feat: add check for quantized model (axolotl-ai-cloud#913)

* feat: add check for quantized model

* chore: refactor and add another check

* Update src/axolotl/utils/models.py

---------

Co-authored-by: Wing Lian <wing.lian@gmail.com>

src/axolotl/utils/models.py

@@ -28,6 +28,27 @@
 LOG = logging.getLogger("axolotl")
 
 
+def check_model_config(cfg: DictDefault, model_config: AutoConfig):
+    quant_config_exists = hasattr(model_config, "quantization_config")
+    quant_config_method_is_gptq = (
+        quant_config_exists
+        and "quant_method" in model_config.quantization_config
+        and model_config.quantization_config["quant_method"] == "gptq"
+    )
+
+    if cfg.gptq and not quant_config_method_is_gptq:
+        raise ValueError(
+            "model_config.quantization_config is not set or quant_method is not set to gptq. "
+            "Please make sure to point to a GPTQ model."
+        )
+
+    if not cfg.gptq and quant_config_exists:
+        raise ValueError(
+            "model_config.quantization_config is set but `gptq` flag is not. "
+            "Please use the `gptq` flag to train quantized model or point to a non-quantized model."
+        )
+
+
 def load_model_config(cfg):
     model_config_name = cfg.base_model_config or cfg.base_model
     trust_remote_code = cfg.trust_remote_code is True
@@ -38,6 +59,8 @@ def load_model_config(cfg):
         for key, val in cfg.model_config.items():
             setattr(model_config, key, val)
 
+    check_model_config(cfg, model_config)
+
     return model_config