[jnigen] Report an empty config list entry as a config error

pkgs/jnigen/CHANGELOG.md

@@ -1,5 +1,7 @@
 ## 1.0.1-wip
 
+- Report an empty entry under `classes` in the config file as a config error
+  instead of failing with a type error.
 - Generate links to method-specific Javadocs for Maven dependencies when
   source Javadocs are unavailable.
 

pkgs/jnigen/lib/src/config/config_types.dart

@@ -356,6 +356,9 @@ bool _isCapitalized(String s) {
 }
 
 void _validateClassName(String className) {
+  if (className.isEmpty) {
+    throw ConfigException('Class names cannot be empty.');
+  }
   final parts = className.split('.');
   assert(parts.isNotEmpty);
   const nestedClassesInfo =
@@ -471,7 +474,12 @@ final class JniGenerator {
       input: Input(
         sourcePath: prov.getPathList(_Props.sourcePath) ?? const [],
         classPath: prov.getPathList(_Props.classPath) ?? const [],
-        classes: must(prov.getStringList, [], _Props.classes),
+        classes: must(prov.getStringList, <String>[], _Props.classes)
+            // An empty YAML entry reads as null. Turn it into an empty name so
+            // that _validateClassName reports it instead of a cast error.
+            .cast<Object?>()
+            .map((className) => className as String? ?? '')
+            .toList(),
         extraArgs: prov.getStringList(_Props.summarizerArgs) ?? const [],
         backend: getSummarizerBackend(prov.getString(_Props.backend), null),
         workingDirectory: prov.getPath(_Props.summarizerWorkingDir),

pkgs/jnigen/test/config_test.dart

@@ -118,5 +118,27 @@ void main() async {
       name: 'Nested class specified',
       overrides: ['-Dclasses=com.android.Clock\$Clock'],
     );
+
+    test('Empty classes entry from YAML', () {
+      final dir = Directory.systemTemp.createTempSync('jnigen_config_test');
+      addTearDown(() => dir.deleteSync(recursive: true));
+      final yaml = File(join(dir.path, 'jnigen.yaml'))..writeAsStringSync('''
+output:
+  dart:
+    path: lib/gen.dart
+    structure: single_file
+classes:
+  - "com.example.Foo"
+  -
+''');
+      expect(
+        () => JniGenerator.parseArgs(['--config', yaml.path]),
+        throwsA(isA<ConfigException>().having(
+          (error) => error.message,
+          'message',
+          'Class names cannot be empty.',
+        )),
+      );
+    });
   });
 }