Chore: enable prefer-arrow-callback on ESLint codebase (fixes #6407) (#7503)

* Chore: enable `prefer-arrow-callback` on ESLint codebase (fixes #6407)

* Move some complex expressions onto multiple lines

* Use `.returns(value)` instead of `() => value` with sinon

Author: not-an-aardvark

Makefile.js

@@ -90,9 +90,7 @@ function getTestFilePatterns() {
         testTemplatesPath = "tests/templates/",
         testBinPath = "tests/bin/";
 
-    return ls(testLibPath).filter(function(pathToCheck) {
-        return test("-d", testLibPath + pathToCheck);
-    }).reduce(function(initialValue, currentValues) {
+    return ls(testLibPath).filter(pathToCheck => test("-d", testLibPath + pathToCheck)).reduce((initialValue, currentValues) => {
         if (currentValues !== "rules") {
             initialValue.push(`"${testLibPath + currentValues}/**/*.js"`);
         }
@@ -135,7 +133,7 @@ function generateRulesIndex(basedir) {
 
     output += "    var rules = Object.create(null);\n";
 
-    find(`${basedir}rules/`).filter(fileType("js")).forEach(function(filename) {
+    find(`${basedir}rules/`).filter(fileType("js")).forEach(filename => {
         const basename = path.basename(filename, ".js");
 
         output += `    rules["${basename}"] = require("./rules/${basename}");\n`;
@@ -204,7 +202,7 @@ function generateRuleIndexPage(basedir) {
         categoryList = "conf/category-list.json",
         categoriesData = JSON.parse(cat(path.resolve(categoryList)));
 
-    find(path.join(basedir, "/lib/rules/")).filter(fileType("js")).forEach(function(filename) {
+    find(path.join(basedir, "/lib/rules/")).filter(fileType("js")).forEach(filename => {
         const rule = require(filename);
         const basename = path.basename(filename, ".js");
 
@@ -324,7 +322,7 @@ function getTagOfFirstOccurrence(filePath) {
     let tags = execSilent(`git tag --contains ${firstCommit}`);
 
     tags = splitCommandResultToLines(tags);
-    return tags.reduce(function(list, version) {
+    return tags.reduce((list, version) => {
         version = semver.valid(version.trim());
         if (version) {
             list.push(version);
@@ -363,12 +361,8 @@ function getFirstVersionOfDeletion(filePath) {
         tags = execSilent(`git tag --contains ${deletionCommit}`);
 
     return splitCommandResultToLines(tags)
-        .map(function(version) {
-            return semver.valid(version.trim());
-        })
-        .filter(function(version) {
-            return version;
-        })
+        .map(version => semver.valid(version.trim()))
+        .filter(version => version)
         .sort(semver.compare)[0];
 }
 
@@ -476,7 +470,7 @@ function getFormatterResults() {
         ].join("\n"),
         rawMessages = cli.executeOnText(codeString, "fullOfProblems.js", true);
 
-    return formatterFiles.reduce(function(data, filename) {
+    return formatterFiles.reduce((data, filename) => {
         const fileExt = path.extname(filename),
             name = path.basename(filename, fileExt);
 
@@ -594,9 +588,7 @@ target.gensite = function(prereleaseVersion) {
 
     // append version
     if (prereleaseVersion) {
-        docFiles = docFiles.map(function(docFile) {
-            return `/${prereleaseVersion}${docFile}`;
-        });
+        docFiles = docFiles.map(docFile => `/${prereleaseVersion}${docFile}`);
     }
 
     // 1. create temp and build directory
@@ -605,7 +597,7 @@ target.gensite = function(prereleaseVersion) {
     }
 
     // 2. remove old files from the site
-    docFiles.forEach(function(filePath) {
+    docFiles.forEach(filePath => {
         const fullPath = path.join(DOCS_DIR, filePath),
             htmlFullPath = fullPath.replace(".md", ".html");
 
@@ -632,7 +624,7 @@ target.gensite = function(prereleaseVersion) {
     }
 
     // 4. Loop through all files in temporary directory
-    find(TEMP_DIR).forEach(function(filename) {
+    find(TEMP_DIR).forEach(filename => {
         if (test("-f", filename) && path.extname(filename) === ".md") {
 
             const rulesUrl = "https://github.com/eslint/eslint/tree/master/lib/rules/",
@@ -763,7 +755,7 @@ target.checkRuleFiles = function() {
     const ruleFiles = find("lib/rules/").filter(fileType("js"));
     let errors = 0;
 
-    ruleFiles.forEach(function(filename) {
+    ruleFiles.forEach(filename => {
         const basename = path.basename(filename, ".js");
         const docFilename = `docs/rules/${basename}.md`;
 
@@ -838,35 +830,27 @@ target.checkLicenses = function() {
         const licenses = dependency.licenses;
 
         if (Array.isArray(licenses)) {
-            return licenses.some(function(license) {
-                return isPermissible({
-                    name: dependency.name,
-                    licenses: license
-                });
-            });
+            return licenses.some(license => isPermissible({
+                name: dependency.name,
+                licenses: license
+            }));
         }
 
