Fix policy.path in YAML configs (PR #3145 followup) (#3597)

PR #3145 added YAML support for policy.path but left two bugs:

1. extract_path_fields_from_config only deleted config_data[field] when
   no sibling overrides existed. With siblings, the dict stayed in place
   and draccus crashed decoding it as PreTrainedConfig (no 'type' key).
   Sibling overrides go into _config_yaml_overrides and are applied later
   by from_pretrained(), so the field can always be removed.

2. wrap() updated config_path_cli to the cleaned temp file path but
   never propagated it to the draccus.parse fallback branch. cli_args
   still contained --config_path=<original>, so draccus read the
   original YAML with path: still present.

Tests passed because they (a) called extract_path_fields_from_config
directly and (b) included type: alongside path: in the YAML, sidestepping
both bugs.

Co-authored-by: Steven Palma <imstevenpmwork@ieee.org>

src/lerobot/configs/parser.py

@@ -255,7 +255,6 @@ def extract_path_fields_from_config(config_path: str, path_fields: list[str]) ->
             remaining = config_data[field]
             if remaining:
                 _config_yaml_overrides[field] = _flatten_to_cli_args(remaining)
-            else:
             del config_data[field]
             modified = True
 
@@ -311,7 +310,13 @@ def wrap(config_path: Path | None = None) -> Callable[[F], F]:
                     cli_args = filter_arg("config_path", cli_args)
                     cfg = argtype.from_pretrained(config_path_cli, cli_args=cli_args)
                 else:
-                    cfg = draccus.parse(config_class=argtype, config_path=config_path, args=cli_args)
+                    if config_path_cli:
+                        cli_args = filter_arg("config_path", cli_args)
+                    cfg = draccus.parse(
+                        config_class=argtype,
+                        config_path=config_path_cli or config_path,
+                        args=cli_args,
+                    )
             response = fn(cfg, *args, **kwargs)
             return response
 

tests/test_yaml_policy_path.py

@@ -1,10 +1,14 @@
 """Tests for policy.path support in YAML config files (issue #2957)."""
 
 import json
+import sys
 import tempfile
+from dataclasses import dataclass, field
+from unittest.mock import patch
 
 import yaml
 
+from lerobot.configs import parser
 from lerobot.configs.parser import (
     _config_path_args,
     _config_yaml_overrides,
@@ -16,7 +20,8 @@ from lerobot.configs.parser import (
 
 
 def test_extract_path_fields_from_yaml():
-    """Test that policy.path is extracted from a YAML config and removed."""
+    """Test that policy.path is extracted from a YAML config and the policy block
+    is removed entirely (siblings are captured separately as cli_overrides)."""
     config = {
         "dataset": {"repo_id": "lerobot/pusht"},
         "policy": {"type": "smolvla", "path": "lerobot/smolvla_base", "push_to_hub": False},
@@ -26,26 +31,33 @@ def test_extract_path_fields_from_yaml():
         config_path = f.name
 
     _config_path_args.clear()
+    _config_yaml_overrides.clear()
     cleaned_path = extract_path_fields_from_config(config_path, ["policy"])
 
     # Path should be extracted and stored
     assert _config_path_args["policy"] == "lerobot/smolvla_base"
 
-    # Cleaned config should not have the path field
+    # Cleaned config should not have the policy block at all -- draccus must not
+    # try to decode it as PreTrainedConfig; the actual config comes from
+    # from_pretrained(path) with the captured overrides applied on top.
     with open(cleaned_path) as f:
         cleaned = yaml.safe_load(f)
-    assert "path" not in cleaned["policy"]
-    assert cleaned["policy"]["type"] == "smolvla"
-    assert cleaned["policy"]["push_to_hub"] is False
+    assert "policy" not in cleaned
 
     # Original dataset should be untouched
     assert cleaned["dataset"]["repo_id"] == "lerobot/pusht"
 
+    # Sibling overrides (excluding type/path) captured for from_pretrained.
+    overrides = get_yaml_overrides("policy")
+    assert any("push_to_hub=false" in o for o in overrides)
+
     _config_path_args.clear()
+    _config_yaml_overrides.clear()
 
 
 def test_extract_path_fields_from_json():
-    """Test that policy.path is extracted from a JSON config."""
+    """Test that policy.path is extracted from a JSON config and the policy
+    block is removed entirely."""
     config = {
         "policy": {"type": "act", "path": "some/local/path"},
     }
@@ -54,15 +66,17 @@ def test_extract_path_fields_from_json():
         config_path = f.name
 
