minter: Add inflation bounds to inflation adjustment algorithm

.github/workflows/test.yaml

@@ -47,6 +47,9 @@ jobs:
           name: ${{ github.event.repository.name }}
           token: ${{ secrets.CI_CODECOV_TOKEN }}
 
+      - name: Enforce test coverage threshold
+        run: yarn test:coverage:check
+
   editorconfig:
     name: Run editorconfig checker
     runs-on: ubuntu-latest

contracts/token/IMinter.sol

@@ -27,6 +27,16 @@ interface IMinter {
 
     function currentMintedTokens() external view returns (uint256);
 
+    function inflation() external view returns (uint256);
+
+    function inflationCeiling() external view returns (uint256);
+
+    function inflationFloor() external view returns (uint256);
+
+    function inflationChange() external view returns (uint256);
+
+    function targetBondingRate() external view returns (uint256);
+
     // Public functions
     function getController() external view returns (IController);
 }

contracts/token/Minter.sol

@@ -23,6 +23,10 @@ contract Minter is Manager, IMinter {
 
     // Per round inflation rate
     uint256 public inflation;
+    // Target maximum inflation rate
+    uint256 public inflationCeiling;
+    // Target minimum inflation rate
+    uint256 public inflationFloor;
     // Change in inflation rate per round until the target bonding rate is achieved
     uint256 public inflationChange;
     // Target bonding rate
@@ -70,15 +74,24 @@ contract Minter is Manager, IMinter {
      * @param _inflation Base inflation rate as a percentage of current total token supply
      * @param _inflationChange Change in inflation rate each round (increase or decrease) if target bonding rate is not achieved
      * @param _targetBondingRate Target bonding rate as a percentage of total bonded tokens / total token supply
+     * @param _inflationCeiling Inflation rate ceiling as a percentage of current total token supply
+     * @param _inflationFloor Inflation rate floor as a percentage of current total token supply
      */
     constructor(
         address _controller,
         uint256 _inflation,
         uint256 _inflationChange,
-        uint256 _targetBondingRate
+        uint256 _targetBondingRate,
+        uint256 _inflationCeiling,
+        uint256 _inflationFloor
     ) Manager(_controller) {
         // Inflation must be valid percentage
         require(MathUtils.validPerc(_inflation), "_inflation is invalid percentage");
+        // Inflation bounds must be valid percentages
+        require(MathUtils.validPerc(_inflationCeiling), "_inflationCeiling is invalid percentage");
+        require(MathUtils.validPerc(_inflationFloor), "_inflationFloor is invalid percentage");
+        // Inflation floor should be lower or equal to the ceiling
+        require(_inflationFloor <= _inflationCeiling, "_inflationFloor must be <= _inflationCeiling");
         // Inflation change must be valid percentage
         require(MathUtils.validPerc(_inflationChange), "_inflationChange is invalid percentage");
         // Target bonding rate must be valid percentage
@@ -87,6 +100,8 @@ contract Minter is Manager, IMinter {
         inflation = _inflation;
         inflationChange = _inflationChange;
         targetBondingRate = _targetBondingRate;
+        inflationCeiling = _inflationCeiling;
+        inflationFloor = _inflationFloor;
     }
 
     /**
@@ -115,6 +130,36 @@ contract Minter is Manager, IMinter {
         emit ParameterUpdate("inflationChange");
     }
 
