Add storage slot derivation tooling and UDVT typed slot representation.

.changeset/kind-planets-cough.md

@@ -0,0 +1,5 @@
+---
+'openzeppelin-solidity': minor
+---
+
+`StorageSlot`: Add storage slot derivation tooling and typed-slot representation with transient storage support.

contracts/mocks/StorageSlotMock.sol

@@ -7,6 +7,14 @@ import {StorageSlot} from "../utils/StorageSlot.sol";
 contract StorageSlotMock {
     using StorageSlot for *;
 
+    function erc1967slot(string memory path) public pure returns (bytes32) {
+        return path.erc1967slot();
+    }
+
+    function erc7201slot(string memory path) public pure returns (bytes32) {
+        return path.erc7201slot();
+    }
+
     function setBooleanSlot(bytes32 slot, bool value) public {
         slot.getBooleanSlot().value = value;
     }
@@ -23,6 +31,10 @@ contract StorageSlotMock {
         slot.getUint256Slot().value = value;
     }
 
+    function setInt256Slot(bytes32 slot, int256 value) public {
+        slot.getInt256Slot().value = value;
+    }
+
     function getBooleanSlot(bytes32 slot) public view returns (bool) {
         return slot.getBooleanSlot().value;
     }
@@ -39,6 +51,10 @@ contract StorageSlotMock {
         return slot.getUint256Slot().value;
     }
 
+    function getInt256Slot(bytes32 slot) public view returns (int256) {
+        return slot.getInt256Slot().value;
+    }
+
     mapping(uint256 key => string) public stringMap;
 
     function setStringSlot(bytes32 slot, string calldata value) public {

contracts/utils/Arrays.sol

@@ -361,15 +361,11 @@ library Arrays {
      */
     function unsafeAccess(address[] storage arr, uint256 pos) internal pure returns (StorageSlot.AddressSlot storage) {
         bytes32 slot;
-        // We use assembly to calculate the storage slot of the element at index `pos` of the dynamic array `arr`
-        // following https://docs.soliditylang.org/en/v0.8.20/internals/layout_in_storage.html#mappings-and-dynamic-arrays.
-
         /// @solidity memory-safe-assembly
         assembly {
-            mstore(0, arr.slot)
-            slot := add(keccak256(0, 0x20), pos)
+            slot := arr.slot
         }
-        return slot.getAddressSlot();
+        return slot.deriveArray().offset(pos).getAddressSlot();
     }
 
     /**
@@ -379,15 +375,11 @@ library Arrays {
      */
     function unsafeAccess(bytes32[] storage arr, uint256 pos) internal pure returns (StorageSlot.Bytes32Slot storage) {
         bytes32 slot;
-        // We use assembly to calculate the storage slot of the element at index `pos` of the dynamic array `arr`
-        // following https://docs.soliditylang.org/en/v0.8.20/internals/layout_in_storage.html#mappings-and-dynamic-arrays.
-
         /// @solidity memory-safe-assembly
         assembly {
-            mstore(0, arr.slot)
-            slot := add(keccak256(0, 0x20), pos)
+            slot := arr.slot
         }
-        return slot.getBytes32Slot();
+        return slot.deriveArray().offset(pos).getBytes32Slot();
     }
 
     /**
@@ -397,15 +389,11 @@ library Arrays {
      */
     function unsafeAccess(uint256[] storage arr, uint256 pos) internal pure returns (StorageSlot.Uint256Slot storage) {
         bytes32 slot;
-        // We use assembly to calculate the storage slot of the element at index `pos` of the dynamic array `arr`
-        // following https://docs.soliditylang.org/en/v0.8.20/internals/layout_in_storage.html#mappings-and-dynamic-arrays.
-
         /// @solidity memory-safe-assembly
         assembly {
-            mstore(0, arr.slot)
-            slot := add(keccak256(0, 0x20), pos)
+            slot := arr.slot
         }
-        return slot.getUint256Slot();
+        return slot.deriveArray().offset(pos).getUint256Slot();
     }
 
     /**