build_runner watch support

packages/core/lib/flutter_generator.dart

@@ -24,19 +24,29 @@ class FlutterGenerator {
   final String colorsName;
   final String fontsName;
 
-  Future<void> build() async {
-    stdout.writeln(flutterGenVersion);
+  Future<Config?> getConfig() async {
     Config config;
+
     try {
       config = await loadPubspecConfig(pubspecFile);
     } on InvalidSettingsException catch (e) {
       stderr.writeln(e.message);
-      return;
+      return null;
     } on FileSystemException catch (e) {
       stderr.writeln(e.message);
-      return;
+      return null;
     }
 
+    return config;
+  }
+
+  Future<void> build({Config? config}) async {
+    stdout.writeln(flutterGenVersion);
+
+    config ??= await getConfig();
+
+    if (config == null) return;
+
     final flutter = config.pubspec.flutter;
     final flutterGen = config.pubspec.flutterGen;
     final output = config.pubspec.flutterGen.output;

packages/core/lib/settings/config.dart

@@ -7,9 +7,10 @@ import '../utils/map.dart';
 import 'pubspec.dart';
 
 class Config {
-  Config._({required this.pubspec});
+  Config._({required this.pubspec, required this.pubspecFile});
 
   final Pubspec pubspec;
+  final File pubspecFile;
 }
 
 Future<Config> loadPubspecConfig(File pubspecFile) async {
@@ -26,7 +27,7 @@ Future<Config> loadPubspecConfig(File pubspecFile) async {
   final defaultMap = loadYaml(_defaultConfig) as Map?;
   final mergedMap = mergeMap([defaultMap, userMap]);
   final pubspec = Pubspec.fromJson(mergedMap);
-  return Config._(pubspec: pubspec);
+  return Config._(pubspec: pubspec, pubspecFile: pubspecFile);
 }
 
 const _defaultConfig = '''

packages/runner/build.yaml

@@ -8,6 +8,6 @@ builders:
   flutter_gen_runner:
     import: "package:flutter_gen_runner/flutter_gen_runner.dart"
     builder_factories: [ "build" ]
-    build_extensions: { "$lib$": [ ".gen.dart" ] }
+    build_extensions: { "$package$": [ ".gen.dart" ] }
     auto_apply: dependents
     build_to: source

packages/runner/lib/flutter_gen_builder.dart

@@ -0,0 +1,83 @@
+import 'dart:async';
+import 'dart:collection';
+import 'dart:io';
+
+import 'package:build/build.dart';
+import 'package:collection/collection.dart';
+import 'package:crypto/crypto.dart';
+import 'package:flutter_gen_core/flutter_generator.dart';
+import 'package:flutter_gen_core/settings/config.dart';
+import 'package:glob/glob.dart';
+
+class FlutterGenBuilder extends Builder {
+  final FlutterGenerator generator = FlutterGenerator(File('pubspec.yaml'));
+  _FlutterGenBuilderState? _currentState;
+
+  @override
+  Future<void> build(BuildStep buildStep) async {
+    var config = await generator.getConfig();
+
+    if (config == null) return;
+
+    var state = await _createState(config, buildStep);
+
+    if (_currentState != null && _currentState!.equals(state)) return;
+
+    _currentState = state;
+
+    await generator.build(config: config);
+  }
+
+  @override
+  Map<String, List<String>> get buildExtensions => {
+        "\$package\$": ['.gen.dart']
+      };
+
+  Future<_FlutterGenBuilderState> _createState(
+      Config config, BuildStep buildStep) async {
+    final pubspec = config.pubspec;
+    final HashMap<String, Digest> colors = HashMap();
+    final HashSet<String> assets = HashSet();
+
+    if (pubspec.flutterGen.colors.enabled) {
+      for (var colorInput in pubspec.flutterGen.colors.inputs) {
+        if (colorInput.isEmpty) continue;
+        await for (var assetId in buildStep.findAssets(Glob(colorInput))) {
+          var digest = await buildStep.digest(assetId);
+          colors[assetId.path] = digest;
+        }
+      }
+    }
+
+    if (pubspec.flutterGen.assets.enabled) {
+      for (var assetInput in pubspec.flutter.assets) {
+        if (assetInput.isEmpty) continue;
+        if (assetInput.endsWith("/")) assetInput += "*";
+        await for (var assetId in buildStep.findAssets(Glob(assetInput))) {
+          assets.add(assetId.path);
+        }
+      }
+    }
+
+    final pubspecAsset =
+        await buildStep.findAssets(Glob(config.pubspecFile.path)).single;
+
+    final pubspecDigest = await buildStep.digest(pubspecAsset);
+
+    return _FlutterGenBuilderState(pubspecDigest, colors, assets);
+  }
+}
+
+class _FlutterGenBuilderState {
+  final Digest pubspecDigest;
+  final HashMap<String, Digest> colors;
+  final HashSet<String> assets;
+
+  _FlutterGenBuilderState(this.pubspecDigest, this.colors, this.assets);
+
+  bool equals(_FlutterGenBuilderState state) {
+    return pubspecDigest == state.pubspecDigest &&
+        const MapEquality().equals(colors, state.colors) &&
+        const SetEquality().equals(assets, state.assets);
+  }
+}

packages/runner/lib/flutter_gen_runner.dart

@@ -1,19 +1,7 @@
-import 'dart:io';
-
 import 'package:build/build.dart';
-import 'package:flutter_gen_core/flutter_generator.dart';
 
-Builder build(BuilderOptions options) {
-  Future(() async {
-    await FlutterGenerator(File('pubspec.yaml')).build();
-  });
-  return EmptyBuilder();
-}
+import 'flutter_gen_builder.dart';
 
-class EmptyBuilder extends Builder {
-  @override
-  Future<void> build(BuildStep buildStep) async {}
-
-  @override
-  Map<String, List<String>> get buildExtensions => {};
+Builder build(BuilderOptions options) {
+  return FlutterGenBuilder();
 }

packages/runner/pubspec.yaml

@@ -13,7 +13,11 @@ environment:
 dependencies:
   flutter_gen_core: ^4.1.6
   build: '>=2.0.0 <3.0.0'
+  collection: ^1.15.0
+  crypto: ^3.0.2
+  glob: ^2.0.2
 
 dev_dependencies:
   flutter_lints: ^2.0.1
   build_test: '>=2.0.0 <3.0.0'
+  flutter_lints: '>=1.0.4 <2.0.0'