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// Copyright 2014 The Flutter Authors. All rights reserved.
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// 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:async/async.dart';
import 'package:convert/convert.dart';
import 'package:crypto/crypto.dart';
import 'package:meta/meta.dart';
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import 'package:platform/platform.dart';
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import 'package:pool/pool.dart';
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import 'package:process/process.dart';
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import '../artifacts.dart';
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import '../base/file_system.dart';
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import '../base/logger.dart';
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import '../base/utils.dart';
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import '../cache.dart';
import '../convert.dart';
import 'exceptions.dart';
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import 'file_store.dart';
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import 'source.dart';

export 'source.dart';

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/// A reasonable amount of files to open at the same time.
///
/// This number is somewhat arbitrary - it is difficult to detect whether
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/// or not we'll run out of file descriptors when using async dart:io
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/// APIs.
const int kMaxOpenFiles = 64;

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/// Configuration for the build system itself.
class BuildSystemConfig {
  /// Create a new [BuildSystemConfig].
  const BuildSystemConfig({this.resourcePoolSize});

  /// The maximum number of concurrent tasks the build system will run.
  ///
  /// If not provided, defaults to [platform.numberOfProcessors].
  final int resourcePoolSize;
}

/// A Target describes a single step during a flutter build.
///
/// The target inputs are required to be files discoverable via a combination
/// of at least one of the environment values and zero or more local values.
///
/// To determine if the action for a target needs to be executed, the
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/// [BuildSystem] computes a key of the file contents for both inputs and
/// outputs. This is tracked separately in the [FileStore]. The key may
/// be either an md5 hash of the file contents or a timestamp.
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///
/// A Target has both implicit and explicit inputs and outputs. Only the
/// later are safe to evaluate before invoking the [buildAction]. For example,
/// a wildcard output pattern requires the outputs to exist before it can
/// glob files correctly.
///
/// - All listed inputs are considered explicit inputs.
/// - Outputs which are provided as [Source.pattern].
///   without wildcards are considered explicit.
/// - The remaining outputs are considered implicit.
///
/// For each target, executing its action creates a corresponding stamp file
/// which records both the input and output files. This file is read by
/// subsequent builds to determine which file hashes need to be checked. If the
/// stamp file is missing, the target's action is always rerun.
///
///  file: `example_target.stamp`
///
/// {
///   "inputs": [
///      "absolute/path/foo",
///      "absolute/path/bar",
///      ...
///    ],
///    "outputs": [
///      "absolute/path/fizz"
///    ]
/// }
///
/// ## Code review
///
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/// ### Targets should only depend on files that are provided as inputs
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///
/// Example: gen_snapshot must be provided as an input to the aot_elf
/// build steps, even though it isn't a source file. This ensures that changes
/// to the gen_snapshot binary (during a local engine build) correctly
/// trigger a corresponding build update.
///
/// Example: aot_elf has a dependency on the dill and packages file
/// produced by the kernel_snapshot step.
///
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/// ### Targets should declare all outputs produced
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///
/// If a target produces an output it should be listed, even if it is not
/// intended to be consumed by another target.
///
/// ## Unit testing
///
/// Most targets will invoke an external binary which makes unit testing
/// trickier. It is recommend that for unit testing that a Fake is used and
/// provided via the dependency injection system. a [Testbed] may be used to
/// set up the environment before the test is run. Unit tests should fully
/// exercise the rule, ensuring that the existing input and output verification
/// logic can run, as well as verifying it correctly handles provided defines
/// and meets any additional contracts present in the target.
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abstract class Target {
  const Target();
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  /// The user-readable name of the target.
  ///
  /// This information is surfaced in the assemble commands and used as an
  /// argument to build a particular target.
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  String get name;
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  /// A name that measurements can be categorized under for this [Target].
  ///
  /// Unlike [name], this is not expected to be unique, so multiple targets
  /// that are conceptually the same can share an analytics name.
  ///
  /// If not provided, defaults to [name]
  String get analyticsName => name;

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  /// The dependencies of this target.
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  List<Target> get dependencies;
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  /// The input [Source]s which are diffed to determine if a target should run.
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  List<Source> get inputs;
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  /// The output [Source]s which we attempt to verify are correctly produced.
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  List<Source> get outputs;
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  /// A list of zero or more depfiles, located directly under {BUILD_DIR}.
  List<String> get depfiles => const <String>[];

