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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 'package:async/async.dart';
import 'package:convert/convert.dart';
import 'package:crypto/crypto.dart';
import 'package:meta/meta.dart';
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/error_handling_io.dart';
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import '../base/file_system.dart';
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import '../base/logger.dart';
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import '../base/platform.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].
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  final int? resourcePoolSize;
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}

/// 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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  /// Whether this target can be executed with the given [environment].
  ///
  /// Returning `true` will cause [build] to be skipped. This is equivalent
  /// to a build that produces no outputs.
  bool canSkip(Environment environment) => false;

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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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  }

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

  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.
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  T fold<T>(T initialValue, T Function(T previousValue, Target target) combine) {
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    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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  }
}

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/// Target that contains multiple other targets.
///
/// This target does not do anything in its own [build]
/// and acts as a wrapper around multiple other targets.
class CompositeTarget extends Target {
  CompositeTarget(this.dependencies);

  @override
  final List<Target> dependencies;

  @override
  String get name => '_composite';

  @override
  Future<void> build(Environment environment) async { }

  @override
  List<Source> get inputs => <Source>[];

  @override
  List<Source> get outputs => <Source>[];
}

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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.
///
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/// ```dart
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///    environment.buildDir.childFile('output')
///      ..createSync()
///      ..writeAsStringSync('output data');
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/// ```
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///
/// Example (Bad):
///
/// Use a hard-coded path or directory relative to the current working
/// directory to write an output file.
///
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/// ```dart
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///   globals.fs.file('build/linux/out')
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///     ..createSync()
///     ..writeAsStringSync('output data');
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/// ```
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///
/// 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].
///
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/// ```dart
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///    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');
///    }
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/// ```
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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({
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    required Directory projectDir,
    required Directory outputDir,
    required Directory cacheDir,
    required Directory flutterRootDir,
    required FileSystem fileSystem,
    required Logger logger,
    required Artifacts artifacts,
    required ProcessManager processManager,
    required Platform platform,
    String? engineVersion,
    required bool generateDartPluginRegistry,
    Directory? buildDir,
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    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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      platform: platform,
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      engineVersion: engineVersion,
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      inputs: inputs,
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      generateDartPluginRegistry: generateDartPluginRegistry,
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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, {
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    Directory? projectDir,
    Directory? outputDir,
    Directory? cacheDir,
    Directory? flutterRootDir,
    Directory? buildDir,
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    Map<String, String> defines = const <String, String>{},
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    Map<String, String> inputs = const <String, String>{},
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    String? engineVersion,
    Platform? platform,
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    bool generateDartPluginRegistry = false,
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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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      platform: platform ?? FakePlatform(),
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      engineVersion: engineVersion,
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      generateDartPluginRegistry: generateDartPluginRegistry,
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    );
  }

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

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  final Platform platform;

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  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.
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  final String? engineVersion;
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  /// Whether to generate the Dart plugin registry.
  /// When [true], the main entrypoint is wrapped and the wrapper becomes
  /// the new entrypoint.
  final bool generateDartPluginRegistry;
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}

/// The result information from the build system.
class BuildResult {
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  BuildResult({
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    required this.success,
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    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.
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abstract class BuildSystem {
  /// Const constructor to allow subclasses to be const.
  const BuildSystem();

  /// Build [target] and all of its dependencies.
  Future<BuildResult> build(
    Target target,
    Environment environment, {
    BuildSystemConfig buildSystemConfig = const BuildSystemConfig(),
  });

  /// 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,
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    BuildResult? previousBuild,
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  );
}

class FlutterBuildSystem extends BuildSystem {
  const FlutterBuildSystem({
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    required FileSystem fileSystem,
    required Platform platform,
    required Logger logger,
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  }) : _fileSystem = fileSystem,
       _platform = platform,
       _logger = logger;

  final FileSystem _fileSystem;
  final Platform _platform;
  final Logger _logger;
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  @override
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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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    // This is a bit of a hack, due to various parts of
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    // 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>();

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  @override
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  Future<BuildResult> buildIncremental(
    Target target,
    Environment environment,
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    BuildResult? previousBuild,
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  ) async {
    environment.buildDir.createSync(recursive: true);
    environment.outputDir.createSync(recursive: true);

