--- /dev/null
+/**
+ * @fileoverview Rule to disallow a duplicate case label.
+ * @author Dieter Oberkofler
+ * @author Burak Yigit Kaya
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+const astUtils = require("./utils/ast-utils");
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+ meta: {
+ type: "problem",
+
+ docs: {
+ description: "disallow duplicate case labels",
+ category: "Possible Errors",
+ recommended: true,
+ url: "https://eslint.org/docs/rules/no-duplicate-case"
+ },
+
+ schema: [],
+
+ messages: {
+ unexpected: "Duplicate case label."
+ }
+ },
+
+ create(context) {
+ const sourceCode = context.getSourceCode();
+
+ /**
+ * Determines whether the two given nodes are considered to be equal.
+ * @param {ASTNode} a First node.
+ * @param {ASTNode} b Second node.
+ * @returns {boolean} `true` if the nodes are considered to be equal.
+ */
+ function equal(a, b) {
+ if (a.type !== b.type) {
+ return false;
+ }
+
+ return astUtils.equalTokens(a, b, sourceCode);
+ }
+ return {
+ SwitchStatement(node) {
+ const previousTests = [];
+
+ for (const switchCase of node.cases) {
+ if (switchCase.test) {
+ const test = switchCase.test;
+
+ if (previousTests.some(previousTest => equal(previousTest, test))) {
+ context.report({ node: switchCase, messageId: "unexpected" });
+ } else {
+ previousTests.push(test);
+ }
+ }
+ }
+ }
+ };
+ }
+};