Improve error message, add another error message

Author: waltdisgrace

src/cachedev.rs

@@ -118,12 +118,19 @@ impl FromStr for CacheTargetParams {
         let policy = vals[end_feature_args_index].to_owned();
 
         if vals.len() <= end_feature_args_index + 1 {
-            let err_msg = format!("Expected more arguments than were provided",);
+            let err_msg = format!("Only {} arguments provided, expected more", vals.len());
             return Err(DmError::Dm(ErrorEnum::Invalid, err_msg));
         }
 
         let num_policy_args: usize =
             parse_value(vals[end_feature_args_index + 1], "number of policy args")?;
+
+        let num_expected_args = 8 + num_feature_args + num_policy_args;
+        if vals.len() < num_expected_args {
+            let err_msg = format!("Based on number of feature arguments and policy args provided, {} arguments were expected, but {} were provided", num_expected_args, vals.len());
+            return Err(DmError::Dm(ErrorEnum::Invalid, err_msg));
+        }
+
         let start_policy_args_index = end_feature_args_index + 2;
         let end_policy_args_index = start_policy_args_index + num_policy_args;
         let policy_args: Vec<(String, String)> = vals