feat: validate sample packing requires flash_attention (#1465)

* feat: validate sample packing requires flash_attention

* fix: check for sdp_attn per suggestion

* feat: add FA to tests

src/axolotl/utils/config/models/input/v0_4_1/__init__.py

@@ -1,6 +1,7 @@
 """
 Module for pydantic models for configuration
 """
+
 # pylint: disable=too-many-lines
 
 import logging
@@ -655,6 +656,20 @@ class AxolotlInputConfig(
 
         return data
 
+    @model_validator(mode="before")
+    @classmethod
+    def check_sample_packing_wo_flash(cls, data):
+        if (
+            data.get("sample_packing")
+            and not data.get("flash_attention")
+            and not data.get("sdp_attention")
+        ):
+            raise ValueError(
+                "sample_packing requires flash_attention or sdp_attention to be set to true"
+            )
+
+        return data
+
     @model_validator(mode="before")
     @classmethod
     def check_sample_packing_w_rl(cls, data):