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  /// The action which performs this build step.
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  Future<void> build(Environment environment);
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  /// Create a [Node] with resolved inputs and outputs.
  Node _toNode(Environment environment) {
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    final ResolvedFiles inputsFiles = resolveInputs(environment);
    final ResolvedFiles outputFiles = resolveOutputs(environment);
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    return Node(
      this,
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      inputsFiles.sources,
      outputFiles.sources,
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      <Node>[
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        for (final Target target in dependencies) target._toNode(environment),
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      ],
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      environment,
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      inputsFiles.containsNewDepfile,
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    );
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  }

  /// Invoke to remove the stamp file if the [buildAction] threw an exception;
  void clearStamp(Environment environment) {
    final File stamp = _findStampFile(environment);
    if (stamp.existsSync()) {
      stamp.deleteSync();
    }
  }

  void _writeStamp(
    List<File> inputs,
    List<File> outputs,
    Environment environment,
  ) {
    final File stamp = _findStampFile(environment);
    final List<String> inputPaths = <String>[];
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    for (final File input in inputs) {
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      inputPaths.add(input.path);
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    }
    final List<String> outputPaths = <String>[];
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    for (final File output in outputs) {
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      outputPaths.add(output.path);
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    }
    final Map<String, Object> result = <String, Object>{
      'inputs': inputPaths,
      'outputs': outputPaths,
    };
    if (!stamp.existsSync()) {
      stamp.createSync();
    }
    stamp.writeAsStringSync(json.encode(result));
  }

  /// Resolve the set of input patterns and functions into a concrete list of
  /// files.
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  ResolvedFiles resolveInputs(Environment environment) {
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    return _resolveConfiguration(inputs, depfiles, environment, implicit: true, inputs: true);
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  }

  /// Find the current set of declared outputs, including wildcard directories.
  ///
  /// The [implicit] flag controls whether it is safe to evaluate [Source]s
  /// which uses functions, behaviors, or patterns.
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  ResolvedFiles resolveOutputs(Environment environment) {
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    return _resolveConfiguration(outputs, depfiles, environment, inputs: false);
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  }

  /// Performs a fold across this target and its dependencies.
  T fold<T>(T initialValue, T combine(T previousValue, Target target)) {
    final T dependencyResult = dependencies.fold(
        initialValue, (T prev, Target t) => t.fold(prev, combine));
    return combine(dependencyResult, this);
  }

  /// Convert the target to a JSON structure appropriate for consumption by
  /// external systems.
  ///
  /// This requires constants from the [Environment] to resolve the paths of
  /// inputs and the output stamp.
  Map<String, Object> toJson(Environment environment) {
    return <String, Object>{
      'name': name,
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      'dependencies': <String>[
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        for (final Target target in dependencies) target.name,
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      ],
      'inputs': <String>[
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        for (final File file in resolveInputs(environment).sources) file.path,
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      ],
      'outputs': <String>[
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        for (final File file in resolveOutputs(environment).sources) file.path,
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      ],
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      'stamp': _findStampFile(environment).absolute.path,
    };
  }

  /// Locate the stamp file for a particular target name and environment.
  File _findStampFile(Environment environment) {
    final String fileName = '$name.stamp';
    return environment.buildDir.childFile(fileName);
  }

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  static ResolvedFiles _resolveConfiguration(List<Source> config,
    List<String> depfiles, Environment environment, { bool implicit = true, bool inputs = true,
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  }) {
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    final SourceVisitor collector = SourceVisitor(environment, inputs);
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    for (final Source source in config) {
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      source.accept(collector);
    }
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    depfiles.forEach(collector.visitDepfile);
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    return collector;
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  }
}

