support latest few-step wan LoRA. (#12541)

* support latest few-step wan LoRA.

* up

* up

src/diffusers/loaders/lora_conversion_utils.py

@@ -1977,14 +1977,34 @@ def _convert_non_diffusers_wan_lora_to_diffusers(state_dict):
                     "time_projection.1.diff_b"
                 )
 
-        if any("head.head" in k for k in state_dict):
+        if any("head.head" in k for k in original_state_dict):
+            if any(f"head.head.{lora_down_key}.weight" in k for k in state_dict):
                 converted_state_dict["proj_out.lora_A.weight"] = original_state_dict.pop(
                     f"head.head.{lora_down_key}.weight"
                 )
-            converted_state_dict["proj_out.lora_B.weight"] = original_state_dict.pop(f"head.head.{lora_up_key}.weight")
+            if any(f"head.head.{lora_up_key}.weight" in k for k in state_dict):
+                converted_state_dict["proj_out.lora_B.weight"] = original_state_dict.pop(
+                    f"head.head.{lora_up_key}.weight"
+                )
             if "head.head.diff_b" in original_state_dict:
                 converted_state_dict["proj_out.lora_B.bias"] = original_state_dict.pop("head.head.diff_b")
 
+            # Notes: https://huggingface.co/lightx2v/Wan2.2-Distill-Loras
+            # This is my (sayakpaul) assumption that this particular key belongs to the down matrix.
+            # Since for this particular LoRA, we don't have the corresponding up matrix, I will use
+            # an identity.
+            if any("head.head" in k and k.endswith(".diff") for k in state_dict):
+                if f"head.head.{lora_down_key}.weight" in state_dict:
+                    logger.info(
+                        f"The state dict seems to be have both `head.head.diff` and `head.head.{lora_down_key}.weight` keys, which is unexpected."
+                    )
+                converted_state_dict["proj_out.lora_A.weight"] = original_state_dict.pop("head.head.diff")
+                down_matrix_head = converted_state_dict["proj_out.lora_A.weight"]
+                up_matrix_shape = (down_matrix_head.shape[0], converted_state_dict["proj_out.lora_B.bias"].shape[0])
+                converted_state_dict["proj_out.lora_B.weight"] = torch.eye(
+                    *up_matrix_shape, dtype=down_matrix_head.dtype, device=down_matrix_head.device
+                ).T
+
         for text_time in ["text_embedding", "time_embedding"]:
             if any(text_time in k for k in original_state_dict):
                 for b_n in [0, 2]: