BERT tokenizer fixes (#6498)

Key changes:
* BERT conversion: fix abuse of LlamaHfVocab, do not set BOS or EOS
* Nomic Embed conversion: pad vocab instead of slicing embedding tensor
* llama_tokenize: handle added special tokens like HF does

1 files changed, 19 insertions, 34 deletions

diff --git a/convert-hf-to-gguf.py b/convert-hf-to-gguf.py
index 37af6328..63710676 100755
--- a/convert-hf-to-gguf.py
+++ b/convert-hf-to-gguf.py
@@ -227,15 +227,14 @@ class Model(ABC):
             return ("pytorch_model.bin",)
         return (f"pytorch_model-{n:05}-of-{self.num_parts:05}.bin" for n in range(1, self.num_parts + 1))
 
-    def _set_vocab_gpt2(self):
-        dir_model = self.dir_model
-        hparams = self.hparams
+    # used for GPT-2 BPE and WordPiece vocabs
+    def get_basic_vocab(self) -> tuple[list[str], list[int]]:
         tokens: list[str] = []
         toktypes: list[int] = []
 
         from transformers import AutoTokenizer
-        tokenizer = AutoTokenizer.from_pretrained(dir_model)
-        vocab_size = hparams.get("vocab_size", len(tokenizer.vocab))
+        tokenizer = AutoTokenizer.from_pretrained(self.dir_model)
+        vocab_size = self.hparams.get("vocab_size", len(tokenizer.vocab))
         assert max(tokenizer.vocab.values()) < vocab_size
 
         reverse_vocab = {id_: encoded_tok for encoded_tok, id_ in tokenizer.vocab.items()}
@@ -255,11 +254,15 @@ class Model(ABC):
                 tokens.append(reverse_vocab[i])
                 toktypes.append(gguf.TokenType.NORMAL)
 
+        return tokens, toktypes
+
+    def _set_vocab_gpt2(self) -> None:
+        tokens, toktypes = self.get_basic_vocab()
         self.gguf_writer.add_tokenizer_model("gpt2")
         self.gguf_writer.add_token_list(tokens)
         self.gguf_writer.add_token_types(toktypes)
 
-        special_vocab = gguf.SpecialVocab(dir_model, load_merges=True)
+        special_vocab = gguf.SpecialVocab(self.dir_model, load_merges=True)
         special_vocab.add_to_gguf(self.gguf_writer)
 
     def _set_vocab_qwen(self):
@@ -2043,34 +2046,25 @@ class BertModel(Model):
             self.gguf_writer.add_pooling_type(pooling_type)
 
     def set_vocab(self):
-        # use huggingface vocab to get all tokens
-        vocab = LlamaHfVocab(self.dir_model, ignore_nonllama=True)
-        tokens, scores, toktypes = zip(*vocab.all_tokens())
-        assert len(tokens) == vocab.vocab_size
-        self.vocab_size = vocab.vocab_size
+        tokens, toktypes = self.get_basic_vocab()
+        self.vocab_size = len(tokens)
 
         # we need this to validate the size of the token_type embeddings
         # though currently we are passing all zeros to the token_type embeddings
-        n_token_types = len(set(toktypes))
-        self.gguf_writer.add_token_type_count(n_token_types)
+        self.gguf_writer.add_token_type_count(2)  # "Sequence A" or "Sequence B"
 
         # convert to phantom space vocab
-        def phantom(tok, typ):
-            if tok.startswith(b"[") and tok.endswith(b"]"):
+        def phantom(tok):
+            if tok.startswith("[") and tok.endswith("]"):
                 return tok
-            if tok.startswith(b"##"):
+            if tok.startswith("##"):
                 return tok[2:]
-            return b"\xe2\x96\x81" + tok
-        tokens = tuple(phantom(t, y) for t, y in zip(tokens, toktypes))
-
-        # set up bos and eos tokens (cls and sep)
-        self.gguf_writer.add_bos_token_id(vocab.tokenizer.cls_token_id)
-        self.gguf_writer.add_eos_token_id(vocab.tokenizer.sep_token_id)
+            return "\u2581" + tok
+        tokens = list(map(phantom, tokens))
 
         # add vocab to gguf
         self.gguf_writer.add_tokenizer_model("bert")
         self.gguf_writer.add_token_list(tokens)
-        self.gguf_writer.add_token_scores(scores)
         self.gguf_writer.add_token_types(toktypes)
 
         # handle special tokens
@@ -2142,16 +2136,6 @@ class NomicBertModel(BertModel):
         super().set_gguf_parameters()
         self.gguf_writer.add_rope_freq_base(self.hparams["rotary_emb_base"])
 
-    def get_tensors(self):
-        assert self.vocab_size is not None
-        for name, data in super().get_tensors():
-            # Nomic Embed's token embeddings tensor is padded, but llama.cpp wants tensor sizes to match exactly.
-            if name == 'embeddings.word_embeddings.weight' and data.shape[1] != self.vocab_size:
-                rounded_vocab_size = (self.vocab_size + 63) // 64 * 64
-                assert data.shape == (rounded_vocab_size, self.hparams["n_embd"])
-                data = data[:self.vocab_size, :]
-            yield name, data
-
 
 @Model.register("GemmaForCausalLM")
 class GemmaModel(Model):
@@ -2327,7 +2311,8 @@ class MambaModel(Model):
                 data = data.astype(np.float32)
 
             # if f16 desired, convert big float32 2-dim weight tensors to float16
-            if self.ftype == 1 and data_dtype == np.float32 and new_name.removesuffix(".weight").endswith((".ssm_in", ".ssm_out", "token_embd", "output")) and n_dims == 2:
+            new_weight_name = new_name[:-len(".weight")] if new_name.endswith(".weight") else ""
+            if self.ftype == 1 and data_dtype == np.float32 and new_weight_name.endswith((".ssm_in", ".ssm_out", "token_embd", "output")) and n_dims == 2:
                 data = data.astype(np.float16)
 
             print(f"{new_name}, n_dims = {n_dims}, {old_dtype} --> {data.dtype}")