fix circular import

Co-authored-by: Patrick von Platen <patrick.v.platen@gmail.com>

docs/source/en/_toctree.yml

@@ -19,6 +19,8 @@
     title: Train a diffusion model
   - local: tutorials/using_peft_for_inference
     title: Inference with PEFT
+  - local: tutorials/custom_pipelines_components
+    title: Working with fully custom pipelines and components
   title: Tutorials
 - sections:
   - sections:

docs/source/en/tutorials/custom_pipelines_components.md

@@ -0,0 +1,135 @@
+<!--Copyright 2023 The HuggingFace Team. All rights reserved.
+
+Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with
+the License. You may obtain a copy of the License at
+
+http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on
+an "AS IS" BASIS, 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.
+-->
+
+# Working with fully custom pipelines and components
+
+Diffusers supports the use [custom pipelines](../using-diffusers/contribute_pipeline) letting the users add any additional features on top of the [`DiffusionPipeline`]. However, it can get cumbersome if you're dealing with a custom pipeline where its components (such as the UNet, VAE, scheduler) are also custom. 
+
+We allow loading of such pipelines by exposing a `trust_remote_code` argument inside [`DiffusionPipeline`]. The advantage of `trust_remote_code` lies in its flexibility. You can have different levels of customizations for a pipeline. Following are a few examples:
+
+* Only UNet is custom 
+* UNet and VAE both are custom
+* Pipeline is custom 
+* UNet, VAE, scheduler, and pipeline are custom 
+
+With `trust_remote_code=True`, you can achieve perform of the above!
+
+This tutorial covers how to author your pipeline repository so that it becomes compatible with `trust_remote_code`. You'll use a custom UNet, a custom scheduler, and a custom pipeline for this purpose. 
+
+<Tip warning={true}>
+
+You should use `trust_remote_code=True` _only_ when you fully trust the code and have verified its usage.
+
+</Tip>
+
+## Pipeline components
+
+In the interest of brevity, you'll use the custom UNet, scheduler, and pipeline classes that we've already authored:
+
+```bash
+# Custom UNet
+wget https://huggingface.co/sayakpaul/custom_pipeline_remote_code/raw/main/unet/my_unet_model.py
+# Custom scheduler
+wget https://huggingface.co/sayakpaul/custom_pipeline_remote_code/raw/main/scheduler/my_scheduler.py
+# Custom pipeline
+wget https://huggingface.co/sayakpaul/custom_pipeline_remote_code/raw/main/my_pipeline.py
+```
+
+<Tip warning={true}>
+
+The above classes are just for references. We encourage you to experiment with these classes for desired customizations.
+
+</Tip>
+
+Load the individual components, starting with the UNet:
+
+```python
+from my_unet_model import MyUNetModel
+
+pretrained_id = "hf-internal-testing/tiny-sdxl-custom-all"
+unet = MyUNetModel.from_pretrained(pretrained_id, subfolder="unet")
+```
+
+Then go for the scheduler:
+
+```python
+from my_scheduler import MyUNetModel
+
+scheduler = MyScheduler.from_pretrained(pretrained_id, subfolder="scheduler")
+```
+
+Finally, the VAE and the text encoders:
+
+```python
+from transformers import CLIPTextModel, CLIPTextModelWithProjection, CLIPTokenizer
+from diffusers import AutoencoderKL
+
+text_encoder = CLIPTextModel.from_pretrained(pretrained_id, subfolder="text_encoder")
+text_encoder_2 = CLIPTextModelWithProjection.from_pretrained(pretrained_id, subfolder="text_encoder_2")
+tokenizer = CLIPTokenizer.from_pretrained(pretrained_id, subfolder="tokenizer")
+tokenizer_2 = CLIPTokenizer.from_pretrained(pretrained_id, subfolder="tokenizer_2")
+
+vae = AutoencoderKL.from_pretrained(pretrained_id, subfolder="vae")
+```
+
+`MyUNetModel`, `MyScheduler`, and `MyPipeline` use blocks that are already supported by Diffusers. If you are using any custom blocks make sure to put them in the module files themselves. 
+
+## Pipeline initialization and serialization
+
+With all the components, you can now initialize the custom pipeline:
+
+```python
+pipeline = MyPipeline(
+    vae=vae, 
+    unet=unet, 
+    text_encoder=text_encoder, 
+    text_encoder_2=text_encoder_2,
+    tokenizer=tokenizer, 
+    tokenizer_2=tokenizer_2, 
+    scheduler=scheduler,
+)
+```
+
+Now, push the pipeline to the Hub:
+
+```python
+pipeline.push_to_hub("custom_pipeline_remote_code")
+```
+
+Since the `pipeline` itself is a custom pipeline, its corresponding Python module will also be pushed ([example](https://huggingface.co/sayakpaul/custom_pipeline_remote_code/blob/main/my_pipeline.py)). If the pipeline has any other custom components, they will be pushed as well ([UNet](https://huggingface.co/sayakpaul/custom_pipeline_remote_code/blob/main/unet/my_unet_model.py), [scheduler](https://huggingface.co/sayakpaul/custom_pipeline_remote_code/blob/main/scheduler/my_scheduler.py)). 
+
+If you want to keep the pipeline local, then use the [`PushToHubMixin.save_pretrained`] method.
+
+## Pipeline loading
+
+You can load this pipeline from the Hub by specifying `trust_remote_code=True`:
+
+```python
+from diffusers import DiffusionPipeline
+
+reloaded_pipeline = DiffusionPipeline.from_pretrained(
+    "sayakpaul/custom_pipeline_remote_code", 
+    torch_dtype=torch.float16,
+    trust_remote_code=True,
+).to("cuda")
+```
+
+And then perform inference:
+
+```python
+prompt = "hey"
+num_inference_steps = 2
+
+_ = reloaded_pipeline(prompt=prompt, num_inference_steps=num_inference_steps)[0]
+```
+
+For more complex pipelines, readers are welcome to check out [this comment](https://github.com/huggingface/diffusers/pull/5472#issuecomment-1775034461) on GitHub.

