feat: two-safe rule

.github/workflows/lint.yml

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+name: Linter
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+        with:
+          version: v1.3.5
+          cache: true
+
+      - name: fmt
+        run: |
+          forge fmt --check
+
+      - name: build
+        run: |
+          forge build
+
+      - name: Lint
+        run: |
+          ! (forge lint 2>&1 | grep "")

.github/workflows/test.yml

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+name: Test
+
+on:
+  push:
+    branches: ["main"]
+  pull_request:
+    branches: ["main"]
+
+jobs:
+  build:
+    runs-on: ubuntu-latest
+
+    steps:
+      - uses: actions/checkout@v4
+
+      - name: Install Foundry
+        uses: foundry-rs/foundry-toolchain@v1
+        with:
+          version: v1.3.5
+          cache: true
+
+      - name: Install Dependencies
+        run: |
+          forge install
+
+      - name: Run tests
+        run: |
+          forge test

.gitignore

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+# forge
+out/
+cache/
+
+# VIM
+*.swp

.gitmodules

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+[submodule "lib/forge-std"]
+	path = lib/forge-std
+	url = https://github.com/foundry-rs/forge-std

foundry.lock

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+{
+  "lib/forge-std": {
+    "tag": {
+      "name": "v1.16.2",
+      "rev": "bf647bd6046f2f7da30d0c2bf435e5c76a780c1b"
+    }
+  }
+}

foundry.toml

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+[profile.default]
+src = 'src'
+test = 'test'
+script = 'script'
+out = 'out'
+libs = ['lib']
+cache_path = 'cache'
+solc = "0.8.36"
+via_ir = false
+optimizer = true
+optimizer_runs = 2000
+bytecode_hash = "none"
+
+# For dependencies
+remappings = [
+    'forge-std/=lib/forge-std/src/',
+    #'@fvm-solidity/=lib/pdp/lib/fvm-solidity/src/',
+]
+
+[lint]
+exclude_lints = [
+    "incorrect-shift",
+]

src/lib/Epoch.sol

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+// SPDX-License-Identifier: Apache-2.0 OR MIT
+pragma solidity ^0.8.36;
+
+type Epoch is uint96;
+
+using {
+    add as +,
+    sub as -,
+    equals as ==,
+    greaterThan as >,
+    lessThan as <,
+    greaterThanOrEqualTo as >=,
+    lessThanOrEqualTo as <=
+} for Epoch global;
+
+/// @return epoch The current block number
+function currentEpoch() view returns (Epoch epoch) {
+    assembly ("memory-safe") {
+        epoch := number()
+    }
+}
+
+function add(Epoch epoch, Epoch other) pure returns (Epoch sum) {
+    assembly ("memory-safe") {
+        sum := add(epoch, other)
+    }
+}
+
+function sub(Epoch epoch, Epoch other) pure returns (Epoch difference) {
+    assembly ("memory-safe") {
+        difference := sub(epoch, other)
+    }
+}
+
+function equals(Epoch epoch, Epoch other) pure returns (bool) {
+    return Epoch.unwrap(epoch) == Epoch.unwrap(other);
+}
+
+function greaterThan(Epoch epoch, Epoch other) pure returns (bool) {
+    return Epoch.unwrap(epoch) > Epoch.unwrap(other);
+}
+
+function lessThan(Epoch epoch, Epoch other) pure returns (bool) {
+    return Epoch.unwrap(epoch) < Epoch.unwrap(other);
+}
+
+function greaterThanOrEqualTo(Epoch epoch, Epoch other) pure returns (bool) {
+    return Epoch.unwrap(epoch) >= Epoch.unwrap(other);
+}
+
+function lessThanOrEqualTo(Epoch epoch, Epoch other) pure returns (bool) {
+    return Epoch.unwrap(epoch) <= Epoch.unwrap(other);
+}

src/lib/OwnerSet.sol

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+// SPDX-License-Identifier: Apache-2.0 OR MIT
+pragma solidity ^0.8.36;
+
+// OwnerSet is a space-efficient bitmask
+// Each owner has a unique representative bit assigned during addOwner
+
+type OwnerSet is uint160;
+
+using {equals as ==, notEquals as !=, or as |, xor as ^, and as &} for OwnerSet global;
+
+OwnerSet constant EMPTY_SET = OwnerSet.wrap(uint160(0));
+OwnerSet constant FULL_SET = OwnerSet.wrap(type(uint160).max);
+
+function equals(OwnerSet a, OwnerSet b) pure returns (bool) {
+    return OwnerSet.unwrap(a) == OwnerSet.unwrap(b);
+}
+
+function notEquals(OwnerSet a, OwnerSet b) pure returns (bool) {
+    return OwnerSet.unwrap(a) != OwnerSet.unwrap(b);
+}
+
+function or(OwnerSet a, OwnerSet b) pure returns (OwnerSet) {
+    return OwnerSet.wrap(OwnerSet.unwrap(a) | OwnerSet.unwrap(b));
+}
+
+function xor(OwnerSet a, OwnerSet b) pure returns (OwnerSet) {
+    return OwnerSet.wrap(OwnerSet.unwrap(a) ^ OwnerSet.unwrap(b));
+}
+
+function and(OwnerSet a, OwnerSet b) pure returns (OwnerSet) {
+    return OwnerSet.wrap(OwnerSet.unwrap(a) & OwnerSet.unwrap(b));
+}