/// The [Environment] defines several constants for use during the build.
///
/// The environment contains configuration and file paths that are safe to
/// depend on and reference during the build.
///
/// Example (Good):
///
/// Use the environment to determine where to write an output file.
///
///    environment.buildDir.childFile('output')
///      ..createSync()
///      ..writeAsStringSync('output data');
///
/// Example (Bad):
///
/// Use a hard-coded path or directory relative to the current working
/// directory to write an output file.
///
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///   globals.fs.file('build/linux/out')
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///     ..createSync()
///     ..writeAsStringSync('output data');
///
/// Example (Good):
///
/// Using the build mode to produce different output. Note that the action
/// is still responsible for outputting a different file, as defined by the
/// corresponding output [Source].
///
///    final BuildMode buildMode = getBuildModeFromDefines(environment.defines);
///    if (buildMode == BuildMode.debug) {
///      environment.buildDir.childFile('debug.output')
///        ..createSync()
///        ..writeAsStringSync('debug');
///    } else {
///      environment.buildDir.childFile('non_debug.output')
///        ..createSync()
///        ..writeAsStringSync('non_debug');
///    }
class Environment {
  /// Create a new [Environment] object.
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  ///
  /// [engineVersion] should be set to null for local engine builds.
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  factory Environment({
    @required Directory projectDir,
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    @required Directory outputDir,
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    @required Directory cacheDir,
    @required Directory flutterRootDir,
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    @required FileSystem fileSystem,
    @required Logger logger,
    @required Artifacts artifacts,
    @required ProcessManager processManager,
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    @required String engineVersion,
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    Directory buildDir,
    Map<String, String> defines = const <String, String>{},
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    Map<String, String> inputs = const <String, String>{},
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  }) {
    // Compute a unique hash of this build's particular environment.
    // Sort the keys by key so that the result is stable. We always
    // include the engine and dart versions.
    String buildPrefix;
    final List<String> keys = defines.keys.toList()..sort();
    final StringBuffer buffer = StringBuffer();
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    // The engine revision is `null` for local or custom engines.
    if (engineVersion != null) {
      buffer.write(engineVersion);
    }
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    for (final String key in keys) {
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      buffer.write(key);
      buffer.write(defines[key]);
    }
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    buffer.write(outputDir.path);
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    final String output = buffer.toString();
    final Digest digest = md5.convert(utf8.encode(output));
    buildPrefix = hex.encode(digest.bytes);

    final Directory rootBuildDir = buildDir ?? projectDir.childDirectory('build');
    final Directory buildDirectory = rootBuildDir.childDirectory(buildPrefix);
    return Environment._(
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      outputDir: outputDir,
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      projectDir: projectDir,
      buildDir: buildDirectory,
      rootBuildDir: rootBuildDir,
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      cacheDir: cacheDir,
      defines: defines,
      flutterRootDir: flutterRootDir,
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      fileSystem: fileSystem,
      logger: logger,
      artifacts: artifacts,
      processManager: processManager,
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      engineVersion: engineVersion,
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      inputs: inputs,
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    );
  }

  /// Create a new [Environment] object for unit testing.
  ///
  /// Any directories not provided will fallback to a [testDirectory]
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  @visibleForTesting
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  factory Environment.test(Directory testDirectory, {
    Directory projectDir,
    Directory outputDir,
    Directory cacheDir,
    Directory flutterRootDir,
    Directory buildDir,
    Map<String, String> defines = const <String, String>{},
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    Map<String, String> inputs = const <String, String>{},
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    String engineVersion,
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    @required FileSystem fileSystem,
    @required Logger logger,
    @required Artifacts artifacts,
    @required ProcessManager processManager,
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  }) {
    return Environment(
      projectDir: projectDir ?? testDirectory,
      outputDir: outputDir ?? testDirectory,
      cacheDir: cacheDir ?? testDirectory,
      flutterRootDir: flutterRootDir ?? testDirectory,
      buildDir: buildDir,
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      defines: defines,
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      inputs: inputs,
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      fileSystem: fileSystem,
      logger: logger,
      artifacts: artifacts,
      processManager: processManager,
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      engineVersion: engineVersion,
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    );
  }

  Environment._({
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    @required this.outputDir,
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    @required this.projectDir,
    @required this.buildDir,
    @required this.rootBuildDir,
    @required this.cacheDir,
    @required this.defines,
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    @required this.flutterRootDir,
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    @required this.processManager,
    @required this.logger,
    @required this.fileSystem,
    @required this.artifacts,
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    @required this.engineVersion,
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    @required this.inputs,
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  });

  /// The [Source] value which is substituted with the path to [projectDir].
  static const String kProjectDirectory = '{PROJECT_DIR}';

  /// The [Source] value which is substituted with the path to [buildDir].
  static const String kBuildDirectory = '{BUILD_DIR}';

  /// The [Source] value which is substituted with the path to [cacheDir].
  static const String kCacheDirectory = '{CACHE_DIR}';

  /// The [Source] value which is substituted with a path to the flutter root.
  static const String kFlutterRootDirectory = '{FLUTTER_ROOT}';

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  /// The [Source] value which is substituted with a path to [outputDir].
  static const String kOutputDirectory = '{OUTPUT_DIR}';

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  /// The `PROJECT_DIR` environment variable.
  ///
  /// This should be root of the flutter project where a pubspec and dart files
  /// can be located.
  final Directory projectDir;

  /// The `BUILD_DIR` environment variable.
  ///
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  /// The root of the output directory where build step intermediates and
  /// outputs are written. Current usages of assemble configure ths to be
  /// a unique directory under `.dart_tool/flutter_build`, though it can
  /// be placed anywhere. The uniqueness is only enforced by callers, and
  /// is currently done by hashing the build configuration.
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  final Directory buildDir;

