Fix use-sequence-for-iteration when unpacking a set with * (#7975)

doc/whatsnew/fragments/5788.false_positive

@@ -0,0 +1,3 @@
+Fix ``use-sequence-for-iteration`` when unpacking a set with ``*``.
+
+Closes #5788

pylint/checkers/refactoring/recommendation_checker.py

@@ -9,6 +9,7 @@
 
 from pylint import checkers
 from pylint.checkers import utils
+from pylint.interfaces import HIGH
 
 
 class RecommendationChecker(checkers.BaseChecker):
@@ -326,9 +327,16 @@ def _check_consider_using_dict_items_comprehension(
     def _check_use_sequence_for_iteration(
         self, node: nodes.For | nodes.Comprehension
     ) -> None:
-        """Check if code iterates over an in-place defined set."""
-        if isinstance(node.iter, nodes.Set):
-            self.add_message("use-sequence-for-iteration", node=node.iter)
+        """Check if code iterates over an in-place defined set.
+
+        Sets using `*` are not considered in-place.
+        """
+        if isinstance(node.iter, nodes.Set) and not any(
+            utils.has_starred_node_recursive(node)
+        ):
+            self.add_message(
+                "use-sequence-for-iteration", node=node.iter, confidence=HIGH
+            )
 
     @utils.only_required_for_messages("consider-using-f-string")
     def visit_const(self, node: nodes.Const) -> None:

pylint/checkers/utils.py

@@ -1961,6 +1961,20 @@ def find_assigned_names_recursive(
             yield from find_assigned_names_recursive(elt)
 
 
+def has_starred_node_recursive(
+    node: nodes.For | nodes.Comprehension | nodes.Set,
+) -> Iterator[bool]:
+    """Yield ``True`` if a Starred node is found recursively."""
+    if isinstance(node, nodes.Starred):
+        yield True
+    elif isinstance(node, nodes.Set):
+        for elt in node.elts:
+            yield from has_starred_node_recursive(elt)
+    elif isinstance(node, (nodes.For, nodes.Comprehension)):
+        for elt in node.iter.elts:
+            yield from has_starred_node_recursive(elt)
+
+
 def is_hashable(node: nodes.NodeNG) -> bool:
     """Return whether any inferred value of `node` is hashable.
 

tests/functional/ext/code_style/cs_consider_using_tuple.py

@@ -28,4 +28,4 @@
 
 # Don't emit warning for sets as this is handled by builtin checker
 (x for x in {1, 2, 3})  # [use-sequence-for-iteration]
-[x for x in {*var, 2}]  # [use-sequence-for-iteration]
+[x for x in {*var, 2}]

tests/functional/ext/code_style/cs_consider_using_tuple.txt

@@ -4,5 +4,4 @@ consider-using-tuple:18:12:18:21::Consider using an in-place tuple instead of li
 consider-using-tuple:21:9:21:15::Consider using an in-place tuple instead of list:UNDEFINED
 consider-using-tuple:23:9:23:18::Consider using an in-place tuple instead of list:UNDEFINED
 consider-using-tuple:26:12:26:21::Consider using an in-place tuple instead of list:UNDEFINED
-use-sequence-for-iteration:30:12:30:21::Use a sequence type when iterating over values:UNDEFINED
-use-sequence-for-iteration:31:12:31:21::Use a sequence type when iterating over values:UNDEFINED
+use-sequence-for-iteration:30:12:30:21::Use a sequence type when iterating over values:HIGH

tests/functional/u/use/use_sequence_for_iteration.py

@@ -13,4 +13,16 @@
 [x for x in var]
 [x for x in {1, 2, 3}]  # [use-sequence-for-iteration]
 
-[x for x in {*var, 4}]  # [use-sequence-for-iteration]
+[x for x in {*var, 4}]
+
+def deduplicate(list_in):
+    for thing in {*list_in}:
+        print(thing)
+
+def deduplicate_two_lists(input1, input2):
+    for thing in {*input1, *input2}:
+        print(thing)
+
+def deduplicate_nested_sets(input1, input2, input3, input4):
+    for thing in {{*input1, *input2}, {*input3, *input4}}:
+        print(thing)

tests/functional/u/use/use_sequence_for_iteration.txt

@@ -1,4 +1,3 @@
-use-sequence-for-iteration:7:9:7:18::Use a sequence type when iterating over values:UNDEFINED
-use-sequence-for-iteration:11:12:11:21::Use a sequence type when iterating over values:UNDEFINED
-use-sequence-for-iteration:14:12:14:21::Use a sequence type when iterating over values:UNDEFINED
-use-sequence-for-iteration:16:12:16:21::Use a sequence type when iterating over values:UNDEFINED
+use-sequence-for-iteration:7:9:7:18::Use a sequence type when iterating over values:HIGH
+use-sequence-for-iteration:11:12:11:21::Use a sequence type when iterating over values:HIGH
+use-sequence-for-iteration:14:12:14:21::Use a sequence type when iterating over values:HIGH