Migrate user-facing apis to null-safety (#2996)

Migrate packages typically imported by build authors to null-safety (part 1 /3). Closes #2920

In this PR, I migrate

- the `build` package
- the `build_test` package (or rather, the parts of that package that don't import `build_resolvers`)
- the `scratch_space` package

After the `graphs` package is migrated, I'll open another PR to migrate the `build_resolvers` package. When that one is done too, we can start to opt the tests of `build` and `build_test` into null-safety and publish, thus enabling build authors to write and test their builders with strong null-safety. 

Migrating the rest of the build system is not a goal for the near future, so we won't run builds with strong null-safety.

build/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 2.0.0-dev
+
+- Migrate to null-safety
+- __Breaking__: Remove the deprecated `rootPackage` argument to `runBuilder`
+
 ## 1.6.3
 
 - Use latest analyzer version `1.x`.

build/lib/src/analyzer/resolver.dart

@@ -64,7 +64,7 @@ abstract class Resolver {
   /// **NOTE**: In general, its recommended to use [libraryFor] with an absolute
   /// asset id instead of a named identifier that has the possibility of not
   /// being unique.
-  Future<LibraryElement> findLibraryByName(String libraryName);
+  Future<LibraryElement?> findLibraryByName(String libraryName);
 
   /// Returns the [AssetId] of the Dart library or part declaring [element].
   ///
@@ -168,7 +168,7 @@ class SyntaxErrorInAssetException implements Exception {
       final error = errorAndResult.key;
       // Use a short name: We present the full context by including the asset id
       // and this is easier to skim through
-      final sourceName = error.source?.shortName ?? '<unknown>';
+      final sourceName = error.source.shortName;
 
       final lineInfo = errorAndResult.value.lineInfo;
       final position = lineInfo.getLocation(error.offset);

build/lib/src/asset/id.dart

@@ -55,7 +55,7 @@ class AssetId implements Comparable<AssetId> {
   ///
   /// `asset:` uris have the format '$package/$path', including the top level
   /// directory.
-  factory AssetId.resolve(String uri, {AssetId from}) {
+  factory AssetId.resolve(String uri, {AssetId? from}) {
     final parsedUri = Uri.parse(uri);
     if (parsedUri.hasScheme) {
       if (parsedUri.scheme == 'package') {
@@ -108,8 +108,7 @@ class AssetId implements Comparable<AssetId> {
   /// A `package:` URI suitable for use directly with other systems if this
   /// asset is under it's package's `lib/` directory, else an `asset:` URI
   /// suitable for use within build tools.
-  Uri get uri => _uri ??= _constructUri(this);
-  Uri _uri;
+  late final Uri uri = _constructUri(this);
 
   /// Deserializes an [AssetId] from [data], which must be the result of
   /// calling [serialize] on an existing [AssetId].

build/lib/src/asset/reader.dart

@@ -28,7 +28,7 @@ abstract class AssetReader {
   /// * Throws a `PackageNotFoundException` if `id.package` is not found.
   /// * Throws a `AssetNotFoundException` if `id.path` is not found.
   /// * Throws an `InvalidInputException` if [id] is an invalid input.
-  Future<String> readAsString(AssetId id, {Encoding encoding});
+  Future<String> readAsString(AssetId id, {Encoding encoding = utf8});
 
   /// Indicates whether asset at [id] is readable.
   Future<bool> canRead(AssetId id);
@@ -68,5 +68,5 @@ abstract class MultiPackageAssetReader extends AssetReader {
   /// Some implementations may require the [package] argument, while others
   /// may have a sane default.
   @override
-  Stream<AssetId> findAssets(Glob glob, {String package});
+  Stream<AssetId> findAssets(Glob glob, {String? package});
 }

build/lib/src/builder/build_step_impl.dart

@@ -25,7 +25,7 @@ import 'exceptions.dart';
 /// This represents a single input and its expected and real outputs. It also
 /// handles tracking of dependencies.
 class BuildStepImpl implements BuildStep {
-  final Resolvers _resolvers;
+  final Resolvers? _resolvers;
   final StageTracker _stageTracker;
 
   /// The primary input id for this build step.
@@ -55,23 +55,28 @@ class BuildStepImpl implements BuildStep {
 
   bool _isComplete = false;
 
-  final void Function(Iterable<AssetId>) _reportUnusedAssets;
+  final void Function(Iterable<AssetId>)? _reportUnusedAssets;
 
