[C#] Taint analysis does not have flow path for non constant field of a class as its source

[kanan1832]

Hello, I'm fairly new to codeql so if I'm using codeql terms or statements incorrectly, apologies for that.

I have this simple Test class, where I'm trying to mimic a path problem.
with Message1 as source and Console.WriteLine(Message1) as sink.

 class Test
    {
        private const string Message1 = "Test Message 1";
        private readonly string Message2 = "Test Message 2";

        public void Run()
        {
            Console.WriteLine(Message1);
            Console.WriteLine(Message2);
        }
    }

import csharp
import DataFlow::PathGraph

class Source extends DataFlow::Node {
  Source() { this.asExpr() instanceof StringLiteral }
}

class WriteLineMethod extends Method {
  WriteLineMethod() { this.hasQualifiedName("System.Console.WriteLine") }
}

class Sink extends DataFlow::Node {
  Sink() {
    exists(MethodCall m |
      m.getTarget() instanceof WriteLineMethod and
      this.asExpr() = m.getArgument(0)
    )
  }
}

class SimpleConfiguration extends TaintTracking::Configuration {
  SimpleConfiguration() { this = "Simple configuration" }

  override predicate isSource(DataFlow::Node source) { source instanceof Source }

  override predicate isSink(DataFlow::Node sink) { sink instanceof Sink }
  
}

from DataFlow::PathNode source, DataFlow::PathNode sink, SimpleConfiguration cfg
where cfg.hasFlowPath(source, sink)
select sink.getNode(), source, sink, "$@ is used in WriteLine method.", source.getNode(),
  "String"

Here I did simple taint tracking analysis on above Test class using above query, for const field private const string Message1 = "Test Message 1"; as source and
Console.WriteLine(Message1); as sink i'm getting correct result, But for non const field private readonly string Message2 = "Test Message 2"; it doesn't seem to work.

Did i miss something here? why does taint tracking works for const field or static field in static class but not for instance field?

I have asked this same question at two different places, below is the link for that.

stackoverflow question
github/codeql/issues/9569

[tamasvajk]

I've added an answer in github/codeql#9728.