VB.NET program using .NET runtime 10.0.2 throws EntryPointNotFoundException

[reduckted]

Description

A specific class definition results in an EntryPointNotFoundException when running on the .NET runtime 10.0.2. The same code runs without error on .NET runtime 10.0.1.

Reproduction Steps

Reproduction is here: https://github.com/reduckted/repro-dotnet-runtime

The error is:

> dotnet run --project VB
Unhandled exception. System.EntryPointNotFoundException: Entry point was not found.
   at System.Collections.Generic.List`1..ctor(IEnumerable`1 collection)
   at System.Linq.Enumerable.ToList[TSource](IEnumerable`1 source)
   at VB.Program.Main(String[] args) in /home/runner/work/repro-dotnet-runtime/repro-dotnet-runtime/VB/Program.vb:line 5

Here's a copy of the code for reference:

Public NotInheritable Class Program

    Public Shared Function Main(args() As String) As Integer
        Dim w As New Widget(Of Integer)
        w.ToList()
        Console.WriteLine("Completed")
        Return 0
    End Function

End Class

Public Class Widget(Of T)
    Implements IWidget(Of T)

    Public ReadOnly Property Count As Integer Implements IReadOnlyCollection(Of T).Count

    Public Function GetEnumerator() As IEnumerator(Of T) Implements IEnumerable(Of T).GetEnumerator
        Return Enumerable.Empty(Of T)().GetEnumerator()
    End Function

    Private Function IEnumerable_GetEnumerator() As IEnumerator Implements IEnumerable.GetEnumerator
        Return GetEnumerator()
    End Function

End Class

Public Interface IWidget(Of T)
    Inherits IReadOnlyCollection(Of T)

End Interface

Some things to note:

• The IWidget class must be generic. Changing it to IWidget and inheriting from IReadOnlyCollection(Of Integer) runs without error.
• The Widget class can be changed to be non-generic by implementing IWidget(Of Integer) and the exception still occurs.
• Equivalent code in C# runs without error.

Here is a workflow run that shows it succeeding for .NET 10.0.1 and failing for 10.0.2:
https://github.com/reduckted/repro-dotnet-runtime/actions/runs/21063712505

Expected behavior

The code runs without error.

Actual behavior

System.EntryPointNotFoundException: Entry point was not found.

Regression?

Yes. This worked in .NET 10.0.1.

Known Workarounds

None.

Configuration

• .NET 10.0.2
• ubuntu-latest GitHub runner
• x64

Other information

No response

[MichalStrehovsky]

In the commit range between 10.0.1 and 10.0.2 v10.0.1...v10.0.2 the most suspect looks to be #120712, cc @davidwrighton.

[davidwrighton]

@MichalStrehovsky I agree, my change is the most likely cause of this.

[davidwrighton]

Yes, this is definitely caused by my change, and I consider this to be a severe regression. The difference between C# and VB.NET here is that the C# compiler injects all inherited interfaces into the explicit interface list, but VB does not. This is mostly a historical curiosity in codegen normally, but it interacts poorly with my PR, and it exposes a chunk of logic that I thought was working, but on closer inspection appears to have been totally wrong and unimplemented. I have a fix, but I'm now working on test cases, as there are quite a few corner cases that the algorithm should have that it currently doesn't have (and your test case doesn't hit all that many of the interesting ones.)

[davidwrighton]

As a workaround for now, on Widget(Of T) you can explicitly implement IEnumerable(Of T) or you could make IWidget(Of T) inherit from IEnumerable(Of T) This should fix this exact issue and won't break when an actual fix is deployed, but there may be some internal runtime data structures in a somewhat invalid state. C# customers are unlikely to encounter this issue as the paths that the C# compiler will cause the runtime to go down are more likely to force the runtime into running an alternative, slower algorithm that is not susceptible to this bug. (The C# compiler will inject the equivalent of implement and inherit operations for all interfaces and interface implementations in the tree of interfaces visible to the compiler.)

[davidwrighton]

Reopening issue as the fix has not yet been backported to 10.0