How to access metadata of Named Fields in a RecordType using Dart Analyzer?

[jodinathan]

I asked at SO before coming here.

I am working on a Dart builder and need to inspect the metadata (annotations) applied to the named fields of a RecordType. However, while I can successfully access RecordType.namedFields, the resulting RecordTypeNamedField objects do not appear to expose any metadata-related members.

Here is an example of the code I am trying to analyze:

Future<({@SomeAnnotation() String foo, int bar})?> someFunction() async {
  return null;
}

In this case, I need to determine programmatically that the foo field is annotated with @SomeAnnotation.

My Setup:
Dart SDK: 3.6.0
Analyzer version: 6.11.0

Question:
How can I access the metadata (annotations) of a named field in a RecordType using Dart's analyzer package in the context of a builder? Is there a specific API or workaround to achieve this?

[dart-github-bot]

Summary: User needs to access metadata (annotations) on named fields within a Dart RecordType using the analyzer package for a Dart builder. Currently, RecordTypeNamedField lacks necessary metadata access.

[keertip]

/cc @bwilkerson, @scheglov

[scheglov]

You cannot access metadata on types. And RecordTypeNamedField is a part of types.
Usually you access metadata of an element, e.g. ClassElement.
But record type fields are not elements, they are not always explicitly defined, e.g. final v = (0, 1);

You can access metadata on RecordTypeAnnotationField, which is AST.
If the AST is resolved, you can access its element, etc.

[jodinathan]

@scheglov Could you provide an example of how to access a RecordTypeAnnotationField from a MethodElement?
Something simple, similar to the example in my post, would be great.

[scheglov]

Unfortunately it is not possible to go directly from a MethodElement to resolved AST.

Something like this works, but is not necessary ideal too.

import 'package:analyzer/dart/analysis/results.dart';
import 'package:analyzer/dart/ast/ast.dart';
import 'package:analyzer/file_system/overlay_file_system.dart';
import 'package:analyzer/file_system/physical_file_system.dart';
import 'package:analyzer/src/dart/analysis/analysis_context_collection.dart';
import 'package:analyzer/src/dart/analysis/byte_store.dart';
import 'package:analyzer/src/dart/ast/extensions.dart';

Future<void> main() async {
  var resourceProvider = OverlayResourceProvider(
    PhysicalResourceProvider.INSTANCE,
  );

  var workspacePath = '/workspace';
  var testPackageRootPath = '$workspacePath/test';
  var testFilePath = '$testPackageRootPath/lib/test.dart';

  resourceProvider.setOverlay(
    testFilePath,
    content: r'''
class A {
  (@deprecated int, String) foo() => (0, '');
}
''',
    modificationStamp: -1,
  );

  var byteStore = MemoryByteStore();

  var collection = AnalysisContextCollectionImpl(
    resourceProvider: resourceProvider,
    includedPaths: [
      workspacePath,
    ],
    byteStore: byteStore,
  );

  var analysisContext = collection.contextFor(testFilePath);
  var analysisSession = analysisContext.currentSession;

  var unitResult = await analysisSession.getUnitElement(testFilePath);
  unitResult as UnitElementResult;
  var foo = unitResult.element.classes[0].methods[0];

  var libraryResult = await analysisSession.getResolvedLibrary(testFilePath);
  libraryResult as ResolvedLibraryResult;
  var fooNodeResult = libraryResult.getElementDeclaration(foo)!;
  var node = fooNodeResult.node as MethodDeclaration;
  print(node);

  var returnType = node.returnType as RecordTypeAnnotation;
  var metadata = returnType.fields[0].metadata;
  print(metadata[0].element);
}