linter.js

/**
 * @fileoverview Main Linter Class
 * @author Gyandeep Singh
 */

"use strict";

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

const path = require("path"),
    eslintScope = require("eslint-scope"),
    evk = require("eslint-visitor-keys"),
    espree = require("espree"),
    lodash = require("lodash"),
    CodePathAnalyzer = require("./code-path-analysis/code-path-analyzer"),
    ConfigOps = require("./config/config-ops"),
    validator = require("./config/config-validator"),
    BuiltInEnvironments = require("../conf/environments"),
    applyDisableDirectives = require("./util/apply-disable-directives"),
    createEmitter = require("./util/safe-emitter"),
    NodeEventGenerator = require("./util/node-event-generator"),
    SourceCode = require("./util/source-code"),
    Traverser = require("./util/traverser"),
    createReportTranslator = require("./util/report-translator"),
    Rules = require("./rules"),
    timing = require("./util/timing"),
    ConfigCommentParser = require("./util/config-comment-parser"),
    astUtils = require("./util/ast-utils"),
    pkg = require("../package.json"),
    SourceCodeFixer = require("./util/source-code-fixer");

const debug = require("debug")("eslint:linter");
const MAX_AUTOFIX_PASSES = 10;
const DEFAULT_PARSER_NAME = "espree";
const commentParser = new ConfigCommentParser();

//------------------------------------------------------------------------------
// Typedefs
//------------------------------------------------------------------------------

/** @typedef {InstanceType<import("./cli-engine/config-array")["ConfigArray"]>} ConfigArray */
/** @typedef {import("./util/types").ConfigData} ConfigData */
/** @typedef {import("./util/types").Environment} Environment */
/** @typedef {import("./util/types").GlobalConf} GlobalConf */
/** @typedef {import("./util/types").LintMessage} LintMessage */
/** @typedef {import("./util/types").ParserOptions} ParserOptions */
/** @typedef {import("./util/types").Rule} Rule */

/**
 * @typedef {Object} DisableDirective
 * @property {("disable"|"enable"|"disable-line"|"disable-next-line")} type
 * @property {number} line
 * @property {number} column
 * @property {(string|null)} ruleId
 */

/**
 * The private data for `Linter` instance.
 * @typedef {Object} LinterInternalSlots
 * @property {ConfigArray|null} lastConfigArray The `ConfigArray` instance that the last `verify()` call used.
 * @property {SourceCode|null} lastSourceCode The `SourceCode` instance that the last `verify()` call used.
 * @property {Map<string, Parser>} parserMap The loaded parsers.
 * @property {Rules} ruleMap The loaded rules.
 */

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

/**
 * Ensures that variables representing built-in properties of the Global Object,
 * and any globals declared by special block comments, are present in the global
 * scope.
 * @param {Scope} globalScope The global scope.
 * @param {Object} configGlobals The globals declared in configuration
 * @param {{exportedVariables: Object, enabledGlobals: Object}} commentDirectives Directives from comment configuration
 * @returns {void}
 */
function addDeclaredGlobals(globalScope, configGlobals, { exportedVariables, enabledGlobals }) {

    // Define configured global variables.
    for (const id of new Set([...Object.keys(configGlobals), ...Object.keys(enabledGlobals)])) {

        /*
         * `ConfigOps.normalizeConfigGlobal` will throw an error if a configured global value is invalid. However, these errors would
         * typically be caught when validating a config anyway (validity for inline global comments is checked separately).
         */
        const configValue = configGlobals[id] === void 0 ? void 0 : ConfigOps.normalizeConfigGlobal(configGlobals[id]);
        const commentValue = enabledGlobals[id] && enabledGlobals[id].value;
        const value = commentValue || configValue;
        const sourceComments = enabledGlobals[id] && enabledGlobals[id].comments;

        if (value === "off") {
            continue;
        }

        let variable = globalScope.set.get(id);

        if (!variable) {
            variable = new eslintScope.Variable(id, globalScope);

            globalScope.variables.push(variable);
            globalScope.set.set(id, variable);
        }

        variable.eslintImplicitGlobalSetting = configValue;
        variable.eslintExplicitGlobal = sourceComments !== void 0;
        variable.eslintExplicitGlobalComments = sourceComments;
        variable.writeable = (value === "writable");
    }

    // mark all exported variables as such
    Object.keys(exportedVariables).forEach(name => {
        const variable = globalScope.set.get(name);

        if (variable) {
            variable.eslintUsed = true;
        }
    });

    /*
     * "through" contains all references which definitions cannot be found.
     * Since we augment the global scope using configuration, we need to update
     * references and remove the ones that were added by configuration.
     */
    globalScope.through = globalScope.through.filter(reference => {
        const name = reference.identifier.name;
        const variable = globalScope.set.get(name);

        if (variable) {

            /*
             * Links the variable and the reference.
             * And this reference is removed from `Scope#through`.
             */
            reference.resolved = variable;
            variable.references.push(reference);

            return false;
        }

        return true;
    });
}

/**
 * Creates a collection of disable directives from a comment
 * @param {("disable"|"enable"|"disable-line"|"disable-next-line")} type The type of directive comment
 * @param {{line: number, column: number}} loc The 0-based location of the comment token
 * @param {string} value The value after the directive in the comment
 * comment specified no specific rules, so it applies to all rules (e.g. `eslint-disable`)
 * @returns {DisableDirective[]} Directives from the comment
 */
function createDisableDirectives(type, loc, value) {
    const ruleIds = Object.keys(commentParser.parseListConfig(value));
    const directiveRules = ruleIds.length ? ruleIds : [null];

    return directiveRules.map(ruleId => ({ type, line: loc.line, column: loc.column + 1, ruleId }));
}

/**
 * Parses comments in file to extract file-specific config of rules, globals
 * and environments and merges them with global config; also code blocks
 * where reporting is disabled or enabled and merges them with reporting config.
 * @param {string} filename The file being checked.
 * @param {ASTNode} ast The top node of the AST.
 * @param {function(string): {create: Function}} ruleMapper A map from rule IDs to defined rules
 * @returns {{configuredRules: Object, enabledGlobals: {value:string,comment:Token}[], exportedVariables: Object, problems: Problem[], disableDirectives: DisableDirective[]}}
 * A collection of the directive comments that were found, along with any problems that occurred when parsing
 */
function getDirectiveComments(filename, ast, ruleMapper) {
    const configuredRules = {};
    const enabledGlobals = {};
    const exportedVariables = {};
    const problems = [];
    const disableDirectives = [];

    ast.comments.filter(token => token.type !== "Shebang").forEach(comment => {
        const trimmedCommentText = comment.value.trim();
        const match = /^(eslint(-\w+){0,3}|exported|globals?)(\s|$)/u.exec(trimmedCommentText);

        if (!match) {
            return;
        }

        const directiveValue = trimmedCommentText.slice(match.index + match[1].length);

        if (/^eslint-disable-(next-)?line$/u.test(match[1])) {
            if (comment.loc.start.line === comment.loc.end.line) {
                const directiveType = match[1].slice("eslint-".length);

                disableDirectives.push(...createDisableDirectives(directiveType, comment.loc.start, directiveValue));
            } else {
                problems.push({
                    ruleId: null,
                    severity: 2,
                    message: `${match[1]} comment should not span multiple lines.`,
                    line: comment.loc.start.line,
                    column: comment.loc.start.column + 1,
                    endLine: comment.loc.end.line,
                    endColumn: comment.loc.end.column + 1,
                    nodeType: null
                });
            }
        } else if (comment.type === "Block") {
            switch (match[1]) {
                case "exported":
                    Object.assign(exportedVariables, commentParser.parseStringConfig(directiveValue, comment));
                    break;

                case "globals":
                case "global":
                    for (const [id, { value }] of Object.entries(commentParser.parseStringConfig(directiveValue, comment))) {
                        let normalizedValue;

                        try {
                            normalizedValue = ConfigOps.normalizeConfigGlobal(value);
                        } catch (err) {
                            problems.push({
                                ruleId: null,
                                severity: 2,
                                message: err.message,
                                line: comment.loc.start.line,
                                column: comment.loc.start.column + 1,
                                endLine: comment.loc.end.line,
                                endColumn: comment.loc.end.column + 1,
                                nodeType: null
                            });
                            continue;
                        }

                        if (enabledGlobals[id]) {
                            enabledGlobals[id].comments.push(comment);
                            enabledGlobals[id].value = normalizedValue;
                        } else {
                            enabledGlobals[id] = {
                                comments: [comment],
                                value: normalizedValue
                            };
                        }
                    }
                    break;

                case "eslint-disable": {
                    const directiveRules = createDisableDirectives("disable", comment.loc.start, directiveValue);

                    // validate disable directives
                    directiveRules.forEach(directive => {
                        const ruleId = directive.ruleId;

                        if (ruleId !== null) {
                            const options = directive.type === "disable" ? [0] : [2];

                            try {
                                validator.validateRuleOptions(ruleMapper(ruleId), ruleId, options);
                            } catch (err) {
                                problems.push({
                                    ruleId,
                                    severity: 2,
                                    message: err.message,
                                    line: comment.loc.start.line,
                                    column: comment.loc.start.column + 1,
                                    endLine: comment.loc.end.line,
                                    endColumn: comment.loc.end.column + 1,
                                    nodeType: null
                                });

                                // do not apply the config, if found invalid options.
                                return;
                            }
                        }

                        disableDirectives.push(directive);
                    });
                    break;
                }

                case "eslint-enable":
                    disableDirectives.push(...createDisableDirectives("enable", comment.loc.start, directiveValue));
                    break;

                case "eslint": {
                    const parseResult = commentParser.parseJsonConfig(directiveValue, comment.loc);

                    if (parseResult.success) {
                        Object.keys(parseResult.config).forEach(name => {
                            const ruleValue = parseResult.config[name];

                            try {
                                validator.validateRuleOptions(ruleMapper(name), name, ruleValue);
                            } catch (err) {
                                problems.push({
                                    ruleId: name,
                                    severity: 2,
                                    message: err.message,
                                    line: comment.loc.start.line,
                                    column: comment.loc.start.column + 1,
                                    endLine: comment.loc.end.line,
                                    endColumn: comment.loc.end.column + 1,
                                    nodeType: null
                                });

                                // do not apply the config, if found invalid options.
                                return;
                            }

                            configuredRules[name] = ruleValue;

                        });
                    } else {
                        problems.push(parseResult.error);
                    }

                    break;
                }

                // no default
            }
        }
    });

    return {
        configuredRules,
        enabledGlobals,
        exportedVariables,
        problems,
        disableDirectives
    };
}

