chore: Upgrade `MIPS.sol` solc version

packages/contracts-bedrock/src/cannon/PreimageKeyLib.sol

 // SPDX-License-Identifier: MIT
-pragma solidity ^0.7.6;
+pragma solidity 0.8.15;
 
 /// @title PreimageKeyLib
 /// @notice Shared utilities for localizing local keys in the preimage oracle.

packages/contracts-bedrock/src/cannon/PreimageOracle.sol

 // SPDX-License-Identifier: MIT
-pragma solidity 0.7.6;
+pragma solidity 0.8.15;
 
+import { IPreimageOracle } from "./interfaces/IPreimageOracle.sol";
 import { PreimageKeyLib } from "./PreimageKeyLib.sol";
 
 /// @title PreimageOracle
 /// @notice A contract for storing permissioned pre-images.
-contract PreimageOracle {
+contract PreimageOracle is IPreimageOracle {
     /// @notice Mapping of pre-image keys to pre-image lengths.
     mapping(bytes32 => uint256) public preimageLengths;
     /// @notice Mapping of pre-image keys to pre-image parts.
@@ -13,11 +14,7 @@ contract PreimageOracle {
     /// @notice Mapping of pre-image keys to pre-image part offsets.
     mapping(bytes32 => mapping(uint256 => bool)) public preimagePartOk;
 
-    /// @notice Reads a pre-image from the oracle.
-    /// @param _key The key of the pre-image to read.
-    /// @param _offset The offset of the pre-image to read.
-    /// @return dat_ The pre-image data.
-    /// @return datLen_ The length of the pre-image data.
+    /// @inheritdoc IPreimageOracle
     function readPreimage(bytes32 _key, uint256 _offset)
         external
         view
@@ -53,24 +50,7 @@ contract PreimageOracle {
         preimageLengths[key] = size;
     }
 
-    /// @notice Loads a word of local data into the preimage oracle in two separate parts.
-    /// @param _ident The identifier of the local data.
-    /// @param _word The local data word.
-    /// @param _size The number of bytes in `_word` to load.
-    /// @dev The local data parts are loaded into the preimage oracle under the context
-    ///      of the caller - no other account can write to the caller's context
-    ///      specific data.
-    ///
-    ///      There are 5 local data identifiers:
-    ///      ┌────────────┬────────────────────────┐
-    ///      │ Identifier │      Data              │
-    ///      ├────────────┼────────────────────────┤
-    ///      │          1 │ L1 Head Hash (bytes32) │
-    ///      │          2 │ Output Root (bytes32)  │
-    ///      │          3 │ Root Claim (bytes32)   │
-    ///      │          4 │ L2 Block Number (u64)  │
-    ///      │          5 │ Chain ID (u64)         │
-    ///      └────────────┴────────────────────────┘
+    /// @inheritdoc IPreimageOracle
     function loadLocalData(
         uint256 _ident,
         bytes32 _word,
@@ -106,10 +86,7 @@ contract PreimageOracle {
         preimageLengths[key_] = _size;
     }
 
-    /// @notice Prepares a pre-image to be read by keccak256 key, starting at
-    ///         the given offset and up to 32 bytes (clipped at pre-image length, if out of data).
-    /// @param _partOffset The offset of the pre-image to read.
-    /// @param _preimage The preimage data.
+    /// @inheritdoc IPreimageOracle
     function loadKeccak256PreimagePart(uint256 _partOffset, bytes calldata _preimage) external {
         uint256 size;
         bytes32 key;

packages/contracts-bedrock/src/cannon/interfaces/IPreimageOracle.sol

 // SPDX-License-Identifier: MIT
-pragma solidity 0.7.6;
+pragma solidity 0.8.15;
 
 /// @title IPreimageOracle
 /// @notice Interface for a preimage oracle.
@@ -14,10 +14,29 @@ interface IPreimageOracle {
         view
         returns (bytes32 dat_, uint256 datLen_);
 
-    /// @notice Computes and returns the key for a pre-image.
-    /// @param _preimage The pre-image.
-    /// @return key_ The pre-image key.
-    function computePreimageKey(bytes calldata _preimage) external pure returns (bytes32 key_);
+    /// @notice Loads a word of local data into the preimage oracle in two separate parts.
+    /// @param _ident The identifier of the local data.
+    /// @param _word The local data word.
+    /// @param _size The number of bytes in `_word` to load.
+    /// @dev The local data parts are loaded into the preimage oracle under the context
+    ///      of the caller - no other account can write to the caller's context
+    ///      specific data.
+    ///
+    ///      There are 5 local data identifiers:
+    ///      ┌────────────┬────────────────────────┐
+    ///      │ Identifier │      Data              │
+    ///      ├────────────┼────────────────────────┤
+    ///      │          1 │ L1 Head Hash (bytes32) │
+    ///      │          2 │ Output Root (bytes32)  │
+    ///      │          3 │ Root Claim (bytes32)   │
+    ///      │          4 │ L2 Block Number (u64)  │
+    ///      │          5 │ Chain ID (u64)         │
+    ///      └────────────┴────────────────────────┘
+    function loadLocalData(
+        uint256 _ident,
+        bytes32 _word,
+        uint8 _size
+    ) external returns (bytes32 key_);
 
     /// @notice Prepares a preimage to be read by keccak256 key, starting at
     ///         the given offset and up to 32 bytes (clipped at preimage length, if out of data).

packages/contracts-bedrock/src/dispute/interfaces/IBigStepper.sol

 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.15;
 
+import { IPreimageOracle } from "../../cannon/interfaces/IPreimageOracle.sol";
+
 /// @title IBigStepper
 /// @notice An interface for a contract with a state transition function that
 ///         will accept a pre state and return a post state.
@@ -35,14 +37,3 @@ interface IBigStepper {
     /// @notice Returns the preimage oracle used by the stepper.
     function oracle() external view returns (IPreimageOracle oracle_);
 }
-
-/// @notice Temporary interface for the `IPreimageOracle`. Remove once we've upgraded
-///         the cannon contracts to a newer version of solc.
-interface IPreimageOracle {
-    function loadLocalData(
-        uint256 _ident,
-        bytes32 _word,
-        uint256 _size,
-        uint256 _partOffset
-    ) external returns (bytes32 key_);
-}

packages/contracts-bedrock/src/periphery/AssetReceiver.sol

@@ -64,6 +64,7 @@ contract AssetReceiver is Transactor {
     function withdrawETH(address payable _to, uint256 _amount) public onlyOwner {
         // slither-disable-next-line reentrancy-unlimited-gas
         (bool success, ) = _to.call{ value: _amount }("");
+        success; // Suppress warning; We ignore the low-level call result.
         emit WithdrewETH(msg.sender, _to, _amount);
     }
 

packages/contracts-bedrock/test/PreimageOracle.t.sol

 // SPDX-License-Identifier: MIT
-pragma solidity 0.7.6;
-pragma abicoder v2;
+pragma solidity 0.8.15;
 
 import { Test } from "forge-std/Test.sol";