Expose build mode in environment of asset transformer processes (flutter#144752)

In service of flutter#143348

When invoking a package to transform an asset, we set `FLUTTER_BUILD_MODE` to the CLI name of the build mode being used. Inspired by flutter#101077 (comment):

> Do transformers know whether they get executed in debug or release mode? I kinda imagine that being useful. Ex: There's a transformer that optimizes the file size of images. Depending on the amount and size of the images, that could take a significant amount of time. Therefore, I might want to only execute it in release builds.

Note for the reviewer: the interesting part of this change can be found in the commit [set environment variable to build mode when running asset transformer�](flutter@579912d). The rest of the change is updating call sites with a new argument.

Author: andrewkolos

packages/flutter_tools/lib/src/build_system/targets/assets.dart

@@ -15,6 +15,7 @@ import '../../devfs.dart';
 import '../../flutter_manifest.dart';
 import '../build_system.dart';
 import '../depfile.dart';
+import '../exceptions.dart';
 import '../tools/asset_transformer.dart';
 import '../tools/scene_importer.dart';
 import '../tools/shader_compiler.dart';
@@ -35,7 +36,7 @@ Future<Depfile> copyAssets(
   Directory outputDirectory, {
   Map<String, DevFSContent> additionalContent = const <String, DevFSContent>{},
   required TargetPlatform targetPlatform,
-  BuildMode? buildMode,
+  required BuildMode buildMode,
   List<File> additionalInputs = const <File>[],
   String? flavor,
 }) async {
@@ -101,6 +102,7 @@ Future<Depfile> copyAssets(
     processManager: environment.processManager,
     fileSystem: environment.fileSystem,
     dartBinaryPath: environment.artifacts.getArtifactPath(Artifact.engineDartBinary),
+    buildMode: buildMode,
   );
 
   final Map<String, AssetBundleEntry> assetEntries = <String, AssetBundleEntry>{
@@ -186,7 +188,7 @@ Future<Depfile> copyAssets(
   // Copy deferred components assets only for release or profile builds.
   // The assets are included in assetBundle.entries as a normal asset when
   // building as debug.
-  if (environment.defines[kDeferredComponents] == 'true' && buildMode != null) {
+  if (environment.defines[kDeferredComponents] == 'true') {
     await Future.wait<void>(assetBundle.deferredComponentsEntries.entries.map<Future<void>>(
       (MapEntry<String, Map<String, AssetBundleEntry>> componentEntries) async {
         final Directory componentOutputDir =
@@ -343,6 +345,11 @@ class CopyAssets extends Target {
 
   @override
   Future<void> build(Environment environment) async {
+    final String? buildModeEnvironment = environment.defines[kBuildMode];
+    if (buildModeEnvironment == null) {
+      throw MissingDefineException(kBuildMode, name);
+    }
+    final BuildMode buildMode = BuildMode.fromCliName(buildModeEnvironment);
     final Directory output = environment
       .buildDir
       .childDirectory('flutter_assets');
@@ -351,6 +358,7 @@ class CopyAssets extends Target {
       environment,
       output,
       targetPlatform: TargetPlatform.android,
+      buildMode: buildMode,
       flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/ios.dart

@@ -503,6 +503,7 @@ abstract class IosAssetBundle extends Target {
       environment,
       assetDirectory,
       targetPlatform: TargetPlatform.ios,
+      buildMode: buildMode,
       additionalInputs: <File>[
         flutterProject.ios.infoPlist,
         flutterProject.ios.appFrameworkInfoPlist,

packages/flutter_tools/lib/src/build_system/targets/linux.dart

@@ -137,6 +137,7 @@ abstract class BundleLinuxAssets extends Target {
       environment,
       outputDirectory,
       targetPlatform: targetPlatform,
+      buildMode: buildMode,
       additionalContent: <String, DevFSContent>{
         'version.json': DevFSStringContent(versionInfo),
       },

packages/flutter_tools/lib/src/build_system/targets/macos.dart

@@ -438,6 +438,7 @@ abstract class MacOSBundleFlutterAssets extends Target {
       environment,
       assetDirectory,
       targetPlatform: TargetPlatform.darwin,
+      buildMode: buildMode,
       flavor: environment.defines[kFlavor],
     );
     environment.depFileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/web.dart

@@ -380,13 +380,21 @@ class WebReleaseBundle extends Target {
       }
     }
 
+    final String? buildModeEnvironment = environment.defines[kBuildMode];
+    if (buildModeEnvironment == null) {
+      throw MissingDefineException(kBuildMode, name);
+    }
+    final BuildMode buildMode = BuildMode.fromCliName(buildModeEnvironment);
+
     createVersionFile(environment, environment.defines);
     final Directory outputDirectory = environment.outputDir.childDirectory('assets');
     outputDirectory.createSync(recursive: true);
+
     final Depfile depfile = await copyAssets(
       environment,
       environment.outputDir.childDirectory('assets'),
       targetPlatform: TargetPlatform.web_javascript,
+      buildMode: buildMode,
     );
     final DepfileService depfileService = environment.depFileService;
     depfileService.writeToFile(

