no-constant-condition.js

/**
 * @fileoverview Rule to flag use constant conditions
 * @author Christian Schulz <http://rndm.de>
 */

"use strict";

const { isConstant } = require("./utils/ast-utils");

//------------------------------------------------------------------------------
// Helpers
//------------------------------------------------------------------------------

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

/** @type {import('../shared/types').Rule} */
module.exports = {
    meta: {
        type: "problem",

        docs: {
            description: "Disallow constant expressions in conditions",
            recommended: true,
            url: "https://eslint.org/docs/latest/rules/no-constant-condition"
        },

        schema: [
            {
                type: "object",
                properties: {
                    checkLoops: {
                        type: "boolean",
                        default: true
                    }
                },
                additionalProperties: false
            }
        ],

        messages: {
            unexpected: "Unexpected constant condition."
        }
    },

    create(context) {
        const options = context.options[0] || {},
            checkLoops = options.checkLoops !== false,
            loopSetStack = [];
        const sourceCode = context.sourceCode;

        let loopsInCurrentScope = new Set();

        //--------------------------------------------------------------------------
        // Helpers
        //--------------------------------------------------------------------------

        /**
         * Tracks when the given node contains a constant condition.
         * @param {ASTNode} node The AST node to check.
         * @returns {void}
         * @private
         */
        function trackConstantConditionLoop(node) {
            if (node.test && isConstant(sourceCode.getScope(node), node.test, true)) {
                loopsInCurrentScope.add(node);
            }
        }

        /**
         * Reports when the set contains the given constant condition node
         * @param {ASTNode} node The AST node to check.
         * @returns {void}
         * @private
         */
        function checkConstantConditionLoopInSet(node) {
            if (loopsInCurrentScope.has(node)) {
                loopsInCurrentScope.delete(node);
                context.report({ node: node.test, messageId: "unexpected" });
            }
        }

        /**
         * Reports when the given node contains a constant condition.
         * @param {ASTNode} node The AST node to check.
         * @returns {void}
         * @private
         */
        function reportIfConstant(node) {
            if (node.test && isConstant(sourceCode.getScope(node), node.test, true)) {
                context.report({ node: node.test, messageId: "unexpected" });
            }
        }

        /**
         * Stores current set of constant loops in loopSetStack temporarily
         * and uses a new set to track constant loops
         * @returns {void}
         * @private
         */
        function enterFunction() {
            loopSetStack.push(loopsInCurrentScope);
            loopsInCurrentScope = new Set();
        }

        /**
         * Reports when the set still contains stored constant conditions
         * @returns {void}
         * @private
         */
        function exitFunction() {
            loopsInCurrentScope = loopSetStack.pop();
        }

        /**
         * Checks node when checkLoops option is enabled
         * @param {ASTNode} node The AST node to check.
         * @returns {void}
         * @private
         */
        function checkLoop(node) {
            if (checkLoops) {
                trackConstantConditionLoop(node);
            }
        }

        //--------------------------------------------------------------------------
        // Public
        //--------------------------------------------------------------------------

        return {
            ConditionalExpression: reportIfConstant,
            IfStatement: reportIfConstant,
            WhileStatement: checkLoop,
            "WhileStatement:exit": checkConstantConditionLoopInSet,
            DoWhileStatement: checkLoop,
            "DoWhileStatement:exit": checkConstantConditionLoopInSet,
            ForStatement: checkLoop,
            "ForStatement > .test": node => checkLoop(node.parent),
            "ForStatement:exit": checkConstantConditionLoopInSet,
            FunctionDeclaration: enterFunction,
            "FunctionDeclaration:exit": exitFunction,
            FunctionExpression: enterFunction,
            "FunctionExpression:exit": exitFunction,
            YieldExpression: () => loopsInCurrentScope.clear()
        };

    }
};