--- /dev/null
+/**
+ * @fileoverview A rule to disallow duplicate name in class members.
+ * @author Toru Nagashima
+ */
+
+"use strict";
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "problem",
+
+ docs: {
+ description: "disallow duplicate class members",
+ category: "ECMAScript 6",
+ recommended: true,
+ url: "https://eslint.org/docs/rules/no-dupe-class-members"
+ },
+
+ schema: [],
+
+ messages: {
+ unexpected: "Duplicate name '{{name}}'."
+ }
+ },
+
+ create(context) {
+ let stack = [];
+
+ /**
+ * Gets state of a given member name.
+ * @param {string} name A name of a member.
+ * @param {boolean} isStatic A flag which specifies that is a static member.
+ * @returns {Object} A state of a given member name.
+ * - retv.init {boolean} A flag which shows the name is declared as normal member.
+ * - retv.get {boolean} A flag which shows the name is declared as getter.
+ * - retv.set {boolean} A flag which shows the name is declared as setter.
+ */
+ function getState(name, isStatic) {
+ const stateMap = stack[stack.length - 1];
+ const key = `$${name}`; // to avoid "__proto__".
+
+ if (!stateMap[key]) {
+ stateMap[key] = {
+ nonStatic: { init: false, get: false, set: false },
+ static: { init: false, get: false, set: false }
+ };
+ }
+
+ return stateMap[key][isStatic ? "static" : "nonStatic"];
+ }
+
+ return {
+
+ // Initializes the stack of state of member declarations.
+ Program() {
+ stack = [];
+ },
+
+ // Initializes state of member declarations for the class.
+ ClassBody() {
+ stack.push(Object.create(null));
+ },
+
+ // Disposes the state for the class.
+ "ClassBody:exit"() {
+ stack.pop();
+ },
+
+ // Reports the node if its name has been declared already.
+ MethodDefinition(node) {
+ const name = astUtils.getStaticPropertyName(node);
+
+ if (name === null || node.kind === "constructor") {
+ return;
+ }
+
+ const state = getState(name, node.static);
+ let isDuplicate = false;
+
+ if (node.kind === "get") {
+ isDuplicate = (state.init || state.get);
+ state.get = true;
+ } else if (node.kind === "set") {
+ isDuplicate = (state.init || state.set);
+ state.set = true;
+ } else {
+ isDuplicate = (state.init || state.get || state.set);
+ state.init = true;
+ }
+
+ if (isDuplicate) {
+ context.report({ node, messageId: "unexpected", data: { name } });
+ }
+ }
+ };
+ }
+};