/**
 * Normalize ECMAScript version from the initial config
 * @param  {number} ecmaVersion ECMAScript version from the initial config
 * @returns {number} normalized ECMAScript version
 */
function normalizeEcmaVersion(ecmaVersion) {

    /*
     * Calculate ECMAScript edition number from official year version starting with
     * ES2015, which corresponds with ES6 (or a difference of 2009).
     */
    return ecmaVersion >= 2015 ? ecmaVersion - 2009 : ecmaVersion;
}

const eslintEnvPattern = /\/\*\s*eslint-env\s(.+?)\*\//gu;

/**
 * Checks whether or not there is a comment which has "eslint-env *" in a given text.
 * @param {string} text - A source code text to check.
 * @returns {Object|null} A result of parseListConfig() with "eslint-env *" comment.
 */
function findEslintEnv(text) {
    let match, retv;

    eslintEnvPattern.lastIndex = 0;

    while ((match = eslintEnvPattern.exec(text))) {
        retv = Object.assign(retv || {}, commentParser.parseListConfig(match[1]));
    }

    return retv;
}

/**
 * Normalizes the possible options for `linter.verify` and `linter.verifyAndFix` to a
 * consistent shape.
 * @param {(string|{reportUnusedDisableDirectives: boolean, filename: string, allowInlineConfig: boolean})} providedOptions Options
 * @returns {{reportUnusedDisableDirectives: boolean, filename: string, allowInlineConfig: boolean}} Normalized options
 */
function normalizeVerifyOptions(providedOptions) {
    const isObjectOptions = typeof providedOptions === "object";
    const providedFilename = isObjectOptions ? providedOptions.filename : providedOptions;

    return {
        filename: typeof providedFilename === "string" ? providedFilename : "<input>",
        allowInlineConfig: !isObjectOptions || providedOptions.allowInlineConfig !== false,
        reportUnusedDisableDirectives: isObjectOptions && !!providedOptions.reportUnusedDisableDirectives,
        disableFixes: Boolean(providedOptions && providedOptions.disableFixes)
    };
}

/**
 * Combines the provided parserOptions with the options from environments
 * @param {string} parserName The parser name which uses this options.
 * @param {ParserOptions} providedOptions The provided 'parserOptions' key in a config
 * @param {Environment[]} enabledEnvironments The environments enabled in configuration and with inline comments
 * @returns {ParserOptions} Resulting parser options after merge
 */
function resolveParserOptions(parserName, providedOptions, enabledEnvironments) {
    const parserOptionsFromEnv = enabledEnvironments
        .filter(env => env.parserOptions)
        .reduce((parserOptions, env) => lodash.merge(parserOptions, env.parserOptions), {});
    const mergedParserOptions = lodash.merge(parserOptionsFromEnv, providedOptions || {});
    const isModule = mergedParserOptions.sourceType === "module";

    if (isModule) {

        /*
         * can't have global return inside of modules
         * TODO: espree validate parserOptions.globalReturn when sourceType is setting to module.(@aladdin-add)
         */
        mergedParserOptions.ecmaFeatures = Object.assign({}, mergedParserOptions.ecmaFeatures, { globalReturn: false });
    }

    /*
     * TODO: @aladdin-add
     * 1. for a 3rd-party parser, do not normalize parserOptions
     * 2. for espree, no need to do this (espree will do it)
     */
    mergedParserOptions.ecmaVersion = normalizeEcmaVersion(mergedParserOptions.ecmaVersion);

    return mergedParserOptions;
}

/**
 * Combines the provided globals object with the globals from environments
 * @param {Record<string, GlobalConf>} providedGlobals The 'globals' key in a config
 * @param {Environment[]} enabledEnvironments The environments enabled in configuration and with inline comments
 * @returns {Record<string, GlobalConf>} The resolved globals object
 */
function resolveGlobals(providedGlobals, enabledEnvironments) {
    return Object.assign(
        {},
        ...enabledEnvironments.filter(env => env.globals).map(env => env.globals),
        providedGlobals
    );
}

/**
 * Strips Unicode BOM from a given text.
 *
 * @param {string} text - A text to strip.
 * @returns {string} The stripped text.
 */
function stripUnicodeBOM(text) {

    /*
     * Check Unicode BOM.
     * In JavaScript, string data is stored as UTF-16, so BOM is 0xFEFF.
     * http://www.ecma-international.org/ecma-262/6.0/#sec-unicode-format-control-characters
     */
    if (text.charCodeAt(0) === 0xFEFF) {
        return text.slice(1);
    }
    return text;
}

/**
 * Get the options for a rule (not including severity), if any
 * @param {Array|number} ruleConfig rule configuration
 * @returns {Array} of rule options, empty Array if none
 */
function getRuleOptions(ruleConfig) {
    if (Array.isArray(ruleConfig)) {
        return ruleConfig.slice(1);
    }
    return [];