src/diffusers/configuration_utils.py

@@ -21,6 +21,7 @@ import inspect
 import json
 import os
 import re
+import sys
 from collections import OrderedDict
 from pathlib import PosixPath
 from typing import Any, Dict, Tuple, Union
@@ -162,6 +163,30 @@ class ConfigMixin:
         self.to_json_file(output_config_file)
         logger.info(f"Configuration saved in {output_config_file}")
 
+        # Additionally, save the implementation file too. It can happen for a pipeline, for a model, and
+        # for a scheduler.
+
+        # To avoid circular import problems.
+        from .models import _import_structure as model_modules
+        from .pipelines import _import_structure as pipeline_modules
+        from .schedulers import _import_structure as scheduler_modules
+
+        _all_available_pipelines_schedulers_model_classes = sum(
+            (list(model_modules.values()) + list(scheduler_modules.values()) + list(pipeline_modules.values())), []
+        )
+        if self.__class__.__name__ not in _all_available_pipelines_schedulers_model_classes:
+            module_to_save = self.__class__.__module__
+            absolute_module_path = sys.modules[module_to_save].__file__
+            try:
+                with open(absolute_module_path, "r") as original_file:
+                    content = original_file.read()
+                path_to_write = os.path.join(save_directory, f"{module_to_save}.py")
+                with open(path_to_write, "w") as new_file:
+                    new_file.write(content)
+                    logger.info(f"{module_to_save}.py saved in {save_directory}")
+            except Exception as e:
+                logger.error(e)
+
         if push_to_hub:
             commit_message = kwargs.pop("commit_message", None)
             private = kwargs.pop("private", False)
@@ -567,7 +592,24 @@ class ConfigMixin:
                 String containing all the attributes that make up the configuration instance in JSON format.
         """
         config_dict = self._internal_dict if hasattr(self, "_internal_dict") else {}
-        config_dict["_class_name"] = self.__class__.__name__
+        cls_name = self.__class__.__name__
+
+        # Additionally, save the implementation file too. It can happen for a pipeline, for a model, and
+        # for a scheduler.
+
+        # To avoid circular import problems.
+        from .models import _import_structure as model_modules
+        from .pipelines import _import_structure as pipeline_modules
+        from .schedulers import _import_structure as scheduler_modules
+
+        _all_available_pipelines_schedulers_model_classes = sum(
+            (list(model_modules.values()) + list(scheduler_modules.values()) + list(pipeline_modules.values())), []
+        )
+
+        if cls_name not in _all_available_pipelines_schedulers_model_classes:
+            config_dict["_class_name"] = [str(self.__class__.__module__), cls_name]
+        else:
+            config_dict["_class_name"] = cls_name
         config_dict["_diffusers_version"] = __version__
 
         def to_json_saveable(value):