codtracker-js/node_modules/eslint/lib/rules/use-isnan.js

/**
 * @fileoverview Rule to flag comparisons to the value NaN
 * @author James Allardice
 */

'use strict';

//------------------------------------------------------------------------------
// Requirements
//------------------------------------------------------------------------------

const astUtils = require('./utils/ast-utils');

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

/**
 * Determines if the given node is a NaN `Identifier` node.
 * @param {ASTNode|null} node The node to check.
 * @returns {boolean} `true` if the node is 'NaN' identifier.
 */
function isNaNIdentifier(node) {
  if (!node) {
    return false;
  }

  const nodeToCheck =
    node.type === 'SequenceExpression' ? node.expressions.at(-1) : node;

  return (
    astUtils.isSpecificId(nodeToCheck, 'NaN') ||
    astUtils.isSpecificMemberAccess(nodeToCheck, 'Number', 'NaN')
  );
}

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

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

    docs: {
      description: 'Require calls to `isNaN()` when checking for `NaN`',
      recommended: true,
      url: 'https://eslint.org/docs/latest/rules/use-isnan',
    },

    schema: [
      {
        type: 'object',
        properties: {
          enforceForSwitchCase: {
            type: 'boolean',
          },
          enforceForIndexOf: {
            type: 'boolean',
          },
        },
        additionalProperties: false,
      },
    ],

    defaultOptions: [
      {
        enforceForIndexOf: false,
        enforceForSwitchCase: true,
      },
    ],

    messages: {
      comparisonWithNaN: 'Use the isNaN function to compare with NaN.',
      switchNaN:
        "'switch(NaN)' can never match a case clause. Use Number.isNaN instead of the switch.",
      caseNaN:
        "'case NaN' can never match. Use Number.isNaN before the switch.",
      indexOfNaN: "Array prototype method '{{ methodName }}' cannot find NaN.",
      replaceWithIsNaN: 'Replace with Number.isNaN.',
      replaceWithCastingAndIsNaN:
        'Replace with Number.isNaN and cast to a Number.',
      replaceWithFindIndex: 'Replace with Array.prototype.{{ methodName }}.',
    },
  },

  create(context) {
    const [{ enforceForIndexOf, enforceForSwitchCase }] = context.options;
    const sourceCode = context.sourceCode;

    const fixableOperators = new Set(['==', '===', '!=', '!==']);
    const castableOperators = new Set(['==', '!=']);

    /**
     * Get a fixer for a binary expression that compares to NaN.
     * @param  {ASTNode} node The node to fix.
     * @param {function(string): string} wrapValue A function that wraps the compared value with a fix.
     * @returns {function(Fixer): Fix} The fixer function.
     */
    function getBinaryExpressionFixer(node, wrapValue) {
      return (fixer) => {
        const comparedValue =
          isNaNIdentifier(node.left) ? node.right : node.left;
        const shouldWrap = comparedValue.type === 'SequenceExpression';
        const shouldNegate = node.operator[0] === '!';

        const negation = shouldNegate ? '!' : '';
        let comparedValueText = sourceCode.getText(comparedValue);

        if (shouldWrap) {
          comparedValueText = `(${comparedValueText})`;
        }

        const fixedValue = wrapValue(comparedValueText);

        return fixer.replaceText(node, `${negation}${fixedValue}`);
      };
    }

    /**
     * Checks the given `BinaryExpression` node for `foo === NaN` and other comparisons.
     * @param {ASTNode} node The node to check.
     * @returns {void}
     */
    function checkBinaryExpression(node) {
      if (
        /^(?:[<>]|[!=]=)=?$/u.test(node.operator) &&
        (isNaNIdentifier(node.left) || isNaNIdentifier(node.right))
      ) {
        const suggestedFixes = [];
        const NaNNode = isNaNIdentifier(node.left) ? node.left : node.right;

        const isSequenceExpression = NaNNode.type === 'SequenceExpression';
        const isSuggestable =
          fixableOperators.has(node.operator) && !isSequenceExpression;
        const isCastable = castableOperators.has(node.operator);

        if (isSuggestable) {
          suggestedFixes.push({
            messageId: 'replaceWithIsNaN',
            fix: getBinaryExpressionFixer(
              node,
              (value) => `Number.isNaN(${value})`
            ),
          });

          if (isCastable) {
            suggestedFixes.push({
              messageId: 'replaceWithCastingAndIsNaN',
              fix: getBinaryExpressionFixer(
                node,
                (value) => `Number.isNaN(Number(${value}))`
              ),
            });
          }
        }

        context.report({
          node,
          messageId: 'comparisonWithNaN',
          suggest: suggestedFixes,
        });
      }
    }

    /**
     * Checks the discriminant and all case clauses of the given `SwitchStatement` node for `switch(NaN)` and `case NaN:`
     * @param {ASTNode} node The node to check.
     * @returns {void}
     */
    function checkSwitchStatement(node) {
      if (isNaNIdentifier(node.discriminant)) {
        context.report({ node, messageId: 'switchNaN' });
      }

      for (const switchCase of node.cases) {
        if (isNaNIdentifier(switchCase.test)) {
          context.report({ node: switchCase, messageId: 'caseNaN' });
        }
      }
    }

    /**
     * Checks the given `CallExpression` node for `.indexOf(NaN)` and `.lastIndexOf(NaN)`.
     * @param {ASTNode} node The node to check.
     * @returns {void}
     */
    function checkCallExpression(node) {
      const callee = astUtils.skipChainExpression(node.callee);

      if (callee.type === 'MemberExpression') {
        const methodName = astUtils.getStaticPropertyName(callee);

        if (
          (methodName === 'indexOf' || methodName === 'lastIndexOf') &&
          node.arguments.length <= 2 &&
          isNaNIdentifier(node.arguments[0])
        ) {
          /*
           * To retain side effects, it's essential to address `NaN` beforehand, which
           * is not possible with fixes like `arr.findIndex(Number.isNaN)`.
           */
          const isSuggestable =
            node.arguments[0].type !== 'SequenceExpression' &&
            !node.arguments[1];
          const suggestedFixes = [];

          if (isSuggestable) {
            const shouldWrap = callee.computed;
            const findIndexMethod =
              methodName === 'indexOf' ? 'findIndex' : 'findLastIndex';
            const propertyName =
              shouldWrap ? `"${findIndexMethod}"` : findIndexMethod;

            suggestedFixes.push({
              messageId: 'replaceWithFindIndex',
              data: { methodName: findIndexMethod },
              fix: (fixer) => [
                fixer.replaceText(callee.property, propertyName),
                fixer.replaceText(node.arguments[0], 'Number.isNaN'),
              ],
            });
          }

          context.report({
            node,
            messageId: 'indexOfNaN',
            data: { methodName },
            suggest: suggestedFixes,
          });
        }
      }
    }

    const listeners = {
      BinaryExpression: checkBinaryExpression,
    };

    if (enforceForSwitchCase) {
      listeners.SwitchStatement = checkSwitchStatement;
    }

    if (enforceForIndexOf) {
      listeners.CallExpression = checkCallExpression;
    }

    return listeners;
  },
};