  /// The `CACHE_DIR` environment variable.
  ///
  /// Defaults to `{FLUTTER_ROOT}/bin/cache`. The root of the artifact cache for
  /// the flutter tool.
  final Directory cacheDir;

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  /// The `FLUTTER_ROOT` environment variable.
  ///
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  /// Defaults to the value of [Cache.flutterRoot].
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  final Directory flutterRootDir;

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  /// The `OUTPUT_DIR` environment variable.
  ///
  /// Must be provided to configure the output location for the final artifacts.
  final Directory outputDir;

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  /// Additional configuration passed to the build targets.
  ///
  /// Setting values here forces a unique build directory to be chosen
  /// which prevents the config from leaking into different builds.
  final Map<String, String> defines;

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  /// Additional input files passed to the build targets.
  ///
  /// Unlike [defines], values set here do not force a new build configuration.
  /// This is useful for passing file inputs that may have changing paths
  /// without running builds from scratch.
  ///
  /// It is the responsibility of the [Target] to declare that an input was
  /// used in an output depfile.
  final Map<String, String> inputs;

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  /// The root build directory shared by all builds.
  final Directory rootBuildDir;
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  final ProcessManager processManager;

  final Logger logger;

  final Artifacts artifacts;

  final FileSystem fileSystem;
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  /// The version of the current engine, or `null` if built with a local engine.
  final String engineVersion;
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}

/// The result information from the build system.
class BuildResult {
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  BuildResult({
    @required this.success,
    this.exceptions = const <String, ExceptionMeasurement>{},
    this.performance = const <String, PerformanceMeasurement>{},
    this.inputFiles = const <File>[],
    this.outputFiles = const <File>[],
  });
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  final bool success;
  final Map<String, ExceptionMeasurement> exceptions;
  final Map<String, PerformanceMeasurement> performance;
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  final List<File> inputFiles;
  final List<File> outputFiles;
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  bool get hasException => exceptions.isNotEmpty;
}

/// The build system is responsible for invoking and ordering [Target]s.
class BuildSystem {
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  const BuildSystem({
    @required FileSystem fileSystem,
    @required Platform platform,
    @required Logger logger,
  }) : _fileSystem = fileSystem,
       _platform = platform,
       _logger = logger;

  final FileSystem _fileSystem;
  final Platform _platform;
  final Logger _logger;
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  /// Build `target` and all of its dependencies.
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  Future<BuildResult> build(
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    Target target,
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    Environment environment, {
    BuildSystemConfig buildSystemConfig = const BuildSystemConfig(),
  }) async {
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    environment.buildDir.createSync(recursive: true);
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    environment.outputDir.createSync(recursive: true);
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    // Load file store from previous builds.
    final File cacheFile = environment.buildDir.childFile(FileStore.kFileCache);
    final FileStore fileCache = FileStore(
      cacheFile: cacheFile,
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      logger: _logger,
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    )..initialize();
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    // Perform sanity checks on build.
    checkCycles(target);

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    final Node node = target._toNode(environment);
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    final _BuildInstance buildInstance = _BuildInstance(
      environment: environment,
      fileCache: fileCache,
      buildSystemConfig: buildSystemConfig,
      logger: _logger,
      fileSystem: _fileSystem,
      platform: _platform,
    );
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    bool passed = true;
    try {
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      passed = await buildInstance.invokeTarget(node);
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    } finally {
      // Always persist the file cache to disk.
      fileCache.persist();
    }
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    // TODO(jonahwilliams): this is a bit of a hack, due to various parts of
    // the flutter tool writing these files unconditionally. Since Xcode uses
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    // timestamps to track files, this leads to unnecessary rebuilds if they
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    // are included. Once all the places that write these files have been
    // tracked down and moved into assemble, these checks should be removable.
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    // We also remove files under .dart_tool, since these are intermediaries
    // and don't need to be tracked by external systems.
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    {
      buildInstance.inputFiles.removeWhere((String path, File file) {
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        return path.contains('.flutter-plugins') ||
                       path.contains('xcconfig') ||
                     path.contains('.dart_tool');
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      });
      buildInstance.outputFiles.removeWhere((String path, File file) {
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        return path.contains('.flutter-plugins') ||
                       path.contains('xcconfig') ||
                     path.contains('.dart_tool');
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      });
    }
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    trackSharedBuildDirectory(
      environment, _fileSystem, buildInstance.outputFiles,
    );
    environment.buildDir.childFile('outputs.json')
      .writeAsStringSync(json.encode(buildInstance.outputFiles.keys.toList()));

