Expose build-dir config option (#36773)

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

@@ -6,6 +6,8 @@ import 'dart:async';
 
 import '../android/android_sdk.dart';
 import '../android/android_studio.dart';
+import '../base/common.dart';
+import '../base/file_system.dart';
 import '../convert.dart';
 import '../features.dart';
 import '../globals.dart';
@@ -24,6 +26,8 @@ class ConfigCommand extends FlutterCommand {
     argParser.addOption('gradle-dir', help: 'The gradle install directory.');
     argParser.addOption('android-sdk', help: 'The Android SDK directory.');
     argParser.addOption('android-studio-dir', help: 'The Android Studio install directory.');
+    argParser.addOption('build-dir', help: 'The relative path to override a projects build directory',
+        valueHelp: 'out/');
     argParser.addFlag('machine',
       negatable: false,
       hide: !verboseHelp,
@@ -128,6 +132,14 @@ class ConfigCommand extends FlutterCommand {
     if (argResults.wasParsed('clear-ios-signing-cert'))
       _updateConfig('ios-signing-cert', '');
 
+    if (argResults.wasParsed('build-dir')) {
+      final String buildDir = argResults['build-dir'];
+      if (fs.path.isAbsolute(buildDir)) {
+        throwToolExit('build-dir should be a relative path');
+      }
+      _updateConfig('build-dir', buildDir);
+    }
+
     for (Feature feature in allFeatures) {
       if (feature.configSetting == null) {
         continue;

packages/flutter_tools/test/general.shard/commands/config_test.dart

@@ -7,9 +7,11 @@ import 'dart:convert';
 import 'package:args/command_runner.dart';
 import 'package:flutter_tools/src/android/android_sdk.dart';
 import 'package:flutter_tools/src/android/android_studio.dart';
+import 'package:flutter_tools/src/base/common.dart';
 import 'package:flutter_tools/src/base/config.dart';
 import 'package:flutter_tools/src/base/context.dart';
 import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/build_info.dart';
 import 'package:flutter_tools/src/cache.dart';
 import 'package:flutter_tools/src/commands/config.dart';
 import 'package:flutter_tools/src/version.dart';
@@ -53,6 +55,28 @@ void main() {
       AndroidSdk: () => mockAndroidSdk,
     });
 
+    testUsingContext('Can set build-dir', () async {
+      final ConfigCommand configCommand = ConfigCommand();
+      final CommandRunner<void> commandRunner = createTestCommandRunner(configCommand);
+
+      await commandRunner.run(<String>[
+        'config',
+        '--build-dir=foo'
+      ]);
+
+      expect(getBuildDirectory(), 'foo');
+    });
+
+    testUsingContext('throws error on absolute path to build-dir', () async {
+      final ConfigCommand configCommand = ConfigCommand();
+      final CommandRunner<void> commandRunner = createTestCommandRunner(configCommand);
+
+      expect(() => commandRunner.run(<String>[
+        'config',
+        '--build-dir=/foo'
+      ]), throwsA(isInstanceOf<ToolExit>()));
+    });
+
     testUsingContext('allows setting and removing feature flags', () async {
       final ConfigCommand configCommand = ConfigCommand();
       final CommandRunner<void> commandRunner = createTestCommandRunner(configCommand);