Goal

Short-term fixes have been made over time to avoid breaking the storage layout during upgrades. Here we want to break the storage layout by removing those short-term fixes and reach the desired storage layout.

Required changes

• Add storage gap arrays at the end of the abstract contract storage and any struct used in an array (eg. Dispute, Round, Vote).

• Unused variables and parameters
  

  kleros-v2/contracts/src/arbitration/SortitionModuleBase.sol

  Line 28 in 5e987c4

  bool alreadyTransferred; // DEPRECATED. True if tokens were already transferred before delayed stake's execution.

  
  

  kleros-v2/contracts/src/arbitration/SortitionModuleBase.sol

  Line 47 in 5e987c4

  uint256 public randomNumberRequestBlock; // DEPRECATED: to be removed in the next redeploy

  
  

  kleros-v2/contracts/src/arbitration/SortitionModuleBase.sol

  Line 51 in 5e987c4

  uint256 public rngLookahead; // DEPRECATED: to be removed in the next redeploy

  
  

  kleros-v2/contracts/src/arbitration/SortitionModuleBase.sol

  Line 57 in 5e987c4

  mapping(address jurorAccount => mapping(uint96 courtId => uint256)) public latestDelayedStakeIndex; // DEPRECATED. Maps the juror to its latest delayed stake. If there is already a delayed stake for this juror then it'll be replaced. latestDelayedStakeIndex[juror][courtID].

  
  Remove DisputeKitClassicBase.Round.nbVotes but keep _nbVotes in IDisputeKit.createDispute() for forward-compatibility with future non-classic DKs.
  

  kleros-v2/contracts/src/arbitration/dispute-kits/DisputeKitClassicBase.sol

  Line 44 in 98f7eac

  uint256 nbVotes; // Maximal number of votes this dispute can get.

• Move state variables inside a struct
  Move DisputeKitClassicBase.alreadyDrawn to the Round struct.
  

  kleros-v2/contracts/src/arbitration/dispute-kits/DisputeKitClassicBase.sol

  Line 68 in 98f7eac

  public alreadyDrawn; // True if the address has already been drawn, false by default. To be added to the Round struct when fully redeploying rather than upgrading.

Out-of-scope

Migration logic, this is left to #2119 .