[Feature] Support overwrite default scope with "_scope_". (#275)

* [Feature] Support overwrite default scope with "_scope_".

* add ut

* add ut

mmengine/registry/default_scope.py

 # Copyright (c) OpenMMLab. All rights reserved.
-from typing import Optional
+import copy
+import time
+from contextlib import contextmanager
+from typing import Generator, Optional
 
 from mmengine.utils.manager import ManagerMixin, _accquire_lock, _release_lock
 
@@ -71,3 +74,17 @@ class DefaultScope(ManagerMixin):
             instance = None
         _release_lock()
         return instance
+
+    @classmethod
+    @contextmanager
+    def overwrite_default_scope(cls, scope_name: Optional[str]) -> Generator:
+        """overwrite the current default scope with `scope_name`"""
+        if scope_name is None:
+            yield
+        else:
+            tmp = copy.deepcopy(cls._instance_dict)
+            cls.get_instance(f'overwrite-{time.time()}', scope_name=scope_name)
+            try:
+                yield
+            finally:
+                cls._instance_dict = tmp

mmengine/registry/registry.py

@@ -468,7 +468,7 @@ class Registry:
 
         return None
 
-    def build(self, *args, **kwargs) -> Any:
+    def build(self, cfg, *args, **kwargs) -> Any:
         """Build an instance.
 
         Build an instance by calling :attr:`build_func`. If the global
@@ -487,27 +487,28 @@ class Registry:
             >>> cfg = dict(type='ResNet', depth=50)
             >>> model = MODELS.build(cfg)
         """
-        # get the global default scope
-        default_scope = DefaultScope.get_current_instance()
-        if default_scope is not None:
-            scope_name = default_scope.scope_name
-            root = self._get_root_registry()
-            registry = root._search_child(scope_name)
-            if registry is None:
-                # if `default_scope` can not be found, fallback to use self
-                warnings.warn(
-                    f'Failed to search registry with scope "{scope_name}" in '
-                    f'the "{root.name}" registry tree. '
-                    f'As a workaround, the current "{self.name}" registry in '
-                    f'"{self.scope}" is used to build instance. This may '
-                    f'cause unexpected failure when running the built '
-                    f'modules. Please check whether "{scope_name}" is a '
-                    f'correct scope, or whether the registry is initialized.')
+        with DefaultScope.overwrite_default_scope(cfg.pop('_scope_', None)):
+            # get the global default scope
+            default_scope = DefaultScope.get_current_instance()
+            if default_scope is not None:
+                scope_name = default_scope.scope_name
+                root = self._get_root_registry()
+                registry = root._search_child(scope_name)
+                if registry is None:
+                    # if `default_scope` can not be found, fallback to use self
+                    warnings.warn(
+                        f'Failed to search registry with scope "{scope_name}" '
+                        f'in the "{root.name}" registry tree. '
+                        f'As a workaround, the current "{self.name}" registry '
+                        f'in "{self.scope}" is used to build instance. This '
+                        f'may cause unexpected failure when running the built '
+                        f'modules. Please check whether "{scope_name}" is a '
+                        f'correct scope, or whether the registry is '
+                        f'initialized.')
+                    registry = self
+            else:
                 registry = self
-        else:
-            registry = self
-
-        return registry.build_func(*args, **kwargs, registry=registry)
+            return registry.build_func(cfg, *args, **kwargs, registry=registry)
 
     def _add_child(self, registry: 'Registry') -> None:
         """Add a child for a registry.

tests/test_registry/test_default_scope.py

@@ -21,3 +21,15 @@ class TestDefaultScope:
         DefaultScope.get_instance('instance_name', scope_name='mmengine')
         default_scope = DefaultScope.get_current_instance()
         assert default_scope.scope_name == 'mmengine'
+
+    def test_overwrite_default_scope(self):
+        origin_scope = DefaultScope.get_instance(
+            'test_overwrite_default_scope', scope_name='origin_scope')
+        with DefaultScope.overwrite_default_scope(scope_name=None):
+            assert DefaultScope.get_current_instance(
+            ).scope_name == 'origin_scope'
+        with DefaultScope.overwrite_default_scope(scope_name='test_overwrite'):
+            assert DefaultScope.get_current_instance(
+            ).scope_name == 'test_overwrite'
+        assert DefaultScope.get_current_instance(
+        ).scope_name == origin_scope.scope_name == 'origin_scope'

tests/test_registry/test_registry.py

@@ -167,16 +167,17 @@ class TestRegistry:
         registries = []
         DOGS = Registry('dogs')
         registries.append(DOGS)
-        HOUNDS = Registry('dogs', parent=DOGS, scope='hound')
+        HOUNDS = Registry('hounds', parent=DOGS, scope='hound')
         registries.append(HOUNDS)
-        LITTLE_HOUNDS = Registry('dogs', parent=HOUNDS, scope='little_hound')
+        LITTLE_HOUNDS = Registry(
+            'little hounds', parent=HOUNDS, scope='little_hound')
         registries.append(LITTLE_HOUNDS)
-        MID_HOUNDS = Registry('dogs', parent=HOUNDS, scope='mid_hound')
+        MID_HOUNDS = Registry('mid hounds', parent=HOUNDS, scope='mid_hound')
         registries.append(MID_HOUNDS)
-        SAMOYEDS = Registry('dogs', parent=DOGS, scope='samoyed')
+        SAMOYEDS = Registry('samoyeds', parent=DOGS, scope='samoyed')
         registries.append(SAMOYEDS)
         LITTLE_SAMOYEDS = Registry(
-            'dogs', parent=SAMOYEDS, scope='little_samoyed')
+            'little samoyeds', parent=SAMOYEDS, scope='little_samoyed')
         registries.append(LITTLE_SAMOYEDS)
 
         return registries
@@ -323,7 +324,7 @@ class TestRegistry:
         #     LITTLE_HOUNDS    MID_HOUNDS   LITTLE_SAMOYEDS
         #     (little_hound)   (mid_hound)  (little_samoyed)
         registries = self._build_registry()
-        DOGS, HOUNDS, LITTLE_HOUNDS, MID_HOUNDS = registries[:4]
+        DOGS, HOUNDS, LITTLE_HOUNDS, MID_HOUNDS, SAMOYEDS = registries[:5]
 
         @DOGS.register_module()
         class GoldenRetriever:
@@ -367,6 +368,37 @@ class TestRegistry:
         dog = MID_HOUNDS.build(b_cfg)
         assert isinstance(dog, Beagle)
 
+        # test overwrite default scope with `_scope_`
+        @SAMOYEDS.register_module()
+        class MySamoyed:
+
+            def __init__(self, friend):
+                self.friend = DOGS.build(friend)
+
+        @SAMOYEDS.register_module()
+        class YourSamoyed:
+            pass
+
+        s_cfg = cfg_type(
+            dict(
+                _scope_='samoyed',
+                type='MySamoyed',
+                friend=dict(type='hound.BloodHound')))
+        dog = DOGS.build(s_cfg)
+        assert isinstance(dog, MySamoyed)
+        assert isinstance(dog.friend, BloodHound)
+        assert DefaultScope.get_current_instance().scope_name != 'samoyed'
+
+        s_cfg = cfg_type(
+            dict(
+                _scope_='samoyed',
+                type='MySamoyed',
+                friend=dict(type='YourSamoyed')))
+        dog = DOGS.build(s_cfg)
+        assert isinstance(dog, MySamoyed)
+        assert isinstance(dog.friend, YourSamoyed)
+        assert DefaultScope.get_current_instance().scope_name != 'samoyed'
+
     def test_repr(self):
         CATS = Registry('cat')