+    /**
+     * @notice Set inflationCeiling. Only callable by Controller owner
+     * @param _inflationCeiling New inflation cap as a percentage of total token supply
+     */
+    function setinflationCeiling(uint256 _inflationCeiling) external onlyControllerOwner {
+        // Must be valid percentage
+        require(MathUtils.validPerc(_inflationCeiling), "_inflationCeiling is invalid percentage");
+        // Inflation ceiling should be higher or equal to the floor
+        require(_inflationCeiling >= inflationFloor, "_inflationCeiling must be >= inflationFloor");
+
+        inflationCeiling = _inflationCeiling;
+
+        emit ParameterUpdate("inflationCeiling");
+    }
+
+    /**
+     * @notice Set inflationFloor. Only callable by Controller owner
+     * @param _inflationFloor New inflation floor as a percentage of total token supply
+     */
+    function setinflationFloor(uint256 _inflationFloor) external onlyControllerOwner {
+        // Must be valid percentage
+        require(MathUtils.validPerc(_inflationFloor), "_inflationFloor is invalid percentage");
+        // Inflation floor should be lower or equal to the ceiling
+        require(_inflationFloor <= inflationCeiling, "_inflationFloor must be <= inflationCeiling");
+
+        inflationFloor = _inflationFloor;
+
+        emit ParameterUpdate("inflationFloor");
+    }
+
     /**
      * @notice Migrate to a new Minter by transferring the current Minter's LPT + ETH balance to the new Minter
      * @dev Only callable by Controller owner
@@ -138,6 +183,21 @@ contract Minter is Manager, IMinter {
         _newMinter.depositETH{ value: address(this).balance }();
     }
 
+    /**
+     * @notice Migrate state variables affected by RoundsManager from the old Minter
+     * @dev Only callable by Controller owner
+     */
+    function migrateOldMinterState() external onlyControllerOwner {
+        IMinter oldMinter = IMinter(controller.getContract(keccak256("Minter")));
+        // Old Minter cannot be the current Minter
+        require(address(oldMinter) != address(this), "old Minter cannot be current Minter");
+
+        // Transfer state from old Minter
+        currentMintableTokens = oldMinter.currentMintableTokens();
+        currentMintedTokens = oldMinter.currentMintedTokens();
+        inflation = oldMinter.inflation();
+    }
+
     /**
      * @notice Create reward based on a fractional portion of the mintable tokens for the current round
      * @param _fracNum Numerator of fraction (active transcoder's stake)
@@ -240,13 +300,22 @@ contract Minter is Manager, IMinter {
             currentBondingRate = MathUtils.percPoints(totalBonded, totalSupply);
         }
 
-        if (currentBondingRate < targetBondingRate) {
+        // Adjust inflation based on current bonding rate and target bonding rate, ensuring it stays within the floor and ceiling
+        if ((currentBondingRate < targetBondingRate && inflation < inflationCeiling) || inflation < inflationFloor) {
             // Bonding rate is below the target - increase inflation
-            inflation = inflation.add(inflationChange);
-        } else if (currentBondingRate > targetBondingRate) {
+            if (inflation.add(inflationChange) > inflationCeiling) {
+                // If inflation would go above the ceiling, set it to the ceiling
+                inflation = inflationCeiling;
+            } else {
+                inflation = inflation.add(inflationChange);
+            }
+        } else if (
+            (currentBondingRate > targetBondingRate && inflation > inflationFloor) || inflation > inflationCeiling
+        ) {
             // Bonding rate is above the target - decrease inflation
-            if (inflationChange > inflation) {
-                inflation = 0;
+            if (inflationFloor.add(inflationChange) > inflation) {
+                // If inflation would go below the floor, set it to the floor
+                inflation = inflationFloor;
             } else {
                 inflation = inflation.sub(inflationChange);
             }

deploy/deploy_contracts.ts

@@ -76,7 +76,9 @@ const func: DeployFunction = async function(hre: HardhatRuntimeEnvironment) {
             Controller.address,
             config.minter.inflation,
             config.minter.inflationChange,
-            config.minter.targetBondingRate
+            config.minter.targetBondingRate,
+            config.minter.inflationCeiling,
+            config.minter.inflationFloor
         ]
     })
 
@@ -372,6 +374,8 @@ const func: DeployFunction = async function(hre: HardhatRuntimeEnvironment) {
 
     await (await Token.grantRole(MINTER_ROLE, minter.address)).wait()
 
