Append change instead of prepending it

It's desirable for a client to be able to predict the index of outputs.
As such we append change to the end so that the index of other outputs
doesn't changed based on whether there's change or not.

Resolves #3725

Author: Robert 'Probie' Offner

cardano-api/ChangeLog.md

@@ -1,5 +1,11 @@
 # Changelog for cardano-api
 
+## vNext
+
+### Features
+
+- Append, not prepend change output when balancing a transaction ([PR 4343](https://github.com/input-output-hk/cardano-node/pull/4343))
+
 ## 1.33.0 -- December 2021
 ## 1.32.1 -- November 2021
 

cardano-api/src/Cardano/Api/Fees.hs

@@ -1129,7 +1129,9 @@ makeTransactionBodyAutoBalance eraInMode systemstart history pparams
    accountForNoChange change@(TxOut _ balance _ _) rest =
      case txOutValueToLovelace balance of
        Lovelace 0 -> rest
-       _ -> change : rest
+       -- We append change at the end so a client can predict the indexes
+       -- out of the outputs
+       _ -> rest ++ [change]
 
    balanceCheck :: TxOutValue era -> Either TxBodyErrorAutoBalance ()
    balanceCheck balance