[native_assets_cli] Make generated syntax files stand on their own

pkgs/json_syntax_generator/lib/src/generator/helper_library.dart

@@ -0,0 +1,112 @@
+// Copyright (c) 2025, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// Helper methods for the code generator that are added to the generated file.
+///
+/// This simplifies the code generator.
+const helperLib = r'''
+extension on Map<String, Object?> {
+  T get<T extends Object?>(String key) {
+    final value = this[key];
+    if (value is T) return value;
+    if (value == null) {
+      throw FormatException('No value was provided for required key: $key');
+    }
+    throw FormatException(
+      'Unexpected value \'$value\' for key \'.$key\'. '
+      'Expected a $T.',
+    );
+  }
+
+  List<T> list<T extends Object?>(String key) =>
+      _castList<T>(get<List<Object?>>(key), key);
+
+  List<T>? optionalList<T extends Object?>(String key) =>
+      switch (get<List<Object?>?>(key)?.cast<T>()) {
+        null => null,
+        final l => _castList<T>(l, key),
+      };
+
+  /// [List.cast] but with [FormatException]s.
+  static List<T> _castList<T extends Object?>(List<Object?> list, String key) {
+    for (final value in list) {
+      if (value is! T) {
+        throw FormatException(
+          'Unexpected value \'$list\' (${list.runtimeType}) for key \'.$key\'. '
+          'Expected a ${List<T>}.',
+        );
+      }
+    }
+    return list.cast();
+  }
+
+  Map<String, T> map$<T extends Object?>(String key) =>
+      _castMap<T>(get<Map<String, Object?>>(key), key);
+
+  Map<String, T>? optionalMap<T extends Object?>(String key) =>
+      switch (get<Map<String, Object?>?>(key)) {
+        null => null,
+        final m => _castMap<T>(m, key),
+      };
+
+  /// [Map.cast] but with [FormatException]s.
+  static Map<String, T> _castMap<T extends Object?>(
+    Map<String, Object?> map_,
+    String key,
+  ) {
+    for (final value in map_.values) {
+      if (value is! T) {
+        throw FormatException(
+          'Unexpected value \'$map_\' (${map_.runtimeType}) for key \'.$key\'.'
+          'Expected a ${Map<String, T>}.',
+        );
+      }
+    }
+    return map_.cast();
+  }
+
+  List<String>? optionalStringList(String key) => optionalList<String>(key);
+
+  List<String> stringList(String key) => list<String>(key);
+
+  Uri path(String key) => _fileSystemPathToUri(get<String>(key));
+
+  Uri? optionalPath(String key) {
+    final value = get<String?>(key);
+    if (value == null) return null;
+    return _fileSystemPathToUri(value);
+  }
+
+  List<Uri>? optionalPathList(String key) {
+    final strings = optionalStringList(key);
+    if (strings == null) {
+      return null;
+    }
+    return [for (final string in strings) _fileSystemPathToUri(string)];
+  }
+
+  static Uri _fileSystemPathToUri(String path) {
+    if (path.endsWith(Platform.pathSeparator)) {
+      return Uri.directory(path);
+    }
+    return Uri.file(path);
+  }
+}
+
+extension on List<Uri> {
+  List<String> toJson() => [for (final uri in this) uri.toFilePath()];
+}
+
+extension <K extends Comparable<K>, V extends Object?> on Map<K, V> {
+  void sortOnKey() {
+    final result = <K, V>{};
+    final keysSorted = keys.toList()..sort();
+    for (final key in keysSorted) {
+      result[key] = this[key] as V;
+    }
+    clear();
+    addAll(result);
+  }
+}
+''';

pkgs/json_syntax_generator/lib/src/generator/syntax_generator.dart

@@ -6,6 +6,7 @@ import '../model/class_info.dart';
 import '../model/dart_type.dart';
 import '../model/property_info.dart';
 import '../model/schema_info.dart';
+import 'helper_library.dart';
 
 /// Generates Dart code from a [SchemaInfo].
 ///
@@ -35,13 +36,17 @@ class SyntaxGenerator {
 
 // This file is generated, do not edit.
 
-import '../utils/json.dart';
+// ignore_for_file: unused_element
+
+import 'dart:io';
 ''');
 
     for (final classInfo in schemaInfo.classes) {
       buffer.writeln(_generateClass(classInfo));
     }
 
+    buffer.writeln(helperLib);
+
     return buffer.toString();
   }
 
@@ -301,7 +306,7 @@ class $className {
       case EnumClassInfo():
         if (required) {
           buffer.writeln('''
-$dartType get $fieldName => $classType.fromJson( json.string('$jsonKey') );
+$dartType get $fieldName => $classType.fromJson( json.get<String>('$jsonKey') );
 ''');
           if (!property.isOverride) {
             buffer.writeln('''
@@ -313,7 +318,7 @@ set $setterName($dartType value) {
         } else {
           buffer.writeln('''
 $dartType get $fieldName {
-  final string = json.optionalString('$jsonKey');
+  final string = json.get<String?>('$jsonKey');
   if(string == null) return null;
   return $classType.fromJson(string);
 }
@@ -384,7 +389,7 @@ set $setterName($dartType value) {
       case 'String':
         if (required) {
           buffer.writeln('''
-String get $fieldName => json.string('$jsonKey');
+String get $fieldName => json.get<String>('$jsonKey');
 
 set $setterName(String value) {
   json['$jsonKey'] = value;
@@ -393,7 +398,7 @@ set $setterName(String value) {
 ''');
         } else {
           buffer.writeln('''
-String? get $fieldName => json.optionalString('$jsonKey');
+String? get $fieldName => json.get<String?>('$jsonKey');
 
 set $setterName(String? value) {
   if (value == null) {
@@ -415,7 +420,7 @@ set $setterName(int value) => json['$jsonKey'] = value;
 ''');
         } else {
           buffer.writeln('''
-int? get $fieldName => json.getOptional<int>('$jsonKey');
+int? get $fieldName => json.get<int?>('$jsonKey');
 
 set $setterName(int? value) {
   if (value == null) {
@@ -440,7 +445,7 @@ set $setterName(bool value) {
 ''');
         } else {
           buffer.writeln('''
-bool? get $fieldName => json.getOptional<bool>('$jsonKey');
+bool? get $fieldName => json.get<bool?>('$jsonKey');
 
 set $setterName(bool? value) {
   if (value == null) {