tweak oracle factory to also support chainlink interface

contracts/facade/factories/ExchangeRateOracleFactory.sol

@@ -0,0 +1,96 @@
+// SPDX-License-Identifier: BlueOak-1.0.0
+pragma solidity 0.8.19;
+
+import { FIX_ONE, divuu } from "../../libraries/Fixed.sol";
+
+// weird circular inheritance preventing us from using proper IRToken, not worth figuring out
+interface IMinimalRToken {
+    function basketsNeeded() external view returns (uint192);
+
+    function totalSupply() external view returns (uint256);
+}
+
+/**
+ * @title ExchangeRateOracle
+ * @notice An immutable Exchange Rate Oracle for an RToken
+ *
+ * Warning! In the event of an RToken taking a loss in excess of the StRSR overcollateralization
+ * layer, the devaluation will not be reflected until the RToken is done trading. This causes
+ * the exchange rate to be too high during the rebalancing phase. If the exchange rate is relied
+ * upon naively, then it could be misleading.
+ *
+ * As a consumer of this oracle, you may want to guard against this case by monitoring:
+ *     `rToken.status() == 0 && rToken.fullyCollateralized()`
+ *
+ * However, note that `fullyCollateralized()` is extremely gas-costly. We recommend executing
+ * the function off-chain. `status()` is cheap and more reasonable to be called from on-chain.
+ */
+contract ExchangeRateOracle {
+    error MissingRToken();
+
+    address public immutable rToken;
+
+    constructor(address _rToken) {
+        // allow address(0)
+        rToken = _rToken;
+    }
+
+    function exchangeRate() public view returns (uint256) {
+        address _rToken = rToken;
+        if (_rToken == address(0)) revert MissingRToken();
+
+        uint256 supply = IMinimalRToken(_rToken).totalSupply();
+        if (supply == 0) return FIX_ONE;
+
+        return divuu(uint256(IMinimalRToken(_rToken).basketsNeeded()), supply);
+    }
+
+    // basic chainlink interface sufficient for Morpho
+    function latestRoundData()
+        external
+        view
+        returns (
+            uint80 roundId,
+            int256 answer,
+            uint256 startedAt,
+            uint256 updatedAt,
+            uint80 answeredInRound
+        )
+    {
+        // TODO
+        // make better to work with more than just Morpho
+        return (0, int256(exchangeRate()), 0, 0, 0);
+    }
+
+    function decimals() external pure returns (uint8) {
+        return 18;
+    }
+}
+
+/**
+ * @title ExchangeRateOracleFactory
+ * @notice An immutable factory for Exchange Rate Oracles
+ */
+contract ExchangeRateOracleFactory {
+    error OracleAlreadyDeployed();
+
+    event OracleDeployed(address indexed rToken, address indexed oracle);
+
+    // {rtoken} => {oracle}
+    mapping(address => ExchangeRateOracle) public oracles;
+
+    function deployOracle(address rToken) external returns (address) {
+        if (address(oracles[rToken]) != address(0)) revert OracleAlreadyDeployed();
+        ExchangeRateOracle oracle = new ExchangeRateOracle(rToken);
+
+        if (rToken != address(0)) {
+            oracle.exchangeRate();
+            oracle.latestRoundData();
+            oracle.decimals();
+        }
+
+        oracles[rToken] = oracle;
+        emit OracleDeployed(address(rToken), address(oracle));
+        return address(oracle);
+    }
+}

tasks/deployment/create-exchange-rate-oracle-factory.ts

@@ -0,0 +1,78 @@
+import { getChainId } from '../../common/blockchain-utils'
+import { task, types } from 'hardhat/config'
+import { ExchangeRateOracleFactory } from '../../typechain'
+
+task('create-exchange-rate-oracle-factory', 'Deploys an ExchangeRateOracleFactory')
+  .addOptionalParam('noOutput', 'Suppress output', false, types.boolean)
+  .setAction(async (params, hre) => {
+    const [wallet] = await hre.ethers.getSigners()
+
+    const chainId = await getChainId(hre)
+
+    if (!params.noOutput) {
+      console.log(
+        `Deploying ExchangeRateOracleFactory to ${hre.network.name} (${chainId}) with burner account ${wallet.address}`
+      )
+    }
+
+    const CurveOracleFactoryFactory = await hre.ethers.getContractFactory(
+      'ExchangeRateOracleFactory'
+    )
+    const oracleFactory = <ExchangeRateOracleFactory>(
+      await CurveOracleFactoryFactory.connect(wallet).deploy()
+    )
+    await oracleFactory.deployed()
+
+    if (!params.noOutput) {
+      console.log(
+        `Deployed ExchangeRateOracleFactory to ${hre.network.name} (${chainId}): ${oracleFactory.address}`
+      )
+      console.log(
+        `Deploying dummy ExchangeRateOracle to ${hre.network.name} (${chainId}): ${oracleFactory.address}`
+      )
+    }
+
+    // Deploy dummy zero address oracle
+    const addr = await oracleFactory.callStatic.deployOracle(hre.ethers.constants.AddressZero)
+    await (await oracleFactory.deployOracle(hre.ethers.constants.AddressZero)).wait()
+
+    if (!params.noOutput) {
+      console.log(`Deployed dummy ExchangeRateOracle to ${hre.network.name} (${chainId}): ${addr}`)
+    }
+
+    // Uncomment to verify
+    if (!params.noOutput) {
+      console.log('sleeping 10s')
+    }
+
+    // Sleep to ensure API is in sync with chain
+    await new Promise((r) => setTimeout(r, 10000)) // 10s
+
+    if (!params.noOutput) {
+      console.log('verifying')
+    }
+
+    /** ******************** Verify ExchangeRateOracleFactory ****************************************/
+    console.time('Verifying ExchangeRateOracleFactory')
+    await hre.run('verify:verify', {
+      address: oracleFactory.address,
+      constructorArguments: [],
+      contract:
+        'contracts/facade/factories/ExchangeRateOracleFactory.sol:ExchangeRateOracleFactory',
+    })
+    console.timeEnd('Verifying ExchangeRateOracleFactory')
+
+    console.time('Verifying ExchangeRateOracle')
+    await hre.run('verify:verify', {
+      address: addr,
+      constructorArguments: [hre.ethers.constants.AddressZero],
+      contract: 'contracts/facade/factories/ExchangeRateOracleFactory.sol:ExchangeRateOracle',
+    })
+    console.timeEnd('Verifying ExchangeRateOracle')
+
+    if (!params.noOutput) {
+      console.log('verified')
+    }
+
+    return { oracleFactory: oracleFactory.address }
+  })

tasks/index.ts

@@ -16,7 +16,7 @@ import './deployment/mock/deploy-mock-aave'
 import './deployment/mock/deploy-mock-wbtc'
 import './deployment/deploy-easyauction'
 import './deployment/create-deployer-registry'
-import './deployment/create-curve-oracle-factory'
+import './deployment/create-exchange-rate-oracle-factory'
 import './deployment/deploy-facade-monitor'
 import './deployment/empty-wallet'
 import './deployment/cancel-tx'