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    FileStore? fileCache;
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    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,
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      fileCache: fileCache!,
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      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
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  void trackSharedBuildDirectory(
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    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()) {
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      lastBuildIdFile.parent.createSync(recursive: true);
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      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;
    }
734
    final List<String> lastOutputs = (json.decode(outputsFile.readAsStringSync()) as List<Object?>)
735 736 737 738
      .cast<String>();
    for (final String lastOutput in lastOutputs) {
      if (!currentOutputs.containsKey(lastOutput)) {
        final File lastOutputFile = fileSystem.file(lastOutput);
739
        ErrorHandlingFileSystem.deleteIfExists(lastOutputFile);
740 741 742
      }
    }
  }
743 744 745 746
}

/// An active instance of a build.
class _BuildInstance {
747
  _BuildInstance({
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    required this.environment,
    required this.fileCache,
    required this.buildSystemConfig,
    required this.logger,
    required this.fileSystem,
    Platform? platform,
754 755 756 757 758
  })
    : resourcePool = Pool(buildSystemConfig.resourcePoolSize ?? platform?.numberOfProcessors ?? 1);

  final Logger logger;
  final FileSystem fileSystem;
759 760
  final BuildSystemConfig buildSystemConfig;
  final Pool resourcePool;
761
  final Map<String, AsyncMemoizer<bool>> pending = <String, AsyncMemoizer<bool>>{};
762
  final Environment environment;
763
  final FileStore fileCache;
764 765
  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>{};

773 774
  Future<bool> invokeTarget(Node node) async {
    final List<bool> results = await Future.wait(node.dependencies.map(invokeTarget));
775 776 777
    if (results.any((bool result) => !result)) {
      return false;
    }
778 779
    final AsyncMemoizer<bool> memoizer = pending[node.target.name] ??= AsyncMemoizer<bool>();
    return memoizer.runOnce(() => _invokeInternal(node));
780 781
  }

782
  Future<bool> _invokeInternal(Node node) async {
783 784
    final PoolResource resource = await resourcePool.request();
    final Stopwatch stopwatch = Stopwatch()..start();
785
    bool succeeded = true;
786
    bool skipped = false;
787 788 789 790 791 792 793 794 795 796 797 798

    // 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() {
799
      for (final File output in node.outputs) {
800 801
        outputFiles[output.path] = output;
      }
802
      for (final File input in node.inputs) {
803
        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 &&
815
        node.computeChanges(environment, fileCache, fileSystem, logger);
816

817
      if (canSkip) {
818
        skipped = true;
819
        logger.printTrace('Skipping target: ${node.target.name}');
820
        updateGraph();
821
        return succeeded;
822
      }
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      // Clear old inputs. These will be replaced with new inputs/outputs
      // after the target is run. In the case of a runtime skip, each list
      // must be empty to ensure the previous outputs are purged.
      node.inputs.clear();
      node.outputs.clear();

      // Check if we can skip via runtime dependencies.
      final bool runtimeSkip = node.target.canSkip(environment);
      if (runtimeSkip) {
        logger.printTrace('Skipping target: ${node.target.name}');
        skipped = true;
      } else {
        logger.printTrace('${node.target.name}: Starting due to ${node.invalidatedReasons}');
        await node.target.build(environment);
        logger.printTrace('${node.target.name}: Complete');
        node.inputs.addAll(node.target.resolveInputs(environment).sources);
        node.outputs.addAll(node.target.resolveOutputs(environment).sources);
      }

      // If we were missing the depfile, resolve input files after executing the
843 844
      // target so that all file hashes are up to date on the next run.
      if (node.missingDepfile) {
845
        fileCache.diffFileList(node.inputs);
846 847
      }

848
      // Always update hashes for output files.
849
      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.
855
      for (final String previousOutput in node.previousOutputs) {
856 857
        if (outputFiles.containsKey(previousOutput)) {
          continue;
858
        }
859
        final File previousFile = fileSystem.file(previousOutput);
860
        ErrorHandlingFileSystem.deleteIfExists(previousFile);
861
      }
862
    } on Exception catch (exception, stackTrace) {
863 864
      // TODO(jonahwilliams): throw specific exception for expected errors to mark
      // as non-fatal. All others should be fatal.
865
      node.target.clearStamp(environment);
866
      succeeded = false;
867
      skipped = false;
868 869
      exceptionMeasurements[node.target.name] = ExceptionMeasurement(
          node.target.name, exception, stackTrace);
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    } finally {
      resource.release();
      stopwatch.stop();
873
      stepTimings[node.target.name] = PerformanceMeasurement(
874 875 876
        target: node.target.name,
        elapsedMilliseconds: stopwatch.elapsedMilliseconds,
        skipped: skipped,
877
        succeeded: succeeded,
878
        analyticsName: node.target.analyticsName,
879
      );
880
    }
881
    return succeeded;
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  }
}

