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

src/axolotl/utils/config.py

@@ -448,6 +448,20 @@ def validate_config(cfg):
     if cfg.neftune_noise_alpha is not None and cfg.neftune_noise_alpha <= 0.0:
         raise ValueError("neftune_noise_alpha must be > 0.0")
 
+    if (
+        cfg.adapter
+        and cfg.tokens
+        and (
+            not cfg.lora_modules_to_save
+            or not all(
+                x in cfg.lora_modules_to_save for x in ["embed_tokens", "lm_head"]
+            )
+        )
+    ):
+        raise ValueError(
+            "lora_modules_to_save not properly set yet adding new tokens. Please add `embed_tokens` and `lm_head` to `lora_modules_to_save`."
+        )
+
     # TODO
     # MPT 7b
     # https://github.com/facebookresearch/bitsandbytes/issues/25

src/axolotl/utils/models.py

@@ -136,6 +136,23 @@ def load_tokenizer(cfg):
 
     if cfg.special_tokens:
         for k, val in cfg.special_tokens.items():
+            # check if new special token is not already in tokenizer and
+            # is adapter training to make sure lora_modules_to_save is set
+            if (
+                (getattr(tokenizer, k) is None or getattr(tokenizer, k) != val)
+                and cfg.adapter
+                and (
+                    not cfg.lora_modules_to_save
+                    or not all(
+                        x in cfg.lora_modules_to_save
+                        for x in ["embed_tokens", "lm_head"]
+                    )
+                )
+            ):
+                raise ValueError(
+                    "Please set lora_modules_to_save to ['embed_tokens', 'lm_head'] when using an adapter and changing the special tokens."
+                )
+
             tokenizer.add_special_tokens(
                 {k: AddedToken(val, rstrip=False, lstrip=False, normalized=False)}
             )