Add CheckpointSave node to save checkpoints.

The created checkpoints contain workflow metadata that can be loaded by
dragging them on top of the UI or loading them with the "Load" button.

Checkpoints will be saved in fp16 or fp32 depending on the format ComfyUI
is using for inference on your hardware. To force fp32 use: --force-fp32

Anything that patches the model weights like merging or loras will be
saved.

The output directory is currently set to: output/checkpoints but that might
change in the future.

comfy_extras/nodes_model_merging.py

@@ -1,4 +1,8 @@
-
+import comfy.sd
+import comfy.utils
+import folder_paths
+import json
+import os
 
 class ModelMergeSimple:
     @classmethod
@@ -49,7 +53,43 @@ class ModelMergeBlocks:
             m.add_patches({k: (sd[k], )}, 1.0 - ratio, ratio)
         return (m, )
 
+class CheckpointSave:
+    def __init__(self):
+        self.output_dir = folder_paths.get_output_directory()
+
+    @classmethod
+    def INPUT_TYPES(s):
+        return {"required": { "model": ("MODEL",),
+                              "clip": ("CLIP",),
+                              "vae": ("VAE",),
+                              "filename_prefix": ("STRING", {"default": "checkpoints/ComfyUI"}),},
+                "hidden": {"prompt": "PROMPT", "extra_pnginfo": "EXTRA_PNGINFO"},}
+    RETURN_TYPES = ()
+    FUNCTION = "save"
+    OUTPUT_NODE = True
+
+    CATEGORY = "_for_testing/model_merging"
+
+    def save(self, model, clip, vae, filename_prefix, prompt=None, extra_pnginfo=None):
+        full_output_folder, filename, counter, subfolder, filename_prefix = folder_paths.get_save_image_path(filename_prefix, self.output_dir)
+        prompt_info = ""
+        if prompt is not None:
+            prompt_info = json.dumps(prompt)
+
+        metadata = {"prompt": prompt_info}
+        if extra_pnginfo is not None:
+            for x in extra_pnginfo:
+                metadata[x] = json.dumps(extra_pnginfo[x])
+
+        output_checkpoint = f"{filename}_{counter:05}_.safetensors"
+        output_checkpoint = os.path.join(full_output_folder, output_checkpoint)
+
+        comfy.sd.save_checkpoint(output_checkpoint, model, clip, vae, metadata=metadata)
+        return {}
+
+
 NODE_CLASS_MAPPINGS = {
     "ModelMergeSimple": ModelMergeSimple,
-    "ModelMergeBlocks": ModelMergeBlocks
+    "ModelMergeBlocks": ModelMergeBlocks,
+    "CheckpointSave": CheckpointSave,
 }