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    return BuildResult(
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      success: passed,
      exceptions: buildInstance.exceptionMeasurements,
      performance: buildInstance.stepTimings,
      inputFiles: buildInstance.inputFiles.values.toList()
          ..sort((File a, File b) => a.path.compareTo(b.path)),
      outputFiles: buildInstance.outputFiles.values.toList()
          ..sort((File a, File b) => a.path.compareTo(b.path)),
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    );
  }
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  static final Expando<FileStore> _incrementalFileStore = Expando<FileStore>();

  /// Perform an incremental build of `target` and all of its dependencies.
  ///
  /// If [previousBuild] is not provided, a new incremental build is
  /// initialized.
  Future<BuildResult> buildIncremental(
    Target target,
    Environment environment,
    BuildResult previousBuild,
  ) async {
    environment.buildDir.createSync(recursive: true);
    environment.outputDir.createSync(recursive: true);

    FileStore fileCache;
    if (previousBuild == null || _incrementalFileStore[previousBuild] == null) {
      final File cacheFile = environment.buildDir.childFile(FileStore.kFileCache);
      fileCache = FileStore(
        cacheFile: cacheFile,
        logger: _logger,
        strategy: FileStoreStrategy.timestamp,
      )..initialize();
    } else {
      fileCache = _incrementalFileStore[previousBuild];
    }
    final Node node = target._toNode(environment);
    final _BuildInstance buildInstance = _BuildInstance(
      environment: environment,
      fileCache: fileCache,
      buildSystemConfig: const BuildSystemConfig(),
      logger: _logger,
      fileSystem: _fileSystem,
      platform: _platform,
    );
    bool passed = true;
    try {
      passed = await buildInstance.invokeTarget(node);
    } finally {
      fileCache.persistIncremental();
    }
    final BuildResult result = BuildResult(
      success: passed,
      exceptions: buildInstance.exceptionMeasurements,
      performance: buildInstance.stepTimings,
    );
    _incrementalFileStore[result] = fileCache;
    return result;
  }

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  /// Write the identifier of the last build into the output directory and
  /// remove the previous build's output.
  ///
  /// The build identifier is the basename of the build directory where
  /// outputs and intermediaries are written, under `.dart_tool/flutter_build`.
  /// This is computed from a hash of the build's configuration.
  ///
  /// This identifier is used to perform a targeted cleanup of the last output
  /// files, if these were not already covered by the built-in cleanup. This
  /// cleanup is only necessary when multiple different build configurations
  /// output to the same directory.
  @visibleForTesting
  static void trackSharedBuildDirectory(
    Environment environment,
    FileSystem fileSystem,
    Map<String, File> currentOutputs,
  ) {
    final String currentBuildId = fileSystem.path.basename(environment.buildDir.path);
    final File lastBuildIdFile = environment.outputDir.childFile('.last_build_id');
    if (!lastBuildIdFile.existsSync()) {
      lastBuildIdFile.writeAsStringSync(currentBuildId);
      // No config file, either output was cleaned or this is the first build.
      return;
    }
    final String lastBuildId = lastBuildIdFile.readAsStringSync().trim();
    if (lastBuildId == currentBuildId) {
      // The last build was the same configuration as the current build
      return;
    }
    // Update the output dir with the latest config.
    lastBuildIdFile
      ..createSync()
      ..writeAsStringSync(currentBuildId);
    final File outputsFile = environment.buildDir
      .parent
      .childDirectory(lastBuildId)
      .childFile('outputs.json');

    if (!outputsFile.existsSync()) {
      // There is no output list. This could happen if the user manually
      // edited .last_config or deleted .dart_tool.
      return;
    }
    final List<String> lastOutputs = (json.decode(outputsFile.readAsStringSync()) as List<Object>)
      .cast<String>();
    for (final String lastOutput in lastOutputs) {
      if (!currentOutputs.containsKey(lastOutput)) {
        final File lastOutputFile = fileSystem.file(lastOutput);
        if (lastOutputFile.existsSync()) {
          lastOutputFile.deleteSync();
        }
      }
    }
  }
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}

