Fix S3257 FP: Following the suggestion to remove the explicit delegate creation, leads to runtime crash

[lsw-sma]

Description

Rule ID: S3257
UserControl provides the method AddHandler(RoutedEvent routedEvent, Delegate handler).
If I pass new RoutedEventHandler(OnErrorEvent) as the handler argument the rule is raised.
If I follow the suggestion and pass OnErrorEvent directly, it leads to the runtime exception: System.ArgumentException: 'Handler type is mismatched.'

Repro steps

1. Create a System.Windows.Controls.UserControl (named UserControl1)
2. Change the codebehind to the following:

public partial class UserControl1 {
    public UserControl1() {
        InitializeComponent();

        // Raises rule, no problem at runtime
        AddHandler(System.Windows.Controls.Validation.ErrorEvent, new RoutedEventHandler(OnErrorEvent));

        // Valid according to rule, but leads to runtime exception
        AddHandler(System.Windows.Controls.Validation.ErrorEvent, OnErrorEvent);
    }

    private void OnErrorEvent(object sender, RoutedEventArgs e) { }
}

Expected behavior

S3257 should not raise for passing new RoutedEventHandler(OnErrorEvent) to AddHandler.

Actual behavior

S3257 falsely suggests to pass the argument as a method group. This leads to a runtime exception: System.ArgumentException: 'Handler type is mismatched.'

Known workarounds

1. Disable the rule locally.
2. Extracting the argument as a variable, i.e.

var eventHandler = new RoutedEventHandler(OnErrorEvent);
AddHandler(System.Windows.Controls.Validation.ErrorEvent, eventHandler);

Related information

• C#/VB.NET Plugins version: 8.0.400
• Visual Studio version: VS 2022
• MSBuild / dotnet version: 17.11.9+a69bbaaf5 for .NET Framework
• Operating System: Win 11