/// Helper class to collect exceptions.
class ExceptionMeasurement {
887
  ExceptionMeasurement(this.target, this.exception, this.stackTrace, {this.fatal = false});
888 889

  final String target;
890
  final Object? exception;
891
  final StackTrace stackTrace;
892

893 894 895
  /// Whether this exception was a fatal build system error.
  final bool fatal;

896 897
  @override
  String toString() => 'target: $target\nexception:$exception\n$stackTrace';
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}

/// Helper class to collect measurement data.
class PerformanceMeasurement {
902
  PerformanceMeasurement({
903 904 905 906 907
    required this.target,
    required this.elapsedMilliseconds,
    required this.skipped,
    required this.succeeded,
    required this.analyticsName,
908 909
  });

910 911
  final int elapsedMilliseconds;
  final String target;
912
  final bool skipped;
913
  final bool succeeded;
914
  final String analyticsName;
915 916 917 918 919 920 921 922 923 924 925 926 927 928 929
}

/// 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);
930
    for (final Target dependency in target.dependencies) {
931 932 933 934 935 936 937 938 939 940 941 942
      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>[];
943
  for (final File sourceFile in outputs) {
944 945 946 947
    if (!sourceFile.existsSync()) {
      missingOutputs.add(sourceFile);
      continue;
    }
948
    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);
  }
}
957 958 959

/// A node in the build graph.
class Node {
960 961 962 963 964 965 966 967
  Node(
    this.target,
    this.inputs,
    this.outputs,
    this.dependencies,
    Environment environment,
    this.missingDepfile,
  ) {
968 969 970 971 972 973 974 975 976 977 978 979 980 981 982 983 984
    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;
    }
985
    Map<String, Object?>? values;
986
    try {
987
      values = castStringKeyedMap(json.decode(content));
988 989 990 991 992
    } on FormatException {
      // The json is malformed in some way.
      _dirty = true;
      return;
    }
993 994 995 996 997
    final Object? inputs = values?['inputs'];
    final Object? outputs = values?['outputs'];
    if (inputs is List<Object?> && outputs is List<Object?>) {
      inputs.cast<String?>().whereType<String>().forEach(previousInputs.add);
      outputs.cast<String?>().whereType<String>().forEach(previousOutputs.add);
998 999 1000 1001 1002 1003 1004 1005 1006 1007 1008 1009 1010 1011 1012 1013
    } 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;

1014 1015 1016 1017 1018 1019
  /// Whether this node is missing a depfile.
  ///
  /// This requires an additional pass of source resolution after the target
  /// has been executed.
  final bool missingDepfile;

1020 1021 1022 1023 1024 1025 1026 1027 1028
  /// 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>{};

1029
  /// Input file paths from the previous invocation of this build node.
1030 1031
  final Set<String> previousInputs = <String>{};

1032 1033 1034
  /// One or more reasons why a task was invalidated.
  ///
  /// May be empty if the task was skipped.
1035
  final Map<InvalidatedReasonKind, InvalidatedReason> invalidatedReasons = <InvalidatedReasonKind, InvalidatedReason>{};
1036

1037 1038 1039 1040
  /// Whether this node needs an action performed.
  bool get dirty => _dirty;
  bool _dirty = false;

1041 1042 1043 1044
  InvalidatedReason _invalidate(InvalidatedReasonKind kind) {
    return invalidatedReasons[kind] ??= InvalidatedReason(kind);
  }

1045 1046 1047
  /// Collect hashes for all inputs to determine if any have changed.
  ///
  /// Returns whether this target can be skipped.
1048
  bool computeChanges(
1049
    Environment environment,
1050
    FileStore fileStore,
1051 1052
    FileSystem fileSystem,
    Logger logger,
1053
  ) {
1054
    final Set<String> currentOutputPaths = <String>{
1055
      for (final File file in outputs) file.path,
1056
    };
1057 1058 1059
    // 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>[];
1060
    final List<File> missingInputs = <File>[];
1061
    for (final File file in inputs) {
1062 1063 1064 1065 1066 1067
      if (!file.existsSync()) {
        missingInputs.add(file);
        continue;
      }

      final String absolutePath = file.path;
1068
      final String? previousAssetKey = fileStore.previousAssetKeys[absolutePath];
1069
      if (fileStore.currentAssetKeys.containsKey(absolutePath)) {
1070
        final String? currentHash = fileStore.currentAssetKeys[absolutePath];
1071
        if (currentHash != previousAssetKey) {
1072 1073
          final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.inputChanged);
          reason.data.add(absolutePath);
1074 1075 1076
          _dirty = true;
        }
      } else {
1077
        sourcesToDiff.add(file);
1078 1079 1080
      }
    }