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/// An active instance of a build.
class _BuildInstance {
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  _BuildInstance({
    this.environment,
    this.fileCache,
    this.buildSystemConfig,
    this.logger,
    this.fileSystem,
    Platform platform,
  })
    : resourcePool = Pool(buildSystemConfig.resourcePoolSize ?? platform?.numberOfProcessors ?? 1);

  final Logger logger;
  final FileSystem fileSystem;
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  final BuildSystemConfig buildSystemConfig;
  final Pool resourcePool;
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  final Map<String, AsyncMemoizer<bool>> pending = <String, AsyncMemoizer<bool>>{};
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  final Environment environment;
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  final FileStore fileCache;
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  final Map<String, File> inputFiles = <String, File>{};
  final Map<String, File> outputFiles = <String, File>{};
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  // Timings collected during target invocation.
  final Map<String, PerformanceMeasurement> stepTimings = <String, PerformanceMeasurement>{};

  // Exceptions caught during the build process.
  final Map<String, ExceptionMeasurement> exceptionMeasurements = <String, ExceptionMeasurement>{};

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  Future<bool> invokeTarget(Node node) async {
    final List<bool> results = await Future.wait(node.dependencies.map(invokeTarget));
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    if (results.any((bool result) => !result)) {
      return false;
    }
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    final AsyncMemoizer<bool> memoizer = pending[node.target.name] ??= AsyncMemoizer<bool>();
    return memoizer.runOnce(() => _invokeInternal(node));
714 715
  }

716
  Future<bool> _invokeInternal(Node node) async {
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    final PoolResource resource = await resourcePool.request();
    final Stopwatch stopwatch = Stopwatch()..start();
719
    bool succeeded = true;
720
    bool skipped = false;
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    // The build system produces a list of aggregate input and output
    // files for the overall build. This list is provided to a hosting build
    // system, such as Xcode, to configure logic for when to skip the
    // rule/phase which contains the flutter build.
    //
    // When looking at the inputs and outputs for the individual rules, we need
    // to be careful to remove inputs that were actually output from previous
    // build steps. This indicates that the file is an intermediary. If
    // these files are included as both inputs and outputs then it isn't
    // possible to construct a DAG describing the build.
    void updateGraph() {
733
      for (final File output in node.outputs) {
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        outputFiles[output.path] = output;
      }
736
      for (final File input in node.inputs) {
737
        final String resolvedPath = input.absolute.path;
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        if (outputFiles.containsKey(resolvedPath)) {
          continue;
        }
        inputFiles[resolvedPath] = input;
      }
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    }

    try {
      // If we're missing a depfile, wait until after evaluating the target to
      // compute changes.
      final bool canSkip = !node.missingDepfile &&
749
        await node.computeChanges(environment, fileCache, fileSystem, logger);
750

751
      if (canSkip) {
752
        skipped = true;
753
        logger.printTrace('Skipping target: ${node.target.name}');
754
        updateGraph();
755
        return succeeded;
756
      }
757
      logger.printTrace('${node.target.name}: Starting due to ${node.invalidatedReasons}');
758
      await node.target.build(environment);
759
      logger.printTrace('${node.target.name}: Complete');
760

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      node.inputs
        ..clear()
        ..addAll(node.target.resolveInputs(environment).sources);
      node.outputs
        ..clear()
        ..addAll(node.target.resolveOutputs(environment).sources);

      // If we were missing the depfile, resolve  input files after executing the
769 770
      // target so that all file hashes are up to date on the next run.
      if (node.missingDepfile) {
771
        await fileCache.diffFileList(node.inputs);
772 773
      }

774
      // Always update hashes for output files.
775
      await fileCache.diffFileList(node.outputs);
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      node.target._writeStamp(node.inputs, node.outputs, environment);
      updateGraph();

      // Delete outputs from previous stages that are no longer a part of the
      // build.
781
      for (final String previousOutput in node.previousOutputs) {
782 783
        if (outputFiles.containsKey(previousOutput)) {
          continue;
784
        }
785
        final File previousFile = fileSystem.file(previousOutput);
786 787
        if (previousFile.existsSync()) {
          previousFile.deleteSync();
788
        }
789
      }
790
    } on Exception catch (exception, stackTrace) {
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      // TODO(jonahwilliams): throw specific exception for expected errors to mark
      // as non-fatal. All others should be fatal.
793
      node.target.clearStamp(environment);
794
      succeeded = false;
795
      skipped = false;
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      exceptionMeasurements[node.target.name] = ExceptionMeasurement(
          node.target.name, exception, stackTrace);
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    } finally {
      resource.release();
      stopwatch.stop();
801
      stepTimings[node.target.name] = PerformanceMeasurement(
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        target: node.target.name,
        elapsedMilliseconds: stopwatch.elapsedMilliseconds,
        skipped: skipped,
805
        succeeded: succeeded,
806 807
        analyicsName: node.target.analyticsName,
      );
808
    }
809
    return succeeded;
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  }
}

