localstack · MEPalma · Jun 2, 2025 · May 19, 2025 · May 20, 2025 · May 21, 2025
@@ -423,6 +423,7 @@ def __init__(self, scope: Scope, value: Any):
 FnFindInMapKey: Final[str] = "Fn::FindInMap"
 FnSubKey: Final[str] = "Fn::Sub"
 FnTransform: Final[str] = "Fn::Transform"
+FnSelect: Final[str] = "Fn::Select"
 INTRINSIC_FUNCTIONS: Final[set[str]] = {
     RefKey,
     FnIfKey,
@@ -433,6 +434,7 @@ def __init__(self, scope: Scope, value: Any):
     FnFindInMapKey,
     FnSubKey,
     FnTransform,
+    FnSelect,
 }
 
 

@@ -646,6 +646,35 @@ def _compute_join(args: list[Any]) -> str:
             after = _compute_join(arguments_after)
         return PreprocEntityDelta(before=before, after=after)
 
+    def visit_node_intrinsic_function_fn_select(
+        self, node_intrinsic_function: NodeIntrinsicFunction
+    ):
+        # TODO: add further support for schema validation
+        arguments_delta = self.visit(node_intrinsic_function.arguments)
+        arguments_before = arguments_delta.before
+        arguments_after = arguments_delta.after
+
+        def _compute_fn_select(args: list[Any]) -> Any:
+            values: list[Any] = args[1]
+            if not isinstance(values, list) or not values:
+                raise RuntimeError(f"Invalid arguments list value for Fn::Select: '{values}'")
+            values_len = len(values)
+            index: int = int(args[0])
+            if not isinstance(index, int) or index < 0 or index > values_len:
+                raise RuntimeError(f"Invalid or out of range index value for Fn::Select: '{index}'")
+            selection = values[index]
+            return selection
+
+        before = Nothing
+        if not is_nothing(arguments_before):
+            before = _compute_fn_select(arguments_before)
+
+        after = Nothing
+        if not is_nothing(arguments_after):
+            after = _compute_fn_select(arguments_after)
+
+        return PreprocEntityDelta(before=before, after=after)
+
     def visit_node_intrinsic_function_fn_find_in_map(
         self, node_intrinsic_function: NodeIntrinsicFunction
     ) -> PreprocEntityDelta:

@@ -118,6 +118,11 @@ def visit_node_intrinsic_function_fn_transform(
     ):
         self.visit_children(node_intrinsic_function)
 
+    def visit_node_intrinsic_function_fn_select(
+        self, node_intrinsic_function: NodeIntrinsicFunction
+    ):
+        self.visit_children(node_intrinsic_function)
+
     def visit_node_intrinsic_function_fn_sub(self, node_intrinsic_function: NodeIntrinsicFunction):
         self.visit_children(node_intrinsic_function)
 

@@ -427,7 +427,6 @@ def test_conditional_in_conditional(self, env, region, deploy_cfn_template, aws_
         else:
             assert stack.outputs["Result"] == "false"
 
-    @pytest.mark.skip(reason="CFNV2:Fn::Select")
     @markers.aws.validated
     def test_conditional_with_select(self, deploy_cfn_template, aws_client):
         stack = deploy_cfn_template(

@@ -1202,7 +1202,6 @@ class TestCfnLambdaDestinations:
 
     """
 
-    @pytest.mark.skip(reason="CFNV2:Fn::Select")
     @pytest.mark.parametrize(
         ["on_success", "on_failure"],
         [

@@ -46,6 +46,7 @@ def _is_executed():
     assert "hello from statemachine" in execution_desc["output"]
 
 
+@pytest.mark.skip(reason="CFNV2:Fn::Split")
 @markers.aws.validated
 def test_nested_statemachine_with_sync2(deploy_cfn_template, aws_client):
     stack = deploy_cfn_template(

