meteor/scripts/admin/check-legacy-syntax/check-syntax.js

// Some packages are unable to be compiled (usually because they are a
// dependency of the packages with the compiler).
// This script checks that these packages do not use new syntax so
// they do not cause syntax errors in old web browsers,
// and when used in build plugins can run in old Meteor versions

const clientEcmascriptVersion = 5;
// Node 8 (Meteor 1.6+) fully supports 2016
const serverEcmascriptVersion = '2016';

// By default, all files in these packages are expected to use es5 syntax
// Files only used on the server can be listed, which allows them to use
// some newer syntax (limited by the oldest Meteor version we want to support
// when the package is used in a build plugin)
const packages = {
  'meteor': {
    serverFiles: [
      'dynamics_nodejs.js',
      'asl-helpers.js',
      'server_environment.js'
    ]
  },
  'accounts-ui': {},
  'audit-argument-checks': {},
  'autopublish': {},
  'babel-compiler': {
    serverFiles: ['babel.js', 'babel-compiler.js']
  },
  'babel-runtime': {},
  'browser-policy': {},
  'browser-policy-common': {},
  'browser-policy-content': {},
  'browser-policy-framing': {},
  // 'constraint-solver': {},
  'crosswalk': {},
  'context': {
    serverFiles: ['context.js']
  },
  'ddp': {},
  'disable-oplog': {},
  'dynamic-import': {
    serverFiles: ['security.js']
  },
  'ecmascript': {
    serverFiles: ['plugin.js', 'ecmascript.js']
  },
  'ecmascript-runtime': {},
  'ecmascript-runtime-client': {
    serverFiles: ['versions.js']
  },
  'ecmascript-runtime-server': {},
  'es5-shim': {},
  'fetch': {},
  'geojson-utils': {},
  'hot-code-push': {},
  'hot-module-replacement': {},
  'insecure': {},
  'inter-process-messaging': {
    serverFiles: ['inter-process-messaging.js']
  },
  'launch-screen': {},
  'localstorage': {},
  'logic-solver': {},
  'meteor-base': {},
  'mobile-experience': {},
  'mobile-status-bar': {},
  'modern-browsers': {
    serverFiles: ['modern.js']
  },
  'modules': {},
  'modules-runtime': {},
  'modules-runtime-hot': {},
  'mongo-dev-server': {},
  'mongo-livedata': {},
  'npm-mongo': {
    serverFiles: ['wrapper.js']
  },
  'package-stats-opt-out': {},
  'package-version-parser': {},
  'promise': {},
  'react-fast-refresh': {},
  'reactive-var': {},
  'reload-safetybelt': {},
  'sha': {},
  'standard-minifiers': {},
  // 'test-in-console': {},
  'test-server-tests-in-console-once': {},
  'tinytest-harness': {},
  'twitter-config-ui': {},
  // 'twitter-oauth': {},
  'typescript': {
    serverFiles: ['plugin.js']
  },
  'underscore': {},
  'url': {},
};

const acorn = require('acorn');
const fs = require('fs');
const path = require('path');

const baseDir = path.resolve(__dirname, '../../../');

Object.keys(packages).forEach(packageName => {
  console.log(`=> Checking ${packageName}`);

  const packagePath = path.resolve(baseDir, 'packages', packageName);
  let files = listPackageFiles(packagePath);

  for(const file of files) {
    let content = fs.readFileSync(file, 'utf-8');
    let relPath = path.relative(packagePath, file);
    let ecmaVersion = clientEcmascriptVersion;

    if (
      packages[packageName].serverFiles?.includes(relPath) ||
      relPath.endsWith('_server.js') ||
      file.endsWith('/server.js')
    ) {
      // Is a server file, which can use some newer syntax
      ecmaVersion = serverEcmascriptVersion;
    }

    try {
      acorn.parse(content, {
        ecmaVersion,
      });
    } catch (error) {
      console.log('');
      console.error(`Failed to parse ${file}: `, error.message);
      let line = content.split('\n')[error.loc.line - 1];
      console.log(line);
      console.log('');

      process.exitCode = 1;
    }
  }
});


function listPackageFiles(rootPath) {
  let result = [];

  function walk(absPath) {
    let dirents = fs.readdirSync(absPath, { withFileTypes: true });
    
    for(const dirent of dirents) {
      if (
        dirent.name === 'package.js' ||
        dirent.name.startsWith('.') ||

        // Only include js files
        !dirent.name.endsWith('.js') ||

        // Exclude tests
        dirent.name === 'tests' ||
        dirent.name === 'tests.js' ||
        dirent.name.endsWith('_tests.js') ||
        dirent.name.endsWith('-tests.js')
      ) {
        continue;
      }

      let childPath = path.resolve(absPath, dirent.name);

      if (dirent.isFile()) {
        result.push(childPath);
      } else if (dirent.isDirectory()) {
        walk(childPath);
      }
    }
  }

  walk(rootPath);

  return result;
}