Skip backwards compatibility on internal data (specifically internal clusters) (#34543)

* Skip backwards compatibility on internal bits

* Added unit test

---------

Co-authored-by: Andrei Litvin <andreilitvin@google.com>

Author: andy31415

scripts/py_matter_idl/matter_idl/backwards_compatibility.py

@@ -54,9 +54,9 @@ def attribute_name(attribute: Attribute) -> str:
 
 def not_stable(maturity: ApiMaturity):
     """Determine if the given api maturity allows binary/api changes or not."""
-    # TODO: internal and deprecated not currently widely used,
-    #       so we enforce stability on them for now.
-    return maturity == ApiMaturity.PROVISIONAL
+    # NOTE: deprecated are not to be used, so we expect no changes. They were
+    #       probably "stable" at some point
+    return (maturity == ApiMaturity.PROVISIONAL) or (maturity == ApiMaturity.INTERNAL)
 
 
 class CompatibilityChecker:

scripts/py_matter_idl/matter_idl/test_backwards_compatibility.py

@@ -188,6 +188,13 @@ def test_provisional_cluster(self):
             "provisional server cluster A = 16 { enum X : ENUM8 { A = 1; B = 3; } info event A = 2 { int16u x = 1;} }",
             Compatibility.ALL_OK)
 
+    def test_internal_cluster(self):
+        self.ValidateUpdate(
+            "Internal cluster changes are ok.",
+            "internal server cluster A = 16 { enum X : ENUM8 { A = 1; B = 2; } info event A = 1 { int8u x = 1;} }",
+            "internal server cluster A = 16 { enum X : ENUM8 { A = 1; B = 3; } info event A = 2 { int16u x = 1;} }",
+            Compatibility.ALL_OK)
+
     def test_clusters_enum_code(self):
         self.ValidateUpdate(
             "Adding an enum is ok. Also validates code formatting",