Fix a bug in LazyMetadataDict where the metadata is not copyable when using **.

PiperOrigin-RevId: 696856102

Author: tomvdw

tensorflow_datasets/core/dataset_info.py

@@ -457,6 +457,8 @@ def alternative_file_formats(self) -> list[file_adapters.FileFormat]:
 
   @property
   def metadata(self) -> Metadata | None:
+    if isinstance(self._metadata, LazyMetadataDict):
+      self._metadata.load_metadata_if_needed()
     return self._metadata
 
   @property
@@ -1414,26 +1416,30 @@ def __init__(self, data_dir: epath.PathLike) -> None:
     self._data_is_loaded = False
     super().__init__()
 
-  def _load_metadata(self):
+  def load_metadata_if_needed(self):
     if not self._data_is_loaded:
       if _metadata_filepath(self._data_dir).exists():
         self.load_metadata(self._data_dir)
       self._data_is_loaded = True
 
   def __getitem__(self, key, /):
-    self._load_metadata()
+    self.load_metadata_if_needed()
     return super().__getitem__(key)
 
   def __eq__(self, value, /):
-    self._load_metadata()
+    self.load_metadata_if_needed()
     return super().__eq__(value)
 
   def keys(self):
-    self._load_metadata()
+    self.load_metadata_if_needed()
     return super().keys()
 
+  def values(self):
+    self.load_metadata_if_needed()
+    return super().values()
+
   def items(self):
-    self._load_metadata()
+    self.load_metadata_if_needed()
     return super().items()
 
   def copy(self):

tensorflow_datasets/core/dataset_info_test.py

@@ -318,6 +318,14 @@ def test_metadata(self):
       )
       self.assertEqual(builder3.info.metadata, {"some_key": 123})
 
+      # Test whether the metadata is copyable.
+      builder = RandomShapedImageGenerator(data_dir=tmp_dir)
+      self.assertIsInstance(
+          builder.info.metadata, dataset_info.LazyMetadataDict
+      )
+      metadata_copy = {**builder.info.metadata}
+      self.assertEqual(metadata_copy, {"some_key": 123})
+
   def test_redistribution_info(self):
     info = dataset_info.DatasetInfo(
         builder=self._builder, license="some license"