Merge branch 'gasreport' into testing/gasreport/erc721

.eslintrc

@@ -36,6 +36,7 @@
     "indent": ["error", 2],
     "linebreak-style": ["error", "unix"],
     "max-len": ["error", 120, 2],
+    "no-control-regex": "off",
     "no-debugger": "off",
     "no-dupe-args": "error",
     "no-dupe-keys": "error",

.github/workflows/checks.yml

@@ -56,3 +56,40 @@ jobs:
       - name: Set up environment
         uses: ./.github/actions/setup
       - uses: crytic/slither-action@v0.1.1
+
+  gas:
+    if: github.event_name == 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - name: 'Download reference report'
+        run: |
+          RUN_ID=`gh run list --repo ${{ github.repository }} --branch ${{ github.base_ref }} --workflow ${{ github.workflow }} --json databaseId --jq '.[0].databaseId'`
+          gh run download ${RUN_ID} --repo ${{ github.repository }} -n gasreport
+        env:
+          GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+      - name: 'Generate new report'
+        run: npm run test
+        env:
+          GAS: true
+          GAS_REPORT: HEAD.gasreport.log~
+      - name: 'Compare reports'
+        run: node scripts/checks/compareGasReports.js HEAD.gasreport.log~ ${{ github.base_ref }}.gasreport.log
+
+  gasCache:
+    if: github.event_name != 'pull_request'
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v3
+      - name: Set up environment
+        uses: ./.github/actions/setup
+      - run: npm run test
+        env:
+          GAS: true
+          GAS_REPORT: ${{ github.ref_name }}.gasreport.log
+      - uses: actions/upload-artifact@v3
+        with:
+          name: gasreport
+          path: ${{ github.ref_name }}.gasreport.log

CHANGELOG.md

@@ -6,6 +6,12 @@
  * `Address`: optimize `functionCall` by calling `functionCallWithValue` directly. ([#3468](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3468))
  * `Address`: optimize `functionCall` functions by checking contract size only if there is no returned data. ([#3469](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3469))
  * `GovernorCompatibilityBravo`: remove unused `using` statements ([#3506](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3506))
+ * `ERC20`: optimize `_transfer`, `_mint` and `_burn` by using `unchecked` arithmetic when possible. ([#3513](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3513))
+ * `ERC721`: optimize transfers by making approval clearing implicit instead of emitting an event. ([#3481](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/3481))
+
+### Compatibility Note
+
+ERC-721 integrators that interpret contract state from events should make sure that they implement the clearing of approval that is implicit in every transfer according to the EIP. Previous versions of OpenZeppellin Contracts emitted an explicit `Approval` event even though it was not required by the specification, and this is no longer the case.
 
 ## 4.7.0 (2022-06-29)
 

contracts/token/ERC20/ERC20.sol

@@ -237,8 +237,10 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         require(fromBalance >= amount, "ERC20: transfer amount exceeds balance");
         unchecked {
             _balances[from] = fromBalance - amount;
+            // Overflow not possible: the sum of all balances is capped by totalSupply, and the sum is preserved by
+            // decrementing then incrementing.
+            _balances[to] += amount;
         }
-        _balances[to] += amount;
 
         emit Transfer(from, to, amount);
 
@@ -260,7 +262,10 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         _beforeTokenTransfer(address(0), account, amount);
 
         _totalSupply += amount;
-        _balances[account] += amount;
+        unchecked {
+            // Overflow not possible: balance + amount is at most totalSupply + amount, which is checked above.
+            _balances[account] += amount;
+        }
         emit Transfer(address(0), account, amount);
 
         _afterTokenTransfer(address(0), account, amount);
@@ -286,8 +291,9 @@ contract ERC20 is Context, IERC20, IERC20Metadata {
         require(accountBalance >= amount, "ERC20: burn amount exceeds balance");
         unchecked {
             _balances[account] = accountBalance - amount;
+            // Overflow not possible: amount <= accountBalance <= totalSupply.
+            _totalSupply -= amount;
         }
-        _totalSupply -= amount;
 
         emit Transfer(account, address(0), amount);
 

contracts/token/ERC721/ERC721.sol

@@ -348,7 +348,7 @@ contract ERC721 is Context, ERC165, IERC721, IERC721Metadata {
         _beforeTokenTransfer(from, to, tokenId);
 
         // Clear approvals from the previous owner
-        _approve(address(0), tokenId);
+        delete _tokenApprovals[tokenId];
 
         unchecked {
             // `_balances[from]` cannot overflow for the same reason as described in `_burn`:

contracts/utils/math/Math.sol

@@ -151,7 +151,7 @@ library Math {
     }
 
     /**
-     * @dev Returns the square root of a number. It the number is not a perfect square, the value is rounded down.
+     * @dev Returns the square root of a number. If the number is not a perfect square, the value is rounded down.
      *
      * Inspired by Henry S. Warren, Jr.'s "Hacker's Delight" (Chapter 11).
      */
@@ -165,8 +165,8 @@ library Math {
         // `msb(a) <= a < 2*msb(a)`.
         // We also know that `k`, the position of the most significant bit, is such that `msb(a) = 2**k`.
         // This gives `2**k < a <= 2**(k+1)` → `2**(k/2) <= sqrt(a) < 2 ** (k/2+1)`.
-        // Using an algorithm similar to the msb conmputation, we are able to compute `result = 2**(k/2)` which is a
-        // good first aproximation of `sqrt(a)` with at least 1 correct bit.
+        // Using an algorithm similar to the msb computation, we are able to compute `result = 2**(k/2)` which is a
+        // good first approximation of `sqrt(a)` with at least 1 correct bit.
         uint256 result = 1;
         uint256 x = a;
         if (x >> 128 > 0) {

hardhat.config.js

@@ -11,10 +11,6 @@ const path = require('path');
 const argv = require('yargs/yargs')()
   .env('')
   .options({
-    ci: {
-      type: 'boolean',
-      default: false,
-    },
     coverage: {
       type: 'boolean',
       default: false,
@@ -24,6 +20,12 @@ const argv = require('yargs/yargs')()
       type: 'boolean',
       default: false,
     },
+    gasReport: {
+      alias: 'enableGasReportPath',
+      type: 'string',
+      implies: 'gas',
+      default: undefined,
+    },
     mode: {
       alias: 'compileMode',
       type: 'string',
@@ -49,15 +51,15 @@ const argv = require('yargs/yargs')()
 
 require('@nomiclabs/hardhat-truffle5');
 
-if (argv.enableGasReport) {
+if (argv.gas) {
   require('hardhat-gas-reporter');
 }
 
 for (const f of fs.readdirSync(path.join(__dirname, 'hardhat'))) {
   require(path.join(__dirname, 'hardhat', f));
 }
 
-const withOptimizations = argv.enableGasReport || argv.compileMode === 'production';
+const withOptimizations = argv.gas || argv.compileMode === 'production';
 
 /**
  * @type import('hardhat/config').HardhatUserConfig
@@ -81,7 +83,7 @@ module.exports = {
   },
   gasReporter: {
     currency: 'USD',
-    outputFile: argv.ci ? 'gas-report.txt' : undefined,
+    outputFile: argv.gasReport,
     coinmarketcap: argv.coinmarketcap,
   },
 };