}

/**
 * Analyze scope of the given AST.
 * @param {ASTNode} ast The `Program` node to analyze.
 * @param {ParserOptions} parserOptions The parser options.
 * @param {Record<string, string[]>} visitorKeys The visitor keys.
 * @returns {ScopeManager} The analysis result.
 */
function analyzeScope(ast, parserOptions, visitorKeys) {
    const ecmaFeatures = parserOptions.ecmaFeatures || {};
    const ecmaVersion = parserOptions.ecmaVersion || 5;

    return eslintScope.analyze(ast, {
        ignoreEval: true,
        nodejsScope: ecmaFeatures.globalReturn,
        impliedStrict: ecmaFeatures.impliedStrict,
        ecmaVersion,
        sourceType: parserOptions.sourceType || "script",
        childVisitorKeys: visitorKeys || evk.KEYS,
        fallback: Traverser.getKeys
    });
}

/**
 * Parses text into an AST. Moved out here because the try-catch prevents
 * optimization of functions, so it's best to keep the try-catch as isolated
 * as possible
 * @param {string} text The text to parse.
 * @param {Parser} parser The parser to parse.
 * @param {ParserOptions} providedParserOptions Options to pass to the parser
 * @param {string} filePath The path to the file being parsed.
 * @returns {{success: false, error: Problem}|{success: true, sourceCode: SourceCode}}
 * An object containing the AST and parser services if parsing was successful, or the error if parsing failed
 * @private
 */
function parse(text, parser, providedParserOptions, filePath) {
    const textToParse = stripUnicodeBOM(text).replace(astUtils.SHEBANG_MATCHER, (match, captured) => `//${captured}`);
    const parserOptions = Object.assign({}, providedParserOptions, {
        loc: true,
        range: true,
        raw: true,
        tokens: true,
        comment: true,
        eslintVisitorKeys: true,
        eslintScopeManager: true,
        filePath
    });

    /*
     * Check for parsing errors first. If there's a parsing error, nothing
     * else can happen. However, a parsing error does not throw an error
     * from this method - it's just considered a fatal error message, a
     * problem that ESLint identified just like any other.
     */
    try {
        const parseResult = (typeof parser.parseForESLint === "function")
            ? parser.parseForESLint(textToParse, parserOptions)
            : { ast: parser.parse(textToParse, parserOptions) };
        const ast = parseResult.ast;
        const parserServices = parseResult.services || {};
        const visitorKeys = parseResult.visitorKeys || evk.KEYS;
        const scopeManager = parseResult.scopeManager || analyzeScope(ast, parserOptions, visitorKeys);

        return {
            success: true,

            /*
             * Save all values that `parseForESLint()` returned.
             * If a `SourceCode` object is given as the first parameter instead of source code text,
             * linter skips the parsing process and reuses the source code object.
             * In that case, linter needs all the values that `parseForESLint()` returned.
             */
            sourceCode: new SourceCode({
                text,
                ast,
                parserServices,
                scopeManager,
                visitorKeys
            })
        };
    } catch (ex) {

        // If the message includes a leading line number, strip it:
        const message = `Parsing error: ${ex.message.replace(/^line \d+:/iu, "").trim()}`;

        return {
            success: false,
            error: {
                ruleId: null,
                fatal: true,
                severity: 2,
                message,
                line: ex.lineNumber,
                column: ex.column
            }
        };
    }
}

/**
 * Gets the scope for the current node
 * @param {ScopeManager} scopeManager The scope manager for this AST
 * @param {ASTNode} currentNode The node to get the scope of
 * @returns {eslint-scope.Scope} The scope information for this node
 */
function getScope(scopeManager, currentNode) {

    // On Program node, get the outermost scope to avoid return Node.js special function scope or ES modules scope.
    const inner = currentNode.type !== "Program";

    for (let node = currentNode; node; node = node.parent) {
        const scope = scopeManager.acquire(node, inner);

        if (scope) {
            if (scope.type === "function-expression-name") {
                return scope.childScopes[0];
            }
            return scope;
        }
    }

    return scopeManager.scopes[0];
}

/**
 * Marks a variable as used in the current scope
 * @param {ScopeManager} scopeManager The scope manager for this AST. The scope may be mutated by this function.
 * @param {ASTNode} currentNode The node currently being traversed
 * @param {Object} parserOptions The options used to parse this text
 * @param {string} name The name of the variable that should be marked as used.
 * @returns {boolean} True if the variable was found and marked as used, false if not.
 */
function markVariableAsUsed(scopeManager, currentNode, parserOptions, name) {
    const hasGlobalReturn = parserOptions.ecmaFeatures && parserOptions.ecmaFeatures.globalReturn;
    const specialScope = hasGlobalReturn || parserOptions.sourceType === "module";
    const currentScope = getScope(scopeManager, currentNode);

    // Special Node.js scope means we need to start one level deeper
    const initialScope = currentScope.type === "global" && specialScope ? currentScope.childScopes[0] : currentScope;

    for (let scope = initialScope; scope; scope = scope.upper) {
        const variable = scope.variables.find(scopeVar => scopeVar.name === name);

        if (variable) {
            variable.eslintUsed = true;
            return true;
        }
    }

    return false;
}

/**
 * Runs a rule, and gets its listeners
 * @param {Rule} rule A normalized rule with a `create` method
 * @param {Context} ruleContext The context that should be passed to the rule
 * @returns {Object} A map of selector listeners provided by the rule
 */
function createRuleListeners(rule, ruleContext) {
    try {
        return rule.create(ruleContext);
    } catch (ex) {
        ex.message = `Error while loading rule '${ruleContext.id}': ${ex.message}`;
        throw ex;
    }
}

