null safety

.github/workflows/ci.yml

@@ -14,13 +14,13 @@ env:
 
 jobs:
   # Check code formatting and static analysis on a single OS (linux)
-  # against Dart dev.
+  # against Dart beta.
   analyze:
     runs-on: ubuntu-latest
     strategy:
       fail-fast: false
       matrix:
-        sdk: [dev]
+        sdk: [beta]
     steps:
       - uses: actions/checkout@v2
       - uses: dart-lang/[email protected]
@@ -38,7 +38,7 @@ jobs:
 
   # Run tests on a matrix consisting of two dimensions:
   # 1. OS: ubuntu-latest, (macos-latest, windows-latest)
-  # 2. release channel: dev
+  # 2. release channel: beta
   test:
     needs: analyze
     runs-on: ${{ matrix.os }}
@@ -47,7 +47,7 @@ jobs:
       matrix:
         # Add macos-latest and/or windows-latest if relevant for this package.
         os: [ubuntu-latest]
-        sdk: [2.3.0, dev]
+        sdk: [beta]
     steps:
       - uses: actions/checkout@v2
       - uses: dart-lang/[email protected]

benchmark/shortest_path_benchmark.dart

@@ -21,7 +21,7 @@ void main() {
     }
   }
 
-  int minTicks;
+  int? minTicks;
   var maxIteration = 0;
 
   final testOutput =
@@ -34,7 +34,7 @@ void main() {
     watch
       ..reset()
       ..start();
-    final length = shortestPath(0, size - 1, (e) => graph[e] ?? []).length;
+    final length = shortestPath(0, size - 1, (e) => graph[e] ?? [])?.length;
     watch.stop();
     assert(length == 4, '$length');
 

example/crawl_async_example.dart

@@ -26,9 +26,9 @@ Future<Null> main() async {
   print(allImports.map((s) => s.uri).toList());
 }
 
-AnalysisContext _analysisContext;
+AnalysisContext? _analysisContext;
 
-Future<AnalysisContext> get analysisContext async {
+Future<AnalysisContext?> get analysisContext async {
   if (_analysisContext == null) {
     var libUri = Uri.parse('package:graphs/');
     var libPath = await pathForUri(libUri);
@@ -39,25 +39,29 @@ Future<AnalysisContext> get analysisContext async {
       throw StateError('Expected to find exactly one context root, got $roots');
     }
 
-    _analysisContext = ContextBuilder().createContext(contextRoot: roots[0]);
+    final analysisContext =
+        ContextBuilder().createContext(contextRoot: roots[0]);
+    _analysisContext = analysisContext;
+    return analysisContext;
   }
 
-  return _analysisContext;
+  return null;
 }
 
-Future<Iterable<Uri>> findImports(Uri from, Source source) async {
-  return source.unit.directives
+Future<Iterable<Uri>?> findImports(Uri from, Source source) async {
+  return source.unit?.directives
       .whereType<UriBasedDirective>()
       .map((d) => d.uri.stringValue)
-      .where((uri) => !uri.startsWith('dart:'))
+      .whereType<String>()
+      .where((uri) => uri.startsWith('dart:') == false)
       .map((import) => resolveImport(import, from));
 }
 
-Future<CompilationUnit> parseUri(Uri uri) async {
+Future<CompilationUnit?> parseUri(Uri uri) async {
   var path = await pathForUri(uri);
-  var analysisSession = (await analysisContext).currentSession;
-  var parseResult = analysisSession.getParsedUnit(path);
-  return parseResult.unit;
+  var analysisSession = (await analysisContext)?.currentSession;
+  var parseResult = analysisSession?.getParsedUnit(path);
+  return parseResult?.unit;
 }
 
 Future<String> pathForUri(Uri uri) async {
@@ -81,7 +85,7 @@ Uri resolveImport(String import, Uri from) {
 
 class Source {
   final Uri uri;
-  final CompilationUnit unit;
+  final CompilationUnit? unit;
 