/// Helper class to collect exceptions.
class ExceptionMeasurement {
815
  ExceptionMeasurement(this.target, this.exception, this.stackTrace, {this.fatal = false});
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  final String target;
  final dynamic exception;
  final StackTrace stackTrace;
820

821 822 823
  /// Whether this exception was a fatal build system error.
  final bool fatal;

824 825
  @override
  String toString() => 'target: $target\nexception:$exception\n$stackTrace';
826 827 828 829
}

/// Helper class to collect measurement data.
class PerformanceMeasurement {
830 831 832 833
  PerformanceMeasurement({
    @required this.target,
    @required this.elapsedMilliseconds,
    @required this.skipped,
834
    @required this.succeeded,
835 836 837
    @required this.analyicsName,
  });

838 839
  final int elapsedMilliseconds;
  final String target;
840
  final bool skipped;
841
  final bool succeeded;
842
  final String analyicsName;
843 844 845 846 847 848 849 850 851 852 853 854 855 856 857
}

/// Check if there are any dependency cycles in the target.
///
/// Throws a [CycleException] if one is encountered.
void checkCycles(Target initial) {
  void checkInternal(Target target, Set<Target> visited, Set<Target> stack) {
    if (stack.contains(target)) {
      throw CycleException(stack..add(target));
    }
    if (visited.contains(target)) {
      return;
    }
    visited.add(target);
    stack.add(target);
858
    for (final Target dependency in target.dependencies) {
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      checkInternal(dependency, visited, stack);
    }
    stack.remove(target);
  }
  checkInternal(initial, <Target>{}, <Target>{});
}

/// Verifies that all files exist and are in a subdirectory of [Environment.buildDir].
void verifyOutputDirectories(List<File> outputs, Environment environment, Target target) {
  final String buildDirectory = environment.buildDir.resolveSymbolicLinksSync();
  final String projectDirectory = environment.projectDir.resolveSymbolicLinksSync();
  final List<File> missingOutputs = <File>[];
871
  for (final File sourceFile in outputs) {
872 873 874 875
    if (!sourceFile.existsSync()) {
      missingOutputs.add(sourceFile);
      continue;
    }
876
    final String path = sourceFile.path;
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    if (!path.startsWith(buildDirectory) && !path.startsWith(projectDirectory)) {
      throw MisplacedOutputException(path, target.name);
    }
  }
  if (missingOutputs.isNotEmpty) {
    throw MissingOutputException(missingOutputs, target.name);
  }
}
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/// A node in the build graph.
class Node {
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  Node(
    this.target,
    this.inputs,
    this.outputs,
    this.dependencies,
    Environment environment,
    this.missingDepfile,
  ) {
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    final File stamp = target._findStampFile(environment);

    // If the stamp file doesn't exist, we haven't run this step before and
    // all inputs were added.
    if (!stamp.existsSync()) {
      // No stamp file, not safe to skip.
      _dirty = true;
      return;
    }
    final String content = stamp.readAsStringSync();
    // Something went wrong writing the stamp file.
    if (content == null || content.isEmpty) {
      stamp.deleteSync();
      // Malformed stamp file, not safe to skip.
      _dirty = true;
      return;
    }
    Map<String, Object> values;
    try {
915
      values = castStringKeyedMap(json.decode(content));
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    } on FormatException {
      // The json is malformed in some way.
      _dirty = true;
      return;
    }
    final Object inputs = values['inputs'];
    final Object outputs = values['outputs'];
    if (inputs is List<Object> && outputs is List<Object>) {
      inputs?.cast<String>()?.forEach(previousInputs.add);
      outputs?.cast<String>()?.forEach(previousOutputs.add);
    } else {
      // The json is malformed in some way.
      _dirty = true;
    }
  }

  /// The resolved input files.
  ///
  /// These files may not yet exist if they are produced by previous steps.
  final List<File> inputs;

  /// The resolved output files.
  ///
  /// These files may not yet exist if the target hasn't run yet.
  final List<File> outputs;

942 943 944 945 946 947
  /// Whether this node is missing a depfile.
  ///
  /// This requires an additional pass of source resolution after the target
  /// has been executed.
  final bool missingDepfile;

948 949 950 951 952 953 954 955 956
  /// The target definition which contains the build action to invoke.
  final Target target;

  /// All of the nodes that this one depends on.
  final List<Node> dependencies;

  /// Output file paths from the previous invocation of this build node.
  final Set<String> previousOutputs = <String>{};

957
  /// Input file paths from the previous invocation of this build node.
958 959
  final Set<String> previousInputs = <String>{};