packages/flutter_tools/lib/src/build_system/targets/windows.dart

@@ -142,6 +142,7 @@ abstract class BundleWindowsAssets extends Target {
       environment,
       outputDirectory,
       targetPlatform: targetPlatform,
+      buildMode: buildMode,
     );
     environment.depFileService.writeToFile(
       depfile,

packages/flutter_tools/lib/src/build_system/tools/asset_transformer.dart

@@ -12,6 +12,7 @@ import '../../base/error_handling_io.dart';
 import '../../base/file_system.dart';
 import '../../base/io.dart';
 import '../../base/logger.dart';
+import '../../build_info.dart';
 import '../../devfs.dart';
 import '../../flutter_manifest.dart';
 import '../build_system.dart';
@@ -22,13 +23,18 @@ final class AssetTransformer {
     required ProcessManager processManager,
     required FileSystem fileSystem,
     required String dartBinaryPath,
+    required BuildMode buildMode,
   })  : _processManager = processManager,
         _fileSystem = fileSystem,
-        _dartBinaryPath = dartBinaryPath;
+        _dartBinaryPath = dartBinaryPath,
+        _buildMode = buildMode;
+
+  static const String buildModeEnvVar = 'FLUTTER_BUILD_MODE';
 
   final ProcessManager _processManager;
   final FileSystem _fileSystem;
   final String _dartBinaryPath;
+  final BuildMode _buildMode;
 
   /// The [Source] inputs that targets using this should depend on.
   ///
@@ -115,6 +121,9 @@ final class AssetTransformer {
     final ProcessResult result = await _processManager.run(
       command,
       workingDirectory: workingDirectory,
+      environment: <String, String>{
+        AssetTransformer.buildModeEnvVar: _buildMode.cliName,
+      }
     );
     final String stdout = result.stdout as String;
     final String stderr = result.stderr as String;

packages/flutter_tools/lib/src/devfs.dart

@@ -442,6 +442,7 @@ class DevFS {
     required FileSystem fileSystem,
     required ProcessManager processManager,
     required Artifacts artifacts,
+    required BuildMode buildMode,
     HttpClient? httpClient,
     Duration? uploadRetryThrottle,
     StopwatchFactory stopwatchFactory = const StopwatchFactory(),
@@ -465,6 +466,7 @@ class DevFS {
             processManager: processManager,
             fileSystem: fileSystem,
             dartBinaryPath: artifacts.getArtifactPath(Artifact.engineDartBinary),
+            buildMode: buildMode,
           ),
           fileSystem: fileSystem,
           logger: logger,

packages/flutter_tools/lib/src/resident_runner.dart

@@ -387,6 +387,7 @@ class FlutterDevice {
       logger: globals.logger,
       processManager: globals.processManager,
       artifacts: globals.artifacts!,
+      buildMode: buildInfo.mode,
     );
     return devFS!.create();
   }

packages/flutter_tools/test/general.shard/build_system/targets/asset_transformer_test.dart

@@ -8,6 +8,7 @@ import 'package:file_testing/file_testing.dart';
 import 'package:flutter_tools/src/artifacts.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
 import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/build_system/tools/asset_transformer.dart';
 import 'package:flutter_tools/src/flutter_manifest.dart';
 
@@ -53,6 +54,7 @@ void main() {
       processManager: processManager,
       fileSystem: fileSystem,
       dartBinaryPath: artifacts.getArtifactPath(Artifact.engineDartBinary),
+      buildMode: BuildMode.debug,
     );
 
     final AssetTransformationFailure? transformationFailure = await transformer.transformAsset(
@@ -112,6 +114,7 @@ void main() {
       processManager: processManager,
       fileSystem: fileSystem,
       dartBinaryPath: dartBinaryPath,
+      buildMode: BuildMode.debug,
     );
 
     final AssetTransformationFailure? failure = await transformer.transformAsset(
@@ -171,6 +174,7 @@ Something went wrong''');
       processManager: processManager,
       fileSystem: fileSystem,
       dartBinaryPath: dartBinaryPath,
+      buildMode: BuildMode.debug,
     );
 
     final AssetTransformationFailure? failure = await transformer.transformAsset(
@@ -265,6 +269,7 @@ Transformation failed, but I forgot to exit with a non-zero code.'''
       processManager: processManager,
       fileSystem: fileSystem,
       dartBinaryPath: dartBinaryPath,
+      buildMode: BuildMode.debug,
     );
 
     final AssetTransformationFailure? failure = await transformer.transformAsset(
@@ -331,14 +336,18 @@ Transformation failed, but I forgot to exit with a non-zero code.'''
         onRun: (List<String> args) {
           // Do nothing.
         },
-        stderr: 'Transformation failed, but I forgot to exit with a non-zero code.'
+        stderr: 'Transformation failed, but I forgot to exit with a non-zero code.',
+        environment: const <String, String>{
+          'FLUTTER_BUILD_MODE': 'debug',
+        },
       ),
     ]);
 
     final AssetTransformer transformer = AssetTransformer(
       processManager: processManager,
       fileSystem: fileSystem,
       dartBinaryPath: dartBinaryPath,
+      buildMode: BuildMode.debug,
     );
 
     final AssetTransformationFailure? failure = await transformer.transformAsset(