FoldingRangeHandler.cs

using System.Threading;
using System.Threading.Tasks;
using OmniSharp.Extensions.LanguageServer.Protocol.Client.Capabilities;
using OmniSharp.Extensions.LanguageServer.Protocol.Document;
using OmniSharp.Extensions.LanguageServer.Protocol.Models;

namespace SampleServer
{
    internal class FoldingRangeHandler : IFoldingRangeHandler
    {
        public FoldingRangeRegistrationOptions GetRegistrationOptions() =>
            new FoldingRangeRegistrationOptions {
                DocumentSelector = TextDocumentSelector.ForLanguage("csharp")
            };

        public Task<Container<FoldingRange>?> Handle(
            FoldingRangeRequestParam request,
            CancellationToken cancellationToken
        ) =>
            Task.FromResult<Container<FoldingRange>?>(
                new Container<FoldingRange>(
                    new FoldingRange {
                        StartLine = 10,
                        EndLine = 20,
                        Kind = FoldingRangeKind.Region,
                        EndCharacter = 0,
                        StartCharacter = 0
                    }
                )
            );

        public FoldingRangeRegistrationOptions GetRegistrationOptions(FoldingRangeCapability capability, ClientCapabilities clientCapabilities) => new FoldingRangeRegistrationOptions {
            DocumentSelector = TextDocumentSelector.ForLanguage("csharp")
        };
    }
}