[TINKERPOP-3029] Gremlin.Net: Traversal enumeration fails on .NET 8

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 3.5.8, 3.6.6, 3.7.1
• Fix Version/s: 3.6.7, 3.7.2
• Component/s: dotnet
• Assignee: Florian Hockmann
• Reporter: Florian Hockmann
• Created: 03/Jan/24 15:40
• Updated: 15/Jan/24 11:31
• Resolved: 15/Jan/24 11:31

Description

This has been reported by Eric Sites on the dev mailing list: https://lists.apache.org/thread/snztwgk3s18h83mx8ql455hmx6ncl2r4

---

I am having a lot of issues using the Gremlin.Net driver version 3.7.1 with .Net 8.

It is almost entirely unusable.

Any request that uses an Iterator throws an exception (MoveNext, Next, Iterate).
System.InvalidOperationException: Enumeration has not started. Call MoveNext.

Tracked it down to a change in .Net 8 IEnumerable<T>.Current behavior. Here is an issue about this filed in dotnet runtime:
https://github.com/dotnet/runtime/issues/85243

New bad code:

var enumerator = saves.GetEnumerator();
while (enumerator.Current == null) // <- Throws exception now
{
   if (!enumerator.MoveNext())
      return list;
}

Should be changed to something like this:

while (enumerator.MoveNext())
{
    var item = enumerator.Current;
}

Here is an example of the issue in the Gremlin.Net code:
https://github.com/apache/tinkerpop/blob/e8b9532fc0ec811460e97ebf5e00b8b9ec9192ac/gremlin-dotnet/src/Gremlin.Net/Process/Traversal/DefaultTraversal.cs#L132

private object? GetCurrent()
{
    // Use dynamic to object to prevent runtime dynamic conversion evaluation
    return TraverserEnumerator.Current?.Object;
}