/**
 * Gets all the ancestors of a given node
 * @param {ASTNode} node The node
 * @returns {ASTNode[]} All the ancestor nodes in the AST, not including the provided node, starting
 * from the root node and going inwards to the parent node.
 */
function getAncestors(node) {
    const ancestorsStartingAtParent = [];

    for (let ancestor = node.parent; ancestor; ancestor = ancestor.parent) {
        ancestorsStartingAtParent.push(ancestor);
    }

    return ancestorsStartingAtParent.reverse();
}

// methods that exist on SourceCode object
const DEPRECATED_SOURCECODE_PASSTHROUGHS = {
    getSource: "getText",
    getSourceLines: "getLines",
    getAllComments: "getAllComments",
    getNodeByRangeIndex: "getNodeByRangeIndex",
    getComments: "getComments",
    getCommentsBefore: "getCommentsBefore",
    getCommentsAfter: "getCommentsAfter",
    getCommentsInside: "getCommentsInside",
    getJSDocComment: "getJSDocComment",
    getFirstToken: "getFirstToken",
    getFirstTokens: "getFirstTokens",
    getLastToken: "getLastToken",
    getLastTokens: "getLastTokens",
    getTokenAfter: "getTokenAfter",
    getTokenBefore: "getTokenBefore",
    getTokenByRangeStart: "getTokenByRangeStart",
    getTokens: "getTokens",
    getTokensAfter: "getTokensAfter",
    getTokensBefore: "getTokensBefore",
    getTokensBetween: "getTokensBetween"
};

const BASE_TRAVERSAL_CONTEXT = Object.freeze(
    Object.keys(DEPRECATED_SOURCECODE_PASSTHROUGHS).reduce(
        (contextInfo, methodName) =>
            Object.assign(contextInfo, {
                [methodName](...args) {
                    return this.getSourceCode()[DEPRECATED_SOURCECODE_PASSTHROUGHS[methodName]](...args);
                }
            }),
        {}
    )
);

/**
 * Runs the given rules on the given SourceCode object
 * @param {SourceCode} sourceCode A SourceCode object for the given text
 * @param {Object} configuredRules The rules configuration
 * @param {function(string): Rule} ruleMapper A mapper function from rule names to rules
 * @param {Object} parserOptions The options that were passed to the parser
 * @param {string} parserName The name of the parser in the config
 * @param {Object} settings The settings that were enabled in the config
 * @param {string} filename The reported filename of the code
 * @param {boolean} disableFixes If true, it doesn't make `fix` properties.
 * @returns {Problem[]} An array of reported problems
 */
function runRules(sourceCode, configuredRules, ruleMapper, parserOptions, parserName, settings, filename, disableFixes) {
    const emitter = createEmitter();
    const nodeQueue = [];
    let currentNode = sourceCode.ast;

    Traverser.traverse(sourceCode.ast, {
        enter(node, parent) {
            node.parent = parent;
            nodeQueue.push({ isEntering: true, node });
        },
        leave(node) {
            nodeQueue.push({ isEntering: false, node });
        },
        visitorKeys: sourceCode.visitorKeys
    });

    /*
     * Create a frozen object with the ruleContext properties and methods that are shared by all rules.
     * All rule contexts will inherit from this object. This avoids the performance penalty of copying all the
     * properties once for each rule.
     */
    const sharedTraversalContext = Object.freeze(
        Object.assign(
            Object.create(BASE_TRAVERSAL_CONTEXT),
            {
                getAncestors: () => getAncestors(currentNode),
                getDeclaredVariables: sourceCode.scopeManager.getDeclaredVariables.bind(sourceCode.scopeManager),
                getFilename: () => filename,
                getScope: () => getScope(sourceCode.scopeManager, currentNode),
                getSourceCode: () => sourceCode,
                markVariableAsUsed: name => markVariableAsUsed(sourceCode.scopeManager, currentNode, parserOptions, name),
                parserOptions,
                parserPath: parserName,
                parserServices: sourceCode.parserServices,
                settings
            }
        )
    );


    const lintingProblems = [];

    Object.keys(configuredRules).forEach(ruleId => {
        const severity = ConfigOps.getRuleSeverity(configuredRules[ruleId]);
        const rule = ruleMapper(ruleId);

        if (severity === 0 || !rule) {
            return;
        }


        const messageIds = rule.meta && rule.meta.messages;
        let reportTranslator = null;
        const ruleContext = Object.freeze(
            Object.assign(
                Object.create(sharedTraversalContext),
                {
                    id: ruleId,
                    options: getRuleOptions(configuredRules[ruleId]),
                    report(...args) {

                        /*
                         * Create a report translator lazily.
                         * In a vast majority of cases, any given rule reports zero errors on a given
                         * piece of code. Creating a translator lazily avoids the performance cost of
                         * creating a new translator function for each rule that usually doesn't get
                         * called.
                         *
                         * Using lazy report translators improves end-to-end performance by about 3%
                         * with Node 8.4.0.
                         */
                        if (reportTranslator === null) {
                            reportTranslator = createReportTranslator({
                                ruleId,
                                severity,
                                sourceCode,
                                messageIds,
                                disableFixes
                            });
                        }
                        const problem = reportTranslator(...args);

                        if (problem.fix && rule.meta && !rule.meta.fixable) {
                            throw new Error("Fixable rules should export a `meta.fixable` property.");
                        }
                        lintingProblems.push(problem);
                    }
                }
            )
        );

        const ruleListeners = createRuleListeners(rule, ruleContext);

