Most changes suggested in Review 1

    * Use final_locals lint rule
    * Fix HelperNotFoundException breaking on flutter
    * Prevent memory leak in presence of exceptions
    * Documentation changes
    * Use inheritStdio in setup.dart
Hopefully most reviews are covered. There might be a few that I missed.

Thanks @liamappelbe and @dcharkes for very detailed reviews!

jni/README.md

@@ -19,20 +19,19 @@ This is intended for one-off / debugging uses of JNI, as well as providing a bas
 __To interface a complete java library, look forward for `jni_gen`.__
 
 ## Platform support
-The focus of this project is Android, since it already has a JVM and JNI allows interop with existing code and Platform APIs. Experimental desktop support exists for Linux using the JVM invocation API.
+The focus of this project is Flutter Android, since Flutter Android apps already have a JVM, and JNI enables interop with existing Java code and Android Platform APIs. This project also (partially) supports Linux desktop by spawning a JVM through JNI.
 
 ## Version note
-This library is at an early stage and the public API may rapidly change based on requirements of `jni_gen`.
+This library is at an early stage of development and we do not provide backwards compatibility of the API at this point.
 
 ## Documentation
-
-There are well-commented test files under `test/` directory and a flutter based example under `example/`.
+The test/ directory contains files with comments explaining the basics of this module, and the example/ directory contains a flutter example which also touches some Android-specifics.
 
 Using this library assumes some familiarity with JNI - it's threading model and object references, among other things.
 
 ## jni_gen
 
 This library is a part of `jni_gen` - a 2022 GSoC project.
 
-The broader aim of jni_gen is making Java APIs accessible from dart in an idiomatic way. The current focus is on the Android platform.
+The broader aim of jni_gen is making Java APIs accessible from dart in an idiomatic way.
 

jni/analysis_options.yaml

@@ -1,4 +1,13 @@
 include: package:flutter_lints/flutter.yaml
 
+analyzer:
+  exclude: [build/**]
+  language:
+    strict-raw-types: true
+
+linter:
+  rules:
+    - prefer_final_locals
+    - prefer_const_declarations
 # Additional information about this file can be found at
 # https://dart.dev/guides/language/analysis-options

jni/bin/setup.dart

@@ -19,11 +19,12 @@ class CommandRunner {
       String exec, List<String> args, String workingDir) async {
     if (printCmds) {
       final cmd = "$exec ${args.join(" ")}";
-      stderr.writeln("+ [$workingDir] $cmd");
+      stderr.writeln("\n+ [$workingDir] $cmd");
     }
-    final process =
-        await Process.start(exec, args, workingDirectory: workingDir);
-    // stdout.addStream(process.stdout);
+    final process = await Process.start(exec, args,
+        workingDirectory: workingDir,
+        runInShell: Platform.isWindows,
+        mode: ProcessStartMode.inheritStdio);
     final exitCode = await process.exitCode;
     if (exitCode != 0) {
       stderr.writeln("command exited with $exitCode");
@@ -107,7 +108,7 @@ void main(List<String> arguments) async {
 
 Future<void> build(Options options, String srcPath, String buildPath) async {
   final runner = CommandRunner(printCmds: true);
-  var cmakeArgs = [srcPath];
+  final cmakeArgs = [srcPath];
   if (options.cmakeArgs != null) {
     cmakeArgs.addAll(options.cmakeArgs!.split(" "));
   }

jni/example/analysis_options.yaml

@@ -9,6 +9,11 @@
 # packages, and plugins designed to encourage good coding practices.
 include: package:flutter_lints/flutter.yaml
 
+analyzer:
+  exclude: [build/**]
+  language:
+    strict-raw-types: true
+
 linter:
   # The lint rules applied to this project can be customized in the
   # section below to disable rules from the `package:flutter_lints/flutter.yaml`
@@ -22,6 +27,8 @@ linter:
   # `// ignore_for_file: name_of_lint` syntax on the line or in the file
   # producing the lint.
   rules:
+    - prefer_final_locals
+    - prefer_const_declarations
     # avoid_print: false  # Uncomment to disable the `avoid_print` rule
     # prefer_single_quotes: true  # Uncomment to enable the `prefer_single_quotes` rule
 

jni/example/integration_test/jni_object_test.dart

@@ -13,7 +13,7 @@ void main() {
     Jni.spawn();
   }
 
-  var jni = Jni.getInstance();
+  final jni = Jni.getInstance();
   testWidgets('get JNI Version', (tester) async {
     final env = jni.getEnv();
     expect(env.GetVersion(), isNot(equals(0)));
@@ -120,7 +120,8 @@ void main() {
     for (int i = 0; i < 100; i++) {
       int r = random.callIntMethod(nextIntMethod, [256 * 256]);
       int bits = 0;
-      int jbc = longClass.callStaticIntMethod(bitCountMethod, [JValueLong(r)]);
+      final jbc =
+          longClass.callStaticIntMethod(bitCountMethod, [JValueLong(r)]);
       while (r != 0) {
         bits += r % 2;
         r = (r / 2).floor();
@@ -133,13 +134,13 @@ void main() {
   });
 
