feat: migrate ios/bitcode.dart to null safety (flutter#92557)

Author: wanglikun7342

packages/flutter_tools/lib/src/ios/bitcode.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.
 
-// @dart = 2.8
-
 import '../artifacts.dart';
 import '../base/common.dart';
 import '../base/context.dart';
@@ -16,21 +14,23 @@ import '../macos/xcode.dart';
 const bool kBitcodeEnabledDefault = false;
 
 Future<void> validateBitcode(BuildMode buildMode, TargetPlatform targetPlatform, EnvironmentType environmentType) async {
-  final Artifacts localArtifacts = globals.artifacts;
-  final String flutterFrameworkPath = localArtifacts.getArtifactPath(
+  final Artifacts? localArtifacts = globals.artifacts;
+  final String? flutterFrameworkPath = localArtifacts?.getArtifactPath(
     Artifact.flutterFramework,
     mode: buildMode,
     platform: targetPlatform,
     environmentType: environmentType,
   );
-  final Xcode xcode = context.get<Xcode>();
+  final Xcode? xcode = context.get<Xcode>();
 
-  final RunResult clangResult = await xcode.clang(<String>['--version']);
-  final String clangVersion = clangResult.stdout.split('\n').first;
-  final String engineClangVersion = globals.plistParser.getValueFromFile(
-    globals.fs.path.join(flutterFrameworkPath, 'Info.plist'),
-    'ClangVersion',
-  );
+  final RunResult? clangResult = await xcode?.clang(<String>['--version']);
+  final String? clangVersion = clangResult?.stdout.split('\n').first;
+  final String? engineClangVersion = flutterFrameworkPath == null
+      ? null
+      : globals.plistParser.getValueFromFile(
+          globals.fs.path.join(flutterFrameworkPath, 'Info.plist'),
+          'ClangVersion',
+        );
   final Version engineClangSemVer = _parseVersionFromClang(engineClangVersion);
   final Version clangSemVer = _parseVersionFromClang(clangVersion);
   if (engineClangSemVer > clangSemVer) {
@@ -44,21 +44,21 @@ Future<void> validateBitcode(BuildMode buildMode, TargetPlatform targetPlatform,
   }
 }
 
-Version _parseVersionFromClang(String clangVersion) {
+Version _parseVersionFromClang(String? clangVersion) {
   final RegExp pattern = RegExp(r'Apple (LLVM|clang) version (\d+\.\d+\.\d+) ');
-  void _invalid() {
+  Never _invalid() {
     throwToolExit('Unable to parse Clang version from "$clangVersion". '
                   'Expected a string like "Apple (LLVM|clang) #.#.# (clang-####.#.##.#)".');
   }
 
   if (clangVersion == null || clangVersion.isEmpty) {
     _invalid();
   }
-  final RegExpMatch match = pattern.firstMatch(clangVersion);
+  final RegExpMatch? match = pattern.firstMatch(clangVersion);
   if (match == null || match.groupCount != 2) {
     _invalid();
   }
-  final Version version = Version.parse(match.group(2));
+  final Version? version = Version.parse(match.group(2));
   if (version == null) {
     _invalid();
   }