@
+# pylint: disable=missing-module-docstring
+
+# Should not trigger undefined-variable (#10562)
+item = (1, 2, 3)
+for item in item:
+    print(item)
+
+# Should trigger undefined-variable
+for iteree in iteree:  # [undefined-variable]
+    print(iteree)

tests/functional/f/for_loop_variable_shadowing.txt

@@ -0,0 +1 @@
+undefined-variable:9:14:9:20::Undefined variable 'iteree':UNDEFINED