   testWidgets("invoke_", (tester) async {
-    var m = jni.invokeLongMethod(
+    final m = jni.invokeLongMethod(
         "java/lang/Long", "min", "(JJ)J", [JValueLong(1234), JValueLong(1324)]);
     expect(m, equals(1234));
   });
 
   testWidgets("retrieve_", (tester) async {
-    var maxLong = jni.retrieveShortField("java/lang/Short", "MAX_VALUE", "S");
+    final maxLong = jni.retrieveShortField("java/lang/Short", "MAX_VALUE", "S");
     expect(maxLong, equals(32767));
   });
 
@@ -163,19 +164,19 @@ void main() {
   });
 
   testWidgets("Passing strings in arguments 2", (tester) async {
-    var twelve = jni.invokeByteMethod(
+    final twelve = jni.invokeByteMethod(
         "java/lang/Byte", "parseByte", "(Ljava/lang/String;)B", ["12"]);
     expect(twelve, equals(12));
   });
 
   testWidgets("use() method", (tester) async {
-    var randomInt = jni.newInstance("java/util/Random", "()V", []).use(
+    final randomInt = jni.newInstance("java/util/Random", "()V", []).use(
         (random) => random.callIntMethodByName("nextInt", "(I)I", [15]));
     expect(randomInt, lessThan(15));
   });
 
   testWidgets("enums", (tester) async {
-    var ordinal = jni
+    final ordinal = jni
         .retrieveObjectField(
             "java/net/Proxy\$Type", "HTTP", "Ljava/net/Proxy\$Type;")
         .use((f) => f.callIntMethodByName("ordinal", "()I", []));
@@ -187,14 +188,14 @@ void main() {
   });
 
   testWidgets("JniGlobalRef", (tester) async {
-    var uri = jni.invokeObjectMethod(
+    final uri = jni.invokeObjectMethod(
         "java/net/URI",
         "create",
         "(Ljava/lang/String;)Ljava/net/URI;",
         ["https://www.google.com/search"]);
-    var rg = uri.getGlobalRef();
+    final rg = uri.getGlobalRef();
     await Future.delayed(const Duration(seconds: 1), () {
-      var env = jni.getEnv();
+      final env = jni.getEnv();
       // Now comment this line & try to directly use uri local ref
       // in outer scope.
       //
@@ -203,8 +204,8 @@ void main() {
       //
       // Therefore, don't share JniObjects across functions that can be
       // scheduled across threads, including async callbacks.
-      var uri = JniObject.fromGlobalRef(env, rg);
-      var scheme =
+      final uri = JniObject.fromGlobalRef(env, rg);
+      final scheme =
           uri.callStringMethodByName("getScheme", "()Ljava/lang/String;", []);
       expect(scheme, "https");
       uri.delete();
@@ -215,8 +216,8 @@ void main() {
 }
 
 void doSomeWorkInIsolate(Void? _) {
-  var jni = Jni.getInstance();
-  var random = jni.newInstance("java/util/Random", "()V", []);
+  final jni = Jni.getInstance();
+  final random = jni.newInstance("java/util/Random", "()V", []);
   // var r = random.callIntMethodByName("nextInt", "(I)I", [256]);
   // expect(r, lessThan(256));
   // Expect throws an OutsideTestException

jni/example/lib/main.dart

@@ -180,7 +180,7 @@ class _ExampleCardState extends State<ExampleCard> {
 
   @override
   Widget build(BuildContext context) {
-    var eg = widget.example;
+    final eg = widget.example;
     var result = "";
     var hasError = false;
     if (_run) {

jni/example/pubspec.lock

@@ -8,6 +8,13 @@ packages:
       url: "https://pub.dartlang.org"
     source: hosted
     version: "3.1.11"
+  args:
+    dependency: transitive
+    description:
+      name: args
+      url: "https://pub.dartlang.org"
+    source: hosted
+    version: "2.3.1"
   async:
     dependency: transitive
     description:

jni/example/test/widget_test.dart

@@ -16,7 +16,7 @@ void main() {
   if (!Platform.isAndroid) {
     Jni.spawn(helperDir: "../src/build");
   }
-  var jni = Jni.getInstance();
+  final jni = Jni.getInstance();
   testWidgets("simple toString example", (tester) async {
     await tester.pumpWidget(ExampleForTest(ExampleCard(Example(
         "toString",