Add error if with CDC if cache_latents or cache_latents_to_disk is not set

library/train_util.py

@@ -2736,6 +2736,29 @@ class DatasetGroup(torch.utils.data.ConcatDataset):
         """
         from pathlib import Path
 
+        # Validate that latent caching is enabled
+        # CDC requires latents to be cached (either to disk or in memory) because:
+        # 1. CDC files are named based on latent cache filenames
+        # 2. CDC files are saved next to latent cache files
+        # 3. Training needs latent paths to load corresponding CDC files
+        has_cached_latents = False
+        for dataset in self.datasets:
+            for info in dataset.image_data.values():
+                if info.latents is not None or info.latents_npz is not None:
+                    has_cached_latents = True
+                    break
+            if has_cached_latents:
+                break
+
+        if not has_cached_latents:
+            raise ValueError(
+                "CDC-FM requires latent caching to be enabled. "
+                "Please enable latent caching by setting one of:\n"
+                "  - cache_latents = true (cache in memory)\n"
+                "  - cache_latents_to_disk = true (cache to disk)\n"
+                "in your training config or command line arguments."
+            )
+
         # Collect dataset/subset directories for config hash
         dataset_dirs = []
         for dataset in self.datasets:

tests/library/test_cdc_cache_detection.py

@@ -243,6 +243,43 @@ def test_cdc_cache_detection_partial_cache():
         assert result is False, "Should detect that some CDC cache files are missing"
 
 
+def test_cdc_requires_latent_caching():
+    """
+    Test that CDC-FM gives a clear error when latent caching is not enabled.
+    """
+
+    with tempfile.TemporaryDirectory() as tmpdir:
+        # Setup mock dataset with NO latent caching (both latents and latents_npz are None)
+        image_info = ImageInfo(
+            image_key="test_image",
+            num_repeats=1,
+            caption="test",
+            is_reg=False,
+            absolute_path=str(Path(tmpdir) / "image.png")
+        )
+        image_info.latents_npz = None  # No disk cache
+        image_info.latents = None  # No memory cache
+        image_info.bucket_reso = (512, 512)
+
+        mock_dataset = MockDataset({"test_image": image_info})
+        dataset_group = DatasetGroup([mock_dataset])
+
+        # Test: Attempt to cache CDC without latent caching enabled
+        with pytest.raises(ValueError) as exc_info:
+            dataset_group.cache_cdc_gamma_b(
+                k_neighbors=256,
+                k_bandwidth=8,
+                d_cdc=8,
+                gamma=1.0
+            )
+
+        # Verify: Error message should mention latent caching requirement
+        error_message = str(exc_info.value)
+        assert "CDC-FM requires latent caching" in error_message
+        assert "cache_latents" in error_message
+        assert "cache_latents_to_disk" in error_message
+
+
 if __name__ == "__main__":
     # Run tests with verbose output
     pytest.main([__file__, "-v"])