fix: add recursion guard to StreamSlicerMeta.__instancecheck__

airbyte_cdk/sources/streams/concurrent/partitions/stream_slicer.py

@@ -1,5 +1,6 @@
 # Copyright (c) 2024 Airbyte, Inc., all rights reserved.
 
+import threading
 from abc import ABC, ABCMeta, abstractmethod
 from typing import Any, Iterable
 
@@ -16,12 +17,28 @@ class StreamSlicerMeta(ABCMeta):
         isinstance(declarative_stream.retriever.stream_slicer,(GlobalSubstreamCursor, PerPartitionWithGlobalCursor))
     """
 
-    def __instancecheck__(cls, instance: Any) -> bool:
-        # Check if it's our wrapper with matching wrapped class
-        if hasattr(instance, "wrapped_slicer"):
-            return isinstance(instance.wrapped_slicer, cls)
+    _checking: threading.local = threading.local()
 
-        return super().__instancecheck__(instance)
+    def __instancecheck__(cls, instance: Any) -> bool:
+        if not hasattr(cls._checking, "in_progress"):
+            cls._checking.in_progress = set()
+
+        instance_id = id(instance)
+        if instance_id in cls._checking.in_progress:
+            return super().__instancecheck__(instance)
+
+        # Use object.__getattribute__ to bypass any custom __getattr__ that
+        # could trigger further isinstance() calls and cause recursion.
+        try:
+            wrapped = object.__getattribute__(instance, "wrapped_slicer")
+        except AttributeError:
+            return super().__instancecheck__(instance)
+
+        cls._checking.in_progress.add(instance_id)
+        try:
+            return isinstance(wrapped, cls)
+        finally:
+            cls._checking.in_progress.discard(instance_id)
 
 
 class StreamSlicer(ABC, metaclass=StreamSlicerMeta):

unit_tests/sources/declarative/stream_slicers/test_stream_slicer_read_decorator.py

@@ -2,6 +2,7 @@
 # Copyright (c) 2025 Airbyte, Inc., all rights reserved.
 #
 from datetime import timedelta
+from typing import Any, Iterable
 from unittest.mock import Mock
 
 import pytest
@@ -251,3 +252,51 @@ def test_slice_limiting_functionality():
     slices = list(wrapped_slicer.stream_slices())
     assert len(slices) == 3
     assert slices == mock_slicer.stream_slices.return_value[:3]
+
+
+def test_no_recursion_error_with_wrapped_slicer_attribute_on_non_decorator():
+    """Verify that isinstance does not cause RecursionError on objects with a wrapped_slicer attribute and custom __getattr__."""
+
+    class SlicerWithGetattr(StreamSlicer):
+        def __init__(self, inner: StreamSlicer) -> None:
+            self.wrapped_slicer = inner
+
+        def stream_slices(self) -> Iterable[StreamSlice]:
+            return self.wrapped_slicer.stream_slices()
+
+        def __getattr__(self, name: str) -> Any:
+            return getattr(self.wrapped_slicer, name)
+
+    inner = SinglePartitionRouter(parameters={})
+    outer = SlicerWithGetattr(inner)
+
+    # This would raise RecursionError before the fix
+    assert isinstance(outer, StreamSlicer)
+    assert isinstance(outer, SlicerWithGetattr)
+    assert not isinstance(outer, SubstreamPartitionRouter)
+
+
+def test_no_recursion_error_with_nested_decorators():
+    """Verify that double-wrapping a slicer does not cause RecursionError."""
+    inner = SinglePartitionRouter(parameters={})
+    first_wrap = StreamSlicerTestReadDecorator(wrapped_slicer=inner, maximum_number_of_slices=5)
+    second_wrap = StreamSlicerTestReadDecorator(
+        wrapped_slicer=first_wrap, maximum_number_of_slices=3
+    )
+
+    assert isinstance(second_wrap, SinglePartitionRouter)
+    assert isinstance(second_wrap, StreamSlicerTestReadDecorator)
+    assert isinstance(first_wrap, SinglePartitionRouter)
+    assert not isinstance(second_wrap, SubstreamPartitionRouter)
+
+
+def test_no_recursion_error_with_self_referencing_wrapped_slicer():
+    """Verify that a circular wrapped_slicer reference does not cause RecursionError."""
+    mock_slicer = Mock(spec=StreamSlicer)
+    wrapped = StreamSlicerTestReadDecorator(wrapped_slicer=mock_slicer, maximum_number_of_slices=5)
+
+    # Simulate a pathological cycle: wrapped_slicer points back to itself
+    object.__setattr__(wrapped, "wrapped_slicer", wrapped)
+
+    # The key assertion: this must not raise RecursionError
+    assert isinstance(wrapped, StreamSlicerTestReadDecorator)