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rag_eval/compat.py

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+"""Compatibility helpers for optional third-party import paths."""
+
+from __future__ import annotations
+
+import sys
+import types
+
+
+def ensure_ragas_import_compat() -> None:
+    """Patch optional langchain module paths that ragas imports eagerly.
+
+    The local environment ships a `langchain_community` build that still exposes
+    `langchain_community.llms.vertexai` but no longer provides
+    `langchain_community.chat_models.vertexai`. Ragas imports the chat module at
+    import time even when only OpenAI is used. Inject a minimal module so ragas
+    can import without mutating site-packages.
+    """
+
+    module_name = "langchain_community.chat_models.vertexai"
+    if module_name in sys.modules:
+        return
+
+    try:
+        import langchain_community.chat_models.vertexai  # type: ignore  # noqa: F401
+
+        return
+    except ModuleNotFoundError:
+        pass
+
+    # Inject a minimal shim so ragas can import successfully in stripped builds.
+    shim = types.ModuleType(module_name)
+
+    class ChatVertexAI:  # pragma: no cover - only used for import compatibility
+        """Compatibility shim for environments that do not ship ChatVertexAI."""
+
+        pass
+
+    shim.ChatVertexAI = ChatVertexAI
+    sys.modules[module_name] = shim