feat: auto-register node replacements from custom node JSON files

Custom node authors can now ship a `node_replacements.json` in their
repo root to define replacements declaratively. During node loading,
ComfyUI reads these files and registers entries via the existing
NodeReplaceManager — no Python registration code needed.

This enables two use cases:
1. Authors deprecate/rename nodes with a migration path for old workflows
2. Authors offer their nodes as drop-in replacements for other packs

The JSON format matches NodeReplace.as_dict() output, keyed by old_node_id.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

nodes.py

@@ -2202,6 +2202,54 @@ def get_module_name(module_path: str) -> str:
     return base_path
 
 
+def load_node_replacements_json(module_dir: str, module_name: str):
+    """Load node_replacements.json from a custom node directory and register replacements.
+
+    Custom node authors can ship a node_replacements.json file in their repo root
+    to define node replacements declaratively, without writing Python registration code.
+    The file format matches the output of NodeReplace.as_dict(), keyed by old_node_id.
+    """
+    replacements_path = os.path.join(module_dir, "node_replacements.json")
+    if not os.path.isfile(replacements_path):
+        return
+
+    try:
+        with open(replacements_path, "r", encoding="utf-8") as f:
+            data = json.load(f)
+
+        if not isinstance(data, dict):
+            logging.warning(f"node_replacements.json in {module_name} must be a JSON object, skipping.")
+            return
+
+        from server import PromptServer
+        from comfy_api.latest._io import NodeReplace
+
+        manager = PromptServer.instance.node_replace_manager
+        count = 0
+        for old_node_id, replacements in data.items():
+            if not isinstance(replacements, list):
+                logging.warning(f"node_replacements.json in {module_name}: value for '{old_node_id}' must be a list, skipping.")
+                continue
+            for entry in replacements:
+                if not isinstance(entry, dict):
+                    continue
+                manager.register(NodeReplace(
+                    new_node_id=entry.get("new_node_id", ""),
+                    old_node_id=entry.get("old_node_id", old_node_id),
+                    old_widget_ids=entry.get("old_widget_ids"),
+                    input_mapping=entry.get("input_mapping"),
+                    output_mapping=entry.get("output_mapping"),
+                ))
+                count += 1
+
+        if count > 0:
+            logging.info(f"Loaded {count} node replacement(s) from {module_name}/node_replacements.json")
+    except json.JSONDecodeError as e:
+        logging.warning(f"Failed to parse node_replacements.json in {module_name}: {e}")
+    except Exception as e:
+        logging.warning(f"Failed to load node_replacements.json from {module_name}: {e}")
+
+
 async def load_custom_node(module_path: str, ignore=set(), module_parent="custom_nodes") -> bool:
     module_name = get_module_name(module_path)
     if os.path.isfile(module_path):
@@ -2226,6 +2274,8 @@ async def load_custom_node(module_path: str, ignore=set(), module_parent="custom
 
         LOADED_MODULE_DIRS[module_name] = os.path.abspath(module_dir)
 
+        load_node_replacements_json(module_dir, module_name)
+
         try:
             from comfy_config import config_parser
 

