contracts-bedrock: modularize the `AlphabetVM`

Moves the `AlphabetVM` contract into its own file
because previously it was resulting in an import cycle.
This was causing compilation errors when refactoring
the code to use the deploy script to set up the tests.

All mock contracts used for testing can now live in `test/mocks`
instead of being randomly placed around the codebase.

op-bindings/bindings/alphabetvm_more.go

@@ -9,7 +9,7 @@ import (
 	"github.com/ethereum-optimism/optimism/op-bindings/solc"
 )
 
-const AlphabetVMStorageLayoutJSON = "{\"storage\":[{\"astId\":1000,\"contract\":\"test/FaultDisputeGame.t.sol:AlphabetVM\",\"label\":\"oracle\",\"offset\":0,\"slot\":\"0\",\"type\":\"t_contract(IPreimageOracle)1001\"}],\"types\":{\"t_contract(IPreimageOracle)1001\":{\"encoding\":\"inplace\",\"label\":\"contract IPreimageOracle\",\"numberOfBytes\":\"20\"}}}"
+const AlphabetVMStorageLayoutJSON = "{\"storage\":[{\"astId\":1000,\"contract\":\"test/mocks/AlphabetVM.sol:AlphabetVM\",\"label\":\"oracle\",\"offset\":0,\"slot\":\"0\",\"type\":\"t_contract(IPreimageOracle)1001\"}],\"types\":{\"t_contract(IPreimageOracle)1001\":{\"encoding\":\"inplace\",\"label\":\"contract IPreimageOracle\",\"numberOfBytes\":\"20\"}}}"
 
 var AlphabetVMStorageLayout = new(solc.StorageLayout)
 

packages/contracts-bedrock/scripts/Deploy.s.sol

@@ -41,7 +41,7 @@ import { Chains } from "scripts/Chains.sol";
 
 import { IBigStepper } from "src/dispute/interfaces/IBigStepper.sol";
 import { IPreimageOracle } from "src/cannon/interfaces/IPreimageOracle.sol";
-import { AlphabetVM } from "../test/FaultDisputeGame.t.sol";
+import { AlphabetVM } from "test/mocks/AlphabetVM.sol";
 import "src/libraries/DisputeTypes.sol";
 
 /// @title Deploy

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

@@ -17,6 +17,8 @@ import { Types } from "src/libraries/Types.sol";
 import { LibClock } from "src/dispute/lib/LibClock.sol";
 import { LibPosition } from "src/dispute/lib/LibPosition.sol";
 import { IBigStepper, IPreimageOracle } from "src/dispute/interfaces/IBigStepper.sol";
+import { AlphabetVM } from "test/mocks/AlphabetVM.sol";
+
 
 contract FaultDisputeGame_Init is DisputeGameFactory_Init {
     /// @dev The type of the game being tested.
@@ -1093,37 +1095,3 @@ contract VariableDivergentPlayer is GamePlayer {
         trace = _trace;
     }
 }
-
-////////////////////////////////////////////////////////////////
-//                          MOCK VMS                          //
-////////////////////////////////////////////////////////////////
-
-contract AlphabetVM is IBigStepper {
-    Claim internal immutable ABSOLUTE_PRESTATE;
-    IPreimageOracle public oracle;
-
-    constructor(Claim _absolutePrestate) {
-        ABSOLUTE_PRESTATE = _absolutePrestate;
-        oracle = new PreimageOracle();
-    }
-
-    /// @inheritdoc IBigStepper
-    function step(bytes calldata _stateData, bytes calldata, uint256) external view returns (bytes32 postState_) {
-        uint256 traceIndex;
-        uint256 claim;
-        if ((keccak256(_stateData) << 8) == (Claim.unwrap(ABSOLUTE_PRESTATE) << 8)) {
-            // If the state data is empty, then the absolute prestate is the claim.
-            traceIndex = 0;
-            (claim) = abi.decode(_stateData, (uint256));
-        } else {
-            // Otherwise, decode the state data.
-            (traceIndex, claim) = abi.decode(_stateData, (uint256, uint256));
-            traceIndex++;
-        }
-        // STF: n -> n + 1
-        postState_ = keccak256(abi.encode(traceIndex, claim + 1));
-        assembly {
-            postState_ := or(and(postState_, not(shl(248, 0xFF))), shl(248, 1))
-        }
-    }
-}

packages/contracts-bedrock/test/mocks/AlphabetVM.sol

+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.15;
+
+import { IBigStepper, IPreimageOracle } from "src/dispute/interfaces/IBigStepper.sol";
+import { PreimageOracle } from "src/cannon/PreimageOracle.sol";
+import "src/libraries/DisputeTypes.sol";
+
+/// @title AlphabetVM
+/// @dev A mock VM for the purpose of testing the dispute game infrastructure.
+contract AlphabetVM is IBigStepper {
+    Claim internal immutable ABSOLUTE_PRESTATE;
+    IPreimageOracle public oracle;
+
+    constructor(Claim _absolutePrestate) {
+        ABSOLUTE_PRESTATE = _absolutePrestate;
+        oracle = new PreimageOracle();
+    }
+
+    /// @inheritdoc IBigStepper
+    function step(bytes calldata _stateData, bytes calldata, uint256) external view returns (bytes32 postState_) {
+        uint256 traceIndex;
+        uint256 claim;
+        if ((keccak256(_stateData) << 8) == (Claim.unwrap(ABSOLUTE_PRESTATE) << 8)) {
+            // If the state data is empty, then the absolute prestate is the claim.
+            traceIndex = 0;
+            (claim) = abi.decode(_stateData, (uint256));
+        } else {
+            // Otherwise, decode the state data.
+            (traceIndex, claim) = abi.decode(_stateData, (uint256, uint256));
+            traceIndex++;
+        }
+        // STF: n -> n + 1
+        postState_ = keccak256(abi.encode(traceIndex, claim + 1));
+        assembly {
+            postState_ := or(and(postState_, not(shl(248, 0xFF))), shl(248, 1))
+        }
+    }
+}