[ Tool ] Use a separate output directory when the native hooks run the build system (flutter#178840)

FlutterBuildSystem.trackSharedBuildDirectory stores a hash of the most
recently run build configuration in the output directory defined in the
environment.

If the build executed by FlutterHookRunnerNative uses the same output
directory as other builds, then trackSharedBuildDirectory may think that
the hook build's output list replaces the outputs of those previous
builds. trackSharedBuildDirectory will then incorrectly delete files in
the previous output list because they are not part of the hook build's
outputs.

See flutter#178529

Author: jason-simmons

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

@@ -455,6 +455,28 @@ class Environment {
     required this.generateDartPluginRegistry,
   });
 
+  Environment copyWith({Directory? outputDir}) {
+    return Environment._(
+      outputDir: outputDir ?? this.outputDir,
+      projectDir: projectDir,
+      packageConfigPath: packageConfigPath,
+      buildDir: buildDir,
+      rootBuildDir: rootBuildDir,
+      cacheDir: cacheDir,
+      defines: defines,
+      flutterRootDir: flutterRootDir,
+      fileSystem: fileSystem,
+      logger: logger,
+      artifacts: artifacts,
+      processManager: processManager,
+      platform: platform,
+      analytics: analytics,
+      engineVersion: engineVersion,
+      inputs: inputs,
+      generateDartPluginRegistry: generateDartPluginRegistry,
+    );
+  }
+
   /// The [Source] value which is substituted with the path to [projectDir].
   static const kProjectDirectory = '{PROJECT_DIR}';
 

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

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'package:meta/meta.dart';
+
 import '../../asset.dart';
 import '../../base/logger.dart' show Logger;
 import '../../build_info.dart';
@@ -14,22 +16,35 @@ import 'native_assets.dart' show DartBuild;
 class FlutterHookRunnerNative implements FlutterHookRunner {
   FlutterHookResult? _flutterHookResult;
 
+  @visibleForTesting
+  static const kHooksOutputDirectory = 'native_hooks';
+
   @override
   Future<FlutterHookResult> runHooks({
     required TargetPlatform targetPlatform,
     required Environment environment,
     Logger? logger,
   }) async {
     logger?.printTrace('runHooks() with ${environment.defines} and $targetPlatform');
-    if (_flutterHookResult != null && !_flutterHookResult!.hasAnyModifiedFiles(globals.fs)) {
+    if (_flutterHookResult != null &&
+        !_flutterHookResult!.hasAnyModifiedFiles(environment.fileSystem)) {
       logger?.printTrace('runHooks() - up-to-date already');
       return _flutterHookResult!;
     }
     logger?.printTrace('runHooks() - will perform dart build');
 
+    // Use a clone of the environment with a different output directory
+    // to avoid conflicts with the primary build's outputs.
+    final String outputDirPath = environment.fileSystem.path.join(
+      environment.outputDir.path,
+      kHooksOutputDirectory,
+    );
+    final Environment hooksEnvironment = environment.copyWith(
+      outputDir: environment.fileSystem.directory(outputDirPath),
+    );
     final BuildResult lastBuild = await globals.buildSystem.build(
       DartBuild(specifiedTargetPlatform: targetPlatform),
-      environment,
+      hooksEnvironment,
     );
     if (!lastBuild.success) {
       for (final ExceptionMeasurement exceptionMeasurement in lastBuild.exceptions.values) {

packages/flutter_tools/test/general.shard/build_system/targets/hook_runner_native_test.dart

@@ -0,0 +1,55 @@
+// Copyright 2014 The Flutter 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 'package:file/memory.dart';
+import 'package:flutter_tools/src/artifacts.dart';
+import 'package:flutter_tools/src/base/file_system.dart';
+import 'package:flutter_tools/src/base/logger.dart';
+import 'package:flutter_tools/src/base/platform.dart';
+import 'package:flutter_tools/src/build_info.dart';
+import 'package:flutter_tools/src/build_system/build_system.dart';
+import 'package:flutter_tools/src/build_system/targets/hook_runner_native.dart';
+
+import '../../../src/common.dart';
+import '../../../src/context.dart';
+import '../../../src/test_build_system.dart';
+
+void main() {
+  late FileSystem fs;
+
+  setUp(() {
+    fs = MemoryFileSystem.test();
+  });
+
+  testUsingContext(
+    'FlutterHookRunnerNative uses a separate output directory',
+    () async {
+      final hookRunner = FlutterHookRunnerNative();
+      final environment = Environment.test(
+        fs.currentDirectory,
+        processManager: FakeProcessManager.any(),
+        artifacts: Artifacts.test(),
+        fileSystem: fs,
+        logger: BufferLogger.test(),
+        platform: FakePlatform(),
+        defines: {},
+      );
+
+      await hookRunner.runHooks(
+        targetPlatform: TargetPlatform.linux_x64,
+        environment: environment,
+        logger: environment.logger,
+      );
+    },
+    overrides: <Type, Generator>{
+      BuildSystem: () =>
+          TestBuildSystem.all(BuildResult(success: true), (Target target, Environment environment) {
+            expect(
+              fs.path.basename(environment.outputDir.path),
+              FlutterHookRunnerNative.kHooksOutputDirectory,
+            );
+          }),
+    },
+  );
+}