Feat: Warns to add to modules_to_save when adding tokens or switching special_tokens (#787)

* Feat: Auto add to modules_to_save when adding tokens

* fix: swap to error instead of warning

* feat: add check when special_tokens differ and add test

tests/test_tokenizers.py

@@ -3,6 +3,8 @@ Test cases for the tokenizer loading
 """
 import unittest
 
+import pytest
+
 from axolotl.utils.dict import DictDefault
 from axolotl.utils.models import load_tokenizer
 
@@ -31,6 +33,40 @@ class TestTokenizers(unittest.TestCase):
         tokenizer = load_tokenizer(cfg)
         assert "Fast" not in tokenizer.__class__.__name__
 
+    def test_special_tokens_modules_to_save(self):
+        # setting special_tokens to new token
+        cfg = DictDefault(
+            {
+                "tokenizer_config": "huggyllama/llama-7b",
+                "adapter": "lora",
+                "special_tokens": {"bos_token": "[INST]"},
+            }
+        )
+        with pytest.raises(
+            ValueError,
+            match=r".*Please set lora_modules_to_save*",
+        ):
+            load_tokenizer(cfg)
+
+        # setting special_tokens but not changing from default
+        cfg = DictDefault(
+            {
+                "tokenizer_config": "huggyllama/llama-7b",
+                "adapter": "lora",
+                "special_tokens": {"bos_token": "<s>"},
+            }
+        )
+        load_tokenizer(cfg)
+
+        # non-adapter setting special_tokens
+        cfg = DictDefault(
+            {
+                "tokenizer_config": "huggyllama/llama-7b",
+                "special_tokens": {"bos_token": "[INST]"},
+            }
+        )
+        load_tokenizer(cfg)
+
 
 if __name__ == "__main__":
     unittest.main()