[Flux LoRA] support parsing alpha from a flux lora state dict. (#9236)

* support parsing alpha from a flux lora state dict.

* conditional import.

* fix breaking changes.

* safeguard alpha.

* fix

src/diffusers/loaders/lora_pipeline.py

@@ -1495,10 +1495,10 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
 
     @classmethod
     @validate_hf_hub_args
-    # Copied from diffusers.loaders.lora_pipeline.SD3LoraLoaderMixin.lora_state_dict
     def lora_state_dict(
         cls,
         pretrained_model_name_or_path_or_dict: Union[str, Dict[str, torch.Tensor]],
+        return_alphas: bool = False,
         **kwargs,
     ):
         r"""
@@ -1583,7 +1583,26 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
             allow_pickle=allow_pickle,
         )
 
-        return state_dict
+        # For state dicts like
+        # https://huggingface.co/TheLastBen/Jon_Snow_Flux_LoRA
+        keys = list(state_dict.keys())
+        network_alphas = {}
+        for k in keys:
+            if "alpha" in k:
+                alpha_value = state_dict.get(k)
+                if (torch.is_tensor(alpha_value) and torch.is_floating_point(alpha_value)) or isinstance(
+                    alpha_value, float
+                ):
+                    network_alphas[k] = state_dict.pop(k)
+                else:
+                    raise ValueError(
+                        f"The alpha key ({k}) seems to be incorrect. If you think this error is unexpected, please open as issue."
+                    )
+
+        if return_alphas:
+            return state_dict, network_alphas
+        else:
+            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
@@ -1617,7 +1636,9 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
             pretrained_model_name_or_path_or_dict = pretrained_model_name_or_path_or_dict.copy()
 
         # 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)
+        state_dict, network_alphas = self.lora_state_dict(
+            pretrained_model_name_or_path_or_dict, return_alphas=True, **kwargs
+        )
 
         is_correct_format = all("lora" in key or "dora_scale" in key for key in state_dict.keys())
         if not is_correct_format:
@@ -1625,6 +1646,7 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
 
         self.load_lora_into_transformer(
             state_dict,
+            network_alphas=network_alphas,
             transformer=getattr(self, self.transformer_name) if not hasattr(self, "transformer") else self.transformer,
             adapter_name=adapter_name,
             _pipeline=self,
@@ -1634,7 +1656,7 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
         if len(text_encoder_state_dict) > 0:
             self.load_lora_into_text_encoder(
                 text_encoder_state_dict,
-                network_alphas=None,
+                network_alphas=network_alphas,
                 text_encoder=self.text_encoder,
                 prefix="text_encoder",
                 lora_scale=self.lora_scale,
@@ -1643,8 +1665,7 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
             )
 
     @classmethod
-    # Copied from diffusers.loaders.lora_pipeline.SD3LoraLoaderMixin.load_lora_into_transformer
-    def load_lora_into_transformer(cls, state_dict, transformer, adapter_name=None, _pipeline=None):
+    def load_lora_into_transformer(cls, state_dict, network_alphas, transformer, adapter_name=None, _pipeline=None):
         """
         This will load the LoRA layers specified in `state_dict` into `transformer`.
 
@@ -1653,6 +1674,10 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
                 A standard state dict containing the lora layer parameters. The keys can either be indexed directly
                 into the unet or prefixed with an additional `unet` which can be used to distinguish between text
                 encoder lora layers.
+            network_alphas (`Dict[str, float]`):
+                The value of the network alpha used for stable learning and preventing underflow. This value has the
+                same meaning as the `--network_alpha` option in the kohya-ss trainer script. Refer to [this
+                link](https://github.com/darkstorm2150/sd-scripts/blob/main/docs/train_network_README-en.md#execute-learning).
             transformer (`SD3Transformer2DModel`):
                 The Transformer model to load the LoRA layers into.
             adapter_name (`str`, *optional*):
@@ -1684,7 +1709,12 @@ class FluxLoraLoaderMixin(LoraBaseMixin):
                 if "lora_B" in key:
                     rank[key] = val.shape[1]
 
