--- /dev/null
+/**
+ * @fileoverview Rule to disallow unsafe optional chaining
+ * @author Yeon JuAn
+ */
+
+"use strict";
+
+const UNSAFE_ARITHMETIC_OPERATORS = new Set(["+", "-", "/", "*", "%", "**"]);
+const UNSAFE_ASSIGNMENT_OPERATORS = new Set(["+=", "-=", "/=", "*=", "%=", "**="]);
+const UNSAFE_RELATIONAL_OPERATORS = new Set(["in", "instanceof"]);
+
+/**
+ * Checks whether a node is a destructuring pattern or not
+ * @param {ASTNode} node node to check
+ * @returns {boolean} `true` if a node is a destructuring pattern, otherwise `false`
+ */
+function isDestructuringPattern(node) {
+ return node.type === "ObjectPattern" || node.type === "ArrayPattern";
+}
+
+module.exports = {
+ meta: {
+ type: "problem",
+
+ docs: {
+ description: "disallow use of optional chaining in contexts where the `undefined` value is not allowed",
+ category: "Possible Errors",
+ recommended: false,
+ url: "https://eslint.org/docs/rules/no-unsafe-optional-chaining"
+ },
+ schema: [{
+ type: "object",
+ properties: {
+ disallowArithmeticOperators: {
+ type: "boolean",
+ default: false
+ }
+ },
+ additionalProperties: false
+ }],
+ fixable: null,
+ messages: {
+ unsafeOptionalChain: "Unsafe usage of optional chaining. If it short-circuits with 'undefined' the evaluation will throw TypeError.",
+ unsafeArithmetic: "Unsafe arithmetic operation on optional chaining. It can result in NaN."
+ }
+ },
+
+ create(context) {
+ const options = context.options[0] || {};
+ const disallowArithmeticOperators = (options.disallowArithmeticOperators) || false;
+
+ /**
+ * Reports unsafe usage of optional chaining
+ * @param {ASTNode} node node to report
+ * @returns {void}
+ */
+ function reportUnsafeUsage(node) {
+ context.report({
+ messageId: "unsafeOptionalChain",
+ node
+ });
+ }
+
+ /**
+ * Reports unsafe arithmetic operation on optional chaining
+ * @param {ASTNode} node node to report
+ * @returns {void}
+ */
+ function reportUnsafeArithmetic(node) {
+ context.report({
+ messageId: "unsafeArithmetic",
+ node
+ });
+ }
+
+ /**
+ * Checks and reports if a node can short-circuit with `undefined` by optional chaining.
+ * @param {ASTNode} [node] node to check
+ * @param {Function} reportFunc report function
+ * @returns {void}
+ */
+ function checkUndefinedShortCircuit(node, reportFunc) {
+ if (!node) {
+ return;
+ }
+ switch (node.type) {
+ case "LogicalExpression":
+ if (node.operator === "||" || node.operator === "??") {
+ checkUndefinedShortCircuit(node.right, reportFunc);
+ } else if (node.operator === "&&") {
+ checkUndefinedShortCircuit(node.left, reportFunc);
+ checkUndefinedShortCircuit(node.right, reportFunc);
+ }
+ break;
+ case "SequenceExpression":
+ checkUndefinedShortCircuit(
+ node.expressions[node.expressions.length - 1],
+ reportFunc
+ );
+ break;
+ case "ConditionalExpression":
+ checkUndefinedShortCircuit(node.consequent, reportFunc);
+ checkUndefinedShortCircuit(node.alternate, reportFunc);
+ break;
+ case "AwaitExpression":
+ checkUndefinedShortCircuit(node.argument, reportFunc);
+ break;
+ case "ChainExpression":
+ reportFunc(node);
+ break;
+ default:
+ break;
+ }
+ }
+
+ /**
+ * Checks unsafe usage of optional chaining
+ * @param {ASTNode} node node to check
+ * @returns {void}
+ */
+ function checkUnsafeUsage(node) {
+ checkUndefinedShortCircuit(node, reportUnsafeUsage);
+ }
+
+ /**
+ * Checks unsafe arithmetic operations on optional chaining
+ * @param {ASTNode} node node to check
+ * @returns {void}
+ */
+ function checkUnsafeArithmetic(node) {
+ checkUndefinedShortCircuit(node, reportUnsafeArithmetic);
+ }
+
+ return {
+ "AssignmentExpression, AssignmentPattern"(node) {
+ if (isDestructuringPattern(node.left)) {
+ checkUnsafeUsage(node.right);
+ }
+ },
+ "ClassDeclaration, ClassExpression"(node) {
+ checkUnsafeUsage(node.superClass);
+ },
+ CallExpression(node) {
+ if (!node.optional) {
+ checkUnsafeUsage(node.callee);
+ }
+ },
+ NewExpression(node) {
+ checkUnsafeUsage(node.callee);
+ },
+ VariableDeclarator(node) {
+ if (isDestructuringPattern(node.id)) {
+ checkUnsafeUsage(node.init);
+ }
+ },
+ MemberExpression(node) {
+ if (!node.optional) {
+ checkUnsafeUsage(node.object);
+ }
+ },
+ TaggedTemplateExpression(node) {
+ checkUnsafeUsage(node.tag);
+ },
+ ForOfStatement(node) {
+ checkUnsafeUsage(node.right);
+ },
+ SpreadElement(node) {
+ if (node.parent && node.parent.type !== "ObjectExpression") {
+ checkUnsafeUsage(node.argument);
+ }
+ },
+ BinaryExpression(node) {
+ if (UNSAFE_RELATIONAL_OPERATORS.has(node.operator)) {
+ checkUnsafeUsage(node.right);
+ }
+ if (
+ disallowArithmeticOperators &&
+ UNSAFE_ARITHMETIC_OPERATORS.has(node.operator)
+ ) {
+ checkUnsafeArithmetic(node.right);
+ checkUnsafeArithmetic(node.left);
+ }
+ },
+ WithStatement(node) {
+ checkUnsafeUsage(node.object);
+ },
+ UnaryExpression(node) {
+ if (
+ disallowArithmeticOperators &&
+ UNSAFE_ARITHMETIC_OPERATORS.has(node.operator)
+ ) {
+ checkUnsafeArithmetic(node.argument);
+ }
+ },
+ AssignmentExpression(node) {
+ if (
+ disallowArithmeticOperators &&
+ UNSAFE_ASSIGNMENT_OPERATORS.has(node.operator)
+ ) {
+ checkUnsafeArithmetic(node.right);
+ }
+ }
+ };
+ }
+};