[dotnet-sdk-8.0.100-preview.7.23374.6] Fail to retarget greenshot app to .NET 8.0 with 'MethodInvoker' ambiguous reference exception between 'System.Windows.Forms.MethodInvoker' and 'System.Reflection.MethodInvoker'

[Junjun-zhao]

Application Name: greenshot
OS： Windows 10 21H2
CPU: X64
.NET Build Number: dotnet-sdk-8.0.100-preview.7.23374.6
App & Source Location checking at: https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1860865

App github link: https://github.com/greenshot/greenshot

Verify Scenarios:
1). Windows10 21h2 x64 + dotnet-sdk-8.0.100-preview.7.23376.3: Fail
2). Windows10 21h2 x64 + dotnet-sdk-8.0.100-preview.7.23375.2: Fail
3). Windows10 21h2 x64 + dotnet-sdk-8.0.100-preview.7.23374.6: Fail
4). Windows10 21h2 x64 + dotnet-sdk-8.0.100-preview.7.23371.2: Fail
5). Windows10 21h2 x64 + dotnet-sdk-8.0.100-preview.7.23364.32: Pass
6). Windows10 21h2 x64 + dotnet-sdk-8.0.100-preview.6.23330.14: Pass
7). Windows10 21h2 x64 + .net 7.0.306: Pass

Minimal Repro steps (Demo attached):
WinFormsApp1.zip

1. Create a winform project（SDK versions before 8.0）.
2. Copy the following code to Form1.cs.

using System.Windows.Forms;
using System.Reflection;
namespace WinFormsApp1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
            this.Invoke((MethodInvoker)delegate
            {
            });
        }
    }
}

3. Build the source.
4. Build successfully.
5. Change the TargetFramework to net8.0-windows in the WinFormsApp1.csproj.
6. Build the source.

Expected Result:

Build successfully.

Actual Result:

Get Following error:

CS0104: 'MethodInvoker' is an amb
iguous reference between 'System.Windows.Forms.MethodInvoker' and 'System.Reflection.MethodInvoker'

Findings:

1. Removing using System. Reflection can solve the problem.
2. Change MethodInvoker to System.Windows.Forms.MethodInvoker can solve the problem.

Dotnet info:

.NET SDK:
 Version:   8.0.100-preview.7.23374.6
 Commit:    3819e84d90

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.22000
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\8.0.100-preview.7.23374.6\

.NET workloads installed:
There are no installed workloads to display.

Host:
  Version:      8.0.0-preview.7.23370.6
  Architecture: x64
  Commit:       ebd23467f0
  RID:          win-x64

.NET SDKs installed:
  8.0.100-preview.7.23374.6 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.0-preview.7.23371.19 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 8.0.0-preview.7.23370.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 8.0.0-preview.7.23371.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

@dotnet-actwx-bot @dotnet/compat

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[Junjun-zhao]

@marcpopMSFT This bug was found in .NET 8 Preview 7 validation, could you please help confirm whether it is a blocker for Preview 7? Please help to move to the right area if this is not correct. Thanks.

[marcpopMSFT]

Not sure if this is a winforms issue or Roslyn issue related to the upgrade but routing to winforms first as it appears to be a winforms app.
CC @merriemcgaw

[gpetrou]

Maybe this happened because of dotnet/runtime#88415?

[merriemcgaw]

@JeremyKuhne - FYI

[JeremyKuhne]

This is expected. There is a new public type that has the same name as our existing one. The source needs updated to explicitly say that they want the WinForms one. This can be done by using the full name or adding a using alias to simplify specifying a known type:

using WinFormsMethodInvoker = System.Windows.Forms.MethodInvoker;

namespace MyNameSpace;

internal class MyClass
{
    public void Foo()
    {
        System.Windows.Forms.MethodInvoker invoker1 = Bar;
        WinFormsMethodInvoker invoker2 = Bar;
    }

    public void Bar() { }
}