[pigeon] Make Kotlin FlutterError a runtime error (#11469)

Change the Kotlin generator's `FlutterError` to inherit from `RuntimeException`, rather than just `Runnable`, so that it behaves as an unchecked error when used from Java (as is the case for the Java version).

Fixes flutter/flutter#184200

## Pre-Review Checklist

[^1]: Regular contributors who have demonstrated familiarity with the repository guidelines only need to comment if the PR is not auto-exempted by repo tooling.

Author: stuartmorgan-g

packages/pigeon/CHANGELOG.md

@@ -1,3 +1,8 @@
+## 26.3.4
+
+* [kotlin] Updates generated error class to inherit from `RuntimeException`
+  instead of `Throwable`, for better Java interoperability.
+
 ## 26.3.3
 
 * Updates `analyzer` dependency to support versions 10 through 12.

packages/pigeon/example/app/android/app/src/main/kotlin/dev/flutter/pigeon_example_app/Messages.g.kt

@@ -191,7 +191,7 @@ class FlutterError(
     val code: String,
     override val message: String? = null,
     val details: Any? = null
-) : Throwable()
+) : RuntimeException()
 
 enum class Code(val raw: Int) {
   ONE(0),

packages/pigeon/lib/src/generator_tools.dart

@@ -15,7 +15,7 @@ import 'generator.dart';
 /// The current version of pigeon.
 ///
 /// This must match the version in pubspec.yaml.
-const String pigeonVersion = '26.3.3';
+const String pigeonVersion = '26.3.4';
 
 /// Default plugin package name.
 const String defaultPluginPackageName = 'dev.flutter.pigeon';

packages/pigeon/lib/src/kotlin/kotlin_generator.dart

@@ -1350,7 +1350,7 @@ if (wrapped == null) {
       indent.writeln('override val message: String? = null,');
       indent.writeln('val details: Any? = null');
     }, addTrailingNewline: false);
-    indent.addln(' : Throwable()');
+    indent.addln(' : RuntimeException()');
   }
 
   void _writeCreateConnectionError(

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/CoreTests.gen.kt

@@ -194,7 +194,7 @@ class FlutterError(
     val code: String,
     override val message: String? = null,
     val details: Any? = null
-) : Throwable()
+) : RuntimeException()
 
 enum class AnEnum(val raw: Int) {
   ONE(0),

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/EventChannelTests.gen.kt

@@ -172,7 +172,7 @@ class EventChannelTestsError(
     val code: String,
     override val message: String? = null,
     val details: Any? = null
-) : Throwable()
+) : RuntimeException()
 
 enum class EventEnum(val raw: Int) {
   ONE(0),

packages/pigeon/platform_tests/test_plugin/android/src/main/kotlin/com/example/test_plugin/ProxyApiTests.gen.kt

@@ -50,7 +50,7 @@ class ProxyApiTestsError(
     val code: String,
     override val message: String? = null,
     val details: Any? = null
-) : Throwable()
+) : RuntimeException()
 /**
  * Maintains instances used to communicate with the corresponding objects in Dart.
  *

packages/pigeon/pubspec.yaml

@@ -2,7 +2,7 @@ name: pigeon
 description: Code generator tool to make communication between Flutter and the host platform type-safe and easier.
 repository: https://github.com/flutter/packages/tree/main/packages/pigeon
 issue_tracker: https://github.com/flutter/flutter/issues?q=is%3Aissue+is%3Aopen+label%3A%22p%3A+pigeon%22
-version: 26.3.3 # This must match the version in lib/src/generator_tools.dart
+version: 26.3.4 # This must match the version in lib/src/generator_tools.dart
 
 environment:
   sdk: ^3.9.0
@@ -27,4 +27,3 @@ topics:
   - interop
   - platform-channels
   - plugin-development
-

packages/pigeon/test/kotlin_generator_test.dart

@@ -1983,6 +1983,45 @@ void main() {
     expect(code, isNot(contains('FlutterError')));
   });
 
+  test('error class inherits from RuntimeException', () {
+    final root = Root(
+      apis: <Api>[
+        AstHostApi(
+          name: 'Api',
+          methods: <Method>[
+            Method(
+              name: 'method',
+              location: ApiLocation.host,
+              returnType: const TypeDeclaration.voidDeclaration(),
+              parameters: <Parameter>[
+                Parameter(
+                  name: 'field',
+                  type: const TypeDeclaration(
+                    baseName: 'int',
+                    isNullable: true,
+                  ),
+                ),
+              ],
+            ),
+          ],
+        ),
+      ],
+      classes: <Class>[],
+      enums: <Enum>[],
+    );
+    final sink = StringBuffer();
+    const kotlinOptions = InternalKotlinOptions(kotlinOut: '');
+    const generator = KotlinGenerator();
+    generator.generate(
+      kotlinOptions,
+      root,
+      sink,
+      dartPackageName: DEFAULT_PACKAGE_NAME,
+    );
+    final code = sink.toString();
+    expect(code, contains(': RuntimeException()'));
+  });
+
   test('do not generate duplicated entries in writeValue', () {
     final root = Root(
       apis: <Api>[