-        return OPEN_SOURCE_LICENSES.some(function(license) {
-            return license.test(licenses);
-        });
+        return OPEN_SOURCE_LICENSES.some(license => license.test(licenses));
     }
 
     echo("Validating licenses");
 
     checker.init({
         start: __dirname
-    }, function(deps) {
-        const impermissible = Object.keys(deps).map(function(dependency) {
-            return {
-                name: dependency,
-                licenses: deps[dependency].licenses
-            };
-        }).filter(function(dependency) {
-            return !isPermissible(dependency);
-        });
+    }, deps => {
+        const impermissible = Object.keys(deps).map(dependency => ({
+            name: dependency,
+            licenses: deps[dependency].licenses
+        })).filter(dependency => !isPermissible(dependency));
 
         if (impermissible.length) {
-            impermissible.forEach(function(dependency) {
+            impermissible.forEach(dependency => {
                 console.error("%s license for %s is impermissible.",
                     dependency.licenses,
                     dependency.name
@@ -960,9 +944,7 @@ function createConfigForPerformanceTest() {
 
     content.push.apply(
         content,
-        ls("lib/rules").map(function(fileName) {
-            return `    ${path.basename(fileName, ".js")}: 1`;
-        })
+        ls("lib/rules").map(fileName => `    ${path.basename(fileName, ".js")}: 1`)
     );
 
     content.join("\n").to(PERF_ESLINTRC);
@@ -981,7 +963,7 @@ function createConfigForPerformanceTest() {
 function time(cmd, runs, runNumber, results, cb) {
     const start = process.hrtime();
 
-    exec(cmd, { silent: true }, function(code, stdout, stderr) {
+    exec(cmd, { silent: true }, (code, stdout, stderr) => {
         const diff = process.hrtime(start),
             actual = (diff[0] * 1e3 + diff[1] / 1e6); // ms
 
@@ -1026,14 +1008,12 @@ function runPerformanceTest(title, targets, multiplier, cb) {
     echo(title);
     echo("  CPU Speed is %d with multiplier %d", cpuSpeed, multiplier);
 
-    time(cmd, 5, 1, [], function(results) {
+    time(cmd, 5, 1, [], results => {
         if (!results || results.length === 0) {  // No results? Something is wrong.
             throw new Error("Performance test failed.");
         }
 
-        results.sort(function(a, b) {
-            return a - b;
-        });
+        results.sort((a, b) => a - b);
 
         const median = results[~~(results.length / 2)];
 
@@ -1068,9 +1048,7 @@ function loadPerformance() {
         results.push(loadPerfData.loadTime);
     }
 
-    results.sort(function(a, b) {
-        return a - b;
-    });
+    results.sort((a, b) => a - b);
     const median = results[~~(results.length / 2)];
 
     echo("");
@@ -1079,7 +1057,7 @@ function loadPerformance() {
 }
 
 target.perf = function() {
-    downloadMultifilesTestTarget(function() {
+    downloadMultifilesTestTarget(() => {
         createConfigForPerformanceTest();
 
         loadPerformance();
@@ -1088,7 +1066,7 @@ target.perf = function() {
             "Single File:",
             "tests/performance/jshint.js",
             PERF_MULTIPLIER,
-            function() {
+            () => {
 
                 // Count test target files.
                 const count = glob.sync(
@@ -1101,7 +1079,7 @@ target.perf = function() {
                     `Multi Files (${count} files):`,
                     PERF_MULTIFILES_TARGETS,
                     3 * PERF_MULTIPLIER,
-                    function() {}
+                    () => {}
                 );
             }
         );

bin/eslint.js

@@ -36,7 +36,7 @@ const concat = require("concat-stream"),
 // Execution
 //------------------------------------------------------------------------------
 
-process.on("uncaughtException", function(err) {
+process.on("uncaughtException", err => {
 
     // lazy load
     const lodash = require("lodash");
@@ -55,13 +55,13 @@ process.on("uncaughtException", function(err) {
 });
 
 if (useStdIn) {
-    process.stdin.pipe(concat({ encoding: "string" }, function(text) {
+    process.stdin.pipe(concat({ encoding: "string" }, text => {
         process.exitCode = cli.execute(process.argv, text);
     }));
 } else if (init) {
     const configInit = require("../lib/config/config-initializer");
 
-    configInit.initializeConfig(function(err) {
+    configInit.initializeConfig(err => {
         if (err) {
             process.exitCode = 1;
             console.error(err.message);

lib/ast-utils.js

@@ -176,9 +176,7 @@ function hasJSDocThisTag(node, sourceCode) {
     // because callbacks don't have its JSDoc comment.
     // e.g.
     //     sinon.test(/* @this sinon.Sandbox */function() { this.spy(); });
-    return sourceCode.getComments(node).leading.some(function(comment) {
-        return thisTagPattern.test(comment.value);
-    });
+    return sourceCode.getComments(node).leading.some(comment => thisTagPattern.test(comment.value));
 }
 