        // add all the selectors from the rule as listeners
        Object.keys(ruleListeners).forEach(selector => {
            emitter.on(
                selector,
                timing.enabled
                    ? timing.time(ruleId, ruleListeners[selector])
                    : ruleListeners[selector]
            );
        });
    });

    const eventGenerator = new CodePathAnalyzer(new NodeEventGenerator(emitter));

    nodeQueue.forEach(traversalInfo => {
        currentNode = traversalInfo.node;

        try {
            if (traversalInfo.isEntering) {
                eventGenerator.enterNode(currentNode);
            } else {
                eventGenerator.leaveNode(currentNode);
            }
        } catch (err) {
            err.currentNode = currentNode;
            throw err;
        }
    });

    return lintingProblems;
}

/**
 * Get an environment.
 * @param {LinterInternalSlots} slots The internal slots of Linter.
 * @param {string} envId The environment ID to get.
 * @returns {Environment|null} The environment.
 */
function getEnv(slots, envId) {
    return (
        (slots.lastConfigArray && slots.lastConfigArray.pluginEnvironments.get(envId)) ||
        BuiltInEnvironments.get(envId) ||
        null
    );
}

/**
 * Get a rule.
 * @param {LinterInternalSlots} slots The internal slots of Linter.
 * @param {string} ruleId The rule ID to get.
 * @returns {Rule} The rule.
 */
function getRule(slots, ruleId) {
    return (
        (slots.lastConfigArray && slots.lastConfigArray.pluginRules.get(ruleId)) ||

        // This returns the stub for missing rules if the rule does not exist.
        slots.ruleMap.get(ruleId)
    );
}

/**
 * The map to store private data.
 * @type {WeakMap<Linter, LinterInternalSlots>}
 */
const internalSlotsMap = new WeakMap();

//------------------------------------------------------------------------------
// Public Interface
//------------------------------------------------------------------------------

/**
 * Object that is responsible for verifying JavaScript text
 * @name eslint
 */
class Linter {

    constructor() {
        internalSlotsMap.set(this, {
            lastConfigArray: null,
            lastSourceCode: null,
            parserMap: new Map([["espree", espree]]),
            ruleMap: new Rules()
        });

        this.version = pkg.version;
    }

    /**
     * Getter for package version.
     * @static
     * @returns {string} The version from package.json.
     */
    static get version() {
        return pkg.version;
    }

    /**
     * Same as linter.verify, except without support for processors.
     * @param {string|SourceCode} textOrSourceCode The text to parse or a SourceCode object.
     * @param {ConfigData} providedConfig An ESLintConfig instance to configure everything.
     * @param {(string|Object)} [filenameOrOptions] The optional filename of the file being checked.
     *      If this is not set, the filename will default to '<input>' in the rule context. If
     *      an object, then it has "filename", "saveState", and "allowInlineConfig" properties.
     * @param {boolean} [filenameOrOptions.allowInlineConfig=true] Allow/disallow inline comments' ability to change config once it is set. Defaults to true if not supplied.
     *      Useful if you want to validate JS without comments overriding rules.
     * @param {boolean} [filenameOrOptions.reportUnusedDisableDirectives=false] Adds reported errors for unused
     *      eslint-disable directives
     * @returns {LintMessage[]} The results as an array of messages or an empty array if no messages.
     */
    _verifyWithoutProcessors(textOrSourceCode, providedConfig, filenameOrOptions) {
        const slots = internalSlotsMap.get(this);
        const config = providedConfig || {};
        const options = normalizeVerifyOptions(filenameOrOptions);
        let text;

        // evaluate arguments
        if (typeof textOrSourceCode === "string") {
            slots.lastSourceCode = null;
            text = textOrSourceCode;
        } else {
            slots.lastSourceCode = textOrSourceCode;
            text = textOrSourceCode.text;
        }

        // Resolve parser.
        let parserName = DEFAULT_PARSER_NAME;
        let parser = espree;

        if (typeof config.parser === "object" && config.parser !== null) {
            parserName = config.parser.filePath;
            parser = config.parser.definition;
        } else if (typeof config.parser === "string") {
            if (!slots.parserMap.has(config.parser)) {
                return [{
                    ruleId: null,
                    fatal: true,
                    severity: 2,
                    message: `Configured parser '${config.parser}' was not found.`,
                    line: 0,
                    column: 0
                }];
            }
            parserName = config.parser;
            parser = slots.parserMap.get(config.parser);
        }

        // search and apply "eslint-env *".
        const envInFile = findEslintEnv(text);
        const resolvedEnvConfig = Object.assign({ builtin: true }, config.env, envInFile);
        const enabledEnvs = Object.keys(resolvedEnvConfig)
            .filter(envName => resolvedEnvConfig[envName])
            .map(envName => getEnv(slots, envName))
            .filter(env => env);

        const parserOptions = resolveParserOptions(parserName, config.parserOptions || {}, enabledEnvs);
        const configuredGlobals = resolveGlobals(config.globals || {}, enabledEnvs);
        const settings = config.settings || {};

        if (!slots.lastSourceCode) {
            const parseResult = parse(
                text,
                parser,
                parserOptions,
                options.filename
            );

            if (!parseResult.success) {
                return [parseResult.error];
            }

