feat(cli) check and warn if npx react-native version is using an old cached version

packages/react-native/cli.js

@@ -10,10 +10,68 @@
 
 'use strict';
 
-var cli = require('@react-native-community/cli');
+const {get} = require('https');
+const {URL} = require('url');
+const chalk = require('chalk');
+const cli = require('@react-native-community/cli');
+
+const {version: currentVersion} = require('./package.json');
+
+const isNpxRuntime = process.env.npm_lifecycle_event === 'npx';
+const DEFAULT_REGISTRY_HOST =
+  process.env.npm_config_registry ?? 'https://registry.npmjs.org/';
+const HEAD = '1000.0.0';
+
+async function getLatestVersion(registryHost = DEFAULT_REGISTRY_HOST) {
+  return new Promise((res, rej) => {
+    const url = new URL(registryHost);
+    url.pathname = 'react-native/latest';
+    get(url.toString(), resp => {
+      const buffer = [];
+      resp.on('data', data => buffer.push(data));
+      resp.on('end', () => {
+        try {
+          res(JSON.parse(Buffer.concat(buffer).toString('utf8')).version);
+        } catch (e) {
+          rej(e);
+        }
+      });
+    }).on('error', e => rej(e));
+  });
+}
+
+/**
+ * npx react-native -> @react-native-comminity/cli
+ *
+ * Will perform a version check and warning if you're not running the latest community cli when executed using npx. If
+ * you know what you're doing, you can skip this check:
+ *
+ *  SKIP=true npx react-native ...
+ *
+ */
+async function main() {
+  if (isNpxRuntime && !process.env.SKIP && currentVersion !== HEAD) {
+    try {
+      const latest = await getLatestVersion();
+      if (latest !== currentVersion) {
+        const msg = `
+  ${chalk.bold.yellow('WARNING:')} You should run ${chalk.white.bold(
+          'npx react-native@latest',
+        )} to ensure you're always using the most current version of the CLI. NPX has cached version (${chalk.bold.yellow(
+          currentVersion,
+        )}) != current release (${chalk.bold.green(latest)})
+  `;
+        console.warn(msg);
+      }
+    } catch (_) {
+      // Ignore errors, since it's a nice to have warning
+    }
+  }
+  return cli.run();
+}
 
 if (require.main === module) {
-  cli.run();
+  main();
 }
 
 module.exports = cli;