feat: Pipeline.connect() will now raise a PipelineConnectError if…

… `sender` and `receiver` are the same Component (#8403)

* Added equality check for sender and receiver in connection function of pipeline

* Update base.py

irrelevant changes reverted

* added release note

* altered a walk with cycle test

* added a test to verify that pipeline raises PipelineConnectError when adding a component to itself

* Update release notes

* Remove self connection feature tests

* Tidy up connect unit test

---------

Co-authored-by: Silvano Cerza <[email protected]>

haystack/core/pipeline/base.py

@@ -454,8 +454,7 @@ def connect(self, sender: str, receiver: str) -> "PipelineBase":  # noqa: PLR091
         receiver_component_name, receiver_socket_name = parse_connect_string(receiver)
 
         if sender_component_name == receiver_component_name:
-            msg = "Connecting a Component to itself is deprecated and will raise an error from version '2.7.0' onwards."
-            warnings.warn(msg, DeprecationWarning)
+            raise PipelineConnectError("Connecting a Component to itself is not supported.")
 
         # Get the nodes data.
         try:

releasenotes/notes/remove-support-to-connect-component-to-self-6eedfb287f2a2a02.yaml

@@ -0,0 +1,5 @@
+---
+upgrade:
+  - |
+    `Pipeline.connect()` will now raise a `PipelineConnectError` if `sender` and `receiver` are the same Component.
+    We do not support this use case anymore.

test/core/pipeline/features/pipeline_run.feature

@@ -27,8 +27,6 @@ Feature: Pipeline running
         | that has components added in a different order from the order of execution |
         | that has a component with only default inputs |
         | that has a component with only default inputs as first to run |
-        | that has only a single component that sends one of its outputs to itself |
-        | that has a component that sends one of its outputs to itself |
         | that has multiple branches that merge into a component with a single variadic input |
         | that has multiple branches of different lengths that merge into a component with a single variadic input |
         | that is linear and returns intermediate outputs |

test/core/pipeline/features/test_run.py

@@ -911,58 +911,6 @@ def fake_generator_run(self, generation_kwargs: Optional[Dict[str, Any]] = None,
     )
 
 
-@given(
-    "a pipeline that has only a single component that sends one of its outputs to itself",
-    target_fixture="pipeline_data",
-)
-def pipeline_that_has_a_single_component_that_send_one_of_outputs_to_itself():
-    pipeline = Pipeline(max_runs_per_component=10)
-    pipeline.add_component("self_loop", SelfLoop())
-    pipeline.connect("self_loop.current_value", "self_loop.values")
-
-    return (
-        pipeline,
-        [
-            PipelineRunData(
-                inputs={"self_loop": {"values": 5}},
-                expected_outputs={"self_loop": {"final_result": 0}},
-                expected_run_order=["self_loop", "self_loop", "self_loop", "self_loop", "self_loop"],
-            )
-        ],
-    )
-
-
-@given("a pipeline that has a component that sends one of its outputs to itself", target_fixture="pipeline_data")
-def pipeline_that_has_a_component_that_sends_one_of_its_outputs_to_itself():
-    pipeline = Pipeline(max_runs_per_component=10)
-    pipeline.add_component("add_1", AddFixedValue())
-    pipeline.add_component("self_loop", SelfLoop())
-    pipeline.add_component("add_2", AddFixedValue())
-    pipeline.connect("add_1", "self_loop.values")
-    pipeline.connect("self_loop.current_value", "self_loop.values")
-    pipeline.connect("self_loop.final_result", "add_2.value")
-
-    return (
-        pipeline,
-        [
-            PipelineRunData(
-                inputs={"add_1": {"value": 5}},
-                expected_outputs={"add_2": {"result": 1}},
-                expected_run_order=[
-                    "add_1",
-                    "self_loop",
-                    "self_loop",
-                    "self_loop",
-                    "self_loop",
-                    "self_loop",
-                    "self_loop",
-                    "add_2",
-                ],
-            )
-        ],
-    )
-
-
 @given(
     "a pipeline that has multiple branches that merge into a component with a single variadic input",
     target_fixture="pipeline_data",

test/core/pipeline/test_pipeline.py

@@ -886,8 +886,8 @@ def run(self, word1: str, word2: str):
 
     def test_walk_pipeline_with_cycles(self):
         """
-        This pipeline consists of one component, which would run three times in a loop.
-        pipeline.walk() should return this component exactly once. The order is not guaranteed.
+        This pipeline consists of two components, which would run three times in a loop.
+        pipeline.walk() should return these components exactly once. The order is not guaranteed.
         """
 
         @component
@@ -907,9 +907,12 @@ def run(self, word: str, intermediate: Optional[str] = None):
 
         pipeline = Pipeline()
         hello = Hello()
+        hello_again = Hello()
         pipeline.add_component("hello", hello)
-        pipeline.connect("hello.intermediate", "hello.intermediate")
-        assert [("hello", hello)] == list(pipeline.walk())
+        pipeline.add_component("hello_again", hello_again)
+        pipeline.connect("hello.intermediate", "hello_again.intermediate")
+        pipeline.connect("hello_again.intermediate", "hello.intermediate")
+        assert {("hello", hello), ("hello_again", hello_again)} == set(pipeline.walk())
 
     def test__init_graph(self):
         pipe = Pipeline()
@@ -1185,6 +1188,17 @@ def test_connect_multiple_outputs_to_variadic_input(self):
         assert comp3.__haystack_input__.value.senders == ["comp1", "comp2"]
         assert list(pipe.graph.edges) == [("comp1", "comp3", "value/value"), ("comp2", "comp3", "value/value")]
 
+    def test_connect_same_component_as_sender_and_receiver(self):
+        """
+        This pipeline consists of one component, which would be connected to itself.
+        Connecting a component to itself is raises PipelineConnectError.
+        """
+        pipe = Pipeline()
+        single_component = FakeComponent()
+        pipe.add_component("single_component", single_component)
+        with pytest.raises(PipelineConnectError):
+            pipe.connect("single_component.out", "single_component.in")
+
     def test__run_component(self, spying_tracer, caplog):
         caplog.set_level(logging.INFO)
         sentence_builder = component_class(