Warn when building on master channel (#25007)

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

@@ -4,7 +4,13 @@
 
 import 'dart:async';
 
+import 'package:meta/meta.dart';
+
+import '../base/terminal.dart';
+import '../globals.dart';
 import '../runner/flutter_command.dart';
+import '../version.dart';
+
 import 'build_aot.dart';
 import 'build_apk.dart';
 import 'build_appbundle.dart';
@@ -36,4 +42,16 @@ abstract class BuildSubCommand extends FlutterCommand {
   BuildSubCommand() {
     requiresPubspecYaml();
   }
+
+  @override
+  @mustCallSuper
+  Future<FlutterCommandResult> runCommand() async {
+    // Warn if building a release app on Master channel
+    final String channel = FlutterVersion.instance.channel;
+    if (channel == 'master') {
+      printStatus('🐉', newline: false, color: TerminalColor.red);
+      printStatus(' This is the $channel channel. Shipping apps from this channel is not recommended as it has not been as heavily tested as the stable channel. To build using the stable channel, consider using:\n    flutter channel stable');
+    }
+    return null;
+  }
 }

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

@@ -57,6 +57,8 @@ class BuildAotCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+
     final String targetPlatform = argResults['target-platform'];
     final TargetPlatform platform = getTargetPlatformForName(targetPlatform);
     if (platform == null)

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

@@ -42,6 +42,8 @@ class BuildApkCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+
     await buildApk(
       project: await FlutterProject.current(),
       target: targetFile,

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

@@ -40,6 +40,8 @@ class BuildAppBundleCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+
     await buildAppBundle(
       project: await FlutterProject.current(),
       target: targetFile,

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

@@ -65,6 +65,8 @@ class BuildBundleCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+
     final String targetPlatform = argResults['target-platform'];
     final TargetPlatform platform = getTargetPlatformForName(targetPlatform);
     if (platform == null)

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

@@ -20,6 +20,8 @@ class BuildFlxCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+
     printError("'build flx' is no longer supported. Instead, use 'build "
                "bundle' to build and assemble the application code and resources "
                'for your app.');

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

@@ -50,6 +50,8 @@ class BuildIOSCommand extends BuildSubCommand {
 
   @override
   Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+
     final bool forSimulator = argResults['simulator'];
     defaultBuildMode = forSimulator ? BuildMode.debug : BuildMode.release;
 

packages/flutter_tools/test/commands/build_test.dart

+// Copyright 2019 The Chromium Authors. All rights reserved.
+// 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:flutter_tools/src/base/context.dart';
+import 'package:flutter_tools/src/commands/build.dart';
+import 'package:flutter_tools/src/cache.dart';
+import 'package:flutter_tools/src/version.dart';
+import 'package:flutter_tools/src/runner/flutter_command.dart';
+
+import '../src/common.dart';
+import '../src/context.dart';
+
+
+void main() {
+  group('Master channel warning', () {
+    testUsingContext('warns on master', () async {
+      final MockBuildCommand buildCommand = MockBuildCommand();
+      try {
+        await createTestCommandRunner(buildCommand).run(<String>['build', 'test']);
+      } finally {}
+      Cache.releaseLockEarly();
+      expect(testLogger.statusText, contains('🐉 This is the master channel. Shipping apps from this channel is not recommended as it has not'));
+    }, overrides: <Type, Generator>{
+      FlutterVersion: () => MockVersion('master'),
+    });
+
+    testUsingContext('no warning on stable', () async {
+      final MockBuildCommand buildCommand = MockBuildCommand();
+      try {
+        await createTestCommandRunner(buildCommand).run(<String>['build', 'test']);
+      } finally {}
+      Cache.releaseLockEarly();
+      expect(testLogger.statusText, '');
+    }, overrides: <Type, Generator>{
+      FlutterVersion: () => MockVersion('stable'),
+    });
+
+    testUsingContext('no warning on dev', () async {
+      final MockBuildCommand buildCommand = MockBuildCommand();
+      try {
+        await createTestCommandRunner(buildCommand).run(<String>['build', 'test']);
+      } finally {}
+      Cache.releaseLockEarly();
+      expect(testLogger.statusText, '');
+    }, overrides: <Type, Generator>{
+      FlutterVersion: () => MockVersion('dev'),
+    });
+
+    testUsingContext('no warning on beta', () async {
+      final MockBuildCommand buildCommand = MockBuildCommand();
+      try {
+        await createTestCommandRunner(buildCommand).run(<String>['build', 'test']);
+      } finally {}
+      print(testLogger.statusText);
+      Cache.releaseLockEarly();
+      expect(testLogger.statusText, '');
+    }, overrides: <Type, Generator>{
+      FlutterVersion: () => MockVersion('beta'),
+    });
+  });
+}
+
+class MockVersion extends FlutterVersion {
+  MockVersion(String channel) : _fakeChannel = channel;
+  String _fakeChannel;
+
+  @override
+  String get channel => _fakeChannel;
+}
+
+class MockBuildCommand extends BuildCommand {
+  MockBuildCommand() {
+    addSubcommand(MockBuildTestCommand());
+  }
+}
+
+// Avoids command validation
+class MockBuildTestCommand extends BuildSubCommand {
+  @override
+  final String name = 'test';
+
+  @override
+  final String description = 'This is a test class only.';
+
+  @override
+  Future<FlutterCommandResult> runCommand() async {
+    await super.runCommand();
+    return null;
+  }
+}