code-server/build/lib/eslint/code-no-unused-expressions.js

/*---------------------------------------------------------------------------------------------
 *  Copyright (c) Microsoft Corporation. All rights reserved.
 *  Licensed under the MIT License. See License.txt in the project root for license information.
 *--------------------------------------------------------------------------------------------*/
// FORKED FROM https://github.com/eslint/eslint/blob/b23ad0d789a909baf8d7c41a35bc53df932eaf30/lib/rules/no-unused-expressions.js
// and added support for `OptionalCallExpression`, see https://github.com/facebook/create-react-app/issues/8107 and https://github.com/eslint/eslint/issues/12642
/**
 * @fileoverview Flag expressions in statement position that do not side effect
 * @author Michael Ficarra
 */
'use strict';
Object.defineProperty(exports, "__esModule", { value: true });
//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------
module.exports = {
    meta: {
        type: 'suggestion',
        docs: {
            description: 'disallow unused expressions',
            category: 'Best Practices',
            recommended: false,
            url: 'https://eslint.org/docs/rules/no-unused-expressions'
        },
        schema: [
            {
                type: 'object',
                properties: {
                    allowShortCircuit: {
                        type: 'boolean',
                        default: false
                    },
                    allowTernary: {
                        type: 'boolean',
                        default: false
                    },
                    allowTaggedTemplates: {
                        type: 'boolean',
                        default: false
                    }
                },
                additionalProperties: false
            }
        ]
    },
    create(context) {
        const config = context.options[0] || {}, allowShortCircuit = config.allowShortCircuit || false, allowTernary = config.allowTernary || false, allowTaggedTemplates = config.allowTaggedTemplates || false;
        // eslint-disable-next-line jsdoc/require-description
        /**
         * @param node any node
         * @returns whether the given node structurally represents a directive
         */
        function looksLikeDirective(node) {
            return node.type === 'ExpressionStatement' &&
                node.expression.type === 'Literal' && typeof node.expression.value === 'string';
        }
        // eslint-disable-next-line jsdoc/require-description
        /**
         * @param predicate ([a] -> Boolean) the function used to make the determination
         * @param list the input list
         * @returns the leading sequence of members in the given list that pass the given predicate
         */
        function takeWhile(predicate, list) {
            for (let i = 0; i < list.length; ++i) {
                if (!predicate(list[i])) {
                    return list.slice(0, i);
                }
            }
            return list.slice();
        }
        // eslint-disable-next-line jsdoc/require-description
        /**
         * @param node a Program or BlockStatement node
         * @returns the leading sequence of directive nodes in the given node's body
         */
        function directives(node) {
            return takeWhile(looksLikeDirective, node.body);
        }
        // eslint-disable-next-line jsdoc/require-description
        /**
         * @param node any node
         * @param ancestors the given node's ancestors
         * @returns whether the given node is considered a directive in its current position
         */
        function isDirective(node, ancestors) {
            const parent = ancestors[ancestors.length - 1], grandparent = ancestors[ancestors.length - 2];
            return (parent.type === 'Program' || parent.type === 'BlockStatement' &&
                (/Function/u.test(grandparent.type))) &&
                directives(parent).indexOf(node) >= 0;
        }
        /**
         * Determines whether or not a given node is a valid expression. Recurses on short circuit eval and ternary nodes if enabled by flags.
         * @param node any node
         * @returns whether the given node is a valid expression
         */
        function isValidExpression(node) {
            if (allowTernary) {
                // Recursive check for ternary and logical expressions
                if (node.type === 'ConditionalExpression') {
                    return isValidExpression(node.consequent) && isValidExpression(node.alternate);
                }
            }
            if (allowShortCircuit) {
                if (node.type === 'LogicalExpression') {
                    return isValidExpression(node.right);
                }
            }
            if (allowTaggedTemplates && node.type === 'TaggedTemplateExpression') {
                return true;
            }
            return /^(?:Assignment|OptionalCall|Call|New|Update|Yield|Await)Expression$/u.test(node.type) ||
                (node.type === 'UnaryExpression' && ['delete', 'void'].indexOf(node.operator) >= 0);
        }
        return {
            ExpressionStatement(node) {
                if (!isValidExpression(node.expression) && !isDirective(node, context.getAncestors())) {
                    context.report({ node: node, message: 'Expected an assignment or function call and instead saw an expression.' });
                }
            }
        };
    }
};