   BuildStepImpl(this.inputId, Iterable<AssetId> expectedOutputs, this._reader,
       this._writer, this._resolvers, this._resourceManager,
-      {StageTracker stageTracker,
-      void Function(Iterable<AssetId>) reportUnusedAssets})
+      {StageTracker? stageTracker,
+      void Function(Iterable<AssetId>)? reportUnusedAssets})
       : _expectedOutputs = expectedOutputs.toSet(),
         _stageTracker = stageTracker ?? NoOpStageTracker.instance,
         _reportUnusedAssets = reportUnusedAssets;
 
   @override
   Resolver get resolver {
     if (_isComplete) throw BuildStepCompletedException();
-    return _DelayedResolver(_resolver ??= _resolvers.get(this));
+    final resolvers = _resolvers;
+    if (resolvers == null) {
+      throw UnsupportedError('Resolvers are not available in this build.');
+    }
+
+    return _DelayedResolver(_resolver ??= resolvers.get(this));
   }
 
-  Future<ReleasableResolver> _resolver;
+  Future<ReleasableResolver>? _resolver;
 
   @override
   Future<bool> canRead(AssetId id) {
@@ -142,7 +147,7 @@ class BuildStepImpl implements BuildStep {
 
   Future<void> _futureOrWrite<T>(
           FutureOr<T> content, Future<void> Function(T content) write) =>
-      (content is Future<T>) ? content.then(write) : write(content as T);
+      (content is Future<T>) ? content.then(write) : write(content);
 
   /// Waits for work to finish and cleans up resources.
   ///
@@ -165,7 +170,7 @@ class BuildStepImpl implements BuildStep {
 
   @override
   void reportUnusedAssets(Iterable<AssetId> assets) {
-    if (_reportUnusedAssets != null) _reportUnusedAssets(assets);
+    _reportUnusedAssets?.call(assets);
   }
 }
 
@@ -202,7 +207,7 @@ class _DelayedResolver implements Resolver {
           .libraryFor(assetId, allowSyntaxErrors: allowSyntaxErrors);
 
   @override
-  Future<LibraryElement> findLibraryByName(String libraryName) async =>
+  Future<LibraryElement?> findLibraryByName(String libraryName) async =>
       (await _delegate).findLibraryByName(libraryName);
 
   @override

build/lib/src/builder/builder.dart

@@ -40,7 +40,7 @@ class BuilderOptions {
   /// Whether or not this builder is running on the root package.
   final bool isRoot;
 
-  const BuilderOptions(this.config, {bool isRoot}) : isRoot = isRoot ?? false;
+  const BuilderOptions(this.config, {this.isRoot = false});
 
   /// Returns a new set of options with keys from [other] overriding options in
   /// this instance.
@@ -50,7 +50,7 @@ class BuilderOptions {
   /// returned directly.
   ///
   /// The `isRoot` value will also be overridden to value from [other].
-  BuilderOptions overrideWith(BuilderOptions other) {
+  BuilderOptions overrideWith(BuilderOptions? other) {
     if (other == null) return this;
     return BuilderOptions({}..addAll(config)..addAll(other.config),
         isRoot: other.isRoot);

build/lib/src/builder/exceptions.dart

@@ -5,7 +5,7 @@ import '../asset/id.dart';
 
 class UnexpectedOutputException implements Exception {
   final AssetId assetId;
-  final Iterable<AssetId> expected;
+  final Iterable<AssetId>? expected;
 
   UnexpectedOutputException(this.assetId, {this.expected});
 

build/lib/src/builder/file_deleting_builder.dart

@@ -24,7 +24,7 @@ class FileDeletingBuilder implements PostProcessBuilder {
   FileDeletingBuilder.withExcludes(
       this.inputExtensions, Iterable<String> exclude,
       {this.isEnabled = true})
-      : exclude = exclude?.map((s) => Glob(s))?.toList() ?? const [];
+      : exclude = exclude.map((s) => Glob(s)).toList();
 
   @override
   FutureOr<Null> build(PostProcessBuildStep buildStep) {

build/lib/src/builder/logging.dart

@@ -13,7 +13,7 @@ final _default = Logger('build.fallback');
 /// The log instance for the currently running BuildStep.
 ///
 /// Will be `null` when not running within a build.
-Logger get log => Zone.current[logKey] as Logger ?? _default;
+Logger get log => Zone.current[logKey] as Logger? ?? _default;
 