@@ -0,0 +1,203 @@
+import pytest
+from localstack_snapshot.snapshots.transformer import RegexTransformer
+
+from localstack.services.cloudformation.v2.utils import is_v2_engine
+from localstack.testing.aws.util import is_aws_cloud
+from localstack.testing.pytest import markers
+from localstack.utils.strings import long_uid
+
+
+@pytest.mark.skipif(
+    condition=not is_v2_engine() and not is_aws_cloud(), reason="Requires the V2 engine"
+)
+@markers.snapshot.skip_snapshot_verify(
+    paths=[
+        "per-resource-events..*",
+        "delete-describe..*",
+        #
+        # Before/After Context
+        "$..Capabilities",
+        "$..NotificationARNs",
+        "$..IncludeNestedStacks",
+        "$..Scope",
+        "$..Details",
+        "$..Parameters",
+        "$..Replacement",
+        "$..PolicyAction",
+    ]
+)
+class TestChangeSetFnSelect:
+    @markers.aws.validated
+    def test_fn_select_add_to_static_property(
+        self,
+        snapshot,
+        capture_update_process,
+    ):
+        name1 = f"topic-name-1-{long_uid()}"
+        snapshot.add_transformer(RegexTransformer(name1, "topic-name-1"))
+        template_1 = {
+            "Resources": {
+                "Topic1": {"Type": "AWS::SNS::Topic", "Properties": {"DisplayName": name1}}
+            }
+        }
+        template_2 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [1, ["1st", "2nd", "3rd"]]}},
+                }
+            }
+        }
+        capture_update_process(snapshot, template_1, template_2)
+
+    @markers.aws.validated
+    def test_fn_select_remove_from_static_property(
+        self,
+        snapshot,
+        capture_update_process,
+    ):
+        name1 = f"topic-name-1-{long_uid()}"
+        snapshot.add_transformer(RegexTransformer(name1, "topic-name-1"))
+        template_1 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [1, ["1st", "2nd", "3rd"]]}},
+                }
+            }
+        }
+        template_2 = {
+            "Resources": {
+                "Topic1": {"Type": "AWS::SNS::Topic", "Properties": {"DisplayName": name1}}
+            }
+        }
+        capture_update_process(snapshot, template_1, template_2)
+
+    @markers.aws.validated
+    def test_fn_select_change_in_selection_list(
+        self,
+        snapshot,
+        capture_update_process,
+    ):
+        name1 = f"topic-name-1-{long_uid()}"
+        snapshot.add_transformer(RegexTransformer(name1, "topic-name-1"))
+        template_1 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [1, ["1st", "2nd"]]}},
+                }
+            }
+        }
+        template_2 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [1, ["1st", "new-2nd", "3rd"]]}},
+                }
+            }
+        }
+        capture_update_process(snapshot, template_1, template_2)
+
+    @markers.aws.validated
+    def test_fn_select_change_in_selection_index_only(
+        self,
+        snapshot,
+        capture_update_process,
+    ):
+        name1 = f"topic-name-1-{long_uid()}"
+        snapshot.add_transformer(RegexTransformer(name1, "topic-name-1"))
+        template_1 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [1, ["1st", "2nd"]]}},
+                }
+            }
+        }
+        template_2 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [0, ["1st", "2nd"]]}},
+                }
+            }
+        }
+        capture_update_process(snapshot, template_1, template_2)
+
+    @markers.aws.validated
+    def test_fn_select_change_in_selected_element_type_ref(
+        self,
+        snapshot,
+        capture_update_process,
+    ):
+        name1 = f"topic-name-1-{long_uid()}"
+        snapshot.add_transformer(RegexTransformer(name1, "topic-name-1"))
+        template_1 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [0, ["1st"]]}},
+                }
+            }
+        }
+        template_2 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": {"Fn::Select": [0, [{"Ref": "AWS::StackName"}]]}},
+                }
+            }
+        }
+        capture_update_process(snapshot, template_1, template_2)
+
+    @markers.snapshot.skip_snapshot_verify(
+        paths=[
+            # Reason: AWS incorrectly does not list the second and third topic as
+            # needing modifying, however it needs to
+            "describe-change-set-2-prop-values..Changes",
+        ]
+    )
+    @markers.aws.validated
+    def test_fn_select_change_get_att_reference(
+        self,
+        snapshot,
+        capture_update_process,
+    ):
+        name1 = f"topic-name-1-{long_uid()}"
+        name2 = f"topic-name-2-{long_uid()}"
+        snapshot.add_transformer(RegexTransformer(name1, "topic-name-1"))
+        snapshot.add_transformer(RegexTransformer(name2, "topic-name-2"))
+        template_1 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": name1},
+                },
+                "Topic2": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {
+                        "DisplayName": {
+                            "Fn::Select": [0, [{"Fn::GetAtt": ["Topic1", "DisplayName"]}]]
+                        }
+                    },
+                },
+            }
+        }
+        template_2 = {
+            "Resources": {
+                "Topic1": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {"DisplayName": name2},
+                },
+                "Topic2": {
+                    "Type": "AWS::SNS::Topic",
+                    "Properties": {
+                        "DisplayName": {
+                            "Fn::Select": [0, [{"Fn::GetAtt": ["Topic1", "DisplayName"]}]]
+                        }
+                    },
+                },
+            }
+        }
+        capture_update_process(snapshot, template_1, template_2)
-Original file line number
+Diff line change
@@ Expand Up / @@ -1202,7 +1202,6 @@ class TestCfnLambdaDestinations: @@
         """
-        @pytest.mark.skip(reason="CFNV2:Fn::Select")
         @pytest.mark.parametrize(
             ["on_success", "on_failure"],
             [
@@ Expand Down @@