Fix S2583 FP: Code wrongly considered unreachable

[drieseng]

Description

S2583 is raised in a while(true) loop with nested conditions.

Repro steps

Compile and run the following code:

namespace SonarRepo
{
    using System;
    using System.Net;

    public static class Program
    {
        private static void Main()
        {
            Run();
        }

        public static void Run()
        {
            HttpStatusCode? statusCode = null;
            var contentLength = 0;

            while (true)
            {
                var response = "5";
                if (response is null)
                {
                    // server shut down socket
                    break;
                }

                if (statusCode is null)
                {
                    statusCode = HttpStatusCode.OK;
                    continue;
                }

                // continue on parsing message headers coming from the server
                if (response == "5" && contentLength == 0)
                {
                    contentLength = 7;
                    continue;
                }

                if (response.Length > 0)
                {
                    if (contentLength > 0)
                    {
                        Console.WriteLine("And you thought we were unreachable??");
                    }

                    break;
                }
            }
        }
    }
}

Expected behavior

S2583 is not reported, and the application writes the following to standard output:

And you thought we were unreachable??

Actual behavior

S2583 is reported, and the application writes the following to standard output:

And you thought we were unreachable??

Known workarounds

None.

Related information

• SonarAnalyzer.CSharp version: 9.12.0.78982
• Visual Studio version: 17.8.0 Preview 2.0

[martin-strecker-sonarsource]

Thank you @drieseng for reporting this false positive. I added a reproducer in #8268 to our code base. The root cause is most likely the complex code flow. It requires three iterations in the loop before contentLength > 0 becomes true and that is likely too much for our rule to handle. We will add the issue to our backlog and will see what we can do about it.

[aldinei-sampaio]

Similar problem here:

var index = 0;
while(true)
{
    var data = parser.Read();
    if (data == null)
        break;
    yield return new JArray(data);
    if (++index % 1000 == 0) // <-- S2583 happens here
        progressAction.Invoke();
}

[aldinei-sampaio]

And here:

 var counter = 0;
while(true)
{
    counter++;
    if (counter == 10)  // <-- S2589 happens here
        return;
}