 /// Runs [fn] in an error handling [Zone].
 ///
@@ -29,7 +29,7 @@ Future<T> scopeLogAsync<T>(Future<T> Function() fn, Logger log) {
     done.completeError(e, st);
   }, zoneSpecification: ZoneSpecification(print: (self, parent, zone, message) {
     log.warning(message);
-  }), zoneValues: {logKey: log}).then((result) {
+  }), zoneValues: {logKey: log})?.then((result) {
     if (done.isCompleted) return;
     done.complete(result);
   });

build/lib/src/builder/multiplexing_builder.dart

@@ -42,8 +42,7 @@ Map<String, List<String>> _mergeMaps(Iterable<Map<String, List<String>>> maps) {
   var result = <String, List<String>>{};
   for (var map in maps) {
     for (var key in map.keys) {
-      result.putIfAbsent(key, () => []);
-      result[key].addAll(map[key]);
+      result.putIfAbsent(key, () => []).addAll(map[key]!);
     }
   }
   return result;

build/lib/src/builder/post_process_build_step.dart

@@ -76,4 +76,4 @@ class PostProcessBuildStep {
 
 Future<void> _futureOrWrite<T>(
         FutureOr<T> content, Future<void> Function(T content) write) =>
-    (content is Future<T>) ? content.then(write) : write(content as T);
+    (content is Future<T>) ? content.then(write) : write(content);

build/lib/src/experiments.dart

@@ -10,7 +10,7 @@ const Symbol _enabledExperimentsKey = #dartLanguageEnabledExperiments;
 ///
 /// This can be overridden for a new [Zone] by using [withEnabledExperiments].
 List<String> get enabledExperiments =>
-    Zone.current[_enabledExperimentsKey] as List<String> ?? const [];
+    Zone.current[_enabledExperimentsKey] as List<String>? ?? const [];
 
 /// Runs [fn] in a [Zone], setting [enabledExperiments] for all code running
 /// in that [Zone].

build/lib/src/generate/expected_outputs.dart

@@ -10,7 +10,7 @@ Iterable<AssetId> expectedOutputs(Builder builder, AssetId input) {
   var matchingExtensions =
       builder.buildExtensions.keys.where((e) => input.path.endsWith(e));
   return matchingExtensions
-      .expand((e) => _replaceExtensions(input, e, builder.buildExtensions[e]));
+      .expand((e) => _replaceExtensions(input, e, builder.buildExtensions[e]!));
 }
 
 Iterable<AssetId> _replaceExtensions(

build/lib/src/generate/run_builder.dart

@@ -29,22 +29,21 @@ import 'expected_outputs.dart';
 /// `BuildStep.reportUnusedAssets` in [builder] will be forwarded to this
 /// function with the associated primary input.
 Future<void> runBuilder(Builder builder, Iterable<AssetId> inputs,
-    AssetReader reader, AssetWriter writer, Resolvers resolvers,
-    {Logger logger,
-    ResourceManager resourceManager,
-    @Deprecated('The rootPackage argument is unused') String rootPackage,
+    AssetReader reader, AssetWriter writer, Resolvers? resolvers,
+    {Logger? logger,
+    ResourceManager? resourceManager,
     StageTracker stageTracker = NoOpStageTracker.instance,
-    void Function(AssetId input, Iterable<AssetId> assets)
+    void Function(AssetId input, Iterable<AssetId> assets)?
         reportUnusedAssetsForInput}) async {
   var shouldDisposeResourceManager = resourceManager == null;
-  resourceManager ??= ResourceManager();
+  final resources = resourceManager ?? ResourceManager();
   logger ??= Logger('runBuilder');
   //TODO(nbosch) check overlapping outputs?
   Future<void> buildForInput(AssetId input) async {
     var outputs = expectedOutputs(builder, input);
     if (outputs.isEmpty) return;
     var buildStep = BuildStepImpl(
-        input, outputs, reader, writer, resolvers, resourceManager,
+        input, outputs, reader, writer, resolvers, resources,
         stageTracker: stageTracker,
         reportUnusedAssets: reportUnusedAssetsForInput == null
             ? null
@@ -59,7 +58,7 @@ Future<void> runBuilder(Builder builder, Iterable<AssetId> inputs,
   await scopeLogAsync(() => Future.wait(inputs.map(buildForInput)), logger);
 
   if (shouldDisposeResourceManager) {
-    await resourceManager.disposeAll();
-    await resourceManager.beforeExit();
+    await resources.disposeAll();
+    await resources.beforeExit();
   }
 }

build/lib/src/generate/run_post_process_builder.dart

@@ -3,7 +3,6 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:logging/logging.dart';
-import 'package:meta/meta.dart';
 
