Fix bug with some LoRA variants when applied to a BnB NF4 quantized m…

…odel. Note the previous commit which added a unit test to trigger this bug.

invokeai/backend/patches/layers/lora_layer_base.py

@@ -4,6 +4,7 @@
 
 import invokeai.backend.util.logging as logger
 from invokeai.backend.patches.layers.base_layer_patch import BaseLayerPatch
+from invokeai.backend.patches.layers.param_shape_utils import get_param_shape
 from invokeai.backend.util.calc_tensor_size import calc_tensors_size
 
 
@@ -67,8 +68,8 @@ def get_parameters(self, orig_parameters: dict[str, torch.Tensor], weight: float
         # Reshape all params to match the original module's shape.
         for param_name, param_weight in params.items():
             orig_param = orig_parameters[param_name]
-            if param_weight.shape != orig_param.shape:
-                params[param_name] = param_weight.reshape(orig_param.shape)
+            if param_weight.shape != get_param_shape(orig_param):
+                params[param_name] = param_weight.reshape(get_param_shape(orig_param))
 
         return params
 

invokeai/backend/patches/layers/param_shape_utils.py

@@ -0,0 +1,19 @@
+import torch
+
+try:
+    from bitsandbytes.nn.modules import Params4bit
+
+    bnb_available: bool = True
+except ImportError:
+    bnb_available: bool = False
+
+
+def get_param_shape(param: torch.Tensor) -> torch.Size:
+    """A helper function to get the shape of a parameter that handles `bitsandbytes.nn.Params4Bit` correctly."""
+    # Accessing the `.shape` attribute of `bitsandbytes.nn.Params4Bit` will return an incorrect result. Instead, we must
+    # access the `.quant_state.shape` attribute.
+    if bnb_available and type(param) is Params4bit:  # type: ignore
+        quant_state = param.quant_state
+        if quant_state is not None:
+            return quant_state.shape
+    return param.shape