[`T5Tokenizer`] Fix fast and extra tokens (#27085)

* v4.35.dev.0

* nit t5fast match t5 slow

src/transformers/models/t5/tokenization_t5_fast.py

@@ -118,17 +118,19 @@ class T5TokenizerFast(PreTrainedTokenizerFast):
         **kwargs,
     ):
         # Add extra_ids to the special token list
-        if extra_ids > 0 and additional_special_tokens is None:
-            additional_special_tokens = [f"<extra_id_{i}>" for i in range(extra_ids)]
-        elif extra_ids > 0 and additional_special_tokens is not None:
-            # Check that we have the right number of extra special tokens
-            extra_tokens = len(set(filter(lambda x: bool("extra_id_" in str(x)), additional_special_tokens)))
-            if extra_tokens != extra_ids:
+        if additional_special_tokens is not None:
+            extra_tokens = [x for x in additional_special_tokens if "<extra_id_" in str(x)]
+            if len(extra_tokens) < 1:
+                additional_special_tokens += [f"<extra_id_{i}>" for i in range(extra_ids)]
+            elif extra_ids > 0 and extra_ids != len(extra_tokens):
                 raise ValueError(
                     f"Both extra_ids ({extra_ids}) and additional_special_tokens ({additional_special_tokens}) are"
                     " provided to T5Tokenizer. In this case the additional_special_tokens must include the extra_ids"
                     " tokens"
                 )
+        else:
+            extra_tokens = [f"<extra_id_{i}>" for i in range(extra_ids)]
+            additional_special_tokens = extra_tokens
 
         super().__init__(
             vocab_file,