dart: use enhanced enums (#8313)

* dart: rename enums.fbs

* feat: use dart enhanced enums

* generate code

---------

Co-authored-by: Wouter van Oortmerssen <aardappel@gmail.com>

dart/test/enums_generated.dart

@@ -0,0 +1,145 @@
+// automatically generated by the FlatBuffers compiler, do not modify
+// ignore_for_file: unused_import, unused_field, unused_element, unused_local_variable, constant_identifier_names
+
+import 'dart:typed_data' show Uint8List;
+import 'package:flat_buffers/flat_buffers.dart' as fb;
+
+
+enum OptionsEnum {
+  A(1),
+  B(2),
+  C(3);
+
+  final int value;
+  const OptionsEnum(this.value);
+
+  factory OptionsEnum.fromValue(int value) {
+    switch (value) {
+      case 1: return OptionsEnum.A;
+      case 2: return OptionsEnum.B;
+      case 3: return OptionsEnum.C;
+      default: throw StateError('Invalid value $value for bit flag enum');
+    }
+  }
+
+  static OptionsEnum? _createOrNull(int? value) =>
+      value == null ? null : OptionsEnum.fromValue(value);
+
+  static const int minValue = 1;
+  static const int maxValue = 3;
+  static const fb.Reader<OptionsEnum> reader = _OptionsEnumReader();
+}
+
+class _OptionsEnumReader extends fb.Reader<OptionsEnum> {
+  const _OptionsEnumReader();
+
+  @override
+  int get size => 4;
+
+  @override
+  OptionsEnum read(fb.BufferContext bc, int offset) =>
+      OptionsEnum.fromValue(const fb.Uint32Reader().read(bc, offset));
+}
+
+class MyTable {
+  MyTable._(this._bc, this._bcOffset);
+  factory MyTable(List<int> bytes) {
+    final rootRef = fb.BufferContext.fromBytes(bytes);
+    return reader.read(rootRef, 0);
+  }
+
+  static const fb.Reader<MyTable> reader = _MyTableReader();
+
+  final fb.BufferContext _bc;
+  final int _bcOffset;
+
+  List<OptionsEnum>? get options => const fb.ListReader<OptionsEnum>(OptionsEnum.reader).vTableGetNullable(_bc, _bcOffset, 4);
+
+  @override
+  String toString() {
+    return 'MyTable{options: ${options}}';
+  }
+
+  MyTableT unpack() => MyTableT(
+      options: const fb.ListReader<OptionsEnum>(OptionsEnum.reader, lazy: false).vTableGetNullable(_bc, _bcOffset, 4));
+
+  static int pack(fb.Builder fbBuilder, MyTableT? object) {
+    if (object == null) return 0;
+    return object.pack(fbBuilder);
+  }
+}
+
+class MyTableT implements fb.Packable {
+  List<OptionsEnum>? options;
+
+  MyTableT({
+      this.options});
+
+  @override
+  int pack(fb.Builder fbBuilder) {
+    final int? optionsOffset = options == null ? null
+        : fbBuilder.writeListUint32(options!.map((f) => f.value).toList());
+    fbBuilder.startTable(1);
+    fbBuilder.addOffset(0, optionsOffset);
+    return fbBuilder.endTable();
+  }
+
+  @override
+  String toString() {
+    return 'MyTableT{options: ${options}}';
+  }
+}
+
+class _MyTableReader extends fb.TableReader<MyTable> {
+  const _MyTableReader();
+
+  @override
+  MyTable createObject(fb.BufferContext bc, int offset) => 
+    MyTable._(bc, offset);
+}
+
+class MyTableBuilder {
+  MyTableBuilder(this.fbBuilder);
+
+  final fb.Builder fbBuilder;
+
+  void begin() {
+    fbBuilder.startTable(1);
+  }
+
+  int addOptionsOffset(int? offset) {
+    fbBuilder.addOffset(0, offset);
+    return fbBuilder.offset;
+  }
+
+  int finish() {
+    return fbBuilder.endTable();
+  }
+}
+
+class MyTableObjectBuilder extends fb.ObjectBuilder {
+  final List<OptionsEnum>? _options;
+
+  MyTableObjectBuilder({
+    List<OptionsEnum>? options,
+  })
+      : _options = options;
+
+  /// Finish building, and store into the [fbBuilder].
+  @override
+  int finish(fb.Builder fbBuilder) {
+    final int? optionsOffset = _options == null ? null
+        : fbBuilder.writeListUint32(_options!.map((f) => f.value).toList());
+    fbBuilder.startTable(1);
+    fbBuilder.addOffset(0, optionsOffset);
+    return fbBuilder.endTable();
+  }
+
+  /// Convenience method to serialize to byte list.
+  @override
+  Uint8List toBytes([String? fileIdentifier]) {
+    final fbBuilder = fb.Builder(deduplicateTables: false);
+    fbBuilder.finish(finish(fbBuilder), fileIdentifier);
+    return fbBuilder.buffer;
+  }
+}