tests/test_node_replacements_json.py

@@ -0,0 +1,220 @@
+"""Tests for auto-registration of node_replacements.json from custom node directories."""
+import json
+import os
+import sys
+import tempfile
+import unittest
+from unittest.mock import MagicMock, patch
+
+# We can't import nodes.py directly (torch dependency), so we test the
+# load_node_replacements_json logic by re-creating it from the same source.
+# This validates the JSON parsing and NodeReplace construction logic.
+
+
+class MockNodeReplace:
+    """Mirrors comfy_api.latest._io.NodeReplace for testing."""
+    def __init__(self, new_node_id, old_node_id, old_widget_ids=None,
+                 input_mapping=None, output_mapping=None):
+        self.new_node_id = new_node_id
+        self.old_node_id = old_node_id
+        self.old_widget_ids = old_widget_ids
+        self.input_mapping = input_mapping
+        self.output_mapping = output_mapping
+
+
+def load_node_replacements_json(module_dir, module_name, manager, NodeReplace=MockNodeReplace):
+    """Standalone version of the function from nodes.py for testing."""
+    import logging
+    replacements_path = os.path.join(module_dir, "node_replacements.json")
+    if not os.path.isfile(replacements_path):
+        return
+
+    try:
+        with open(replacements_path, "r", encoding="utf-8") as f:
+            data = json.load(f)
+
+        if not isinstance(data, dict):
+            logging.warning(f"node_replacements.json in {module_name} must be a JSON object, skipping.")
+            return
+
+        count = 0
+        for old_node_id, replacements in data.items():
+            if not isinstance(replacements, list):
+                logging.warning(f"node_replacements.json in {module_name}: value for '{old_node_id}' must be a list, skipping.")
+                continue
+            for entry in replacements:
+                if not isinstance(entry, dict):
+                    continue
+                manager.register(NodeReplace(
+                    new_node_id=entry.get("new_node_id", ""),
+                    old_node_id=entry.get("old_node_id", old_node_id),
+                    old_widget_ids=entry.get("old_widget_ids"),
+                    input_mapping=entry.get("input_mapping"),
+                    output_mapping=entry.get("output_mapping"),
+                ))
+                count += 1
+
+        if count > 0:
+            logging.info(f"Loaded {count} node replacement(s) from {module_name}/node_replacements.json")
+    except json.JSONDecodeError as e:
+        logging.warning(f"Failed to parse node_replacements.json in {module_name}: {e}")
+    except Exception as e:
+        logging.warning(f"Failed to load node_replacements.json from {module_name}: {e}")
+
+
+class TestLoadNodeReplacementsJson(unittest.TestCase):
+    """Test auto-registration of node_replacements.json from custom node directories."""
+
+    def setUp(self):
+        self.tmpdir = tempfile.mkdtemp()
+        self.mock_manager = MagicMock()
+
+    def _write_json(self, data):
+        path = os.path.join(self.tmpdir, "node_replacements.json")
+        with open(path, "w") as f:
+            json.dump(data, f)
+
+    def _load(self):
+        load_node_replacements_json(self.tmpdir, "test-node-pack", self.mock_manager)
+
+    def test_no_file_does_nothing(self):
+        """No node_replacements.json — should silently do nothing."""
+        self._load()
+        self.mock_manager.register.assert_not_called()
+
+    def test_empty_object(self):
+        """Empty {} — should do nothing."""
+        self._write_json({})
+        self._load()
+        self.mock_manager.register.assert_not_called()
+
+    def test_single_replacement(self):
+        """Single replacement entry registers correctly."""
+        self._write_json({
+            "OldNode": [{
+                "new_node_id": "NewNode",
+                "old_node_id": "OldNode",
+                "input_mapping": [{"new_id": "model", "old_id": "ckpt_name"}],
+                "output_mapping": [{"new_idx": 0, "old_idx": 0}],
+            }]
+        })
+        self._load()
+        self.mock_manager.register.assert_called_once()
+        registered = self.mock_manager.register.call_args[0][0]
+        self.assertEqual(registered.new_node_id, "NewNode")
+        self.assertEqual(registered.old_node_id, "OldNode")
+        self.assertEqual(registered.input_mapping, [{"new_id": "model", "old_id": "ckpt_name"}])
