Stop writing package_config_subset (flutter#169125)

Fixes flutter#168764 

As of dart-lang/pub#4549 pub no longer rewrites
the package_config.json file when nothing changes. And it doesn't write
a timestamp in it.

Author: sigurdm

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

@@ -125,11 +125,6 @@ class ReleaseCopyFlutterBundle extends CopyFlutterBundle {
 }
 
 /// Generate a snapshot of the dart code used in the program.
-///
-/// This target depends on the `.dart_tool/package_config.json` file
-/// even though it is not listed as an input. Pub inserts a timestamp into
-/// the file which causes unnecessary rebuilds, so instead a subset of the contents
-/// are used an input instead.
 class KernelSnapshot extends Target {
   const KernelSnapshot();
 
@@ -138,7 +133,7 @@ class KernelSnapshot extends Target {
 
   @override
   List<Source> get inputs => const <Source>[
-    Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config_subset'),
+    Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config.json'),
     Source.pattern(
       '{FLUTTER_ROOT}/packages/flutter_tools/lib/src/build_system/targets/common.dart',
     ),

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

@@ -68,7 +68,7 @@ class DartPluginRegistrantTarget extends Target {
 
   @override
   List<Source> get inputs => <Source>[
-    const Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config_subset'),
+    const Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config.json'),
   ];
 
   @override

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

@@ -99,7 +99,7 @@ abstract class DartBuild extends Target {
       '{FLUTTER_ROOT}/packages/flutter_tools/lib/src/build_system/targets/native_assets.dart',
     ),
     // If different packages are resolved, different native assets might need to be built.
-    Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config_subset'),
+    Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config.json'),
     // TODO(mosuem): Should consume resources.json. https://github.com/flutter/flutter/issues/146263
   ];
 
@@ -187,7 +187,7 @@ class InstallCodeAssets extends Target {
       '{FLUTTER_ROOT}/packages/flutter_tools/lib/src/build_system/targets/native_assets.dart',
     ),
     // If different packages are resolved, different native assets might need to be built.
-    Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config_subset'),
+    Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config.json'),
   ];
 
   @override

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

@@ -132,7 +132,7 @@ abstract class Dart2WebTarget extends Target {
     const Source.hostArtifact(HostArtifact.flutterWebSdk),
     const Source.artifact(Artifact.engineDartBinary),
     const Source.pattern('{BUILD_DIR}/main.dart'),
-    const Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config_subset'),
+    const Source.pattern('{WORKSPACE_DIR}/.dart_tool/package_config.json'),
   ];
 
   @override

packages/flutter_tools/lib/src/dart/pub.dart

@@ -8,7 +8,6 @@ library;
 import 'dart:async';
 
 import 'package:meta/meta.dart';
-import 'package:package_config/package_config.dart';
 import 'package:process/process.dart';
 import '../base/bot_detector.dart';
 import '../base/common.dart';
@@ -663,9 +662,6 @@ class _DefaultPub implements Pub {
   /// Updates the .dart_tool/version file to be equal to current Flutter
   /// version.
   ///
-  /// Calls [_updatePackageConfig] for [project] and [FlutterProject.example]
-  /// (if it exists).
-  ///
   /// This should be called after pub invocations that are expected to update
   /// the packageConfig.
   Future<void> _updateVersionAndPackageConfig(FlutterProject project) async {
@@ -683,44 +679,13 @@ class _DefaultPub implements Pub {
     );
     lastVersion.writeAsStringSync(currentVersion.readAsStringSync());
 
-    await _updatePackageConfig(project, packageConfig);
     if (project.hasExampleApp && project.example.pubspecFile.existsSync()) {
       final File? examplePackageConfig = findPackageConfigFile(project.example.directory);
       if (examplePackageConfig == null) {
         throwToolExit(
           '${project.directory}: pub did not create example/.dart_tools/package_config.json file.',
         );
       }
-      await _updatePackageConfig(project.example, examplePackageConfig);
     }
   }
-
-  /// Update the package configuration file in [project].
-  ///
-  /// Creates a corresponding `package_config_subset` file that is used by the
-  /// build system to avoid rebuilds caused by an updated pub timestamp.
-  Future<void> _updatePackageConfig(FlutterProject project, File packageConfigFile) async {
-    final PackageConfig packageConfig = await loadPackageConfigWithLogging(
-      packageConfigFile,
-      logger: _logger,
-    );
-
-    packageConfigFile.parent
-        .childFile('package_config_subset')
-        .writeAsStringSync(_computePackageConfigSubset(packageConfig, _fileSystem));
-  }
-
-  // Subset the package config file to only the parts that are relevant for
-  // rerunning the dart compiler.
-  String _computePackageConfigSubset(PackageConfig packageConfig, FileSystem fileSystem) {
-    final StringBuffer buffer = StringBuffer();
-    for (final Package package in packageConfig.packages) {
-      buffer.writeln(package.name);
-      buffer.writeln(package.languageVersion);
-      buffer.writeln(package.root);
-      buffer.writeln(package.packageUriRoot);
-    }
-    buffer.writeln(packageConfig.version);
-    return buffer.toString();
-  }
 }