[flutter_tools] fix cast error when dart-defines-json file includes null (#128909)

Fixes https://github.com/flutter/flutter/issues/128787

packages/flutter_tools/lib/src/build_info.dart

@@ -38,7 +38,7 @@ class BuildInfo {
     this.webRenderer = WebRendererMode.auto,
     required this.treeShakeIcons,
     this.performanceMeasurementFile,
-    this.dartDefineConfigJsonMap,
+    this.dartDefineConfigJsonMap = const <String, Object?>{},
     this.packagesPath = '.dart_tool/package_config.json', // TODO(zanderso): make this required and remove the default.
     this.nullSafetyMode = NullSafetyMode.sound,
     this.codeSizeDirectory,
@@ -144,7 +144,7 @@ class BuildInfo {
   ///
   /// An additional field `dartDefineConfigJsonMap` is provided to represent the native JSON value of the configuration file
   ///
-  final Map<String, Object>? dartDefineConfigJsonMap;
+  final Map<String, Object?> dartDefineConfigJsonMap;
 
   /// If provided, an output directory where one or more v8-style heap snapshots
   /// will be written for code size profiling.
@@ -267,7 +267,7 @@ class BuildInfo {
   /// Fields that are `null` are excluded from this configuration.
   Map<String, String> toEnvironmentConfig() {
     final Map<String, String> map = <String, String>{};
-    dartDefineConfigJsonMap?.forEach((String key, Object value) {
+    dartDefineConfigJsonMap.forEach((String key, Object? value) {
       map[key] = '$value';
     });
     final Map<String, String> environmentMap = <String, String>{
@@ -327,9 +327,8 @@ class BuildInfo {
       for (final String projectArg in androidProjectArgs)
         '-P$projectArg',
     ];
-    if (dartDefineConfigJsonMap != null) {
     final Iterable<String> gradleConfKeys = result.map((final String gradleConf) => gradleConf.split('=')[0].substring(2));
-      dartDefineConfigJsonMap!.forEach((String key, Object value) {
+    dartDefineConfigJsonMap.forEach((String key, Object? value) {
       if (gradleConfKeys.contains(key)) {
         globals.printWarning(
             'The key: [$key] already exists, you cannot use gradle variables that have been used by the system!');
@@ -337,7 +336,6 @@ class BuildInfo {
         result.add('-P$key=$value');
       }
     });
-    }
     return result;
   }
 }

packages/flutter_tools/lib/src/bundle_builder.dart

@@ -21,7 +21,6 @@ import 'devfs.dart';
 import 'globals.dart' as globals;
 import 'project.dart';
 
-
 /// Provides a `build` method that builds the bundle.
 class BundleBuilder {
   /// Builds the bundle for the given target platform.

packages/flutter_tools/lib/src/commands/assemble.dart

@@ -258,7 +258,7 @@ class AssembleCommand extends FlutterCommand {
       results[kExtraGenSnapshotOptions] = (argumentResults[FlutterOptions.kExtraGenSnapshotOptions] as List<String>).join(',');
     }
 
-    final Map<String, Object>? defineConfigJsonMap = extractDartDefineConfigJsonMap();
+    final Map<String, Object?> defineConfigJsonMap = extractDartDefineConfigJsonMap();
     final List<String> dartDefines = extractDartDefines(defineConfigJsonMap: defineConfigJsonMap);
     if (dartDefines.isNotEmpty){
       results[kDartDefines] = dartDefines.join(',');

packages/flutter_tools/lib/src/run_hot.dart

@@ -2,8 +2,6 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-
-
 import 'dart:async';
 
 import 'package:meta/meta.dart';

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -1190,7 +1190,7 @@ abstract class FlutterCommand extends Command<void> {
       ? stringArg(FlutterOptions.kPerformanceMeasurementFile)
       : null;
 
-    final Map<String, Object>? defineConfigJsonMap = extractDartDefineConfigJsonMap();
+    final Map<String, Object?> defineConfigJsonMap = extractDartDefineConfigJsonMap();
     List<String> dartDefines = extractDartDefines(defineConfigJsonMap: defineConfigJsonMap);
 
     WebRendererMode webRenderer = WebRendererMode.auto;
@@ -1323,25 +1323,22 @@ abstract class FlutterCommand extends Command<void> {
     }
   }
 
-  List<String> extractDartDefines({Map<String, Object>? defineConfigJsonMap}) {
+  List<String> extractDartDefines({required Map<String, Object?> defineConfigJsonMap}) {
     final List<String> dartDefines = <String>[];
 
     if (argParser.options.containsKey(FlutterOptions.kDartDefinesOption)) {
       dartDefines.addAll(stringsArg(FlutterOptions.kDartDefinesOption));
     }
 
