eslint/lib/rules/no-constant-condition.js

   1 /**
   2  * @fileoverview Rule to flag use constant conditions
   3  * @author Christian Schulz <http://rndm.de>
   4  */
   5
   6 "use strict";
   7
   8 const { isConstant } = require("./utils/ast-utils");
   9
  10 //------------------------------------------------------------------------------
  11 // Helpers
  12 //------------------------------------------------------------------------------
  13
  14 //------------------------------------------------------------------------------
  15 // Rule Definition
  16 //------------------------------------------------------------------------------
  17
  18 /** @type {import('../shared/types').Rule} */
  19 module.exports = {
  20     meta: {
  21         type: "problem",
  22
  23         docs: {
  24             description: "Disallow constant expressions in conditions",
  25             recommended: true,
  26             url: "https://eslint.org/docs/rules/no-constant-condition"
  27         },
  28
  29         schema: [
  30             {
  31                 type: "object",
  32                 properties: {
  33                     checkLoops: {
  34                         type: "boolean",
  35                         default: true
  36                     }
  37                 },
  38                 additionalProperties: false
  39             }
  40         ],
  41
  42         messages: {
  43             unexpected: "Unexpected constant condition."
  44         }
  45     },
  46
  47     create(context) {
  48         const options = context.options[0] || {},
  49             checkLoops = options.checkLoops !== false,
  50             loopSetStack = [];
  51
  52         let loopsInCurrentScope = new Set();
  53
  54         //--------------------------------------------------------------------------
  55         // Helpers
  56         //--------------------------------------------------------------------------
  57
  58         /**
  59          * Tracks when the given node contains a constant condition.
  60          * @param {ASTNode} node The AST node to check.
  61          * @returns {void}
  62          * @private
  63          */
  64         function trackConstantConditionLoop(node) {
  65             if (node.test && isConstant(context.getScope(), node.test, true)) {
  66                 loopsInCurrentScope.add(node);
  67             }
  68         }
  69
  70         /**
  71          * Reports when the set contains the given constant condition node
  72          * @param {ASTNode} node The AST node to check.
  73          * @returns {void}
  74          * @private
  75          */
  76         function checkConstantConditionLoopInSet(node) {
  77             if (loopsInCurrentScope.has(node)) {
  78                 loopsInCurrentScope.delete(node);
  79                 context.report({ node: node.test, messageId: "unexpected" });
  80             }
  81         }
  82
  83         /**
  84          * Reports when the given node contains a constant condition.
  85          * @param {ASTNode} node The AST node to check.
  86          * @returns {void}
  87          * @private
  88          */
  89         function reportIfConstant(node) {
  90             if (node.test && isConstant(context.getScope(), node.test, true)) {
  91                 context.report({ node: node.test, messageId: "unexpected" });
  92             }
  93         }
  94
  95         /**
  96          * Stores current set of constant loops in loopSetStack temporarily
  97          * and uses a new set to track constant loops
  98          * @returns {void}
  99          * @private
 100          */
 101         function enterFunction() {
 102             loopSetStack.push(loopsInCurrentScope);
 103             loopsInCurrentScope = new Set();
 104         }
 105
 106         /**
 107          * Reports when the set still contains stored constant conditions
 108          * @returns {void}
 109          * @private
 110          */
 111         function exitFunction() {
 112             loopsInCurrentScope = loopSetStack.pop();
 113         }
 114
 115         /**
 116          * Checks node when checkLoops option is enabled
 117          * @param {ASTNode} node The AST node to check.
 118          * @returns {void}
 119          * @private
 120          */
 121         function checkLoop(node) {
 122             if (checkLoops) {
 123                 trackConstantConditionLoop(node);
 124             }
 125         }
 126
 127         //--------------------------------------------------------------------------
 128         // Public
 129         //--------------------------------------------------------------------------
 130
 131         return {
 132             ConditionalExpression: reportIfConstant,
 133             IfStatement: reportIfConstant,
 134             WhileStatement: checkLoop,
 135             "WhileStatement:exit": checkConstantConditionLoopInSet,
 136             DoWhileStatement: checkLoop,
 137             "DoWhileStatement:exit": checkConstantConditionLoopInSet,
 138             ForStatement: checkLoop,
 139             "ForStatement > .test": node => checkLoop(node.parent),
 140             "ForStatement:exit": checkConstantConditionLoopInSet,
 141             FunctionDeclaration: enterFunction,
 142             "FunctionDeclaration:exit": exitFunction,
 143             FunctionExpression: enterFunction,
 144             "FunctionExpression:exit": exitFunction,
 145             YieldExpression: () => loopsInCurrentScope.clear()
 146         };
 147
 148     }
 149 };