Migrate flutter_project_metadata to null safety (#78944)

packages/flutter_tools/lib/src/dart/package_map.dart

@@ -2,11 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-// @dart = 2.8
-
 import 'dart:typed_data';
 
-import 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
 import '../base/common.dart';
@@ -19,14 +16,14 @@ import '../base/logger.dart';
 /// If [throwOnError] is false, in the event of an error an empty package
 /// config is returned.
 Future<PackageConfig> loadPackageConfigWithLogging(File file, {
-  @required Logger logger,
+  required Logger logger,
   bool throwOnError = true,
 }) async {
   final FileSystem fileSystem = file.fileSystem;
   bool didError = false;
   final PackageConfig result = await loadPackageConfigUri(
     file.absolute.uri,
-    loader: (Uri uri) {
+    loader: (Uri uri) async {
       final File configFile = fileSystem.file(uri);
       if (!configFile.existsSync()) {
         return null;
@@ -50,7 +47,7 @@ Future<PackageConfig> loadPackageConfigWithLogging(File file, {
     }
   );
   if (didError) {
-    throwToolExit(null);
+    throwToolExit('');
   }
   return result;
 }

packages/flutter_tools/lib/src/flutter_project_metadata.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 'package:yaml/yaml.dart';
 
 import 'base/file_system.dart';
@@ -29,8 +27,8 @@ String flutterProjectTypeToString(FlutterProjectType type) {
   return getEnumName(type);
 }
 
-FlutterProjectType stringToProjectType(String value) {
-  FlutterProjectType result;
+FlutterProjectType? stringToProjectType(String value) {
+  FlutterProjectType? result;
   for (final FlutterProjectType type in FlutterProjectType.values) {
     if (value == flutterProjectTypeToString(type)) {
       result = type;
@@ -51,10 +49,10 @@ class FlutterProjectMetadata {
   final File _metadataFile;
   final Logger _logger;
 
-  String get versionChannel => _versionValue('channel');
-  String get versionRevision => _versionValue('revision');
+  String? get versionChannel => _versionValue('channel');
+  String? get versionRevision => _versionValue('revision');
 
-  FlutterProjectType get projectType {
+  FlutterProjectType? get projectType {
     final dynamic projectTypeYaml = _metadataValue('project_type');
     if (projectTypeYaml is String) {
       return stringToProjectType(projectTypeYaml);
@@ -64,8 +62,8 @@ class FlutterProjectMetadata {
     }
   }
 
-  YamlMap _versionYaml;
-  String _versionValue(String key) {
+  YamlMap? _versionYaml;
+  String? _versionValue(String key) {
     if (_versionYaml == null) {
       final dynamic versionYaml = _metadataValue('version');
       if (versionYaml is YamlMap) {
@@ -75,13 +73,13 @@ class FlutterProjectMetadata {
         return null;
       }
     }
-    if (_versionYaml != null && _versionYaml.containsKey(key) && _versionYaml[key] is String) {
-      return _versionYaml[key] as String;
+    if (_versionYaml != null && _versionYaml!.containsKey(key) && _versionYaml![key] is String) {
+      return _versionYaml![key] as String;
     }
     return null;
   }
 
-  YamlMap _metadataYaml;
+  YamlMap? _metadataYaml;
   dynamic _metadataValue(String key) {
     if (_metadataYaml == null) {
       if (!_metadataFile.existsSync()) {
@@ -101,6 +99,6 @@ class FlutterProjectMetadata {
       }
     }
 
-    return _metadataYaml[key];
+    return _metadataYaml![key];
   }
 }

packages/flutter_tools/lib/src/license_collector.dart

@@ -2,9 +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 'package:meta/meta.dart';
 import 'package:package_config/package_config.dart';
 
 import 'base/file_system.dart';
@@ -28,7 +25,7 @@ import 'base/file_system.dart';
 /// sources, and might need to include a license for each one.
 class LicenseCollector {
   LicenseCollector({
-    @required FileSystem fileSystem
+    required FileSystem fileSystem
   }) : _fileSystem = fileSystem;
 
   final FileSystem _fileSystem;
@@ -67,8 +64,8 @@ class LicenseCollector {
         .readAsStringSync()
         .split(licenseSeparator);
       for (final String rawLicense in rawLicenses) {
-        List<String> packageNames;
-        String licenseText;
+        List<String> packageNames = <String>[];
+        String? licenseText;
         if (rawLicenses.length > 1) {
           final int split = rawLicense.indexOf('\n\n');
           if (split >= 0) {
@@ -87,7 +84,7 @@ class LicenseCollector {
 
     final List<String> combinedLicensesList = packageLicenses.keys
       .map<String>((String license) {
-        final List<String> packageNames = packageLicenses[license].toList()
+        final List<String> packageNames = packageLicenses[license]!.toList()
           ..sort();
         return packageNames.join('\n') + '\n\n' + license;
       }).toList();
@@ -97,7 +94,7 @@ class LicenseCollector {
     final List<String> additionalLicenseText = <String>[];
     final List<String> errorMessages = <String>[];
     for (final String package in additionalLicenses.keys) {
-      for (final File license in additionalLicenses[package]) {
+      for (final File license in additionalLicenses[package]!) {
         if (!license.existsSync()) {
           errorMessages.add(
             'package $package specified an additional license at ${license.path}, but this file '
@@ -146,9 +143,9 @@ class LicenseCollector {
 /// The result of processing licenses with a [LicenseCollector].
 class LicenseResult {
   const LicenseResult({
-    @required this.combinedLicenses,
-    @required this.dependencies,
-    @required this.errorMessages,
+    required this.combinedLicenses,
+    required this.dependencies,
+    required this.errorMessages,
   });
 
   /// The raw text of the consumed licenses.

packages/flutter_tools/lib/src/web/memory_fs.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 'dart:typed_data';
 
 import '../base/file_system.dart';
@@ -20,8 +18,8 @@ class WebMemoryFS {
   final Map<String, Uint8List> files = <String, Uint8List>{};
   final Map<String, Uint8List> sourcemaps = <String, Uint8List>{};
 
-  String get mergedMetadata => _mergedMetadata;
-  String _mergedMetadata;
+  String? get mergedMetadata => _mergedMetadata;
+  String? _mergedMetadata;
 
   /// Update the filesystem with the provided source and manifest files.
   ///
@@ -37,13 +35,13 @@ class WebMemoryFS {
     final Uint8List sourcemapBytes = sourcemapFile.readAsBytesSync();
     final Uint8List metadataBytes = metadataFile.readAsBytesSync();
     final Map<String, dynamic> manifest =
-        castStringKeyedMap(json.decode(manifestFile.readAsStringSync()));
+        castStringKeyedMap(json.decode(manifestFile.readAsStringSync()))!;
     for (final String filePath in manifest.keys) {
       if (filePath == null) {
         continue;
       }
       final Map<String, dynamic> offsets =
-          castStringKeyedMap(manifest[filePath]);
+          castStringKeyedMap(manifest[filePath])!;
       final List<int> codeOffsets =
           (offsets['code'] as List<dynamic>).cast<int>();
       final List<int> sourcemapOffsets =