feat: Add LSP7Votes and LSP8Votes extension to support LSP-based Governance

packages/lsp7-contracts/contracts/LSP7DigitalAssetCore.sol

@@ -441,19 +441,7 @@ abstract contract LSP7DigitalAssetCore is ILSP7DigitalAsset {
 
         _beforeTokenTransfer(address(0), to, amount, data);
 
-        // tokens being minted
-        _existingTokens += amount;
-
-        _tokenOwnerBalances[to] += amount;
-
-        emit Transfer({
-            operator: msg.sender,
-            from: address(0),
-            to: to,
-            amount: amount,
-            force: force,
-            data: data
-        });
+        _update(address(0), to, amount, force, data);
 
         _afterTokenTransfer(address(0), to, amount, data);
 
@@ -503,23 +491,7 @@ abstract contract LSP7DigitalAssetCore is ILSP7DigitalAsset {
 
         _beforeTokenTransfer(from, address(0), amount, data);
 
-        uint256 balance = _tokenOwnerBalances[from];
-        if (amount > balance) {
-            revert LSP7AmountExceedsBalance(balance, from, amount);
-        }
-        // tokens being burnt
-        _existingTokens -= amount;
-
-        _tokenOwnerBalances[from] -= amount;
-
-        emit Transfer({
-            operator: msg.sender,
-            from: from,
-            to: address(0),
-            amount: amount,
-            force: false,
-            data: data
-        });
+        _update(from, address(0), amount, false, data);
 
         _afterTokenTransfer(from, address(0), amount, data);
 
@@ -614,29 +586,64 @@ abstract contract LSP7DigitalAssetCore is ILSP7DigitalAsset {
 
         _beforeTokenTransfer(from, to, amount, data);
 
-        uint256 balance = _tokenOwnerBalances[from];
-        if (amount > balance) {
-            revert LSP7AmountExceedsBalance(balance, from, amount);
+        _update(from, to, amount, force, data);
+
+        _afterTokenTransfer(from, to, amount, data);
+
+        bytes memory lsp1Data = abi.encode(msg.sender, from, to, amount, data);
+
+        _notifyTokenSender(from, lsp1Data);
+        _notifyTokenReceiver(to, force, lsp1Data);
+    }
+
+    /**
+     * @dev Transfers a `value` amount of tokens from `from` to `to`, or alternatively mints (or burns) if `from`
+     * (or `to`) is the zero address. All customizations to transfers, mints, and burns should be done by overriding
+     * this function.
+     *
+     * Emits a {Transfer} event.
+     */
+    function _update(
+        address from,
+        address to,
+        uint256 value,
+        bool force,
+        bytes memory data
+    ) internal virtual {
+        if (from == address(0)) {
+            // Overflow check required: The rest of the code assumes that totalSupply never overflows
+            _existingTokens += value;
+        } else {
+            uint256 fromBalance = _tokenOwnerBalances[from];
+            if (fromBalance < value) {
+                revert LSP7AmountExceedsBalance(fromBalance, from, value);
+            }
+            unchecked {
+                // Overflow not possible: value <= fromBalance <= totalSupply.
+                _tokenOwnerBalances[from] = fromBalance - value;
+            }
         }
 
-        _tokenOwnerBalances[from] -= amount;
-        _tokenOwnerBalances[to] += amount;
+        if (to == address(0)) {
+            unchecked {
+                // Overflow not possible: value <= totalSupply or value <= fromBalance <= totalSupply.
+                _existingTokens -= value;
+            }
+        } else {
+            unchecked {
+                // Overflow not possible: balance + value is at most totalSupply, which we know fits into a uint256.
+                _tokenOwnerBalances[to] += value;
+            }
+        }
 
         emit Transfer({
             operator: msg.sender,
             from: from,
             to: to,
-            amount: amount,
+            amount: value,
             force: force,
             data: data
         });
-
-        _afterTokenTransfer(from, to, amount, data);
-
-        bytes memory lsp1Data = abi.encode(msg.sender, from, to, amount, data);
-
-        _notifyTokenSender(from, lsp1Data);
-        _notifyTokenReceiver(to, force, lsp1Data);
     }
 
     /**

packages/lsp7-contracts/contracts/Mocks/MyGovernor.sol

@@ -0,0 +1,65 @@
+// SPDX-License-Identifier: MIT
+pragma solidity ^0.8.0;
+
+import "@openzeppelin/contracts/governance/Governor.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorSettings.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorCountingSimple.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorVotes.sol";
+import "@openzeppelin/contracts/governance/extensions/GovernorVotesQuorumFraction.sol";
+
+contract MyGovernor is
+    Governor,
+    GovernorSettings,
+    GovernorCountingSimple,
+    GovernorVotes,
+    GovernorVotesQuorumFraction
+{
+    constructor(
+        IVotes _token
+    )
+        Governor("MyGovernor")
+        GovernorSettings(7200 /* 1 day */, 7200 /* 1 day */, 1e18)
+        GovernorVotes(_token)
+        GovernorVotesQuorumFraction(1)
+    {}
+
+    // The following functions are overrides required by Solidity.
+
+    function votingDelay()
+        public
+        view
+        override(IGovernor, GovernorSettings)
+        returns (uint256)
+    {
+        return super.votingDelay();
+    }
+
+    function votingPeriod()
+        public
+        view
+        override(IGovernor, GovernorSettings)
+        returns (uint256)
+    {
+        return super.votingPeriod();
+    }
+
+    function quorum(
+        uint256 blockNumber
+    )
+        public
+        view
+        override(IGovernor, GovernorVotesQuorumFraction)
+        returns (uint256)
+    {
+        return super.quorum(blockNumber);
+    }
+
+    function proposalThreshold()
+        public
+        view
+        override(Governor, GovernorSettings)
+        returns (uint256)
+    {
+        return super.proposalThreshold();
+    }
+}

packages/lsp7-contracts/contracts/Mocks/MyVotingToken.sol

@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: MIT
+
+pragma solidity ^0.8.0;
+
+import "../extensions/LSP7Votes.sol";
+
+/**
+ * @dev Mock of an LSP7Votes token
+ */
+contract MyVotingToken is LSP7Votes {
+    constructor()
+        LSP7DigitalAsset("MyVotingToken", "MYVTKN", msg.sender, 0, false)
+        EIP712("MyVotingToken", "1")
+    {}
+
+    function mint(address rec, uint256 amount) public {
+        _mint(rec, amount, true, "");
+    }
+}