codtracker-js/node_modules/eslint/lib/rules/no-unneeded-ternary.js

/**
 * @fileoverview Rule to flag no-unneeded-ternary
 * @author Gyandeep Singh
 */

'use strict';

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

// Operators that always result in a boolean value
const BOOLEAN_OPERATORS = new Set([
  '==',
  '===',
  '!=',
  '!==',
  '>',
  '>=',
  '<',
  '<=',
  'in',
  'instanceof',
]);
const OPERATOR_INVERSES = {
  '==': '!=',
  '!=': '==',
  '===': '!==',
  '!==': '===',

  // Operators like < and >= are not true inverses, since both will return false with NaN.
};
const OR_PRECEDENCE = astUtils.getPrecedence({
  type: 'LogicalExpression',
  operator: '||',
});

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

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

    defaultOptions: [{ defaultAssignment: true }],

    docs: {
      description: 'Disallow ternary operators when simpler alternatives exist',
      recommended: false,
      frozen: true,
      url: 'https://eslint.org/docs/latest/rules/no-unneeded-ternary',
    },

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

    fixable: 'code',

    messages: {
      unnecessaryConditionalExpression:
        'Unnecessary use of boolean literals in conditional expression.',
      unnecessaryConditionalAssignment:
        'Unnecessary use of conditional expression for default assignment.',
    },
  },

  create(context) {
    const [{ defaultAssignment }] = context.options;
    const sourceCode = context.sourceCode;

    /**
     * Test if the node is a boolean literal
     * @param {ASTNode} node The node to report.
     * @returns {boolean} True if the its a boolean literal
     * @private
     */
    function isBooleanLiteral(node) {
      return node.type === 'Literal' && typeof node.value === 'boolean';
    }

    /**
     * Creates an expression that represents the boolean inverse of the expression represented by the original node
     * @param {ASTNode} node A node representing an expression
     * @returns {string} A string representing an inverted expression
     */
    function invertExpression(node) {
      if (
        node.type === 'BinaryExpression' &&
        Object.hasOwn(OPERATOR_INVERSES, node.operator)
      ) {
        const operatorToken = sourceCode.getFirstTokenBetween(
          node.left,
          node.right,
          (token) => token.value === node.operator
        );
        const text = sourceCode.getText();

        return (
          text.slice(node.range[0], operatorToken.range[0]) +
          OPERATOR_INVERSES[node.operator] +
          text.slice(operatorToken.range[1], node.range[1])
        );
      }

      if (
        astUtils.getPrecedence(node) <
        astUtils.getPrecedence({ type: 'UnaryExpression' })
      ) {
        return `!(${astUtils.getParenthesisedText(sourceCode, node)})`;
      }
      return `!${astUtils.getParenthesisedText(sourceCode, node)}`;
    }

    /**
     * Tests if a given node always evaluates to a boolean value
     * @param {ASTNode} node An expression node
     * @returns {boolean} True if it is determined that the node will always evaluate to a boolean value
     */
    function isBooleanExpression(node) {
      return (
        (node.type === 'BinaryExpression' &&
          BOOLEAN_OPERATORS.has(node.operator)) ||
        (node.type === 'UnaryExpression' && node.operator === '!')
      );
    }

    /**
     * Test if the node matches the pattern id ? id : expression
     * @param {ASTNode} node The ConditionalExpression to check.
     * @returns {boolean} True if the pattern is matched, and false otherwise
     * @private
     */
    function matchesDefaultAssignment(node) {
      return (
        node.test.type === 'Identifier' &&
        node.consequent.type === 'Identifier' &&
        node.test.name === node.consequent.name
      );
    }

    return {
      ConditionalExpression(node) {
        if (
          isBooleanLiteral(node.alternate) &&
          isBooleanLiteral(node.consequent)
        ) {
          context.report({
            node,
            messageId: 'unnecessaryConditionalExpression',
            fix(fixer) {
              if (node.consequent.value === node.alternate.value) {
                // Replace `foo ? true : true` with just `true`, but don't replace `foo() ? true : true`
                return node.test.type === 'Identifier' ?
                    fixer.replaceText(node, node.consequent.value.toString())
                  : null;
              }
              if (node.alternate.value) {
                // Replace `foo() ? false : true` with `!(foo())`
                return fixer.replaceText(node, invertExpression(node.test));
              }

              // Replace `foo ? true : false` with `foo` if `foo` is guaranteed to be a boolean, or `!!foo` otherwise.

              return fixer.replaceText(
                node,
                isBooleanExpression(node.test) ?
                  astUtils.getParenthesisedText(sourceCode, node.test)
                : `!${invertExpression(node.test)}`
              );
            },
          });
        } else if (!defaultAssignment && matchesDefaultAssignment(node)) {
          context.report({
            node,
            messageId: 'unnecessaryConditionalAssignment',
            fix(fixer) {
              const shouldParenthesizeAlternate =
                (astUtils.getPrecedence(node.alternate) < OR_PRECEDENCE ||
                  astUtils.isCoalesceExpression(node.alternate)) &&
                !astUtils.isParenthesised(sourceCode, node.alternate);
              const alternateText =
                shouldParenthesizeAlternate ?
                  `(${sourceCode.getText(node.alternate)})`
                : astUtils.getParenthesisedText(sourceCode, node.alternate);
              const testText = astUtils.getParenthesisedText(
                sourceCode,
                node.test
              );

              return fixer.replaceText(node, `${testText} || ${alternateText}`);
            },
          });
        }
      },
    };
  },
};