 import '../asset/id.dart';
 import '../asset/reader.dart';
@@ -20,8 +19,8 @@ import '../builder/post_process_builder.dart';
 /// deleted on disk since the `writer` has no mechanism for delete.
 Future<void> runPostProcessBuilder(PostProcessBuilder builder, AssetId inputId,
     AssetReader reader, AssetWriter writer, Logger logger,
-    {@required void Function(AssetId) addAsset,
-    @required void Function(AssetId) deleteAsset}) async {
+    {required void Function(AssetId) addAsset,
+    required void Function(AssetId) deleteAsset}) async {
   await scopeLogAsync(() async {
     var buildStep =
         postProcessBuildStep(inputId, reader, writer, addAsset, deleteAsset);

build/lib/src/resource/resource.dart

@@ -22,18 +22,18 @@ class Resource<T> {
 
   /// Optional method which is given an existing instance that is ready to be
   /// disposed.
-  final DisposeInstance<T> _userDispose;
+  final DisposeInstance<T>? _userDispose;
 
   /// Optional method which is called before the process is going to exit.
   ///
   /// This allows resources to do any final cleanup, and is not given an
   /// instance.
-  final BeforeExit _userBeforeExit;
+  final BeforeExit? _userBeforeExit;
 
   /// A Future instance of this resource if one has ever been requested.
   final _instanceByManager = <ResourceManager, Future<T>>{};
 
-  Resource(this._create, {DisposeInstance<T> dispose, BeforeExit beforeExit})
+  Resource(this._create, {DisposeInstance<T>? dispose, BeforeExit? beforeExit})
       : _userDispose = dispose,
         _userBeforeExit = beforeExit;
 
@@ -47,7 +47,7 @@ class Resource<T> {
     var oldInstance = _fetch(manager);
     _instanceByManager.remove(manager);
     if (_userDispose != null) {
-      return oldInstance.then(_userDispose);
+      return oldInstance.then(_userDispose!);
     } else {
       return Future.value(null);
     }
@@ -88,7 +88,7 @@ class ResourceManager {
   /// Invokes the `beforeExit` callbacks of all [Resource]s that had one.
   Future<Null> beforeExit() async {
     await Future.wait(_resourcesWithBeforeExit.map((r) async {
-      if (r._userBeforeExit != null) return r._userBeforeExit();
+      return r._userBeforeExit?.call();
     }));
     _resourcesWithBeforeExit.clear();
   }

build/pubspec.yaml

@@ -1,23 +1,30 @@
 name: build
-version: 1.6.3
+version: 2.0.0-dev
 description: A build system for Dart.
 homepage: https://github.com/dart-lang/build/tree/master/build
 
 environment:
-  sdk: ">=2.11.99 <3.0.0"
+  sdk: ">=2.12.0-0 <3.0.0"
 
 dependencies:
   analyzer: ^1.0.0
-  async: ">=1.13.3 <3.0.0"
-  convert: ">=2.0.0 <4.0.0"
-  crypto: ">=0.9.2 <4.0.0"
+  async: ^2.0.0
+  convert: ^3.0.0
+  crypto: ^3.0.0
   glob: ^2.0.0
-  logging: ">=0.11.2 <2.0.0"
-  meta: ^1.1.0
-  path: ^1.1.0
+  logging: ^1.0.0
+  meta: ^1.3.0
+  path: ^1.8.0
 
 dev_dependencies:
   build_resolvers: ^1.0.0
-  build_test: ^1.0.0
+  build_test: ^1.4.0
   pedantic: ^1.0.0
-  test: ^1.2.0
+  test: ^1.16.0
+
+dependency_overrides:
+  build_resolvers:
+    path: ../build_resolvers
+  build_test:
+    path: ../build_test
+  ## Remove each of the above as they are published

build/test/builder/build_step_impl_test.dart

@@ -1,6 +1,7 @@
 // Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+//@dart=2.9
 @TestOn('vm')
 import 'dart:async';
 import 'dart:convert';

build/test/builder/multiplexing_builder_test.dart

@@ -1,6 +1,7 @@
 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+// @dart=2.9
 
 import 'package:build/build.dart';
 import 'package:build_test/build_test.dart';

build/test/generate/run_builder_test.dart

@@ -1,6 +1,7 @@
 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+// @dart=2.9
 @TestOn('vm')
 import 'dart:async';
 

build/test/generate/run_post_process_builder_test.dart

@@ -1,6 +1,7 @@
 // Copyright (c) 2018, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+// @dart=2.9
 
 import 'package:build/build.dart';
 import 'package:build_test/build_test.dart';

build/test/resource/resource_test.dart

@@ -9,7 +9,7 @@ import 'package:test/test.dart';
 import 'package:build/build.dart';
 
 void main() {
-  ResourceManager resourceManager;
+  late ResourceManager resourceManager;
   setUp(() {
     resourceManager = ResourceManager();
   });