960 961 962
  /// One or more reasons why a task was invalidated.
  ///
  /// May be empty if the task was skipped.
963
  final Set<InvalidatedReason> invalidatedReasons = <InvalidatedReason>{};
964

965 966 967 968 969 970 971 972 973
  /// Whether this node needs an action performed.
  bool get dirty => _dirty;
  bool _dirty = false;

  /// Collect hashes for all inputs to determine if any have changed.
  ///
  /// Returns whether this target can be skipped.
  Future<bool> computeChanges(
    Environment environment,
974
    FileStore fileStore,
975 976
    FileSystem fileSystem,
    Logger logger,
977 978
  ) async {
    final Set<String> currentOutputPaths = <String>{
979
      for (final File file in outputs) file.path,
980
    };
981 982 983
    // For each input, first determine if we've already computed the key
    // for it. Then collect it to be sent off for diffing as a group.
    final List<File> sourcesToDiff = <File>[];
984
    final List<File> missingInputs = <File>[];
985
    for (final File file in inputs) {
986 987 988 989 990 991
      if (!file.existsSync()) {
        missingInputs.add(file);
        continue;
      }

      final String absolutePath = file.path;
992 993 994 995
      final String previousAssetKey = fileStore.previousAssetKeys[absolutePath];
      if (fileStore.currentAssetKeys.containsKey(absolutePath)) {
        final String currentHash = fileStore.currentAssetKeys[absolutePath];
        if (currentHash != previousAssetKey) {
996
          invalidatedReasons.add(InvalidatedReason.inputChanged);
997 998 999
          _dirty = true;
        }
      } else {
1000
        sourcesToDiff.add(file);
1001 1002 1003
      }
    }

1004
    // For each output, first determine if we've already computed the key
1005
    // for it. Then collect it to be sent off for hashing as a group.
1006
    for (final String previousOutput in previousOutputs) {
1007 1008 1009
      // output paths changed.
      if (!currentOutputPaths.contains(previousOutput)) {
        _dirty = true;
1010
        invalidatedReasons.add(InvalidatedReason.outputSetChanged);
1011
        // if this isn't a current output file there is no reason to compute the key.
1012 1013
        continue;
      }
1014
      final File file = fileSystem.file(previousOutput);
1015
      if (!file.existsSync()) {
1016
        invalidatedReasons.add(InvalidatedReason.outputMissing);
1017 1018 1019 1020
        _dirty = true;
        continue;
      }
      final String absolutePath = file.path;
1021 1022 1023
      final String previousHash = fileStore.previousAssetKeys[absolutePath];
      if (fileStore.currentAssetKeys.containsKey(absolutePath)) {
        final String currentHash = fileStore.currentAssetKeys[absolutePath];
1024
        if (currentHash != previousHash) {
1025
          invalidatedReasons.add(InvalidatedReason.outputChanged);
1026 1027 1028
          _dirty = true;
        }
      } else {
1029
        sourcesToDiff.add(file);
1030 1031 1032
      }
    }

1033 1034 1035
    // If we depend on a file that doesnt exist on disk, mark the build as
    // dirty. if the rule is not correctly specified, this will result in it
    // always being rerun.
1036
    if (missingInputs.isNotEmpty) {
1037 1038
      _dirty = true;
      final String missingMessage = missingInputs.map((File file) => file.path).join(', ');
1039
      logger.printTrace('invalidated build due to missing files: $missingMessage');
1040
      invalidatedReasons.add(InvalidatedReason.inputMissing);
1041 1042
    }

1043
    // If we have files to diff, compute them asynchronously and then
1044
    // update the result.
1045 1046
    if (sourcesToDiff.isNotEmpty) {
      final List<File> dirty = await fileStore.diffFileList(sourcesToDiff);
1047
      if (dirty.isNotEmpty) {
1048
        invalidatedReasons.add(InvalidatedReason.inputChanged);
1049 1050 1051 1052 1053 1054
        _dirty = true;
      }
    }
    return !_dirty;
  }
}
1055

1056 1057 1058 1059 1060 1061
/// A description of why a target was rerun.
enum InvalidatedReason {
  /// An input file that was expected is missing. This can occur when using
  /// depfile dependencies, or if a target is incorrectly specified.
  inputMissing,

1062
  /// An input file has an updated key.
1063 1064
  inputChanged,

1065
  /// An output file has an updated key.
1066 1067 1068 1069 1070 1071 1072 1073
  outputChanged,

  /// An output file that is expected is missing.
  outputMissing,

  /// The set of expected output files changed.
  outputSetChanged,
}