fix: log non-OpenAI format= assumption once at init (#1502)

mellea/backends/openai.py

@@ -207,6 +207,16 @@ def __init__(
             if self._base_url is not None
             else _ServerType.OPENAI
         )  # type: ignore
+        if self._server_type != _ServerType.OPENAI:
+            MelleaLogger.get_logger().info(
+                "Mellea assumes you are NOT using the OpenAI platform, and that "
+                "other model providers have less strict requirements on supporting "
+                "JSON schemas passed into `format=`. If you encounter a server-side "
+                "error when using format=, then you found an exception to this "
+                "assumption. Please open an issue at "
+                "github.com/generative_computing/mellea with the stack trace and "
+                "your inference engine / model provider."
+            )
 
         self._openai_client_kwargs = self.filter_openai_client_kwargs(**kwargs)
 
@@ -934,9 +944,6 @@ async def _generate_from_chat_context_standard(
                     },
                 }
             else:
-                MelleaLogger.get_logger().info(
-                    "Mellea assumes you are NOT using the OpenAI platform, and that other model providers have less strict requirements on supporting JSON schemas passed into `format=`. If you encounter a server-side error following this message, then you found an exception to this assumption. Please open an issue at github.com/generative_computing/mellea with this stack trace and your inference engine / model provider."
-                )
                 extra_params["response_format"] = {
                     "type": "json_schema",
                     "json_schema": {

test/backends/test_openai_unit.py

@@ -429,5 +429,50 @@ class Answer(pydantic.BaseModel):
     assert "guided_json" in extra_body or "structured_outputs" in extra_body
 
 
+# --- #1502: non-OpenAI format= warning only at init ---
+
+_FORMAT_ASSUMPTION = "NOT using the OpenAI platform"
+
+
+def _info_msgs(mock_logger) -> list[str]:
+    return [str(c.args[0]) for c in mock_logger.info.call_args_list if c.args]
+
+
+def test_non_openai_format_assumption_logged_once_at_init():
+    mock_logger = MagicMock()
+    with patch(
+        "mellea.backends.openai.MelleaLogger.get_logger", return_value=mock_logger
+    ):
+        OpenAIBackend(
+            model_id="gpt-4o",
+            api_key="fake-key",
+            base_url="http://localhost:9999/v1",
+        )
+        OpenAIBackend(
+            model_id="gpt-4o",
+            api_key="fake-key",
+            base_url="http://localhost:9999/v1",
+        )
+
+    matches = [m for m in _info_msgs(mock_logger) if _FORMAT_ASSUMPTION in m]
+    assert len(matches) == 2  # once per backend instance
+
+
+def test_openai_platform_skips_format_assumption_log():
+    mock_logger = MagicMock()
+    with patch(
+        "mellea.backends.openai.MelleaLogger.get_logger", return_value=mock_logger
+    ):
+        OpenAIBackend(
+            model_id="gpt-4o",
+            api_key="fake-key",
+            base_url="https://api.openai.com/v1",
+        )
+        OpenAIBackend(model_id="gpt-4o", api_key="fake-key")
+
+    matches = [m for m in _info_msgs(mock_logger) if _FORMAT_ASSUMPTION in m]
+    assert matches == []
+
+
 if __name__ == "__main__":
     pytest.main([__file__, "-v"])