eslint/lib/rules/require-yield.js

   1 /**
   2  * @fileoverview Rule to flag the generator functions that does not have yield.
   3  * @author Toru Nagashima
   4  */
   5
   6 "use strict";
   7
   8 //------------------------------------------------------------------------------
   9 // Rule Definition
  10 //------------------------------------------------------------------------------
  11
  12 /** @type {import('../shared/types').Rule} */
  13 module.exports = {
  14     meta: {
  15         type: "suggestion",
  16
  17         docs: {
  18             description: "Require generator functions to contain `yield`",
  19             recommended: true,
  20             url: "https://eslint.org/docs/rules/require-yield"
  21         },
  22
  23         schema: [],
  24
  25         messages: {
  26             missingYield: "This generator function does not have 'yield'."
  27         }
  28     },
  29
  30     create(context) {
  31         const stack = [];
  32
  33         /**
  34          * If the node is a generator function, start counting `yield` keywords.
  35          * @param {Node} node A function node to check.
  36          * @returns {void}
  37          */
  38         function beginChecking(node) {
  39             if (node.generator) {
  40                 stack.push(0);
  41             }
  42         }
  43
  44         /**
  45          * If the node is a generator function, end counting `yield` keywords, then
  46          * reports result.
  47          * @param {Node} node A function node to check.
  48          * @returns {void}
  49          */
  50         function endChecking(node) {
  51             if (!node.generator) {
  52                 return;
  53             }
  54
  55             const countYield = stack.pop();
  56
  57             if (countYield === 0 && node.body.body.length > 0) {
  58                 context.report({ node, messageId: "missingYield" });
  59             }
  60         }
  61
  62         return {
  63             FunctionDeclaration: beginChecking,
  64             "FunctionDeclaration:exit": endChecking,
  65             FunctionExpression: beginChecking,
  66             "FunctionExpression:exit": endChecking,
  67
  68             // Increases the count of `yield` keyword.
  69             YieldExpression() {
  70
  71                 if (stack.length > 0) {
  72                     stack[stack.length - 1] += 1;
  73                 }
  74             }
  75         };
  76     }
  77 };