How to request document diagnostics using Omnisharp?

Question

I try to request diagnostics from my LSP using the following code

var report = await client.RequestDocumentDiagnostic(new DocumentDiagnosticParams()
{
    TextDocument = textDocument,
    Identifier = "luau"
});

Console.WriteLine(report);

Where client is my LanguageClient that I've initialized. Other methods like RequestCompletion and RequestHover work as expected.

However, when I try to call the RequestDocumentDiagnostic method, it gives me the following error:

Unhandled exception. System.NotImplementedException: The method or operation is not implemented.
   at OmniSharp.Extensions.LanguageServer.Protocol.Models.RelatedDocumentDiagnosticReport.Converter.ReadJson(JsonReader reader, Type objectType, RelatedDocumentDiagnosticReport existingValue, Boolean hasExistingValue, JsonSerializer serializer)
   at Newtonsoft.Json.JsonConverter`1.ReadJson(JsonReader reader, Type objectType, Object existingValue, JsonSerializer serializer)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.DeserializeConvertable(JsonConverter converter, JsonReader reader, Type objectType, Object existingValue)
   at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.Deserialize(JsonReader reader, Type objectType, Boolean checkAdditionalContent)
   at Newtonsoft.Json.JsonSerializer.DeserializeInternal(JsonReader reader, Type objectType)
   at Newtonsoft.Json.JsonSerializer.Deserialize(JsonReader reader, Type objectType)
   at Newtonsoft.Json.Linq.JToken.ToObject(Type objectType, JsonSerializer jsonSerializer)
   at Newtonsoft.Json.Linq.JToken.ToObject[T](JsonSerializer jsonSerializer)
   at OmniSharp.Extensions.JsonRpc.ResponseRouter.ResponseRouterReturnsImpl.Returning[TResponse](CancellationToken cancellationToken)
   at OmniSharp.Extensions.LanguageServer.Protocol.Progress.ProgressManager.<>c__DisplayClass26_0`1.<<MakeRequest>b__0>d.MoveNext()

There is little documentation on the language client package from Omnisharp and I don't know why I'm getting this error.

I tried different methods of getting the diagnostics from the LSP like directly using client.SendRequest but I couldn't get that to work.

Answer 1

Figured it out.

            var report = Client.SendRequest("textDocument/diagnostic", new DocumentDiagnosticParams
        {
            TextDocument = document,
            
        });

        var item = await report.Returning<DiagnosticItem>(CancellationToken.None);

        return item;