Make it easier for users to discover that copying arrays and structs …

…to storage is unimplemented only in legacy codegen and works via IR (#15432)

libsolidity/codegen/ArrayUtils.cpp

@@ -224,7 +224,7 @@ void ArrayUtils::copyArrayToStorage(ArrayType const& _targetType, ArrayType cons
 				else if (sourceBaseType->isValueType())
 					CompilerUtils(_context).loadFromMemoryDynamic(*sourceBaseType, fromCalldata, true, false);
 				else
-					solUnimplemented("Copying of type " + _sourceType.toString(false) + " to storage not yet supported.");
+					solUnimplemented("Copying of type " + _sourceType.toString(false) + " to storage is not supported in legacy (only supported by the IR pipeline). Hint: try compiling with `--via-ir` (CLI) or the equivalent `viaIR: true` (Standard JSON)");
 				// stack: target_ref target_data_end source_data_pos target_data_pos source_data_end [target_byte_offset] [source_byte_offset] <source_value>...
 				assertThrow(
 					2 + byteOffsetSize + sourceBaseType->sizeOnStack() <= 16,