fix: allow merge lora on pre-quantized model (axolotl-ai-cloud#2511)

* fix: allow merge lora on pre-quantized model

* fix: remove unused sections per comment

Author: NanoCode012

src/axolotl/cli/merge_lora.py

@@ -32,7 +32,13 @@ def do_merge_lora(*, cfg: DictDefault) -> None:
 
     LOG.info("Running merge of LoRA with base model...")
     model = model.merge_and_unload(progressbar=True)
-    model.to(dtype=cfg.torch_dtype)
+    try:
+        model.to(dtype=cfg.torch_dtype)
+    except ValueError as e:
+        LOG.warning("Failed to convert model to dtype %s", cfg.torch_dtype)
+        LOG.warning("Ignore this if the base_model is pre-quantized.")
+        LOG.warning("Error raised: %s", e)
+
     model.generation_config.do_sample = True
 
     if cfg.local_rank == 0:

src/axolotl/utils/models.py

@@ -151,12 +151,6 @@ def check_model_config(cfg: DictDefault, model_config: PretrainedConfig):
             "Please make sure to point to a GPTQ model."
         )
 
-    if not cfg.gptq and quant_config_exists and not cfg.load_in_4bit:
-        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."
-        )
-
     lora_modules_to_save = get_linear_embedding_layers(model_config.model_type)
     if (
         cfg.adapter