cli: add list-locales flag

lighthouse-cli/bin.js

@@ -61,6 +61,11 @@ async function begin() {
     commands.listAudits();
   }
 
+  // Process terminating command
+  if (cliFlags.listLocales) {
+    commands.listLocales();
+  }
+
   // Process terminating command
   if (cliFlags.listTraceCategories) {
     commands.listTraceCategories();

lighthouse-cli/cli-flags.js

@@ -105,6 +105,11 @@ function getFlags(manualArgv, options = {}) {
           default: false,
           describe: 'Prints a list of all available audits and exits',
         },
+        'list-locales': {
+          type: 'boolean',
+          default: false,
+          describe: 'Prints a list of all supported locales and exits',
+        },
         'list-trace-categories': {
           type: 'boolean',
           default: false,
@@ -210,7 +215,7 @@ function getFlags(manualArgv, options = {}) {
         },
       })
       .group([
-        'save-assets', 'list-all-audits', 'list-trace-categories', 'print-config', 'additional-trace-categories',
+        'save-assets', 'list-all-audits', 'list-locales', 'list-trace-categories', 'print-config', 'additional-trace-categories',
         'config-path', 'preset', 'chrome-flags', 'port', 'hostname', 'form-factor', 'screenEmulation', 'emulatedUserAgent',
         'max-wait-for-load', 'enable-error-reporting', 'gather-mode', 'audit-mode',
         'only-audits', 'only-categories', 'skip-audits', 'budget-path',
@@ -314,7 +319,7 @@ function getFlags(manualArgv, options = {}) {
         //   - We're just printing the config.
         //   - We're in auditMode (and we have artifacts already)
         // If one of these don't apply, if no URL, stop the program and ask for one.
-        const isPrintSomethingMode = argv.listAllAudits || argv.listTraceCategories || argv.printConfig;
+        const isPrintSomethingMode = argv.listAllAudits || argv.listLocales || argv.listTraceCategories || argv.printConfig;
         const isOnlyAuditMode = !!argv.auditMode && !argv.gatherMode;
         if (isPrintSomethingMode || isOnlyAuditMode) {
           return true;

lighthouse-cli/commands/commands.js

@@ -7,3 +7,4 @@
 
 export {listAudits} from './list-audits.js';
 export {listTraceCategories} from './list-trace-categories.js';
+export {listLocales} from './list-locales.js';

lighthouse-cli/commands/list-locales.js

@@ -0,0 +1,16 @@
+/**
+ * @license Copyright 2021 The Lighthouse Authors. All Rights Reserved.
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
+ */
+'use strict';
+
+import locales from '../../shared/localization/locales.js';
+
+function listLocales() {
+  const localesList = Object.keys(locales);
+  process.stdout.write(JSON.stringify({locales: localesList}, null, 2));
+  process.exit(0);
+}
+
+export {listLocales};

lighthouse-cli/test/cli/bin-test.js

@@ -76,6 +76,7 @@ beforeEach(async () => {
     hostname: '',
     // Command modes
     listAllAudits: false,
+    listLocales: false,
     listTraceCategories: false,
     printConfig: false,
   };

lighthouse-cli/test/cli/index-test.js

@@ -46,6 +46,17 @@ describe('CLI Tests', function() {
     assert.ok(output.traceCategories.length > 0);
   });
 
+  it('accepts just the list-locales flag and exit immediately after', () => {
+    const ret = spawnSync('node', [indexPath, '--list-locales'], {encoding: 'utf8'});
+
+    const output = JSON.parse(ret.stdout);
+    assert.ok(Array.isArray(output.locales));
+    assert.ok(output.locales.length > 52);
+    for (const lang of ['en', 'es', 'ru', 'zh']) {
+      assert.ok(output.locales.includes(lang));
+    }
+  });
+
   describe('extra-headers', () => {
     it('should exit with a error if the path is not valid', () => {
       const ret = spawnSync('node', [indexPath, 'https://www.google.com',

types/externs.d.ts

@@ -155,6 +155,8 @@ export interface CliFlags extends Flags {
   enableErrorReporting?: boolean;
   /** Flag to print a list of all audits + categories. */
   listAllAudits: boolean;
+  /** Flag to print a list of all supported locales. */
+  listLocales: boolean;
   /** Flag to print a list of all required trace categories. */
   listTraceCategories: boolean;
   /** A preset audit of selected audit categories to run. */