Built files are not built, only asserted when the app starts in a container.

Dockerfile.app

@@ -10,6 +10,9 @@ RUN apt-get update && \
 # Let the pub server know that this is not a "typical" pub client but rather a bot.
 ENV PUB_ENVIRONMENT="bot.pub_dartlang_org.docker"
 ENV PUB_CACHE="/project/.pub-cache"
+# Let the pub server know that it is running inside a container.
+# It will not rebuild web-app assets, only assert their presence.
+ENV PUB_DEV_ENVIRONMENT="production"
 
 COPY app /project/app
 COPY pkg /project/pkg

app/lib/frontend/static_files.dart

@@ -12,6 +12,7 @@ import 'package:meta/meta.dart';
 import 'package:mime/mime.dart' as mime;
 import 'package:pana/pana.dart' show runConstrained;
 import 'package:path/path.dart' as path;
+import 'package:pub_dev/shared/monitoring.dart';
 
 final _logger = Logger('pub.static_files');
 
@@ -344,6 +345,25 @@ Future updateLocalBuiltFilesIfNeeded() async {
     _logger.info('Building pkg/web_css');
     await updateWebCssBuild();
   }
+
+  await assertLocalBuiltFilesArePresent();
+}
+
+/// Checks whether the local built files are present, throws
+/// [AssertionError] if anything is missing.
+Future assertLocalBuiltFilesArePresent() async {
+  Future<void> assertExists(String path) async {
+    final file = File(path);
+    if (!file.existsSync()) {
+      _logger.pubNoticeShout(
+          'missing-built-file', 'The local built file is missing: $path');
+    }
+  }
+
+  final staticDirPath = resolveStaticDirPath();
+  await assertExists(path.join(staticDirPath, 'js', 'script.dart.js'));
+  await assertExists(path.join(staticDirPath, 'css', 'style.css'));
+  await assertExists(path.join(staticDirPath, 'css', 'dartdoc.css'));
 }
 
 /// Runs build.sh in pkg/web_app

app/lib/search/backend.dart

@@ -19,6 +19,7 @@ import 'package:meta/meta.dart';
 import 'package:pana/src/dartdoc/pub_dartdoc_data.dart';
 import 'package:path/path.dart' as p;
 import 'package:pool/pool.dart';
+import 'package:pub_dev/shared/env_config.dart';
 import 'package:pub_dev/shared/monitoring.dart';
 import 'package:retry/retry.dart';
 
@@ -451,6 +452,9 @@ class SearchBackend {
       }
       if (canUseCached) {
         return await file.readAsString();
+      } else if (envConfig.isInProductionEnvironment) {
+        _logger.pubNoticeShout('missing-sdk-index-json',
+            'The SDK index.json file is missing: fileName');
       }
     }
 

app/lib/service/entrypoint/frontend.dart

@@ -41,7 +41,11 @@ class DefaultCommand extends Command {
 }
 
 Future _main() async {
-  await updateLocalBuiltFilesIfNeeded();
+  if (envConfig.isInProductionEnvironment) {
+    await assertLocalBuiltFilesArePresent();
+  } else {
+    await updateLocalBuiltFilesIfNeeded();
+  }
   final appHandler = createAppHandler();
 
   if (envConfig.isRunningLocally) {

app/lib/shared/env_config.dart

@@ -53,6 +53,10 @@ class _EnvConfig {
   /// True, if running inside AppEngine.
   bool get isRunningInAppengine => _gaeService != null && _gaeVersion != null;
 
+  /// True, if the application is running inside a container environment.
+  late final isInProductionEnvironment =
+      Platform.environment['PUB_DEV_ENVIRONMENT'] == 'production';
+
   /// True, if running locally and not inside AppEngine.
   bool get isRunningLocally => !isRunningInAppengine;