Import check_inits handling of duplicate definitions. (#12467)

* Import fix_inits handling of duplicate definitions.

* Style fix

utils/check_inits.py

@@ -13,6 +13,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
+import collections
 import os
 import re
 
@@ -154,12 +155,23 @@ def analyze_results(import_dict_objects, type_hint_objects):
     """
     Analyze the differences between _import_structure objects and TYPE_CHECKING objects found in an init.
     """
+
+    def find_duplicates(seq):
+        return [k for k, v in collections.Counter(seq).items() if v > 1]
+
     if list(import_dict_objects.keys()) != list(type_hint_objects.keys()):
         return ["Both sides of the init do not have the same backends!"]
 
     errors = []
     for key in import_dict_objects.keys():
-        if sorted(import_dict_objects[key]) != sorted(type_hint_objects[key]):
+        duplicate_imports = find_duplicates(import_dict_objects[key])
+        if duplicate_imports:
+            errors.append(f"Duplicate _import_structure definitions for: {duplicate_imports}")
+        duplicate_type_hints = find_duplicates(type_hint_objects[key])
+        if duplicate_type_hints:
+            errors.append(f"Duplicate TYPE_CHECKING objects for: {duplicate_type_hints}")
+
+        if sorted(set(import_dict_objects[key])) != sorted(set(type_hint_objects[key])):
             name = "base imports" if key == "none" else f"{key} backend"
             errors.append(f"Differences for {name}:")
             for a in type_hint_objects[key]: