Fix potiential bug in `deprecated_api_warning` (#1395)

* assert both dep and new args exist at same time

* add unintest

* Update tests/test_utils/test_misc.py
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* Update tests/test_utils/test_misc.py
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

* polish warning

* polish warning
Co-authored-by: Zaida Zhou <58739961+zhouzaida@users.noreply.github.com>

mmcv/utils/misc.py

@@ -320,6 +320,16 @@ def deprecated_api_warning(name_dict, cls_name=None):
             if kwargs:
                 for src_arg_name, dst_arg_name in name_dict.items():
                     if src_arg_name in kwargs:
+
+                        assert dst_arg_name not in kwargs, (
+                            f'The expected behavior is to replace '
+                            f'the deprecated key `{src_arg_name}` to '
+                            f'new key `{dst_arg_name}`, but got them '
+                            f'in the arguments at the same time, which '
+                            f'is confusing. `{src_arg_name} will be '
+                            f'deprecated in the future, please '
+                            f'use `{dst_arg_name}` instead.')
+
                         warnings.warn(
                             f'"{src_arg_name}" is deprecated in '
                             f'`{func_name}`, please use "{dst_arg_name}" '

tests/test_utils/test_misc.py

@@ -2,6 +2,7 @@
 import pytest
 
 import mmcv
+from mmcv import deprecated_api_warning
 
 
 def test_to_ntuple():
@@ -190,3 +191,19 @@ def test_is_method_overridden():
     base_instance = Base()
     with pytest.raises(AssertionError):
         mmcv.is_method_overridden('foo1', base_instance, sub_instance)
+
+
+def test_deprecated_api_warning():
+
+    @deprecated_api_warning(name_dict=dict(old_key='new_key'))
+    def dummy_func(new_key=1):
+        return new_key
+
+    # replace `old_key` to `new_key`
+    assert dummy_func(old_key=2) == 2
+
+    # The expected behavior is to replace the
+    # deprecated key `old_key` to `new_key`,
+    # but got them in the arguments at the same time
+    with pytest.raises(AssertionError):
+        dummy_func(old_key=1, new_key=2)