eslint/lib/rules/no-duplicate-case.js

   1 /**
   2  * @fileoverview Rule to disallow a duplicate case label.
   3  * @author Dieter Oberkofler
   4  * @author Burak Yigit Kaya
   5  */
   6
   7 "use strict";
   8
   9 //------------------------------------------------------------------------------
  10 // Requirements
  11 //------------------------------------------------------------------------------
  12
  13 const astUtils = require("./utils/ast-utils");
  14
  15 //------------------------------------------------------------------------------
  16 // Rule Definition
  17 //------------------------------------------------------------------------------
  18
  19 module.exports = {
  20     meta: {
  21         type: "problem",
  22
  23         docs: {
  24             description: "disallow duplicate case labels",
  25             category: "Possible Errors",
  26             recommended: true,
  27             url: "https://eslint.org/docs/rules/no-duplicate-case"
  28         },
  29
  30         schema: [],
  31
  32         messages: {
  33             unexpected: "Duplicate case label."
  34         }
  35     },
  36
  37     create(context) {
  38         const sourceCode = context.getSourceCode();
  39
  40         /**
  41          * Determines whether the two given nodes are considered to be equal.
  42          * @param {ASTNode} a First node.
  43          * @param {ASTNode} b Second node.
  44          * @returns {boolean} `true` if the nodes are considered to be equal.
  45          */
  46         function equal(a, b) {
  47             if (a.type !== b.type) {
  48                 return false;
  49             }
  50
  51             return astUtils.equalTokens(a, b, sourceCode);
  52         }
  53         return {
  54             SwitchStatement(node) {
  55                 const previousTests = [];
  56
  57                 for (const switchCase of node.cases) {
  58                     if (switchCase.test) {
  59                         const test = switchCase.test;
  60
  61                         if (previousTests.some(previousTest => equal(previousTest, test))) {
  62                             context.report({ node: switchCase, messageId: "unexpected" });
  63                         } else {
  64                             previousTests.push(test);
  65                         }
  66                     }
  67                 }
  68             }
  69         };
  70     }
  71 };