node/tools/eslint/lib/rules/no-extra-label.js

/**
 * @fileoverview Rule to disallow unnecessary labels
 * @author Toru Nagashima
 * @copyright 2016 Toru Nagashima. All rights reserved.
 * See LICENSE file in root directory for full license.
 */

"use strict";

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

var astUtils = require("../ast-utils");

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

module.exports = function(context) {
    var scopeInfo = null;

    /**
     * Creates a new scope with a breakable statement.
     *
     * @param {ASTNode} node - A node to create. This is a BreakableStatement.
     * @returns {void}
     */
    function enterBreakableStatement(node) {
        scopeInfo = {
            label: astUtils.getLabel(node),
            breakable: true,
            upper: scopeInfo
        };
    }

    /**
     * Removes the top scope of the stack.
     *
     * @returns {void}
     */
    function exitBreakableStatement() {
        scopeInfo = scopeInfo.upper;
    }

    /**
     * Creates a new scope with a labeled statement.
     *
     * This ignores it if the body is a breakable statement.
     * In this case it's handled in the `enterBreakableStatement` function.
     *
     * @param {ASTNode} node - A node to create. This is a LabeledStatement.
     * @returns {void}
     */
    function enterLabeledStatement(node) {
        if (!astUtils.isBreakableStatement(node.body)) {
            scopeInfo = {
                label: node.label.name,
                breakable: false,
                upper: scopeInfo
            };
        }
    }

    /**
     * Removes the top scope of the stack.
     *
     * This ignores it if the body is a breakable statement.
     * In this case it's handled in the `exitBreakableStatement` function.
     *
     * @param {ASTNode} node - A node. This is a LabeledStatement.
     * @returns {void}
     */
    function exitLabeledStatement(node) {
        if (!astUtils.isBreakableStatement(node.body)) {
            scopeInfo = scopeInfo.upper;
        }
    }

    /**
     * Reports a given control node if it's unnecessary.
     *
     * @param {ASTNode} node - A node. This is a BreakStatement or a
     *      ContinueStatement.
     * @returns {void}
     */
    function reportIfUnnecessary(node) {
        if (!node.label) {
            return;
        }

        var labelNode = node.label;
        var label = labelNode.name;
        var info = scopeInfo;

        while (info) {
            if (info.breakable || info.label === label) {
                if (info.breakable && info.label === label) {
                    context.report({
                        node: labelNode,
                        message: "This label '{{name}}' is unnecessary.",
                        data: labelNode
                    });
                }
                return;
            }

            info = info.upper;
        }
    }

    return {
        "WhileStatement": enterBreakableStatement,
        "WhileStatement:exit": exitBreakableStatement,
        "DoWhileStatement": enterBreakableStatement,
        "DoWhileStatement:exit": exitBreakableStatement,
        "ForStatement": enterBreakableStatement,
        "ForStatement:exit": exitBreakableStatement,
        "ForInStatement": enterBreakableStatement,
        "ForInStatement:exit": exitBreakableStatement,
        "ForOfStatement": enterBreakableStatement,
        "ForOfStatement:exit": exitBreakableStatement,
        "SwitchStatement": enterBreakableStatement,
        "SwitchStatement:exit": exitBreakableStatement,
        "LabeledStatement": enterLabeledStatement,
        "LabeledStatement:exit": exitLabeledStatement,
        "BreakStatement": reportIfUnnecessary,
        "ContinueStatement": reportIfUnnecessary
    };
};

module.exports.schema = [];