Raise a8wxdq load errors only when quant scheme is used (#1231)

* Show a8wxdq load error only when the quant is used

* Update Error check

Author: Jack-Khuu

torchchat/utils/quantize.py

@@ -51,6 +51,9 @@
 )
 
 
+# Flag for whether the a8wxdq quantizer is available.
+a8wxdq_load_error: Optional[Exception] = None
+
 #########################################################################
 ###                  torchchat quantization API                       ###
 
@@ -76,6 +79,10 @@ def quantize_model(
         quantize_options = json.loads(quantize_options)
 
     for quantizer, q_kwargs in quantize_options.items():
+        # Test if a8wxdq quantizer is available; Surface error if not.
+        if quantizer == "linear:a8wxdq" and a8wxdq_load_error is not None:
+            raise Exception(f"Note: Failed to load torchao experimental a8wxdq quantizer with error: {a8wxdq_load_error}")
+
         if (
             quantizer not in quantizer_class_dict
             and quantizer not in ao_quantizer_class_dict
@@ -899,4 +906,4 @@ def quantized_model(self) -> nn.Module:
         print("Slow fallback kernels will be used.")
 
 except Exception as e:
-    print(f"Failed to load torchao experimental a8wxdq quantizer with error: {e}")
+    a8wxdq_load_error = e