Procedural SafeCast.sol generation (#3245)

scripts/generate/format-lines.js

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+function formatLines (...lines) {
+  return [...indentEach(0, lines)].join('\n') + '\n';
+}
+
+function *indentEach (indent, lines) {
+  for (const line of lines) {
+    if (Array.isArray(line)) {
+      yield * indentEach(indent + 1, line);
+    } else {
+      const padding = '    '.repeat(indent);
+      yield * line.split('\n').map(subline => subline === '' ? '' : padding + subline);
+    }
+  }
+}
+
+module.exports = formatLines;

scripts/generate/run.js

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+#!/usr/bin/env node
+
+const fs = require('fs');
+const format = require('./format-lines');
+
+function getVersion (path) {
+  try {
+    return fs
+      .readFileSync(path, 'utf8')
+      .match(/\/\/ OpenZeppelin Contracts \(last updated v\d+\.\d+\.\d+\)/)[0];
+  } catch (err) {
+    return null;
+  }
+}
+
+for (const [ file, template ] of Object.entries({
+  'utils/math/SafeCast.sol': './templates/SafeCast',
+  'mocks/SafeCastMock.sol': './templates/SafeCastMock',
+})) {
+  const path = `./contracts/${file}`;
+  const version = getVersion(path);
+  const content = format(
+    '// SPDX-License-Identifier: MIT',
+    (version ? version + ` (${file})\n` : ''),
+    require(template).trimEnd(),
+  );
+
+  fs.writeFileSync(path, content);
+}

