generateForAnnotatedElement method

@override Future<String> generateForAnnotatedElement(Element element, ConstantReader annotation, BuildStep buildStep)

Implement to return source code to generate for element.

This method is invoked based on finding elements annotated with an instance of T. The annotation is provided as a ConstantReader.

Supported return values include a single String or multiple String instances within an Iterable or Stream. It is also valid to return a Future of String, Iterable, or Stream.

Implementations should return null when no content is generated. Empty or whitespace-only String instances are also ignored.

Implementation

@override
Future<String> generateForAnnotatedElement(
  Element element,
  ConstantReader annotation,
  BuildStep buildStep,
) async {
  // Check if [@InferFromJsonFile] annotation is used on type alias element.
  // If not, throw an exception.
  if (element is! TypeAliasElement) {
    throw InvalidGenerationSourceError(
      '`@InferFromJsonFile` can only be used on type aliases.',
      element: element,
    );
  }

  // The type aliasing is performed using `typedef <TypeName> = <dynamic>;`.
  // Get the [TypeName] and use it as a generated class name - e.g.
  // `Inferred<TypeName>`.
  final className = element.name;

  // Read the [file] and [mergeStrategy] fields from annotation.
  late String jsonFilePath;
  try {
    jsonFilePath = annotation.read('file').stringValue;
  } on FormatException {
    throw InvalidGenerationSourceError(
      '`@InferFromJsonFile` path should not be null.',
      element: element,
    );
  }
  final mergeStrategy = getMergeStrategy(annotation);

  // Use [file] path to get [AssetId] object so we can read it using the
  // [BuildStep] object. The [file] path should be relative to current
  // file package.
  final jsonFileUri = Uri(path: jsonFilePath);
  final jsonAsset = AssetId.resolve(jsonFileUri, from: buildStep.inputId);

  // Read JSON file.
  final contents = await buildStep.readAsString(jsonAsset);

  // Infer object types and return generated Dart code.
  final result = inferObjectType(
    contents,
    className: className,
    mergeStrategy: mergeStrategy,
  );

  return result;
}