+        self.assertEqual(registered.output_mapping, [{"new_idx": 0, "old_idx": 0}])
+
+    def test_multiple_replacements(self):
+        """Multiple old_node_ids each with entries."""
+        self._write_json({
+            "NodeA": [{"new_node_id": "NodeB", "old_node_id": "NodeA"}],
+            "NodeC": [{"new_node_id": "NodeD", "old_node_id": "NodeC"}],
+        })
+        self._load()
+        self.assertEqual(self.mock_manager.register.call_count, 2)
+
+    def test_multiple_alternatives_for_same_node(self):
+        """Multiple replacement options for the same old node."""
+        self._write_json({
+            "OldNode": [
+                {"new_node_id": "AltA", "old_node_id": "OldNode"},
+                {"new_node_id": "AltB", "old_node_id": "OldNode"},
+            ]
+        })
+        self._load()
+        self.assertEqual(self.mock_manager.register.call_count, 2)
+
+    def test_null_mappings(self):
+        """Null input/output mappings (trivial replacement)."""
+        self._write_json({
+            "OldNode": [{
+                "new_node_id": "NewNode",
+                "old_node_id": "OldNode",
+                "input_mapping": None,
+                "output_mapping": None,
+            }]
+        })
+        self._load()
+        registered = self.mock_manager.register.call_args[0][0]
+        self.assertIsNone(registered.input_mapping)
+        self.assertIsNone(registered.output_mapping)
+
+    def test_old_node_id_defaults_to_key(self):
+        """If old_node_id is missing from entry, uses the dict key."""
+        self._write_json({
+            "OldNode": [{"new_node_id": "NewNode"}]
+        })
+        self._load()
+        registered = self.mock_manager.register.call_args[0][0]
+        self.assertEqual(registered.old_node_id, "OldNode")
+
+    def test_invalid_json_skips(self):
+        """Invalid JSON file — should warn and skip, not crash."""
+        path = os.path.join(self.tmpdir, "node_replacements.json")
+        with open(path, "w") as f:
+            f.write("{invalid json")
+        self._load()
+        self.mock_manager.register.assert_not_called()
+
+    def test_non_object_json_skips(self):
+        """JSON array instead of object — should warn and skip."""
+        self._write_json([1, 2, 3])
+        self._load()
+        self.mock_manager.register.assert_not_called()
+
+    def test_non_list_value_skips(self):
+        """Value is not a list — should warn and skip that key."""
+        self._write_json({
+            "OldNode": "not a list",
+            "GoodNode": [{"new_node_id": "NewNode", "old_node_id": "GoodNode"}],
+        })
+        self._load()
+        self.assertEqual(self.mock_manager.register.call_count, 1)
+
+    def test_with_old_widget_ids(self):
+        """old_widget_ids are passed through."""
+        self._write_json({
+            "OldNode": [{
+                "new_node_id": "NewNode",
+                "old_node_id": "OldNode",
+                "old_widget_ids": ["width", "height"],
+            }]
+        })
+        self._load()
+        registered = self.mock_manager.register.call_args[0][0]
+        self.assertEqual(registered.old_widget_ids, ["width", "height"])
+
+    def test_set_value_in_input_mapping(self):
+        """input_mapping with set_value entries."""
+        self._write_json({
+            "OldNode": [{
+                "new_node_id": "NewNode",
+                "old_node_id": "OldNode",
+                "input_mapping": [
+                    {"new_id": "method", "set_value": "lanczos"},
+                    {"new_id": "size", "old_id": "dimension"},
+                ],
+            }]
+        })
+        self._load()
+        registered = self.mock_manager.register.call_args[0][0]
+        self.assertEqual(len(registered.input_mapping), 2)
+        self.assertEqual(registered.input_mapping[0]["set_value"], "lanczos")
+        self.assertEqual(registered.input_mapping[1]["old_id"], "dimension")
+
+    def test_non_dict_entry_skipped(self):
+        """Non-dict entries in the list are silently skipped."""
+        self._write_json({
+            "OldNode": [
+                "not a dict",
+                {"new_node_id": "NewNode", "old_node_id": "OldNode"},
+            ]
+        })
+        self._load()
+        self.assertEqual(self.mock_manager.register.call_count, 1)
+
+
+if __name__ == "__main__":
+    unittest.main()