CS8619 is reported on anonymous types

Version Used:

• .NET 6.0.301
• Visual C# Compiler version 4.2.0-4.22281.5 (8d3180e5)

Steps to Reproduce: I am unable to create a small project that reproduces the compiler warning. Instead, I’ll give what I can so you can investigate the issue.

This is our data class:

  public class DataType
  {
    public string ModuleId { get; set; }
    public Module Module { get; set; }
    public string Name { get; set; }
    public string TypeName { get; set; }
    public string DisplayName { get; set; }
    public string? Description { get; set; }
    public string? BaseTypes { get; set; }
  }

The code that uses it, and have the CS8619 warning:

var dbTypes = await _db.DataTypes
    .Where(s => typeIds.Contains(s.Id))
    .Select(s => new
    {
        s.Id,
        s.BaseTypes, //<-- here is the type that generates the warning
        ModuleName = s.Module.Name,
    })
    .ToListAsync(token)
    .ConfigureAwait(false);

When we compile it, we get the following warning:

DataTypeInfoManager.cs(43, 26): [CS8619] Nullability of reference types in value of type '<anonymous type: string Id, string Name, string TypeName, string DisplayName, string BaseTypes, string ModuleName, ICollection<DataField> DataFields>' doesn't match target type '<anonymous type: string Id, string Name, string TypeName, string DisplayName, string? BaseTypes, string ModuleName, ICollection<DataField> DataFields>'.

Note how the signatures mismatch on string/string? for BaseTypes.

I’ve put the code into sharplab.io and looked at the compiler output. It seems that anonymous types are not generated with nullable reference types, so s.BaseTypes above becomes a string, instead of string?. The compiler detects this string -> string? mismatch and report CS8619.

[Youssef1313]

Ah, I managed to create a reproduction. I’ve uploaded it here: https://github.com/Genbox/Repo-62500

Simply run “dotnet build” in the folder and it should give the error:

DataTypeInfoManager.cs(16,36): error CS8619: Nullability of reference types in value of type '<anonymous type: string 
BaseTypes, ICollection<DataField> DataFields>' doesn't match target type '<anonymous type: string? BaseTypes, 
ICollection<DataField> DataFields>'

I minimized your repro to this:

#nullable enable

using System.Collections.Generic;
using System.Linq;

public class DataType
{
    public string? BaseTypes { get; set; }
}

internal class DataTypeInfoManager
{
    private async void GetTypesByIdsAsync()
    {
        List<DataType> dataTypes = new List<DataType>();

        var dbTypes = dataTypes
                      .Select(s => new
                      {
                          s.BaseTypes,
                      });

        foreach (var field in new[] { "" })
        {
            #nullable disable
            string x = null; // comment this out. Warning disappear
            _ = x;
            #nullable enable
        }
    }
}

[jcouv]

Thanks for reporting this. Closing as duplicate of https://github.com/dotnet/roslyn/issues/51886