fix(peft): allow fresh LoRA fine-tuning from a base-model checkpoint

tests/policies/test_peft_base_model_loading.py

@@ -0,0 +1,142 @@
+# Copyright 2024 The HuggingFace Inc. team. All rights reserved.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+"""Regression tests for PEFT loading when the checkpoint is a base model (see issue #3975).
+
+Starting a fresh LoRA/PEFT fine-tune points ``--policy.path`` at a *base model* (no
+``adapter_config.json``) while also setting ``use_peft=True``. This must NOT be mistaken for
+loading an existing PEFT adapter. These tests lock in the base-model vs. adapter distinction
+made by ``lerobot.policies.factory._has_peft_adapter_config`` and the branch it drives in
+``make_policy``. They are pure/fast (no network, no ``peft``), so they run in CI.
+"""
+
+import json
+from unittest.mock import MagicMock, patch
+
+import torch
+from huggingface_hub.errors import HfHubHTTPError
+
+from lerobot.policies.factory import _has_peft_adapter_config
+
+
+def test_local_base_model_dir_has_no_adapter_config(tmp_path):
+    # A base-model checkpoint directory (only model weights, no adapter config).
+    (tmp_path / "model.safetensors").write_bytes(b"")
+    (tmp_path / "config.json").write_text("{}")
+    assert _has_peft_adapter_config(str(tmp_path)) is False
+
+
+def test_local_adapter_dir_has_adapter_config(tmp_path):
+    (tmp_path / "adapter_config.json").write_text(json.dumps({"peft_type": "LORA"}))
+    (tmp_path / "adapter_model.safetensors").write_bytes(b"")
+    assert _has_peft_adapter_config(str(tmp_path)) is True
+
+
+def test_hub_base_model_repo_has_no_adapter_config():
+    with patch("huggingface_hub.file_exists", return_value=False) as mock_exists:
+        assert _has_peft_adapter_config("lerobot/lingbot_va_base") is False
+    mock_exists.assert_called_once()
+    assert mock_exists.call_args.args[1] == "adapter_config.json"
+
+
+def test_hub_adapter_repo_has_adapter_config():
+    with patch("huggingface_hub.file_exists", return_value=True):
+        assert _has_peft_adapter_config("some/adapter-repo", revision="main") is True
+
+
+def test_hub_lookup_error_falls_back_to_base_model():
+    # Offline / private / transient Hub errors must not crash; treat as "not an adapter".
+    with patch(
+        "huggingface_hub.file_exists",
+        side_effect=HfHubHTTPError("boom", response=MagicMock()),
+    ):
+        assert _has_peft_adapter_config("some/private-repo") is False
+    with patch("huggingface_hub.file_exists", side_effect=OSError("offline")):
+        assert _has_peft_adapter_config("some/repo") is False
+
+
+def _make_dummy_policy_cfg(pretrained_path, use_peft):
+    cfg = MagicMock()
+    cfg.type = "act"
+    cfg.device = "cpu"
+    cfg.pretrained_path = pretrained_path
+    cfg.pretrained_revision = None
+    cfg.use_peft = use_peft
+    cfg.input_features = {}
+    cfg.output_features = {}
+    return cfg
+
+
+@patch("lerobot.policies.factory.validate_visual_features_consistency")
+@patch("lerobot.policies.factory.env_to_policy_features", return_value={})
+@patch("lerobot.policies.factory.get_policy_class")
+def test_make_policy_base_model_with_use_peft_loads_base_not_adapter(
+    mock_get_cls, _mock_features, _mock_validate
+):
+    """`use_peft=True` on a base model must load the base weights, not a PEFT adapter.
+
+    Before the #3975 fix this went down the ``PeftConfig.from_pretrained`` path and failed
+    looking for a non-existent ``adapter_config.json``.
+    """
+    from lerobot.policies import factory
+
+    policy_cls = MagicMock()
+    loaded_policy = torch.nn.Linear(1, 1)  # a real nn.Module so make_policy's assert passes
+    policy_cls.from_pretrained.return_value = loaded_policy
+    mock_get_cls.return_value = policy_cls
+
+    cfg = _make_dummy_policy_cfg(pretrained_path="lerobot/lingbot_va_base", use_peft=True)
+    env_cfg = MagicMock()
+
+    with patch.object(factory, "_has_peft_adapter_config", return_value=False) as mock_has_adapter:
+        policy = factory.make_policy(cfg=cfg, env_cfg=env_cfg)
+
+    mock_has_adapter.assert_called_once()
+    # Base model is loaded via the normal pretrained path...
+    policy_cls.from_pretrained.assert_called_once()
+    assert policy_cls.from_pretrained.call_args.kwargs["pretrained_name_or_path"] == (
+        "lerobot/lingbot_va_base"
+    )
+    # ...and PEFT adapter loading is NOT attempted (would need peft + adapter_config.json).
+    assert policy is loaded_policy
+
+
+@patch("lerobot.policies.factory.validate_visual_features_consistency")
+@patch("lerobot.policies.factory.env_to_policy_features", return_value={})
+@patch("lerobot.policies.factory.get_policy_class")
+def test_make_policy_existing_adapter_uses_peft_loading(mock_get_cls, _mock_features, _mock_validate):
+    """A real adapter checkpoint (has ``adapter_config.json``) must go through PEFT loading."""
+    from lerobot.policies import factory
+
+    policy_cls = MagicMock()
+    mock_get_cls.return_value = policy_cls
+
+    cfg = _make_dummy_policy_cfg(pretrained_path="some/adapter-repo", use_peft=True)
+    env_cfg = MagicMock()
+
+    policy_cls.from_pretrained.return_value = torch.nn.Linear(1, 1)
+
+    fake_peft = MagicMock()
+    fake_peft_config = MagicMock()
+    fake_peft_config.base_model_name_or_path = "lerobot/lingbot_va_base"
+    fake_peft.PeftConfig.from_pretrained.return_value = fake_peft_config
+    fake_peft.PeftModel.from_pretrained.return_value = torch.nn.Linear(1, 1)
+
+    with (
+        patch.object(factory, "_has_peft_adapter_config", return_value=True),
+        patch.dict("sys.modules", {"peft": fake_peft}),
+    ):
+        factory.make_policy(cfg=cfg, env_cfg=env_cfg)
+
+    fake_peft.PeftConfig.from_pretrained.assert_called_once_with("some/adapter-repo")
+    fake_peft.PeftModel.from_pretrained.assert_called_once()