Ensure precache --web works on dev branch (#42289)

packages/flutter_tools/lib/src/cache.dart

@@ -16,21 +16,25 @@ import 'base/net.dart';
 import 'base/os.dart';
 import 'base/platform.dart';
 import 'base/process.dart';
+import 'features.dart';
 import 'globals.dart';
 
 /// A tag for a set of development artifacts that need to be cached.
 class DevelopmentArtifact {
 
-  const DevelopmentArtifact._(this.name, {this.unstable = false});
+  const DevelopmentArtifact._(this.name, {this.unstable = false, this.feature});
 
   /// The name of the artifact.
   ///
   /// This should match the flag name in precache.dart
   final String name;
 
-  /// Whether this artifact should be unavailable on stable branches.
+  /// Whether this artifact should be unavailable on master branch only.
   final bool unstable;
 
+  /// A feature to control the visibility of this artifact.
+  final Feature feature;
+
   /// Artifacts required for Android development.
   static const DevelopmentArtifact androidGenSnapshot = DevelopmentArtifact._('android_gen_snapshot');
   static const DevelopmentArtifact androidMaven = DevelopmentArtifact._('android_maven');
@@ -41,7 +45,7 @@ class DevelopmentArtifact {
   static const DevelopmentArtifact iOS = DevelopmentArtifact._('ios');
 
   /// Artifacts required for web development.
-  static const DevelopmentArtifact web = DevelopmentArtifact._('web', unstable: true);
+  static const DevelopmentArtifact web = DevelopmentArtifact._('web', feature: flutterWebFeature);
 
   /// Artifacts required for desktop macOS.
   static const DevelopmentArtifact macOS = DevelopmentArtifact._('macos', unstable: true);
@@ -75,6 +79,9 @@ class DevelopmentArtifact {
     universal,
     flutterRunner,
   ];
+
+  @override
+  String toString() => 'Artifact($name, $unstable)';
 }
 
 /// A wrapper around the `bin/cache/` directory.

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

@@ -5,6 +5,7 @@
 import 'dart:async';
 
 import '../cache.dart';
+import '../features.dart';
 import '../globals.dart';
 import '../runner/flutter_command.dart';
 import '../version.dart';
@@ -65,6 +66,9 @@ class PrecacheCommand extends FlutterCommand {
       if (!FlutterVersion.instance.isMaster && artifact.unstable) {
         continue;
       }
+      if (artifact.feature != null && !featureFlags.isEnabled(artifact.feature)) {
+        continue;
+      }
       if (argResults[artifact.name]) {
         requiredArtifacts.add(artifact);
       }

packages/flutter_tools/lib/src/features.dart

@@ -17,7 +17,7 @@ FeatureFlags get featureFlags => context.get<FeatureFlags>();
 /// The interface used to determine if a particular [Feature] is enabled.
 ///
 /// The rest of the tools code should use this class instead of looking up
-/// features directly. To faciliate rolls to google3 and other clients, all
+/// features directly. To facilitate rolls to google3 and other clients, all
 /// flags should be provided with a default implementation here. Clients that
 /// use this class should extent instead of implement, so that new flags are
 /// picked up automatically.
@@ -25,22 +25,24 @@ class FeatureFlags {
   const FeatureFlags();
 
   /// Whether flutter desktop for linux is enabled.
-  bool get isLinuxEnabled => _isEnabled(flutterLinuxDesktopFeature);
+  bool get isLinuxEnabled => isEnabled(flutterLinuxDesktopFeature);
 
   /// Whether flutter desktop for macOS is enabled.
-  bool get isMacOSEnabled => _isEnabled(flutterMacOSDesktopFeature);
+  bool get isMacOSEnabled => isEnabled(flutterMacOSDesktopFeature);
 
   /// Whether flutter web is enabled.
-  bool get isWebEnabled => _isEnabled(flutterWebFeature);
+  bool get isWebEnabled => isEnabled(flutterWebFeature);
 
   /// Whether flutter desktop for Windows is enabled.
-  bool get isWindowsEnabled => _isEnabled(flutterWindowsDesktopFeature);
+  bool get isWindowsEnabled => isEnabled(flutterWindowsDesktopFeature);
 
   /// Whether the new Android embedding is enabled.
-  bool get isNewAndroidEmbeddingEnabled => _isEnabled(flutterNewAndroidEmbeddingFeature);
+  bool get isNewAndroidEmbeddingEnabled => isEnabled(flutterNewAndroidEmbeddingFeature);
 
-  // Calculate whether a particular feature is enabled for the current channel.
-  static bool _isEnabled(Feature feature) {
+  /// Whether a particular feature is enabled for the current channel.
+  ///
+  /// Prefer using one of the specific getters above instead of this API.
+  bool isEnabled(Feature feature) {
     final String currentChannel = FlutterVersion.instance.channel;
     final FeatureChannelSetting featureSetting = feature.getSettingForChannel(currentChannel);
     if (!featureSetting.available) {

packages/flutter_tools/test/general.shard/cache_test.dart

@@ -209,7 +209,7 @@ void main() {
   });
 
   test('Unstable artifacts', () {
-    expect(DevelopmentArtifact.web.unstable, true);
+    expect(DevelopmentArtifact.web.unstable, false);
     expect(DevelopmentArtifact.linux.unstable, true);
     expect(DevelopmentArtifact.macOS.unstable, true);
     expect(DevelopmentArtifact.windows.unstable, true);

packages/flutter_tools/test/src/testbed.dart

@@ -712,6 +712,23 @@ class TestFeatureFlags implements FeatureFlags {
 
   @override
   final bool isNewAndroidEmbeddingEnabled;
+
+  @override
+  bool isEnabled(Feature feature) {
+    switch (feature) {
+      case flutterWebFeature:
+        return isWebEnabled;
+      case flutterLinuxDesktopFeature:
+        return isLinuxEnabled;
+      case flutterMacOSDesktopFeature:
+        return isMacOSEnabled;
+      case flutterWindowsDesktopFeature:
+        return isWindowsEnabled;
+      case flutterNewAndroidEmbeddingFeature:
+        return isNewAndroidEmbeddingEnabled;
+    }
+    return false;
+  }
 }
 
 class ThrowingPub implements Pub {