[WIP] Check UNet shapes in StableDiffusionInpaintPipeline __init__ (#2853)

Add warning in __init__ if user loads a checkpoint with pipeline.unet.config.in_channels other than 9.

src/diffusers/pipelines/stable_diffusion/pipeline_stable_diffusion_inpaint.py

@@ -243,6 +243,14 @@ class StableDiffusionInpaintPipeline(DiffusionPipeline):
             new_config = dict(unet.config)
             new_config["sample_size"] = 64
             unet._internal_dict = FrozenDict(new_config)
+        # Check shapes, assume num_channels_latents == 4, num_channels_mask == 1, num_channels_masked == 4
+        if unet.config.in_channels != 9:
+            logger.warning(
+                f"You have loaded a UNet with {unet.config.in_channels} input channels, whereas by default,"
+                f" {self.__class__} assumes that `pipeline.unet` has 9 input channels: 4 for `num_channels_latents`,"
+                " 1 for `num_channels_mask`, and 4 for `num_channels_masked_image`. If you did not intend to modify"
+                " this behavior, please check whether you have loaded the right checkpoint."
+            )
 
         self.register_modules(
             vae=vae,