1081
    // For each output, first determine if we've already computed the key
1082
    // for it. Then collect it to be sent off for hashing as a group.
1083
    for (final String previousOutput in previousOutputs) {
1084 1085 1086
      // output paths changed.
      if (!currentOutputPaths.contains(previousOutput)) {
        _dirty = true;
1087 1088
        final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.outputSetChanged);
        reason.data.add(previousOutput);
1089
        // if this isn't a current output file there is no reason to compute the key.
1090 1091
        continue;
      }
1092
      final File file = fileSystem.file(previousOutput);
1093
      if (!file.existsSync()) {
1094 1095
        final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.outputMissing);
        reason.data.add(file.path);
1096 1097 1098 1099
        _dirty = true;
        continue;
      }
      final String absolutePath = file.path;
1100
      final String? previousHash = fileStore.previousAssetKeys[absolutePath];
1101
      if (fileStore.currentAssetKeys.containsKey(absolutePath)) {
1102
        final String? currentHash = fileStore.currentAssetKeys[absolutePath];
1103
        if (currentHash != previousHash) {
1104 1105
          final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.outputChanged);
          reason.data.add(absolutePath);
1106 1107 1108
          _dirty = true;
        }
      } else {
1109
        sourcesToDiff.add(file);
1110 1111 1112
      }
    }

1113
    // If we depend on a file that doesn't exist on disk, mark the build as
1114 1115
    // dirty. if the rule is not correctly specified, this will result in it
    // always being rerun.
1116
    if (missingInputs.isNotEmpty) {
1117 1118
      _dirty = true;
      final String missingMessage = missingInputs.map((File file) => file.path).join(', ');
1119
      logger.printTrace('invalidated build due to missing files: $missingMessage');
1120 1121
      final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.inputMissing);
      reason.data.addAll(missingInputs.map((File file) => file.path));
1122 1123
    }

1124
    // If we have files to diff, compute them asynchronously and then
1125
    // update the result.
1126
    if (sourcesToDiff.isNotEmpty) {
1127
      final List<File> dirty = fileStore.diffFileList(sourcesToDiff);
1128
      if (dirty.isNotEmpty) {
1129 1130
        final InvalidatedReason reason = _invalidate(InvalidatedReasonKind.inputChanged);
        reason.data.addAll(dirty.map((File file) => file.path));
1131 1132 1133 1134 1135 1136
        _dirty = true;
      }
    }
    return !_dirty;
  }
}
1137

1138 1139 1140 1141 1142 1143 1144 1145 1146 1147 1148 1149 1150 1151 1152 1153 1154 1155 1156 1157 1158 1159 1160 1161 1162
/// Data about why a target was re-run.
class InvalidatedReason {
  InvalidatedReason(this.kind);

  final InvalidatedReasonKind kind;
  /// Absolute file paths of inputs or outputs, depending on [kind].
  final List<String> data = <String>[];

  @override
  String toString() {
    switch (kind) {
      case InvalidatedReasonKind.inputMissing:
        return 'The following inputs were missing: ${data.join(',')}';
      case InvalidatedReasonKind.inputChanged:
        return 'The following inputs have updated contents: ${data.join(',')}';
      case InvalidatedReasonKind.outputChanged:
        return 'The following outputs have updated contents: ${data.join(',')}';
      case InvalidatedReasonKind.outputMissing:
        return 'The following outputs were missing: ${data.join(',')}';
      case InvalidatedReasonKind.outputSetChanged:
        return 'The following outputs were removed from the output set: ${data.join(',')}';
    }
  }
}

1163
/// A description of why a target was rerun.
1164
enum InvalidatedReasonKind {
1165 1166 1167 1168
  /// An input file that was expected is missing. This can occur when using
  /// depfile dependencies, or if a target is incorrectly specified.
  inputMissing,

1169
  /// An input file has an updated key.
1170 1171
  inputChanged,

1172
  /// An output file has an updated key.
1173 1174 1175 1176 1177 1178 1179 1180
  outputChanged,

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

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