src/lib/Owners.sol

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+// SPDX-License-Identifier: Apache-2.0 OR MIT
+pragma solidity ^0.8.36;
+
+import {EMPTY_SET, FULL_SET, OwnerSet} from "./OwnerSet.sol";
+
+library OwnersLibrary {
+    struct OwnerInfo {
+        uint8 bitId; // [0, 160]
+    }
+
+    /// @custom:storage-location erc7201:Solstice.Owners
+    struct Owners {
+        mapping(address => OwnerInfo) ownerInfo;
+        uint8 nextBitCursor; // [0, 160)
+        OwnerSet allOwners;
+    }
+
+    // keccak256(abi.encode(uint256(keccak256("Solstice.Owners")) - 1)) & ~bytes32(uint256(0xff));
+    bytes32 private constant OWNERS_SLOT = 0x7d2e7f914625694dd929b468ac404d7943373f4d24421c78ac93b57cc8efb500;
+
+    function getOwnersSlot() internal pure returns (Owners storage owners) {
+        assembly ("memory-safe") {
+            owners.slot := OWNERS_SLOT
+        }
+    }
+
+    event OwnerAdded(address indexed owner);
+    event OwnerRemoved(address indexed owner);
+
+    function isOwner(address someone) internal view returns (bool) {
+        return getOwnersSlot().ownerInfo[someone].bitId != 0;
+    }
+
+    /// @dev Returns EMPTY_SET if `owner` is not a current owner.
+    function asOwnerSet(address owner) internal view returns (OwnerSet mask) {
+        uint8 ownerBit = getOwnersSlot().ownerInfo[owner].bitId;
+        assembly ("memory-safe") {
+            mask := shl(sub(ownerBit, 1), 1)
+        }
+    }
+
+    function getAllOwners() internal view returns (OwnerSet) {
+        return getOwnersSlot().allOwners;
+    }
+
+    // Proposed owner is already an owner
+    error AlreadyOwner(address owner);
+    // Unsupported ownership count (> 160)
+    error MaximumOwnersReached();
+
+    /// @param owner The address to grant ownership to
+    function addOwner(address owner) internal {
+        require(!isOwner(owner), AlreadyOwner(owner));
+
+        Owners storage owners = getOwnersSlot();
+        uint8 ownerBit = owners.nextBitCursor;
+        OwnerSet allOwners = owners.allOwners;
+
+        require(allOwners != FULL_SET, MaximumOwnersReached());
+
+        OwnerSet ownerSet = EMPTY_SET;
+
+        // assign next free bit
+        while (true) {
+            assembly ("memory-safe") {
+                ownerSet := shl(ownerBit, 1)
+                ownerBit := add(1, ownerBit)
+            }
+            if (ownerSet & allOwners == EMPTY_SET) {
+                break;
+            } else {
+                ownerBit %= 160;
+            }
+        }
+
+        owners.ownerInfo[owner].bitId = ownerBit;
+        owners.allOwners = allOwners | ownerSet;
+        owners.nextBitCursor = ownerBit % 160;
+
+        emit OwnerAdded(owner);
+    }
+
+    // Address to remove is not a current owner
+    error NotOwner(address owner);
+
+    /// @param owner The address to revoke ownership from
+    /// @dev A removed owner's bit may be recycled to a future owner by addOwner.
+    /// @dev Veto stale PendingTasks when removing an owner to avoid approvals carrying over.
+    function removeOwner(address owner) internal {
+        require(isOwner(owner), NotOwner(owner));
+
+        Owners storage owners = getOwnersSlot();
+        OwnerSet mask = asOwnerSet(owner);
+        owners.allOwners = owners.allOwners ^ mask;
+        delete owners.ownerInfo[owner];
+
+        emit OwnerRemoved(owner);
+    }
+}

src/lib/PendingTask.sol

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+// SPDX-License-Identifier: Apache-2.0 OR MIT
+pragma solidity ^0.8.36;
+
+import {Epoch} from "./Epoch.sol";
+import {OwnerSet} from "./OwnerSet.sol";
+
+struct PendingTask {
+    Epoch modified;
+    OwnerSet approvals;
+}
+
+struct PendingTaskInfo {
+    PendingTask task;
+}
+
+library PendingTaskLibrary {
+    /// @custom:storage-location erc7201:Solstice.PendingTasks
+    struct PendingTasks {
+        mapping(bytes32 taskId => PendingTaskInfo) tasks;
+    }
+
+    // keccak256(abi.encode(uint256(keccak256("Solstice.PendingTasks")) - 1)) & ~bytes32(uint256(0xff));
+    bytes32 private constant PENDING_TASKS_SLOT = 0x635f64a8ec66823e68578973f5bc466fd4e0eadd655f760cfc91e860524aa300;
+
+    function getTasksSlot() internal pure returns (mapping(bytes32 taskId => PendingTaskInfo) storage tasks) {
+        assembly ("memory-safe") {
+            tasks.slot := PENDING_TASKS_SLOT
+        }
+    }
+}