 /**

lib/cli-engine.js

@@ -90,7 +90,7 @@ const debug = require("debug")("eslint:cli-engine");
  * @private
  */
 function calculateStatsPerFile(messages) {
-    return messages.reduce(function(stat, message) {
+    return messages.reduce((stat, message) => {
         if (message.fatal || message.severity === 2) {
             stat.errorCount++;
         } else {
@@ -110,7 +110,7 @@ function calculateStatsPerFile(messages) {
  * @private
  */
 function calculateStatsPerRun(results) {
-    return results.reduce(function(stat, result) {
+    return results.reduce((stat, result) => {
         stat.errorCount += result.errorCount;
         stat.warningCount += result.warningCount;
         return stat;
@@ -241,7 +241,7 @@ function processText(text, configHelper, filename, fix, allowInlineConfig) {
         const parsedBlocks = processor.preprocess(text, filename);
         const unprocessedMessages = [];
 
-        parsedBlocks.forEach(function(block) {
+        parsedBlocks.forEach(block => {
             unprocessedMessages.push(eslint.verify(block, config, {
                 filename,
                 allowInlineConfig
@@ -466,15 +466,15 @@ function CLIEngine(options) {
     if (this.options.rulePaths) {
         const cwd = this.options.cwd;
 
-        this.options.rulePaths.forEach(function(rulesdir) {
+        this.options.rulePaths.forEach(rulesdir => {
             debug(`Loading rules from ${rulesdir}`);
             rules.load(rulesdir, cwd);
         });
     }
 
-    Object.keys(this.options.rules || {}).forEach(function(name) {
+    Object.keys(this.options.rules || {}).forEach(name => {
         validator.validateRuleOptions(name, this.options.rules[name], "CLI");
-    }.bind(this));
+    });
 }
 
 /**
@@ -526,7 +526,7 @@ CLIEngine.getFormatter = function(format) {
 CLIEngine.getErrorResults = function(results) {
     const filtered = [];
 
-    results.forEach(function(result) {
+    results.forEach(result => {
         const filteredMessages = result.messages.filter(isErrorMessage);
 
         if (filteredMessages.length > 0) {
@@ -549,9 +549,7 @@ CLIEngine.getErrorResults = function(results) {
  * @returns {void}
  */
 CLIEngine.outputFixes = function(report) {
-    report.results.filter(function(result) {
-        return result.hasOwnProperty("output");
-    }).forEach(function(result) {
+    report.results.filter(result => result.hasOwnProperty("output")).forEach(result => {
         fs.writeFileSync(result.filePath, result.output);
     });
 };
@@ -708,7 +706,7 @@ CLIEngine.prototype = {
         patterns = this.resolveFileGlobPatterns(patterns);
         const fileList = globUtil.listFilesToProcess(patterns, options);
 
-        fileList.forEach(function(fileInfo) {
+        fileList.forEach(fileInfo => {
             executeOnFile(fileInfo.filename, fileInfo.ignored);
         });
 

lib/code-path-analysis/debug-helpers.js

@@ -108,15 +108,15 @@ module.exports = {
             }
 
             if (segment.internal.nodes.length > 0) {
-                text += segment.internal.nodes.map(function(node) {
+                text += segment.internal.nodes.map(node => {
                     switch (node.type) {
                         case "Identifier": return `${node.type} (${node.name})`;
                         case "Literal": return `${node.type} (${node.value})`;
                         default: return node.type;
                     }
                 }).join("\\n");
             } else if (segment.internal.exitNodes.length > 0) {
-                text += segment.internal.exitNodes.map(function(node) {
+                text += segment.internal.exitNodes.map(node => {
                     switch (node.type) {
                         case "Identifier": return `${node.type}:exit (${node.name})`;
                         case "Literal": return `${node.type}:exit (${node.value})`;
@@ -176,7 +176,7 @@ module.exports = {
             stack.push([nextSegment, 0]);
         }
 
-        codePath.returnedSegments.forEach(function(finalSegment) {
+        codePath.returnedSegments.forEach(finalSegment => {
             if (lastId === finalSegment.id) {
                 text += "->final";
             } else {
@@ -185,7 +185,7 @@ module.exports = {
             lastId = null;
         });
 
-        codePath.thrownSegments.forEach(function(finalSegment) {
+        codePath.thrownSegments.forEach(finalSegment => {
             if (lastId === finalSegment.id) {
                 text += "->thrown";
             } else {

lib/config.js

@@ -197,7 +197,7 @@ function Config(options) {
 
     this.useEslintrc = (options.useEslintrc !== false);
 
-    this.env = (options.envs || []).reduce(function(envs, name) {
+    this.env = (options.envs || []).reduce((envs, name) => {
         envs[name] = true;
         return envs;
     }, {});
@@ -208,7 +208,7 @@ function Config(options) {
      * whether global is writable.
      * If user declares "foo", convert to "foo:false".
      */
-    this.globals = (options.globals || []).reduce(function(globals, def) {
+    this.globals = (options.globals || []).reduce((globals, def) => {
         const parts = def.split(":");
 
         globals[parts[0]] = (parts.length > 1 && parts[1] === "true");