Validate circular reference for yaml

sdks/python/apache_beam/yaml/yaml_transform.py

@@ -955,6 +955,21 @@ def preprocess_languages(spec):
     else:
       return spec
 
+  def validate_transform_references(spec):
+    name = spec.get('name', '')
+    transform_type = spec.get('type')
+    inputs = spec.get('input').get('input', [])
+
+    if not is_empty(inputs):
+      input_values = [inputs] if isinstance(inputs, str) else inputs
+      for input_value in input_values:
+        if input_value in (name, transform_type):
+          raise ValueError(
+              f"Circular reference detected: Transform {name} "
+              f"references itself as input in {identify_object(spec)}")
+
+    return spec
+
   for phase in [
       ensure_transforms_have_types,
       normalize_mapping,
@@ -965,6 +980,7 @@ def preprocess_languages(spec):
       preprocess_chain,
       tag_explicit_inputs,
       normalize_inputs_outputs,
+      validate_transform_references,
       preprocess_flattened_inputs,
       ensure_errors_consumed,
       preprocess_windowing,

sdks/python/apache_beam/yaml/yaml_transform_test.py

@@ -259,6 +259,51 @@ def test_csv_to_json(self):
           lines=True).sort_values('rank').reindex()
       pd.testing.assert_frame_equal(data, result)
 
+  def test_circular_reference_validation(self):
+    with beam.Pipeline(options=beam.options.pipeline_options.PipelineOptions(
+        pickle_library='cloudpickle')) as p:
+      # pylint: disable=expression-not-assigned
+      with self.assertRaisesRegex(ValueError, r'Circular reference detected.*'):
+        p | YamlTransform(
+            '''
+                type: composite
+                transforms:
+                  - type: Create
+                    name: Create
+                    config:
+                        elements: [0, 1, 3, 4]
+                    input: Create
+                  - type: PyMap
+                    name: PyMap
+                    config:
+                        fn: "lambda row: row.element * row.element"
+                    input: Create
+                output: PyMap
+                ''',
+            providers=TEST_PROVIDERS)
+
+  def test_circular_reference_multi_inputs_validation(self):
+    with beam.Pipeline(options=beam.options.pipeline_options.PipelineOptions(
+        pickle_library='cloudpickle')) as p:
+      # pylint: disable=expression-not-assigned
+      with self.assertRaisesRegex(ValueError, r'Circular reference detected.*'):
+        p | YamlTransform(
+            '''
+                  type: composite
+                  transforms:
+                    - type: Create
+                      name: Create
+                      config:
+                        elements: [0, 1, 3, 4]
+                    - type: PyMap
+                      name: PyMap
+                      config:
+                        fn: "lambda row: row.element * row.element"
+                      input: [Create, PyMap]
+                  output: PyMap
+                ''',
+            providers=TEST_PROVIDERS)
+
   def test_name_is_not_ambiguous(self):
     with beam.Pipeline(options=beam.options.pipeline_options.PipelineOptions(
         pickle_library='cloudpickle')) as p:
@@ -285,7 +330,7 @@ def test_name_is_ambiguous(self):
     with beam.Pipeline(options=beam.options.pipeline_options.PipelineOptions(
         pickle_library='cloudpickle')) as p:
       # pylint: disable=expression-not-assigned
-      with self.assertRaisesRegex(ValueError, r'Ambiguous.*'):
+      with self.assertRaisesRegex(ValueError, r'Circular reference detected.*'):
         p | YamlTransform(
             '''
             type: composite