add kernel debugging output on build failure

hysop/backend/device/opencl/operator/custom.py

@@ -67,6 +67,15 @@ class OpenClCustomOperator(CustomOperatorBase, OpenClOperator):
             self.func,
             f"__{self.name}_elementwise", preamble=str(cg))
 
+        # Build testing:
+        try:
+            self.__elementwise.get_kernel(False)
+        except cl.RuntimeError as e:
+            print("USED KERNEL")
+            print(",".join(kernel_args))
+            print(str(cg)+self.func)
+            raise e
+
     @op_apply
     def apply(self, **kwds):
         super().apply(**kwds)