            slots.lastSourceCode = parseResult.sourceCode;
        } else {

            /*
             * If the given source code object as the first argument does not have scopeManager, analyze the scope.
             * This is for backward compatibility (SourceCode is frozen so it cannot rebind).
             */
            if (!slots.lastSourceCode.scopeManager) {
                slots.lastSourceCode = new SourceCode({
                    text: slots.lastSourceCode.text,
                    ast: slots.lastSourceCode.ast,
                    parserServices: slots.lastSourceCode.parserServices,
                    visitorKeys: slots.lastSourceCode.visitorKeys,
                    scopeManager: analyzeScope(slots.lastSourceCode.ast, parserOptions)
                });
            }
        }

        const sourceCode = slots.lastSourceCode;
        const commentDirectives = options.allowInlineConfig
            ? getDirectiveComments(options.filename, sourceCode.ast, ruleId => getRule(slots, ruleId))
            : { configuredRules: {}, enabledGlobals: {}, exportedVariables: {}, problems: [], disableDirectives: [] };

        // augment global scope with declared global variables
        addDeclaredGlobals(
            sourceCode.scopeManager.scopes[0],
            configuredGlobals,
            { exportedVariables: commentDirectives.exportedVariables, enabledGlobals: commentDirectives.enabledGlobals }
        );
        let lintingProblems = [];

        const configuredRules = Object.assign({}, config.rules, commentDirectives.configuredRules);


        try {
            lintingProblems = lintingProblems.concat(runRules(
                sourceCode,
                configuredRules,
                ruleId => getRule(slots, ruleId),
                parserOptions,
                parserName,
                settings,
                options.filename,
                options.disableFixes
            ));
        } catch (err) {
            err.message += `\nOccurred while linting ${options.filename}`;
            debug("An error occurred while traversing");
            debug("Filename:", options.filename);
            if (err.currentNode) {
                const { line } = err.currentNode.loc.start;

                debug("Line:", line);
                err.message += `:${line}`;
            }
            debug("Parser Options:", parserOptions);
            debug("Parser Path:", parserName);
            debug("Settings:", settings);
            throw err;
        }

        return applyDisableDirectives({
            directives: commentDirectives.disableDirectives,
            problems: lintingProblems
                .concat(commentDirectives.problems)
                .sort((problemA, problemB) => problemA.line - problemB.line || problemA.column - problemB.column),
            reportUnusedDisableDirectives: options.reportUnusedDisableDirectives
        });
    }

    /**
     * Verifies the text against the rules specified by the second argument.
     * @param {string|SourceCode} textOrSourceCode The text to parse or a SourceCode object.
     * @param {ConfigData|ConfigArray} config An ESLintConfig instance to configure everything.
     * @param {(string|Object)} [filenameOrOptions] The optional filename of the file being checked.
     *      If this is not set, the filename will default to '<input>' in the rule context. If
     *      an object, then it has "filename", "saveState", and "allowInlineConfig" properties.
     * @param {boolean} [filenameOrOptions.allowInlineConfig] Allow/disallow inline comments' ability to change config once it is set. Defaults to true if not supplied.
     *      Useful if you want to validate JS without comments overriding rules.
     * @param {function(string): string[]} [filenameOrOptions.preprocess] preprocessor for source text. If provided,
     *      this should accept a string of source text, and return an array of code blocks to lint.
     * @param {function(Array<LintMessage[]>): LintMessage[]} [filenameOrOptions.postprocess] postprocessor for report messages. If provided,
     *      this should accept an array of the message lists for each code block returned from the preprocessor,
     *      apply a mapping to the messages as appropriate, and return a one-dimensional array of messages
     * @returns {LintMessage[]} The results as an array of messages or an empty array if no messages.
     */
    verify(textOrSourceCode, config, filenameOrOptions) {
        if (config && typeof config.extractConfig === "function") {
            return this._verifyWithConfigArray(
                textOrSourceCode,
                config,
                typeof filenameOrOptions === "string"
                    ? { filename: filenameOrOptions }
                    : filenameOrOptions || {}
            );
        }

        const preprocess = filenameOrOptions && filenameOrOptions.preprocess || (rawText => [rawText]);
        const postprocess = filenameOrOptions && filenameOrOptions.postprocess || lodash.flatten;

        return postprocess(
            preprocess(textOrSourceCode).map(
                textBlock => this._verifyWithoutProcessors(textBlock, config, filenameOrOptions)
            )
        );
    }

    /**
     * Verify a given code with `ConfigArray`.
     * @param {string} text The source code string.
     * @param {ConfigArray} configArray The config array.
     * @param {Object} providedOptions The options.
     * @returns {LintMessage[]} The found problems.
     */
    _verifyWithConfigArray(text, configArray, providedOptions) {
        debug("Verify with ConfigArray");

        // Store the config array in order to get plugin envs and rules later.
        internalSlotsMap.get(this).lastConfigArray = configArray;

        /*
         * TODO: implement https://github.com/eslint/rfcs/tree/master/designs/2018-processors-improvements here.
         */

        // Extract the final config for this file.
        const config = configArray.extractConfig(providedOptions.filename);

        /*
         * Convert "/path/to/<text>" to "<text>".
         * `CLIEngine#executeOnText()` method gives "/path/to/<text>" if the
         * filename was omitted because `configArray.extractConfig()` requires
         * an absolute path. But linter should pass `<text>` to
         * `RuleContext#getFilename()` in that case.
         */
        const filename = path.basename(providedOptions.filename) === "<text>"
            ? "<text>"
            : providedOptions.filename;

