feat: add support for external plugin config dataclasses (#807)

Co-authored-by: Steven Palma <imstevenpmwork@ieee.org>
Co-authored-by: Simon Alibert <75076266+aliberts@users.noreply.github.com>

tests/configs/test_plugin_loading.py

@@ -0,0 +1,89 @@
+import sys
+from dataclasses import dataclass
+from pathlib import Path
+from typing import Generator
+
+import pytest
+
+from lerobot.common.envs.configs import EnvConfig
+from lerobot.configs.parser import PluginLoadError, load_plugin, parse_plugin_args, wrap
+
+
+def create_plugin_code(*, base_class: str = "EnvConfig", plugin_name: str = "test_env") -> str:
+    """Creates a dummy plugin module that implements its own EnvConfig subclass."""
+    return f"""
+from dataclasses import dataclass
+from lerobot.common.envs.configs import {base_class}
+
+@{base_class}.register_subclass("{plugin_name}")
+@dataclass
+class TestPluginConfig:
+    value: int = 42
+    """
+
+
+@pytest.fixture
+def plugin_dir(tmp_path: Path) -> Generator[Path, None, None]:
+    """Creates a temporary plugin package structure."""
+    plugin_pkg = tmp_path / "test_plugin"
+    plugin_pkg.mkdir()
+    (plugin_pkg / "__init__.py").touch()
+
+    with open(plugin_pkg / "my_plugin.py", "w") as f:
+        f.write(create_plugin_code())
+
+    # Add tmp_path to Python path so we can import from it
+    sys.path.insert(0, str(tmp_path))
+    yield plugin_pkg
+    sys.path.pop(0)
+
+
+def test_parse_plugin_args():
+    cli_args = [
+        "--env.type=test",
+        "--model.discover_packages_path=some.package",
+        "--env.discover_packages_path=other.package",
+    ]
+    plugin_args = parse_plugin_args("discover_packages_path", cli_args)
+    assert plugin_args == {
+        "model.discover_packages_path": "some.package",
+        "env.discover_packages_path": "other.package",
+    }
+
+
+def test_load_plugin_success(plugin_dir: Path):
+    # Import should work and register the plugin with the real EnvConfig
+    load_plugin("test_plugin")
+
+    assert "test_env" in EnvConfig.get_known_choices()
+    plugin_cls = EnvConfig.get_choice_class("test_env")
+    plugin_instance = plugin_cls()
+    assert plugin_instance.value == 42
+
+
+def test_load_plugin_failure():
+    with pytest.raises(PluginLoadError) as exc_info:
+        load_plugin("nonexistent_plugin")
+    assert "Failed to load plugin 'nonexistent_plugin'" in str(exc_info.value)
+
+
+def test_wrap_with_plugin(plugin_dir: Path):
+    @dataclass
+    class Config:
+        env: EnvConfig
+
+    @wrap()
+    def dummy_func(cfg: Config):
+        return cfg
+
+    # Test loading plugin via CLI args
+    sys.argv = [
+        "dummy_script.py",
+        "--env.discover_packages_path=test_plugin",
+        "--env.type=test_env",
+    ]
+
+    cfg = dummy_func()
+    assert isinstance(cfg, Config)
+    assert isinstance(cfg.env, EnvConfig.get_choice_class("test_env"))
+    assert cfg.env.value == 42