   Source(this.uri, this.unit);
 }

example/example.dart

@@ -41,7 +41,7 @@ void main() {
   });
 
   var components = stronglyConnectedComponents<Node>(
-      graph.nodes.keys, (node) => graph.nodes[node]);
+      graph.nodes.keys, (node) => graph.nodes[node] ?? []);
 
   print(components);
 }

lib/src/crawl_async.dart

@@ -34,7 +34,7 @@ final _empty = Future<Null>.value(null);
 /// have not completed. If the [edges] callback needs to be limited or throttled
 /// that must be done by wrapping it before calling [crawlAsync].
 Stream<V> crawlAsync<K, V>(Iterable<K> roots, FutureOr<V> Function(K) readNode,
-    FutureOr<Iterable<K>> Function(K, V) edges) {
+    FutureOr<Iterable<K>?> Function(K, V) edges) {
   final crawl = _CrawlAsync(roots, readNode, edges)..run();
   return crawl.result.stream;
 }
@@ -43,7 +43,7 @@ class _CrawlAsync<K, V> {
   final result = StreamController<V>();
 
   final FutureOr<V> Function(K) readNode;
-  final FutureOr<Iterable<K>> Function(K, V) edges;
+  final FutureOr<Iterable<K>?> Function(K, V) edges;
   final Iterable<K> roots;
 
   final _seen = HashSet<K>();

lib/src/shortest_path.dart

@@ -24,12 +24,12 @@ import 'dart:collection';
 ///
 /// If you supply one of [equals] or [hashCode], you should generally also to
 /// supply the other.
-List<T> shortestPath<T>(
+List<T>? shortestPath<T>(
   T start,
   T target,
   Iterable<T> Function(T) edges, {
-  bool Function(T, T) equals,
-  int Function(T) hashCode,
+  bool Function(T?, T?)? equals,
+  int Function(T)? hashCode,
 }) =>
     _shortestPaths<T>(
       start,
@@ -61,8 +61,8 @@ List<T> shortestPath<T>(
 Map<T, List<T>> shortestPaths<T>(
   T start,
   Iterable<T> Function(T) edges, {
-  bool Function(T, T) equals,
-  int Function(T) hashCode,
+  bool Function(T?, T?)? equals,
+  int Function(T)? hashCode,
 }) =>
     _shortestPaths<T>(
       start,
@@ -74,29 +74,28 @@ Map<T, List<T>> shortestPaths<T>(
 Map<T, List<T>> _shortestPaths<T>(
   T start,
   Iterable<T> Function(T) edges, {
-  T target,
-  bool Function(T, T) equals,
-  int Function(T) hashCode,
+  T? target,
+  bool Function(T?, T?)? equals,
+  int Function(T)? hashCode,
 }) {
   assert(start != null, '`start` cannot be null');
-  assert(edges != null, '`edges` cannot be null');
 
   final distances = HashMap<T, List<T>>(equals: equals, hashCode: hashCode);
   distances[start] = const [];
 
   equals ??= _defaultEquals;
-  if (equals(start, target)) {
+  if (equals.call(start, target)) {
     return distances;
   }
 
   final toVisit = ListQueue<T>()..add(start);
 
-  List<T> bestOption;
+  List<T>? bestOption;
 
   while (toVisit.isNotEmpty) {
     final current = toVisit.removeFirst();
     final currentPath = distances[current];
-    final currentPathLength = currentPath.length;
+    final currentPathLength = currentPath?.length ?? 0;
 
     if (bestOption != null && (currentPathLength + 1) >= bestOption.length) {
       // Skip any existing `toVisit` items that have no chance of being
@@ -111,13 +110,13 @@ Map<T, List<T>> _shortestPaths<T>(
       assert(existingPath == null ||
           existingPath.length <= (currentPathLength + 1));
 
-      if (existingPath == null) {
+      if (existingPath == null && currentPath != null) {
         final newOption = [
           ...currentPath,
           edge,
         ];
 
