[Wan LoRAs] make T2V LoRAs compatible with Wan I2V (#11107)

* @hlky t2v->i2v

* Apply style fixes

* try with ones to not nullify layers

* fix method name

* revert to zeros

* add check to state_dict keys

* add comment

* copies fix

* Revert "copies fix"

This reverts commit 051f534d185c0ea065bf36a9926c4b48f496d429.

* remove copied from

* Update src/diffusers/loaders/lora_pipeline.py
Co-authored-by: hlky <hlky@hlky.ac>

* Update src/diffusers/loaders/lora_pipeline.py
Co-authored-by: hlky <hlky@hlky.ac>

* update

* update

* Update src/diffusers/loaders/lora_pipeline.py
Co-authored-by: hlky <hlky@hlky.ac>

* Apply style fixes

---------
Co-authored-by: github-actions[bot] <github-actions[bot]@users.noreply.github.com>
Co-authored-by: Linoy <linoy@hf.co>
Co-authored-by: hlky <hlky@hlky.ac>

src/diffusers/loaders/lora_pipeline.py

@@ -4249,7 +4249,33 @@ class WanLoraLoaderMixin(LoraBaseMixin):
 
         return state_dict
 
-    # Copied from diffusers.loaders.lora_pipeline.CogVideoXLoraLoaderMixin.load_lora_weights
+    @classmethod
+    def _maybe_expand_t2v_lora_for_i2v(
+        cls,
+        transformer: torch.nn.Module,
+        state_dict,
+    ):
+        if transformer.config.image_dim is None:
+            return state_dict
+
+        if any(k.startswith("transformer.blocks.") for k in state_dict):
+            num_blocks = len({k.split("blocks.")[1].split(".")[0] for k in state_dict})
+            is_i2v_lora = any("add_k_proj" in k for k in state_dict) and any("add_v_proj" in k for k in state_dict)
+
+            if is_i2v_lora:
+                return state_dict
+
+            for i in range(num_blocks):
+                for o, c in zip(["k_img", "v_img"], ["add_k_proj", "add_v_proj"]):
+                    state_dict[f"transformer.blocks.{i}.attn2.{c}.lora_A.weight"] = torch.zeros_like(
+                        state_dict[f"transformer.blocks.{i}.attn2.to_k.lora_A.weight"]
+                    )
+                    state_dict[f"transformer.blocks.{i}.attn2.{c}.lora_B.weight"] = torch.zeros_like(
+                        state_dict[f"transformer.blocks.{i}.attn2.to_k.lora_B.weight"]
+                    )
+
+        return state_dict
+
     def load_lora_weights(
         self, pretrained_model_name_or_path_or_dict: Union[str, Dict[str, torch.Tensor]], adapter_name=None, **kwargs
     ):
@@ -4287,7 +4313,11 @@ class WanLoraLoaderMixin(LoraBaseMixin):
 
         # First, ensure that the checkpoint is a compatible one and can be successfully loaded.
         state_dict = self.lora_state_dict(pretrained_model_name_or_path_or_dict, **kwargs)
-
+        # convert T2V LoRA to I2V LoRA (when loaded to Wan I2V) by adding zeros for the additional (missing) _img layers
+        state_dict = self._maybe_expand_t2v_lora_for_i2v(
+            transformer=getattr(self, self.transformer_name) if not hasattr(self, "transformer") else self.transformer,
+            state_dict=state_dict,
+        )
         is_correct_format = all("lora" in key for key in state_dict.keys())
         if not is_correct_format:
             raise ValueError("Invalid LoRA checkpoint.")