Disallow duplicate keys in yaml tags

src/datasets/utils/metadata.py

@@ -1,5 +1,6 @@
 import json
 import logging
+from collections import Counter
 from dataclasses import dataclass
 from pathlib import Path
 from typing import Any, Callable, Dict, List, Optional, Tuple
@@ -38,6 +39,21 @@ def load_json_resource(resource: str) -> Tuple[Any, str]:
 known_multilingualities, known_multilingualities_url = load_json_resource("multilingualities.json")
 
 
+class NoDuplicateSafeLoader(yaml.SafeLoader):
+    def _check_no_duplicates_on_constructed_node(self, node):
+        keys = [self.constructed_objects[key_node] for key_node, _ in node.value]
+        keys = [tuple(key) if isinstance(key, list) else key for key in keys]
+        counter = Counter(keys)
+        duplicate_keys = [key for key in counter if counter[key] > 1]
+        if duplicate_keys:
+            raise TypeError(f"Got duplicate yaml keys: {duplicate_keys}")
+
+    def construct_mapping(self, node, deep=False):
+        mapping = super().construct_mapping(node, deep=deep)
+        self._check_no_duplicates_on_constructed_node(node)
+        return mapping
+
+
 def yaml_block_from_readme(path: Path) -> Optional[str]:
     with path.open() as readme_file:
         content = [line.strip() for line in readme_file]
@@ -54,7 +70,7 @@ def metadata_dict_from_readme(path: Path) -> Optional[Dict[str, List[str]]]:
     yaml_block = yaml_block_from_readme(path=path)
     if yaml_block is None:
         return None
-    metada_dict = yaml.safe_load(yaml_block) or dict()
+    metada_dict = yaml.load(yaml_block, Loader=NoDuplicateSafeLoader) or dict()
     return metada_dict
 
 
@@ -174,7 +190,7 @@ def from_yaml_string(cls, string: str) -> "DatasetMetadata":
         Raises:
             :obj:`TypeError`: If the dataset's metadata is invalid
         """
-        metada_dict = yaml.safe_load(string) or dict()
+        metada_dict = yaml.load(string, Loader=NoDuplicateSafeLoader) or dict()
         # flatten the metadata of each config
         for key in metada_dict:
             if isinstance(metada_dict[key], dict):

tests/test_metadata_util.py

@@ -15,7 +15,7 @@
 
 def _dedent(string: str) -> str:
     indent_level = min(re.search("^ +", t).end() if t.startswith(" ") else 0 for t in string.splitlines())
-    return "\n".join([line[indent_level:] for line in string.splitlines()])
+    return "\n".join([line[indent_level:] for line in string.splitlines() if indent_level < len(line)])
 
 
 README_YAML = """\
@@ -126,7 +126,7 @@ def test_yaml_block_from_readme(self):
                     - en
                     task_ids:
                     - sentiment-classification
-"""
+                    """
                 ),
             )
 
@@ -263,3 +263,56 @@ def test_from_yaml_string(self):
         )
         with self.assertRaises(TypeError):
             DatasetMetadata.from_yaml_string(missing_tag_yaml)
+
+        duplicate_yaml_keys = _dedent(
+            """\
+            annotations_creators:
+            - found
+            languages:
+            - en
+            licenses:
+            - unknown
+            multilinguality:
+            - monolingual
+            size_categories:
+            - 10K<n<100K
+            source_datasets:
+            - extended|other-yahoo-webscope-l6
+            task_categories:
+            - question-answering
+            task_ids:
+            - open-domain-qa
+            task_ids:
+            - open-domain-qa
+            """
+        )
+        with self.assertRaises(TypeError):
+            DatasetMetadata.from_yaml_string(duplicate_yaml_keys)
+
+        valid_yaml_string_with_duplicate_configs = _dedent(
+            """\
+            annotations_creators:
+            - found
+            language_creators:
+            - found
+            languages:
+              en:
+              - en
+              en:
+              - en
+            licenses:
+            - unknown
+            multilinguality:
+            - monolingual
+            size_categories:
+            - 10K<n<100K
+            source_datasets:
+            - extended|other-yahoo-webscope-l6
+            task_categories:
+            - question-answering
+            task_ids:
+            - open-domain-qa
+            """
+        )
+        with self.assertRaises(TypeError):
+            DatasetMetadata.from_yaml_string(valid_yaml_string_with_duplicate_configs)