+    await (await Token.grantRole(DEFAULT_ADMIN_ROLE, governor.address)).wait()
+
     // Controller is owned by the deployer at this point
     // transferOwnership() needs to be called separately to give ownership to the Governor
 }

deploy/deploy_minter.ts

@@ -2,10 +2,12 @@ import {HardhatRuntimeEnvironment} from "hardhat/types"
 import {DeployFunction} from "hardhat-deploy/types"
 import {ethers} from "hardhat"
 import {Minter} from "../typechain"
+import getNetworkConfig from "./migrations.config"
 
 const func: DeployFunction = async function(hre: HardhatRuntimeEnvironment) {
     const {deployments, getNamedAccounts} = hre // Get the deployments and getNamedAccounts which are provided by hardhat-deploy
     const {deploy} = deployments // the deployments object itself contains the deploy function
+    const config = getNetworkConfig(hre.network.name)
 
     const {deployer} = await getNamedAccounts() // Fetch named accounts from hardhat.config.ts
 
@@ -18,16 +20,17 @@ const func: DeployFunction = async function(hre: HardhatRuntimeEnvironment) {
     )) as Minter
 
     const inflation = await minter.inflation()
-    const inflationChange = await minter.inflationChange()
     const targetBondingRate = await minter.targetBondingRate()
 
     await deploy("Minter", {
         from: deployer,
         args: [
             controllerDeployment.address,
             inflation,
-            inflationChange,
-            targetBondingRate
+            config.minter.inflationChange,
+            targetBondingRate,
+            config.minter.inflationCeiling,
+            config.minter.inflationFloor
         ]
     })
 }

deploy/migrations.config.ts

@@ -23,7 +23,9 @@ const gethDev = {
     minter: {
         inflation: 137,
         inflationChange: 3,
-        targetBondingRate: 500000
+        targetBondingRate: 500000,
+        inflationCeiling: 200,
+        inflationFloor: 100
     }
 }
 
@@ -51,7 +53,9 @@ const defaultConfig = {
     minter: {
         inflation: 137,
         inflationChange: 3,
-        targetBondingRate: 500000
+        targetBondingRate: 500000,
+        inflationCeiling: 200,
+        inflationFloor: 100
     },
     treasury: {
         minDelay: 0 // 0s initial proposal execution delay
@@ -99,7 +103,9 @@ const rinkeby = {
     minter: {
         inflation: 137,
         inflationChange: 3,
-        targetBondingRate: 0
+        targetBondingRate: 0,
+        inflationCeiling: 200,
+        inflationFloor: 100
     }
 }
 
@@ -126,7 +132,9 @@ const arbitrumRinkeby = {
     minter: {
         inflation: 137,
         inflationChange: 3,
-        targetBondingRate: 0
+        targetBondingRate: 0,
+        inflationCeiling: 200,
+        inflationFloor: 100
     }
 }
 
@@ -154,14 +162,11 @@ const arbitrumMainnet = {
         roundLockAmount: 100000
     },
     minter: {
-        // As of L1 round 2460 inflation was 221500 and bonding rate > 50% so inflation was declining
-        // The switch to L2 projected to occur in L1 round 2466
-        // If inflation continues to decrease inflation projected to be 221500 - (6 * 500) = 218500 in L1 round 2466
-        // No reward calls will happen on L2 until the round after migrations start since it takes a round for orchestrators to become active
-        // The inflation at the start of that round will be 218500 - 500 = 218000
-        inflation: 218500,
-        inflationChange: 500,
-        targetBondingRate: 500000000
+        inflation: 651000, // Current value at round 3766, but is overwritten by `migrateOldMinterState`
+        inflationChange: 1000, // Set according to LIP-100
+        targetBondingRate: 500000000,
+        inflationCeiling: 750000, // Set according to LIP-100
+        inflationFloor: 50000 // Set according to LIP-100
     },
     treasury: {
         minDelay: 0 // 0s initial proposal execution delay

package.json

@@ -21,6 +21,7 @@
     "clean": "rm -rf cache artifacts typechain",
     "compile": "npx hardhat compile",
     "test:coverage": "npx hardhat coverage",
+    "test:coverage:check": "npx istanbul check-coverage ./coverage.json --statements 100 --branches 100 --functions 100 --lines 100",
     "test": "npx hardhat test",
     "test:unit": "npx hardhat test test/unit/*.*",
     "test:integration": "npx hardhat test test/integration/**",