create-app: add a yarn.lock seed file

Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

packages/create-app/src/createApp.ts

@@ -30,6 +30,7 @@ import {
   templatingTask,
   tryInitGitRepository,
   readGitConfig,
+  fetchYarnLockSeedTask,
 } from './lib/tasks';
 
 const DEFAULT_BRANCH = 'master';
@@ -110,6 +111,8 @@ export default async (opts: OptionValues): Promise<void> => {
       await moveAppTask(tempDir, appDir, answers.name);
     }
 
+    const fetchedYarnLockSeed = await fetchYarnLockSeedTask(appDir);
+
     if (gitConfig) {
       if (await tryInitGitRepository(appDir)) {
         // Since we don't know whether we were able to init git before we
@@ -128,6 +131,20 @@ export default async (opts: OptionValues): Promise<void> => {
       chalk.green(`🥇  Successfully created ${chalk.cyan(answers.name)}`),
     );
     Task.log();
+
+    if (!fetchedYarnLockSeed) {
+      Task.log(
+        chalk.yellow(
+          [
+            'Warning: Failed to fetch the yarn.lock seed file.',
+            '         You may end up with incompatible dependencies that break the app.',
+            '         If you run into any errors, please search the issues at',
+            '         https://github.com/backstage/backstage/issues for potential solutions',
+          ].join('\n'),
+        ),
+      );
+    }
+
     Task.section('All set! Now you might want to');
     if (opts.skipInstall) {
       Task.log(

packages/create-app/src/lib/tasks.ts

@@ -304,3 +304,45 @@ export async function tryInitGitRepository(dir: string) {
     return false;
   }
 }
+
+/**
+ * This fetches the yarn.lock seed file at https://github.com/backstage/backstage/blob/master/packages/create-app/seed-yarn.lock
+ * Its purpose is to lock individual dependencies with broken releases to known working versions.
+ * This flow is decoupled from the release of the create-app package in order to avoid
+ * the need to re-publish the create-app package whenever we want to update the seed file.
+ *
+ * @returns true if the yarn.lock seed file was fetched successfully
+ */
+export async function fetchYarnLockSeedTask(dir: string) {
+  try {
+    await Task.forItem('fetching', 'yarn.lock seed', async () => {
+      const controller = new AbortController();
+      setTimeout(() => controller.abort(), 5000);
+      const res = await fetch(
+        'https://raw.githubusercontent.com/backstage/backstage/master/packages/create-app/seed-yarn.lock',
+        {
+          signal: controller.signal,
+        },
+      );
+      if (!res.ok) {
+        throw new Error(
+          `Request failed with status ${res.status} ${res.statusText}`,
+        );
+      }
+
+      const initialYarnLockContent = await res.text();
+
+      await fs.writeFile(
+        resolvePath(dir, 'yarn.lock'),
+        initialYarnLockContent
+          .split('\n')
+          .filter(l => !l.startsWith('//'))
+          .join('\n'),
+        'utf8',
+      );
+    });
+    return true;
+  } catch {
+    return false;
+  }
+}