Support deferred imports on profile/release builds of Flutter Web (#41222)

packages/flutter_tools/lib/src/build_runner/build_script.dart

@@ -11,6 +11,7 @@ import 'dart:isolate';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/utilities.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:archive/archive.dart';
 import 'package:build/build.dart';
 import 'package:build_config/build_config.dart';
 import 'package:build_modules/build_modules.dart';
@@ -26,6 +27,7 @@ import 'package:build_web_compilers/build_web_compilers.dart';
 import 'package:build_web_compilers/builders.dart';
 import 'package:build_web_compilers/src/dev_compiler_bootstrap.dart';
 import 'package:crypto/crypto.dart';
+import 'package:glob/glob.dart';
 import 'package:path/path.dart' as path; // ignore: package_path_import
 import 'package:scratch_space/scratch_space.dart';
 import 'package:test_core/backend.dart';
@@ -461,8 +463,32 @@ Future<void> bootstrapDart2Js(BuildStep buildStep, String flutterWebSdk, bool pr
   final AssetId jsOutputId = dartEntrypointId.changeExtension(jsEntrypointExtension);
   final File jsOutputFile = scratchSpace.fileFor(jsOutputId);
   if (result.succeeded && jsOutputFile.existsSync()) {
-    log.info(result.output);
-    // Explicitly write out the original js file and sourcemap.
+    final String rootDir = path.dirname(jsOutputFile.path);
+    final String dartFile = path.basename(dartEntrypointId.path);
+    final Glob fileGlob = Glob('$dartFile.js*');
+    final Archive archive = Archive();
+    await for (FileSystemEntity jsFile in fileGlob.list(root: rootDir)) {
+      if (jsFile.path.endsWith(jsEntrypointExtension) ||
+          jsFile.path.endsWith(jsEntrypointSourceMapExtension)) {
+        // These are explicitly output, and are not part of the archive.
+        continue;
+      }
+      if (jsFile is File) {
+        final String fileName = path.relative(jsFile.path, from: rootDir);
+        final FileStat fileStats = jsFile.statSync();
+        archive.addFile(
+            ArchiveFile(fileName, fileStats.size, await jsFile.readAsBytes())
+              ..mode = fileStats.mode
+              ..lastModTime = fileStats.modified.millisecondsSinceEpoch);
+      }
+    }
+    if (archive.isNotEmpty) {
+      final AssetId archiveId = dartEntrypointId.changeExtension(jsEntrypointArchiveExtension);
+      await buildStep.writeAsBytes(archiveId, TarEncoder().encode(archive));
+    }
+
+    // Explicitly write out the original js file and sourcemap - we can't output
+    // these as part of the archive because they already have asset nodes.
     await scratchSpace.copyOutput(jsOutputId, buildStep);
     final AssetId jsSourceMapId =
         dartEntrypointId.changeExtension(jsEntrypointSourceMapExtension);

packages/flutter_tools/lib/src/web/compile.dart

@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:archive/archive.dart';
 import 'package:meta/meta.dart';
 
 import '../asset.dart';
@@ -48,9 +49,23 @@ Future<void> buildWeb(FlutterProject flutterProject, String target, BuildInfo bu
         flutterProject.manifest.appName,
         '${fs.path.withoutExtension(target)}_web_entrypoint.dart.js',
       );
+      // Check for deferred import outputs.
+      final File dart2jsArchive = fs.file(fs.path.join(
+        flutterProject.dartTool.path,
+        'build',
+        'flutter_web',
+        '${flutterProject.manifest.appName}',
+        '${fs.path.withoutExtension(target)}_web_entrypoint.dart.js.tar.gz'),
+      );
       fs.file(outputPath).copySync(fs.path.join(outputDir.path, 'main.dart.js'));
       fs.file('$outputPath.map').copySync(fs.path.join(outputDir.path, 'main.dart.js.map'));
       flutterProject.web.indexFile.copySync(fs.path.join(outputDir.path, 'index.html'));
+      if (dart2jsArchive.existsSync()) {
+        final Archive archive = TarDecoder().decodeBytes(dart2jsArchive.readAsBytesSync());
+        for (ArchiveFile file in archive.files) {
+          outputDir.childFile(file.name).writeAsBytesSync(file.content);
+        }
+      }
     }
   } catch (err) {
     printError(err.toString());

packages/flutter_tools/test/general.shard/commands/build_web_test.dart

@@ -2,7 +2,11 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:convert';
+
+import 'package:archive/archive.dart';
 import 'package:args/command_runner.dart';
+import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/platform.dart';
@@ -25,6 +29,7 @@ void main() {
   MockWebCompilationProxy mockWebCompilationProxy;
   Testbed testbed;
   MockPlatform mockPlatform;
+  bool addArchive = false;
 
   setUpAll(() {
     Cache.flutterRoot = '';
@@ -32,6 +37,7 @@ void main() {
   });
 
   setUp(() {
+    addArchive = false;
     mockWebCompilationProxy = MockWebCompilationProxy();
     testbed = Testbed(setup: () {
       fs.file('pubspec.yaml')
@@ -46,9 +52,18 @@ void main() {
         mode: anyNamed('mode'),
         initializePlatform: anyNamed('initializePlatform'),
       )).thenAnswer((Invocation invocation) {
-        final String path = fs.path.join('.dart_tool', 'build', 'flutter_web', 'foo', 'lib', 'main_web_entrypoint.dart.js');
+        final String prefix = fs.path.join('.dart_tool', 'build', 'flutter_web', 'foo', 'lib');
+        final String path = fs.path.join(prefix, 'main_web_entrypoint.dart.js');
         fs.file(path).createSync(recursive: true);
         fs.file('$path.map').createSync();
+        if (addArchive) {
+          final List<int> bytes = utf8.encode('void main() {}');
+          final TarEncoder encoder = TarEncoder();
+          final Archive archive = Archive()
+            ..addFile(ArchiveFile.noCompress('main_web_entrypoint.1.dart.js', bytes.length, bytes));
+          fs.file(fs.path.join(prefix, 'main_web_entrypoint.dart.js.tar.gz'))
+            ..writeAsBytes(encoder.encode(archive));
+        }
         return Future<bool>.value(true);
       });
     }, overrides: <Type, Generator>{
@@ -59,6 +74,19 @@ void main() {
     });
   });
 
+  test('Copies generated part files out of build directory', () => testbed.run(() async {
+    addArchive = true;
+    await buildWeb(
+      FlutterProject.current(),
+      fs.path.join('lib', 'main.dart'),
+      BuildInfo.release,
+      false,
+    );
+
+    expect(fs.file(fs.path.join('build', 'web', 'main_web_entrypoint.1.dart.js')), exists);
+    expect(fs.file(fs.path.join('build', 'web', 'main.dart.js')), exists);
+  }));
+
   test('Refuses to build for web when missing index.html', () => testbed.run(() async {
     fs.file(fs.path.join('web', 'index.html')).deleteSync();
 
@@ -82,16 +110,6 @@ void main() {
     expect(await runner.run(), 1);
   }));
 
-  test('Can build for web', () => testbed.run(() async {
-
-    await buildWeb(
-      FlutterProject.current(),
-      fs.path.join('lib', 'main.dart'),
-      BuildInfo.debug,
-      false,
-    );
-  }));
-
   test('Refuses to build a debug build for web', () => testbed.run(() async {
     final CommandRunner<void> runner = createTestCommandRunner(BuildCommand());