CFn: validate Type is provided

simonrw · simonrw · commit b6af98b28d64 · 2025-12-22T17:09:01.000Z
# Motivation While discusing #13496 I asserted that we can safely access `resource["Type"]` in the visitors since we validate that the `Type` key is always present. However this _was not true_! This PR resolves this # Changes * Add test deploying resource without a `Type` key * Validate that the type is present during the modelling phase
diff --git a/localstack-core/localstack/services/cloudformation/engine/v2/change_set_model.py b/localstack-core/localstack/services/cloudformation/engine/v2/change_set_model.py
@@ -9,6 +9,7 @@
 from typing_extensions import TypeVar
 
 from localstack.aws.api.cloudformation import ChangeAction
+from localstack.services.cloudformation.engine.validations import ValidationError
 from localstack.services.cloudformation.resource_provider import ResourceProviderExecutor
 from localstack.services.cloudformation.v2.types import (
     EngineParameter,
@@ -1079,6 +1080,15 @@ def _visit_resource(
         scope_type, (before_type, after_type) = self._safe_access_in(
             scope, TypeKey, before_resource, after_resource
         )
+
+        # If both before and after types are Nothing then the user did
+        # not specify a value for the type of this resource, which is
+        # a hard error in cloudFormation.
+        if is_nothing(before_type) and is_nothing(after_type):
+            raise ValidationError(
+                f"Template format error: [{scope}] Every Resources object must contain a Type member."
+            )
+
         terminal_value_type = self._visit_type(
             scope=scope_type, before_type=before_type, after_type=after_type
         )
diff --git a/tests/aws/services/cloudformation/test_template_engine.py b/tests/aws/services/cloudformation/test_template_engine.py
@@ -1317,3 +1317,28 @@ def test_stack_id(self, deploy_cfn_template, snapshot):
         snapshot.add_transformer(snapshot.transform.regex(stack.stack_id, "<stack-id>"))
 
         snapshot.match("StackId", stack.outputs["StackId"])
+
+
+@markers.aws.validated
+def test_no_type(aws_client, snapshot):
+    template = {
+        "Resources": {
+            "Foo": {
+                "Properties": {
+                    "Name": "foo",
+                },
+            },
+        },
+    }
+
+    stack_name = f"stack-{short_uid()}"
+    change_set_name = f"cs-{short_uid()}"
+    with pytest.raises(ClientError) as e:
+        aws_client.cloudformation.create_change_set(
+            ChangeSetName=change_set_name,
+            StackName=stack_name,
+            TemplateBody=json.dumps(template),
+            ChangeSetType="CREATE",
+        )
+
+    snapshot.match("error", e.value)
diff --git a/tests/aws/services/cloudformation/test_template_engine.snapshot.json b/tests/aws/services/cloudformation/test_template_engine.snapshot.json
@@ -700,5 +700,11 @@
         "TopicName": "<parameter-value>"
       }
     }
+  },
+  "tests/aws/services/cloudformation/test_template_engine.py::test_no_type": {
+    "recorded-date": "15-12-2025, 10:55:28",
+    "recorded-content": {
+      "error": "An error occurred (ValidationError) when calling the CreateChangeSet operation: Template format error: [/Resources/Foo] Every Resources object must contain a Type member."
+    }
   }
 }
diff --git a/tests/aws/services/cloudformation/test_template_engine.validation.json b/tests/aws/services/cloudformation/test_template_engine.validation.json
@@ -151,5 +151,14 @@
       "teardown": 50.06,
       "total": 90.44
     }
+  },
+  "tests/aws/services/cloudformation/test_template_engine.py::test_no_type": {
+    "last_validated_date": "2025-12-15T10:55:28+00:00",
+    "durations_in_seconds": {
+      "setup": 0.75,
+      "call": 0.27,
+      "teardown": 0.0,
+      "total": 1.02
+    }
   }
 }

Original file line number	Diff line number	Diff line change
`@@ -700,5 +700,11 @@`
`700`	`700`	`"TopicName": "<parameter-value>"`
`701`	`701`	`}`
`702`	`702`	`}`
	`703`	`+ },`
	`704`	`+ "tests/aws/services/cloudformation/test_template_engine.py::test_no_type": {`
	`705`	`+ "recorded-date": "15-12-2025, 10:55:28",`
	`706`	`+ "recorded-content": {`
	`707`	`+ "error": "An error occurred (ValidationError) when calling the CreateChangeSet operation: Template format error: [/Resources/Foo] Every Resources object must contain a Type member."`
	`708`	`+ }`
`703`	`709`	`}`
`704`	`710`	`}`
Original file line number	Diff line number	Diff line change
`@@ -151,5 +151,14 @@`
`151`	`151`	`"teardown": 50.06,`
`152`	`152`	`"total": 90.44`
`153`	`153`	`}`
	`154`	`+ },`
	`155`	`+ "tests/aws/services/cloudformation/test_template_engine.py::test_no_type": {`
	`156`	`+ "last_validated_date": "2025-12-15T10:55:28+00:00",`
	`157`	`+ "durations_in_seconds": {`
	`158`	`+ "setup": 0.75,`
	`159`	`+ "call": 0.27,`
	`160`	`+ "teardown": 0.0,`
	`161`	`+ "total": 1.02`
	`162`	`+ }`
`154`	`163`	`}`
`155`	`164`	`}`