chore: import upstream snapshot with attribution

python/ray/train/v2/horovod/__init__.py

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+import ray.train.horovod  # noqa: F401

python/ray/train/v2/horovod/horovod_trainer.py

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+from typing import Any, Callable, Dict, Optional, Union
+
+from ray.air.config import RunConfig, ScalingConfig
+from ray.train import Checkpoint, DataConfig
+from ray.train.data_parallel_trainer import DataParallelTrainer
+from ray.train.horovod.config import HorovodConfig
+from ray.train.trainer import GenDataset
+from ray.util.annotations import Deprecated
+
+
+@Deprecated
+class HorovodTrainer(DataParallelTrainer):
+    """A Trainer for data parallel Horovod training. HorovodTrainer is deprecated."""
+
+    def __init__(
+        self,
+        train_loop_per_worker: Union[Callable[[], None], Callable[[Dict], None]],
+        *,
+        train_loop_config: Optional[Dict] = None,
+        horovod_config: Optional[HorovodConfig] = None,
+        scaling_config: Optional[ScalingConfig] = None,
+        dataset_config: Optional[DataConfig] = None,
+        run_config: Optional[RunConfig] = None,
+        datasets: Optional[Dict[str, GenDataset]] = None,
+        metadata: Optional[Dict[str, Any]] = None,
+        resume_from_checkpoint: Optional[Checkpoint] = None,
+    ):
+        raise DeprecationWarning(
+            "`HorovodTrainer` is not supported and is scheduled to be removed "
+            "in the future. "
+            "Please consider using `TorchTrainer` or `TensorflowTrainer`, "
+            "fall back to the old implementation with `RAY_TRAIN_V2_ENABLED=0`, "
+            "or file an issue on Github describing your use case."
+        )