get dart doc information

main.dart

import 'package:analyzer/analyzer.dart';
import 'package:analyzer/src/string_source.dart';
import 'package:analyzer/src/generated/element.dart';
import 'package:analyzer/src/generated/engine.dart';
import 'package:analyzer/src/generated/sdk_io.dart';
import 'package:analyzer/src/generated/source.dart';

main() {
  String doc = dartDoc("main() => print('hello world');", 10);
  print(doc);
}

String dartDoc(String dartString, int offset) {
  var sdk = DirectoryBasedDartSdk.defaultSdk;

  AnalysisContext context = AnalysisEngine.instance.createAnalysisContext()
    ..sourceFactory = new SourceFactory([new DartUriResolver(sdk)]);

  StringSource source = new StringSource(dartString, "main.dart");
  LibraryElement library = context.computeLibraryElement(source);
  CompilationUnit unit = context.resolveCompilationUnit(source, library);
  AstNode node = new NodeLocator(offset).searchWithin(unit);
  Element element = ElementLocator.locateWithOffset(node, offset);

  String rawDartDoc = element?.computeDocumentationComment();
  return prettifyDartDoc(rawDartDoc);
}

String prettifyDartDoc(rawDartDoc) => rawDartDoc
    ?.split('\n')
    ?.map((s) => s.trim().replaceAll(commentChars, '').isEmpty
        ? ''
        : s.trim().replaceAll(commentChars, '').substring(1))
    ?.join('\n');

RegExp commentChars = new RegExp(r'[\&*|\*/|\/\*\*|///]');