Visual Studio IDE0059 C# Unnecessary assignment of a value bug?

问题

I have the following C# Code (I reduced it to the bare minimum to simplify it). Visual Studio 2019, .NET Framework 4.7.2.

public void Demo()
{
    ReportStart();
    var success = false;
    try
    {
        int no = 1;
        switch (no)
        {
            case 1:
            default:
                break;
        }

        DoSomething();

        success = true;
    }
    finally
    {
        ReportEnd(success);
    }
}

From my understanding, there is nothing wrong about it. The function may fail (I don't want to catch it) but before leaving, it will report successful execution to another method. When debugging, it does exactly what it should.

Interestingly, Visual Studio 2019 will report the following:

When I follow the suggestion by choosing "Remove redundant assignment", it will remove the line success = true;, effectively changing the outcome!

Now what is the switch/case for, you'd ask? When removing it, the recommendation disappears:

Is there any reason for that, or is it a bug in Visual Studio?

回答1:

It seems to be a known issue with Roslyn and Visual Studio 2019 16.4, please refer to the GitHub issues #39755 and #39344.

The milestone is set to the version 16.5 Preview 2, so it was already fixed and you can try the preview 2 of 16.5 version or wait for stable one (personally, I'm not using a Preview versions)

来源：https://stackoverflow.com/questions/60420358/visual-studio-ide0059-c-sharp-unnecessary-assignment-of-a-value-bug