        // Make options.
        const options = {
            ...providedOptions,
            filename
        };

        // Apply processor.
        if (config.processor) {
            const processor = configArray.pluginProcessors.get(config.processor);

            options.preprocess = processor.preprocess;
            options.postprocess = processor.postprocess;
            if (!processor.supportsAutofix) {

                // Use `disableFixes` of https://github.com/eslint/rfcs/tree/master/designs/2018-processors-improvements
                options.disableFixes = true;
            }
        }

        // Verify.
        return this.verify(text, config, options);
    }

    /**
     * Gets the SourceCode object representing the parsed source.
     * @returns {SourceCode} The SourceCode object.
     */
    getSourceCode() {
        return internalSlotsMap.get(this).lastSourceCode;
    }

    /**
     * Defines a new linting rule.
     * @param {string} ruleId A unique rule identifier
     * @param {Function | Rule} ruleModule Function from context to object mapping AST node types to event handlers
     * @returns {void}
     */
    defineRule(ruleId, ruleModule) {
        internalSlotsMap.get(this).ruleMap.define(ruleId, ruleModule);
    }

    /**
     * Defines many new linting rules.
     * @param {Record<string, Function | Rule>} rulesToDefine map from unique rule identifier to rule
     * @returns {void}
     */
    defineRules(rulesToDefine) {
        Object.getOwnPropertyNames(rulesToDefine).forEach(ruleId => {
            this.defineRule(ruleId, rulesToDefine[ruleId]);
        });
    }

    /**
     * Gets an object with all loaded rules.
     * @returns {Map<string, Rule>} All loaded rules
     */
    getRules() {
        const { lastConfigArray, ruleMap } = internalSlotsMap.get(this);

        return new Map(function *() {
            yield* ruleMap;

            if (lastConfigArray) {
                yield* lastConfigArray.pluginRules;
            }
        }());
    }

    /**
     * Define a new parser module
     * @param {string} parserId Name of the parser
     * @param {Parser} parserModule The parser object
     * @returns {void}
     */
    defineParser(parserId, parserModule) {
        internalSlotsMap.get(this).parserMap.set(parserId, parserModule);
    }

    /**
     * Performs multiple autofix passes over the text until as many fixes as possible
     * have been applied.
     * @param {string} text The source text to apply fixes to.
     * @param {ConfigData|ConfigArray} config The ESLint config object to use.
     * @param {Object} options The ESLint options object to use.
     * @param {string} options.filename The filename from which the text was read.
     * @param {boolean} options.allowInlineConfig Flag indicating if inline comments
     *      should be allowed.
     * @param {boolean|Function} options.fix Determines whether fixes should be applied
     * @param {Function} options.preprocess preprocessor for source text. If provided, this should
     *      accept a string of source text, and return an array of code blocks to lint.
     * @param {Function} options.postprocess postprocessor for report messages. If provided,
     *      this should accept an array of the message lists for each code block returned from the preprocessor,
     *      apply a mapping to the messages as appropriate, and return a one-dimensional array of messages
     * @returns {{fixed:boolean,messages:LintMessage[],output:string}} The result of the fix operation as returned from the
     *      SourceCodeFixer.
     */
    verifyAndFix(text, config, options) {
        let messages = [],
            fixedResult,
            fixed = false,
            passNumber = 0,
            currentText = text;
        const debugTextDescription = options && options.filename || `${text.slice(0, 10)}...`;
        const shouldFix = options && typeof options.fix !== "undefined" ? options.fix : true;

        /**
         * This loop continues until one of the following is true:
         *
         * 1. No more fixes have been applied.
         * 2. Ten passes have been made.
         *
         * That means anytime a fix is successfully applied, there will be another pass.
         * Essentially, guaranteeing a minimum of two passes.
         */
        do {
            passNumber++;

            debug(`Linting code for ${debugTextDescription} (pass ${passNumber})`);
            messages = this.verify(currentText, config, options);

            debug(`Generating fixed text for ${debugTextDescription} (pass ${passNumber})`);
            fixedResult = SourceCodeFixer.applyFixes(currentText, messages, shouldFix);

            /*
             * stop if there are any syntax errors.
             * 'fixedResult.output' is a empty string.
             */
            if (messages.length === 1 && messages[0].fatal) {
                break;
            }

            // keep track if any fixes were ever applied - important for return value
            fixed = fixed || fixedResult.fixed;

            // update to use the fixed output instead of the original text
            currentText = fixedResult.output;

        } while (
            fixedResult.fixed &&
            passNumber < MAX_AUTOFIX_PASSES
        );

        /*
         * If the last result had fixes, we need to lint again to be sure we have
         * the most up-to-date information.
         */
        if (fixedResult.fixed) {
            fixedResult.messages = this.verify(currentText, config, options);
        }

        // ensure the last result properly reflects if fixes were done
        fixedResult.fixed = fixed;
        fixedResult.output = currentText;

        return fixedResult;
    }
}

module.exports = {
    Linter,

    /**
     * Get the internal slots of a given Linter instance for tests.
     * @param {Linter} instance The Linter instance to get.
     * @returns {LinterInternalSlots} The internal slots.
     */
    getLinterInternalSlots(instance) {
        return internalSlotsMap.get(instance);
    }
};