-        if (equals(edge, target)) {
+        if (target != null && equals(edge, target)) {
           assert(bestOption == null || bestOption.length > newOption.length);
           bestOption = newOption;
         }
@@ -135,4 +134,4 @@ Map<T, List<T>> _shortestPaths<T>(
   return distances;
 }
 
-bool _defaultEquals(Object a, Object b) => a == b;
+bool _defaultEquals<T>(T a, T b) => a == b;

lib/src/strongly_connected_components.dart

@@ -32,8 +32,8 @@ import 'dart:math' show min;
 List<List<T>> stronglyConnectedComponents<T>(
   Iterable<T> nodes,
   Iterable<T> Function(T) edges, {
-  bool Function(T, T) equals,
-  int Function(T) hashCode,
+  bool Function(T?, T?)? equals,
+  int Function(T)? hashCode,
 }) {
   final result = <List<T>>[];
   final lowLinks = HashMap<T, int>(equals: equals, hashCode: hashCode);
@@ -52,12 +52,20 @@ List<List<T>> stronglyConnectedComponents<T>(
     lastVisited.addLast(node);
     onStack.add(node);
     // ignore: omit_local_variable_types
-    for (final T next in edges(node) ?? const []) {
+    for (final T next in edges(node)) {
       if (!indexes.containsKey(next)) {
         strongConnect(next);
-        lowLinks[node] = min(lowLinks[node], lowLinks[next]);
+        final n = lowLinks[node];
+        final x = lowLinks[next];
+        if (n != null && x != null) {
+          lowLinks[node] = min(n, x);
+        }
       } else if (onStack.contains(next)) {
-        lowLinks[node] = min(lowLinks[node], indexes[next]);
+        final n = lowLinks[node];
+        final x = indexes[next];
+        if (n != null && x != null) {
+          lowLinks[node] = min(n, x);
+        }
       }
     }
     if (lowLinks[node] == indexes[node]) {
@@ -67,7 +75,7 @@ List<List<T>> stronglyConnectedComponents<T>(
         next = lastVisited.removeLast();
         onStack.remove(next);
         component.add(next);
-      } while (!equals(next, node));
+      } while (equals?.call(next, node) == false);
       result.add(component);
     }
   }
@@ -78,4 +86,4 @@ List<List<T>> stronglyConnectedComponents<T>(
   return result;
 }
 
-bool _defaultEquals(Object a, Object b) => a == b;
+bool _defaultEquals<T>(T a, T b) => a == b;

pubspec.yaml

@@ -1,16 +1,16 @@
 name: graphs
-version: 0.2.1-dev
+version: 0.3.0-nullsafety.0
 description: Graph algorithms that operate on graphs in any representation
 homepage: https://github.com/dart-lang/graphs
 
 environment:
-  sdk: '>=2.3.0 <3.0.0'
-
+  sdk: '>=2.12.0-0 <3.0.0'
+dependency_overrides:
+  analyzer: ^0.42.0-nullsafety.0
 dev_dependencies:
-  pedantic: ^1.3.0
-  test: ^1.5.1
+  pedantic: ^1.10.0
+  test: ^1.16.0
 
   # For examples
-  analyzer: '>=0.35.0 <0.42.0'
-  path: ^1.1.0
-  pool: ^1.3.0
+  path: ^1.8.0
+  pool: ^1.5.0

test/crawl_async_test.dart

@@ -2,16 +2,15 @@
 // 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.
 
-import 'package:test/test.dart';
-
 import 'package:graphs/graphs.dart';
+import 'package:test/test.dart';
 
 import 'utils/graph.dart';
 
 void main() {
   group('asyncCrawl', () {
-    Future<List<String>> crawl(
-        Map<String, List<String>> g, Iterable<String> roots) {
+    Future<List<String?>> crawl(
+        Map<String, List<String>?> g, Iterable<String> roots) {
       var graph = AsyncGraph(g);
       return crawlAsync(roots, graph.readNode, graph.edges).toList();
     }