-    if (defineConfigJsonMap == null) {
-      return dartDefines;
-    }
-    defineConfigJsonMap.forEach((String key, Object value) {
+    defineConfigJsonMap.forEach((String key, Object? value) {
       dartDefines.add('$key=$value');
     });
 
     return dartDefines;
   }
 
-  Map<String, Object>? extractDartDefineConfigJsonMap() {
-    final Map<String, Object> dartDefineConfigJsonMap = <String, Object>{};
+  Map<String, Object?> extractDartDefineConfigJsonMap() {
+    final Map<String, Object?> dartDefineConfigJsonMap = <String, Object?>{};
 
     if (argParser.options.containsKey(FlutterOptions.kDartDefineFromFileOption)) {
       final List<String> configJsonPaths = stringsArg(
@@ -1359,8 +1356,8 @@ abstract class FlutterCommand extends Command<void> {
         try {
           // Fix json convert Object value :type '_InternalLinkedHashMap<String, dynamic>' is not a subtype of type 'Map<String, Object>' in type cast
           (json.decode(configJsonRaw) as Map<String, dynamic>)
-              .forEach((String key, dynamic value) {
-            dartDefineConfigJsonMap[key] = value as Object;
+              .forEach((String key, Object? value) {
+            dartDefineConfigJsonMap[key] = value;
           });
         } on FormatException catch (err) {
           throwToolExit('Json config define file "--${FlutterOptions

packages/flutter_tools/test/commands.shard/permeable/build_bundle_test.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:typed_data';
+
 import 'package:args/command_runner.dart';
 import 'package:file/memory.dart';
 import 'package:flutter_tools/src/base/file_system.dart';
@@ -12,6 +14,7 @@ import 'package:flutter_tools/src/bundle.dart';
 import 'package:flutter_tools/src/bundle_builder.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/build_bundle.dart';
+import 'package:flutter_tools/src/convert.dart';
 import 'package:flutter_tools/src/features.dart';
 import 'package:flutter_tools/src/globals.dart' as globals;
 import 'package:flutter_tools/src/project.dart';
@@ -504,7 +507,7 @@ void main() {
     ProcessManager: () => FakeProcessManager.any(),
   });
 
-  testUsingContext('test --dart-define-from-file option', () async {
+  testUsingContext('--dart-define-from-file successfully forwards values to build env', () async {
     globals.fs.file(globals.fs.path.join('lib', 'main.dart')).createSync(recursive: true);
     globals.fs.file('pubspec.yaml').createSync();
     globals.fs.file('.packages').createSync();
@@ -514,7 +517,8 @@ void main() {
           "kInt": 1,
           "kDouble": 1.1,
           "name": "denghaizhu",
-          "title": "this is title from config json file"
+          "title": "this is title from config json file",
+          "nullValue": null
         }
       '''
     );
@@ -537,7 +541,17 @@ void main() {
     ]);
   }, overrides: <Type, Generator>{
     BuildSystem: () => TestBuildSystem.all(BuildResult(success: true), (Target target, Environment environment) {
-      expect(environment.defines[kDartDefines], 'a0ludD0x,a0RvdWJsZT0xLjE=,bmFtZT1kZW5naGFpemh1,dGl0bGU9dGhpcyBpcyB0aXRsZSBmcm9tIGNvbmZpZyBqc29uIGZpbGU=,Ym9keT10aGlzIGlzIGJvZHkgZnJvbSBjb25maWcganNvbiBmaWxl');
+      expect(
+        _decodeDartDefines(environment),
+        containsAllInOrder(const <String>[
+          'kInt=1',
+          'kDouble=1.1',
+          'name=denghaizhu',
+          'title=this is title from config json file',
+          'nullValue=null',
+          'body=this is body from config json file',
+        ]),
+      );
     }),
     FileSystem: fsFactory,
     ProcessManager: () => FakeProcessManager.any(),
@@ -576,7 +590,10 @@ void main() {
     ]);
   }, overrides: <Type, Generator>{
     BuildSystem: () => TestBuildSystem.all(BuildResult(success: true), (Target target, Environment environment) {
-      expect(environment.defines[kDartDefines], 'a0ludD0y,a0RvdWJsZT0xLjE=,bmFtZT1kZW5naGFpemh1,dGl0bGU9dGhpcyBpcyB0aXRsZSBmcm9tIGNvbmZpZyBqc29uIGZpbGU=');
+      expect(
+        _decodeDartDefines(environment),
+        containsAllInOrder(<String>['kInt=2', 'kDouble=1.1', 'name=denghaizhu', 'title=this is title from config json file']),
+      );
     }),
     FileSystem: fsFactory,
     ProcessManager: () => FakeProcessManager.any(),
@@ -632,6 +649,15 @@ void main() {
   });
 }
 
+Iterable<String> _decodeDartDefines(Environment environment) {
+  final String encodedDefines = environment.defines[kDartDefines]!;
+  const Utf8Decoder byteDecoder = Utf8Decoder();
+  return encodedDefines
+      .split(',')
+      .map<Uint8List>(base64.decode)
+      .map<String>(byteDecoder.convert);
+}
+
 class FakeBundleBuilder extends Fake implements BundleBuilder {
   @override
   Future<void> build({