Restore 1.1 behavior for backwards compatibility

Author: timkpaine

README.md

@@ -221,6 +221,34 @@ defaults:
 
 Hydra breaks with importlib-resources 6.2+ due to `OrphanPath` objects not having `is_file()`/`is_dir()` methods. Lerna handles this gracefully.
 
+### Plugin Registration Compatible with Hydra
+
+Lerna provides a bridge that allows plugins registered via lerna to work with hydra-core. This enables you to write plugins once and have them work with both frameworks.
+
+#### Registering Plugins via Entry Points
+
+Add your plugin to `pyproject.toml` using the `hydra.lernaplugins` entry point group:
+
+```toml
+# For SearchPathPlugin modules:
+[project.entry-points."hydra.lernaplugins"]
+my-plugin = "my_package.plugin_module"
+
+# For package-style config directories:
+[project.entry-points."hydra.lernaplugins"]
+my-plugin = "pkg:my_package.hydra"
+```
+
+**Module-style entry points** (like `my_package.plugin_module`) are imported and scanned for `SearchPathPlugin` subclasses.
+
+**Package-style entry points** (like `pkg:my_package.hydra`) register config search paths directly.
+
+#### How It Works
+
+When hydra-core is used, lerna's `LernaGenericSearchPathPlugin` (installed in the `hydra_plugins` namespace) discovers all plugins registered under `hydra.lernaplugins` and makes them available to hydra's plugin system.
+
+This enables gradual migration: you can write plugins for lerna and they'll automatically work with existing hydra-core installations.
+
 ### Third-Party Plugins
 
 Hydra's plugin ecosystem (Optuna, Ray, Submitit, etc.) references `hydra` internally. To use them with Lerna:

hydra_plugins/lerna/__init__.py

@@ -0,0 +1,2 @@
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
+from .searchpath import LernaGenericSearchPathPlugin  # noqa: F401

hydra_plugins/lerna/searchpath.py

@@ -0,0 +1,66 @@
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
+"""
+Bridge plugin that enables hydra-core to discover plugins registered via lerna.
+
+When using hydra-core (not lerna directly), this plugin discovers plugins
+registered under the `hydra.lernaplugins` entry point group and makes them
+available to hydra's plugin system.
+
+This enables gradual migration: plugins can be written for lerna and still
+work with hydra-core installations.
+"""
+
+import sys
+from importlib import import_module
+from logging import getLogger
+
+from hydra.core.config_search_path import ConfigSearchPath
+from hydra.core.config_store import ConfigStore
+from hydra.plugins.search_path_plugin import SearchPathPlugin
+
+if sys.version_info < (3, 10):
+    from importlib_metadata import entry_points
+else:
+    from importlib.metadata import entry_points
+
+_log = getLogger("lerna")
+
+# NOTE: use `lernaplugins` instead of `plugins`
+# for https://github.com/facebookresearch/hydra/pull/3052
+_discovered_plugins = entry_points(group="hydra.lernaplugins")
+_searchpaths_pkg = {}
+for entry_point in _discovered_plugins:
+    if entry_point.value.startswith(("pkg:", "file:")):
+        # This is a package style entry point
+        kind, pkg_name = entry_point.value.split(":", 1)
+        _searchpaths_pkg[entry_point.name] = f"{kind}://{pkg_name}"
+        continue
+    # Otherwise, it's a module style entry point
+    try:
+        mod = import_module(entry_point.value)
+    except ImportError as e:
+        _log.warning(f"Failed to import entry point {entry_point.name} from {entry_point.value}: {e}")
+        continue
+    for attr in dir(mod):
+        thing = getattr(mod, attr)
+        if isinstance(thing, type) and issubclass(thing, SearchPathPlugin):
+            _log.info(f"Discovered search path plugin: {thing.__name__}")
+            globals()[thing.__name__] = thing
+    # search_path.append(provider=entry_point.name, path=entry_point.value)
+
+
+class LernaGenericSearchPathPlugin(SearchPathPlugin):
+    """
+    A SearchPathPlugin that bridges lerna plugins to hydra-core.
+
+    This plugin is automatically discovered by hydra-core due to being in
+    the hydra_plugins namespace. It then discovers any plugins registered
+    under the `hydra.lernaplugins` entry point group.
+    """
+
+    def manipulate_search_path(self, search_path: ConfigSearchPath) -> None:
+        if _searchpaths_pkg:
+            for provider, path in _searchpaths_pkg.items():
+                inst = ConfigStore.instance()
+                inst.store(name=provider, node=None, group=provider, provider=provider)
+                search_path.append(provider=provider, path=path)

lerna/tests/fake_package/fake_package/__init__.py

@@ -0,0 +1 @@
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

lerna/tests/fake_package/fake_package/hydra/.gitkeep

@@ -0,0 +1,11 @@
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
+from hydra.core.config_search_path import ConfigSearchPath
+from hydra.core.config_store import ConfigStore
+from hydra.plugins.search_path_plugin import SearchPathPlugin
+
+
+class FakePackageSearchPathPlugin(SearchPathPlugin):
+    def manipulate_search_path(self, search_path: ConfigSearchPath) -> None:
+        inst = ConfigStore.instance()
+        inst.store(name="fake-package", node=None, group="fake_package", provider="fake-package")
+        search_path.append(provider="fake-package", path="pkg://fake_package/hydra")

lerna/tests/fake_package/fake_package/plugin.py

@@ -0,0 +1,8 @@
+[project]
+name = "fake-package"
+version = "0.0.0"
+requires-python = ">=3.9"
+dependencies = []
+
+[project.entry-points."hydra.lernaplugins"]
+fake-package = "fake_package.plugin"

lerna/tests/fake_package/pyproject.toml

@@ -0,0 +1 @@
+# Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved

lerna/tests/fake_package2/fake_package2/__init__.py

@@ -0,0 +1,8 @@
+[project]
+name = "fake-package2"
+version = "0.0.0"
+requires-python = ">=3.9"
+dependencies = []
+
+[project.entry-points."hydra.lernaplugins"]
+fake-package2 = "pkg:fake_package2.hydra"