Sample Upgrade Handler

upgrade.go

/* 
	Before writing your upgrade handler, you will need to use the escrow-checker tool or some other means for identifying discrepancies 
	in the balances of escrow account addresses and the total supply of the assets on the associated counterparty chain.

	Once you have identified which escrow accounts have discrepancies and what the delta is between the escrow balance and the counterparty's total supply,
	you can define some type that contains the address and the assets that should be minted to reach parity between the escrow account and the counterparty total supply.

	Then inside of the upgrade handler you can mint the necessary assets to the transfer module and send them from the transfer module to the escrow account.

	NOTE: For v7 chains, you will have to modify the NewKeeper to remove the GetParams (moved to the AppModule()) and add a govMod address.
	https://github.com/cosmos/ibc-apps/releases/tag/middleware%2Fpacket-forward-middleware%2Fv7.1.1

	packetforwardkeeper.NewKeeper(
		appCodec, appKeepers.keys[packetforwardtypes.StoreKey],
		appKeepers.TransferKeeper,
		appKeepers.IBCKeeper.ChannelKeeper,
		appKeepers.DistrKeeper,
		appKeepers.BankKeeper,
		appKeepers.HooksICS4Wrapper,
		govModAddress,
	)

	...

	packetforward.NewAppModule(app.PacketForwardKeeper, app.GetSubspace(packetforwardtypes.ModuleName)),
*/

type EscrowUpdate struct {
	EscrowAddress string
	Assets []sdk.Coin
}

func CreateUpgradeHandler(
	mm *module.Manager,
	cfg module.Configurator,
	k *keepers.AppKeepers,
) upgradetypes.UpgradeHandler {
	return func(ctx sdk.Context, plan upgradetypes.Plan, vm module.VersionMap) (module.VersionMap, error) {
		// This slice needs to be initialized with objects that describe the escrow account address and the coins that need to be minted to fix the discrepancy.
		updates := []EscrowUpdate{}

		for _, update := range updates {		
			for _, coin := range update.Assets {
				coins := sdk.NewCoins(coin)

				if err := k.bankKeeper.MintCoins(ctx, transfertypes.ModuleName, coins); err != nil {
					return nil, err
				}
		
				if err := k.bankKeeper.SendCoinsFromModuleToAccount(ctx, transfertypes.ModuleName, update.EscrowAddress, coins); err != nil {
					return nil, err
				}
		
				// For ibc-go v7+ you will also need to update the transfer module's store for the total escrow amounts.
				currentTotalEscrow := k.transferKeeper.GetTotalEscrowForDenom(ctx, coin.GetDenom())
				newTotalEscrow := currentTotalEscrow.Add(coin)
				k.transferKeeper.SetTotalEscrowForDenom(ctx, newTotalEscrow)
			}
		}

		// Run migrations.
		versionMap, err := mm.RunMigrations(ctx, cfg, vm)
		if err != nil {
			return nil, err
		}

		return versionMap, err
	}
}