     _config_path_args.clear()
+    _config_yaml_overrides.clear()
     cleaned_path = extract_path_fields_from_config(config_path, ["policy"])
 
     assert _config_path_args["policy"] == "some/local/path"
 
     with open(cleaned_path) as f:
         cleaned = json.load(f)
-    assert "path" not in cleaned["policy"]
+    assert "policy" not in cleaned
 
     _config_path_args.clear()
+    _config_yaml_overrides.clear()
 
 
 def test_extract_no_path_returns_original():
@@ -216,3 +230,91 @@ def test_flatten_nested_with_bools():
     args = _flatten_to_cli_args(d)
     assert "--optimizer.use_warmup=true" in args
     assert "--optimizer.lr=0.01" in args
+
+
+def test_extract_removes_field_with_siblings_and_no_type():
+    """Regression: when policy.path has siblings but no type:, the entire policy
+    block must still be removed from the cleaned config. Otherwise draccus tries
+    to decode the leftover dict as PreTrainedConfig and crashes on the missing
+    type discriminator.
+    """
+    config = {
+        "dataset": {"repo_id": "lerobot/pusht"},
+        "policy": {
+            "path": "lerobot/smolvla_base",
+            "n_action_steps": 10,
+            "dtype": "bfloat16",
+        },
+    }
+    with tempfile.NamedTemporaryFile(mode="w", suffix=".yaml", delete=False) as f:
+        yaml.dump(config, f)
+        config_path = f.name
+
+    _config_path_args.clear()
+    _config_yaml_overrides.clear()
+    cleaned_path = extract_path_fields_from_config(config_path, ["policy"])
+
+    with open(cleaned_path) as f:
+        cleaned = yaml.safe_load(f) or {}
+    assert "policy" not in cleaned, "policy block should be fully removed when path is present"
+    assert cleaned["dataset"]["repo_id"] == "lerobot/pusht"
+    assert _config_path_args["policy"] == "lerobot/smolvla_base"
+    overrides = get_yaml_overrides("policy")
+    assert any("n_action_steps=10" in o for o in overrides)
+    assert any("dtype=bfloat16" in o for o in overrides)
+
+    _config_path_args.clear()
+    _config_yaml_overrides.clear()
+
+
+@dataclass
+class _DummyNested:
+    foo: int = 0
+
+
+@dataclass
+class _DummyConfig:
+    nested: _DummyNested = field(default_factory=_DummyNested)
+    other: str = "default"
+
+    @classmethod
+    def __get_path_fields__(cls):
+        return ["nested"]
+
+
+def test_wrap_uses_cleaned_config_for_draccus_parse():
+    """Regression: wrap() updates config_path_cli to point at the cleaned temp
+    file but must propagate that to the draccus.parse fallback branch. Without
+    the fix, cli_args still contains --config_path=<original> and draccus reads
+    the original YAML with `path:` still in it, crashing on the unknown field.
+    """
+    config = {
+        "nested": {"path": "some/checkpoint", "foo": 42},
+        "other": "set-via-yaml",
+    }
+    with tempfile.NamedTemporaryFile(mode="w", suffix=".yaml", delete=False) as f:
+        yaml.dump(config, f)
+        config_path = f.name
+
+    _config_path_args.clear()
+    _config_yaml_overrides.clear()
+
+    captured: dict = {}
+
+    @parser.wrap()
+    def main(cfg: _DummyConfig) -> _DummyConfig:
+        captured["cfg"] = cfg
+        return cfg
+
+    with patch.object(sys, "argv", ["prog", f"--config_path={config_path}"]):
+        main()
+
+    assert captured["cfg"].other == "set-via-yaml"
+    assert _config_path_args["nested"] == "some/checkpoint"
+    # Cleaned config dropped `nested:` entirely; defaults stand for this wrapper
+    # class (a real PreTrainedConfig would now load the checkpoint and apply
+    # the captured yaml_overrides via from_pretrained()).
+    assert captured["cfg"].nested.foo == 0
+
+    _config_path_args.clear()
+    _config_yaml_overrides.clear()