Add check for outdated/duplicate packages to yarn start

.changeset/orange-pets-whisper.md

@@ -0,0 +1,5 @@
+---
+'@backstage/cli': patch
+---
+
+Add check for outdated/duplicate packages to yarn start

packages/cli/src/commands/app/serve.ts

@@ -15,12 +15,40 @@
  */
 
 import fs from 'fs-extra';
+import chalk from 'chalk';
 import { Command } from 'commander';
 import { serveBundle } from '../../lib/bundler';
 import { loadCliConfig } from '../../lib/config';
 import { paths } from '../../lib/paths';
+import { Lockfile } from '../../lib/versioning';
+import { includedFilter } from '../versions/lint';
 
 export default async (cmd: Command) => {
+  const lockfile = await Lockfile.load(paths.resolveTargetRoot('yarn.lock'));
+  const result = lockfile.analyze({
+    filter: includedFilter,
+  });
+  const problemPackages = result.newVersions.map(({ name }) => name);
+
+  if (problemPackages.length > 1) {
+    console.log(
+      chalk.yellow(
+        `The following packages may be outdated or have duplicate installations:
+
+          ${problemPackages.join(', ')}
+        `,
+      ),
+    );
+    console.log(
+      chalk.yellow(
+        `This can be resolved using the following command:
+
+          yarn backstage-cli versions:check --fix
+      `,
+      ),
+    );
+  }
+
   const { name } = await fs.readJson(paths.resolveTarget('package.json'));
   const waitForExit = await serveBundle({
     entry: 'src/index',