scripts/generate/templates/SafeCast.js

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+const assert = require('assert');
+const format = require('../format-lines');
+const { range } = require('../../helpers');
+
+const LENGTHS = range(8, 256, 8).reverse(); // 248 → 8 (in steps of 8)
+
+// Returns the version of OpenZeppelin Contracts in which a particular function was introduced.
+// This is used in the docs for each function.
+const version = (selector, length) => {
+  switch (selector) {
+  case 'toUint(uint)': {
+    switch (length) {
+    case 8:
+    case 16:
+    case 32:
+    case 64:
+    case 128:
+      return '2.5';
+    case 96:
+    case 224:
+      return '4.2';
+    default:
+      assert(LENGTHS.includes(length));
+      return '4.7';
+    }
+  }
+  case 'toInt(int)': {
+    switch (length) {
+    case 8:
+    case 16:
+    case 32:
+    case 64:
+    case 128:
+      return '3.1';
+    default:
+      assert(LENGTHS.includes(length));
+      return '4.7';
+    }
+  }
+  case 'toUint(int)': {
+    switch (length) {
+    case 256:
+      return '3.0';
+    default:
+      assert(false);
+      return;
+    }
+  }
+  case 'toInt(uint)': {
+    switch (length) {
+    case 256:
+      return '3.0';
+    default:
+      assert(false);
+      return;
+    }
+  }
+  default:
+    assert(false);
+  }
+};
+
+const header = `\
+pragma solidity ^0.8.0;
+
+/**
+ * @dev Wrappers over Solidity's uintXX/intXX casting operators with added overflow
+ * checks.
+ *
+ * Downcasting from uint256/int256 in Solidity does not revert on overflow. This can
+ * easily result in undesired exploitation or bugs, since developers usually
+ * assume that overflows raise errors. \`SafeCast\` restores this intuition by
+ * reverting the transaction when such an operation overflows.
+ *
+ * Using this library instead of the unchecked operations eliminates an entire
+ * class of bugs, so it's recommended to use it always.
+ *
+ * Can be combined with {SafeMath} and {SignedSafeMath} to extend it to smaller types, by performing
+ * all math on \`uint256\` and \`int256\` and then downcasting.
+ */
+`;
+
+const toUintDownCast = length => `\
+/**
+ * @dev Returns the downcasted uint${length} from uint256, reverting on
+ * overflow (when the input is greater than largest uint${length}).
+ *
+ * Counterpart to Solidity's \`uint${length}\` operator.
+ *
+ * Requirements:
+ *
+ * - input must fit into ${length} bits
+ *
+ * _Available since v${version('toUint(uint)', length)}._
+ */
+function toUint${length}(uint256 value) internal pure returns (uint${length}) {
+    require(value <= type(uint${length}).max, "SafeCast: value doesn't fit in ${length} bits");
+    return uint${length}(value);
+}
+`;
+
+/* eslint-disable max-len */
+const toIntDownCast = length => `\
+/**
+ * @dev Returns the downcasted int${length} from int256, reverting on
+ * overflow (when the input is less than smallest int${length} or
+ * greater than largest int${length}).
+ *
+ * Counterpart to Solidity's \`int${length}\` operator.
+ *
+ * Requirements:
+ *
+ * - input must fit into ${length} bits
+ *
+ * _Available since v${version('toInt(int)', length)}._
+ */
+function toInt${length}(int256 value) internal pure returns (int${length}) {
+    require(value >= type(int${length}).min && value <= type(int${length}).max, "SafeCast: value doesn't fit in ${length} bits");
+    return int${length}(value);
+}
+`;
+/* eslint-enable max-len */
+
+const toInt = length => `\
+/**
+ * @dev Converts an unsigned uint${length} into a signed int${length}.
+ *
+ * Requirements:
+ *
+ * - input must be less than or equal to maxInt${length}.
+ *
+ * _Available since v${version('toInt(uint)', length)}._
+ */
+function toInt${length}(uint${length} value) internal pure returns (int${length}) {
+    // Note: Unsafe cast below is okay because \`type(int${length}).max\` is guaranteed to be positive
+    require(value <= uint${length}(type(int${length}).max), "SafeCast: value doesn't fit in an int${length}");
+    return int${length}(value);
+}
+`;
+
+const toUint = length => `\
+/**
+ * @dev Converts a signed int${length} into an unsigned uint${length}.
+ *
+ * Requirements:
+ *
+ * - input must be greater than or equal to 0.
+ *
+ * _Available since v${version('toUint(int)', length)}._
+ */
+function toUint${length}(int${length} value) internal pure returns (uint${length}) {
+    require(value >= 0, "SafeCast: value must be positive");
+    return uint${length}(value);
+}
+`;
+
+// GENERATE
+module.exports = format(
+  header.trimEnd(),
+  'library SafeCast {',
+  [
+    ...LENGTHS.map(size => toUintDownCast(size)),
+    toUint(256),
+    ...LENGTHS.map(size => toIntDownCast(size)),
+    toInt(256).trimEnd(),
+  ],
+  '}',
+);

scripts/generate/templates/SafeCastMock.js

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+const format = require('../format-lines');
+const { range } = require('../../helpers');
+
+const LENGTHS = range(8, 256, 8).reverse(); // 248 → 8 (in steps of 8)
+
+const header = `\
+pragma solidity ^0.8.0;
+
+import "../utils/math/SafeCast.sol";
+`;
+
+const toInt = length => `\
+function toInt${length}(uint${length} a) public pure returns (int${length}) {
+    return a.toInt${length}();
+}
+`;
+
+const toUint = length => `\
+function toUint${length}(int${length} a) public pure returns (uint${length}) {
+    return a.toUint${length}();
+}
+`;
+
+const toIntDownCast = length => `\
+function toInt${length}(int256 a) public pure returns (int${length}) {
+    return a.toInt${length}();
+}
+`;
+
+const toUintDownCast = length => `\
+function toUint${length}(uint256 a) public pure returns (uint${length}) {
+    return a.toUint${length}();
+}
+`;
+
+// GENERATE
+module.exports = format(
+  header,
+  'contract SafeCastMock {',
+  [
+    'using SafeCast for uint256;',
+    'using SafeCast for int256;',
+    '',
+    toUint(256),
+    ...LENGTHS.map(size => toUintDownCast(size)),
+    toInt(256),
+    ...LENGTHS.map(size => toIntDownCast(size)),
+  ].flatMap(fn => fn.split('\n')).slice(0, -1),
+  '}',
+);