S3172 False-positive, pattern matching switch expression, deems it a chain

[JJoensuu (Juho Joensuu)]

Make sure to read this post before raising a thread here:

How to Report a False-positive / False-negative

Hey SonarSource Community! False-positives happen, as do false-negatives, and we’re eager to fix them. We are thrilled when our users report problems, so we can make our products better. What is a false-positive (FP)? A false-positive is when an issue is raised unexpectedly on code that should not trigger an issue, or where the suggested action doesn’t make any sense for the code. What is a false-negative (FN)? A false-negative is when an issue should be raised on a piece of code, but isn’t…

Then tell us:

• What language is this for?
  C#

• Which rule?
  S3172 Delegates should not be subtracted

• Why do you believe it’s a false-positive/false-negative?
  The exact same code but written as a traditional switch statement does not trigger this analyzer

• Are you using

  • SonarLint - 7.4.0.80741 / Visual Studio 17.8.2

• How can we reproduce the problem? Give us a self-contained snippet of code (formatted text, no screenshots)

    public static void UnSubscribeActions<T>(this IEnumerable<IDbSaveActions> dbSaveActions, Action<T> action, /*enum to switch on*/RequiredActions requiredAction) where T : DbContext
    {
        foreach (var saveAction in dbSaveActions.Where(x => x.RequiredActions.HasFlag(requiredAction)))
        {
            action -= requiredAction switch
            {
                RequiredActions.PreSaveAction => saveAction.Pre,
                RequiredActions.PostSaveAction => saveAction.Post,
                _ => throw new NotImplementedException(NotImplemented(requiredAction)),
            };
        }
    }

[cristian.ambrosini]

Hi @JJoensuu, welcome to the community!

I can confirm this as a FP, you can follow the ticket on GitHub. I’ll add a reproducer shortly in our repository.

Thanks for your feedback!