-            lora_config_kwargs = get_peft_kwargs(rank, network_alpha_dict=None, peft_state_dict=state_dict)
+            if network_alphas is not None and len(network_alphas) >= 1:
+                prefix = cls.transformer_name
+                alpha_keys = [k for k in network_alphas.keys() if k.startswith(prefix) and k.split(".")[0] == prefix]
+                network_alphas = {k.replace(f"{prefix}.", ""): v for k, v in network_alphas.items() if k in alpha_keys}
+
+            lora_config_kwargs = get_peft_kwargs(rank, network_alpha_dict=network_alphas, peft_state_dict=state_dict)
             if "use_dora" in lora_config_kwargs:
                 if lora_config_kwargs["use_dora"] and is_peft_version("<", "0.9.0"):
                     raise ValueError(

tests/lora/test_lora_layers_flux.py

@@ -12,19 +12,26 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+import os
 import sys
+import tempfile
 import unittest
 
+import numpy as np
+import safetensors.torch
 import torch
 from transformers import AutoTokenizer, CLIPTextModel, CLIPTokenizer, T5EncoderModel
 
 from diffusers import FlowMatchEulerDiscreteScheduler, FluxPipeline, FluxTransformer2DModel
-from diffusers.utils.testing_utils import floats_tensor, require_peft_backend
+from diffusers.utils.testing_utils import floats_tensor, is_peft_available, require_peft_backend, torch_device
 
 
+if is_peft_available():
+    from peft.utils import get_peft_model_state_dict
+
 sys.path.append(".")
 
-from utils import PeftLoraLoaderMixinTests  # noqa: E402
+from utils import PeftLoraLoaderMixinTests, check_if_lora_correctly_set  # noqa: E402
 
 
 @require_peft_backend
@@ -90,3 +97,51 @@ class FluxLoRATests(unittest.TestCase, PeftLoraLoaderMixinTests):
             pipeline_inputs.update({"generator": generator})
 
         return noise, input_ids, pipeline_inputs
+
+    def test_with_alpha_in_state_dict(self):
+        components, _, denoiser_lora_config = self.get_dummy_components(FlowMatchEulerDiscreteScheduler)
+        pipe = self.pipeline_class(**components)
+        pipe = pipe.to(torch_device)
+        pipe.set_progress_bar_config(disable=None)
+        _, _, inputs = self.get_dummy_inputs(with_generator=False)
+
+        output_no_lora = pipe(**inputs, generator=torch.manual_seed(0)).images
+        self.assertTrue(output_no_lora.shape == self.output_shape)
+
+        pipe.transformer.add_adapter(denoiser_lora_config)
+        self.assertTrue(check_if_lora_correctly_set(pipe.transformer), "Lora not correctly set in transformer")
+
+        images_lora = pipe(**inputs, generator=torch.manual_seed(0)).images
+
+        with tempfile.TemporaryDirectory() as tmpdirname:
+            denoiser_state_dict = get_peft_model_state_dict(pipe.transformer)
+            self.pipeline_class.save_lora_weights(tmpdirname, transformer_lora_layers=denoiser_state_dict)
+
+            self.assertTrue(os.path.isfile(os.path.join(tmpdirname, "pytorch_lora_weights.safetensors")))
+            pipe.unload_lora_weights()
+            pipe.load_lora_weights(os.path.join(tmpdirname, "pytorch_lora_weights.safetensors"))
+
+            # modify the state dict to have alpha values following
+            # https://huggingface.co/TheLastBen/Jon_Snow_Flux_LoRA/blob/main/jon_snow.safetensors
+            state_dict_with_alpha = safetensors.torch.load_file(
+                os.path.join(tmpdirname, "pytorch_lora_weights.safetensors")
+            )
+            alpha_dict = {}
+            for k, v in state_dict_with_alpha.items():
+                # only do for `transformer` and for the k projections -- should be enough to test.
+                if "transformer" in k and "to_k" in k and "lora_A" in k:
+                    alpha_dict[f"{k}.alpha"] = float(torch.randint(10, 100, size=()))
+            state_dict_with_alpha.update(alpha_dict)
+
+        images_lora_from_pretrained = pipe(**inputs, generator=torch.manual_seed(0)).images
+        self.assertTrue(check_if_lora_correctly_set(pipe.transformer), "Lora not correctly set in denoiser")
+
+        pipe.unload_lora_weights()
+        pipe.load_lora_weights(state_dict_with_alpha)
+        images_lora_with_alpha = pipe(**inputs, generator=torch.manual_seed(0)).images
+
+        self.assertTrue(
+            np.allclose(images_lora, images_lora_from_pretrained, atol=1e-3, rtol=1e-3),
+            "Loading from saved checkpoints should give same results.",
+        )
+        self.assertFalse(np.allclose(images_lora_with_alpha, images_lora, atol=1e-3, rtol=1e-3))