From c0f07cca91a3a533b96139e18d1c44ba09fa012d Mon Sep 17 00:00:00 2001
From: Eustache Le Bihan <eulebihan@gmail.com>
Date: Mon, 8 Sep 2025 15:27:21 +0200
Subject: [PATCH] CanaryConverter draft

---
 src/transformers/convert_slow_tokenizer.py | 51 ++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/src/transformers/convert_slow_tokenizer.py b/src/transformers/convert_slow_tokenizer.py
index a9e7c9bff5bc..4a01308bece5 100644
--- a/src/transformers/convert_slow_tokenizer.py
+++ b/src/transformers/convert_slow_tokenizer.py
@@ -1451,6 +1451,57 @@ def pre_tokenizer(self, replacement, add_prefix_space):
         return pre_tokenizers.Metaspace(replacement=replacement, prepend_scheme=prepend_scheme, split=False)
 
 
+class CanaryConverter(SpmConverter):
+    handle_byte_fallback = True
+
+    def __init__(self, vocab_file=None, *args):
+        self.vocab_file = vocab_file
+
+        requires_backends(self, "protobuf")
+
+        Converter.__init__(self, vocab_file)
+
+        model_pb2 = import_protobuf()
+        m = model_pb2.ModelProto()
+        with open(vocab_file, "rb") as f:
+            m.ParseFromString(f.read())
+        self.proto = m
+
+    def tokenizer(self, proto):
+        vocab_scores = self.vocab(proto)
+
+        _, merges = self.SpmExtractor(self.vocab_file).extract(vocab_scores)
+        bpe_vocab = {word: i for i, (word, score) in enumerate(vocab_scores)}
+        tokenizer = Tokenizer(
+            BPE(
+                bpe_vocab,
+                merges,
+                unk_token=proto.trainer_spec.unk_piece,
+                fuse_unk=True,
+                byte_fallback=self.handle_byte_fallback,
+                dropout=None,
+            )
+        )
+
+        # control tokens are special
+        # user defined symbols are not
+        # both user and control tokens are AddedTokens
+        # Add user defined symbols (type == 4) from sentencepiece (https://github.com/google/sentencepiece/blob/6225e08edb2577757163b3f5dbba4c0b670ef445/src/sentencepiece_model.proto#L299C29-L299C33)
+        spm_added_tokens = [
+            (id, p.piece, p.type == 3 or p.piece in self.special_tokens)
+            for id, p in enumerate(proto.pieces)
+            if p.type in [3, 4]
+        ]
+        tokenizer.add_tokens(
+            [
+                AddedToken(token, normalized=False, special=special)
+                for id, token, special in sorted(spm_added_tokens, key=lambda x: x[0])
+            ]
+        )
+
+        return tokenizer
+
+
 class HeliumConverter(SpmConverter):
     handle_byte_fallback = True