Allow an option called run_only_if_triggered.

Author: davidmorgan

json_serializable/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 6.12.0-wip
+
+- Allow `run_only_if_triggered` to be specified in `build.yaml` to turn on the
+  `build_runner` triggers heuristic.
+
 ## 6.11.1
 
 - Allow `build: '>=3.0.0 <5.0.0'`.

json_serializable/lib/builder.dart

@@ -23,7 +23,12 @@ import 'src/json_part_builder.dart';
 /// Not meant to be invoked by hand-authored code.
 Builder jsonSerializable(BuilderOptions options) {
   try {
-    final config = JsonSerializable.fromJson(options.config);
+    var configJson = options.config;
+    // Ignore `run_only_if_triggered` if present, it's used by `build_runner`.
+    if (configJson.containsKey('run_only_if_triggered')) {
+      configJson = Map.of(configJson)..remove('run_only_if_triggered');
+    }
+    final config = JsonSerializable.fromJson(configJson);
     return jsonPartBuilder(config: config);
   } on CheckedFromJsonException catch (e) {
     final lines = <String>[

json_serializable/pubspec.yaml

@@ -1,5 +1,5 @@
 name: json_serializable
-version: 6.11.1
+version: 6.12.0-wip
 description: >-
   Automatically generate code for converting to and from JSON by annotating
   Dart classes.

json_serializable/test/config_test.dart

@@ -36,6 +36,11 @@ void main() {
     expect(builder, isNotNull);
   });
 
+  test('triggers config is ignored', () async {
+    // This key is used by build_runner so it's meaningful for any builder.
+    jsonSerializable(const BuilderOptions({'run_only_if_triggered': true}));
+  });
+
   test('valid, non-default config', () {
     expect(
       generatorConfigNonDefaultJson.keys,