AppDomain.CurrentDomain.SetupInformation.PrivateBinPath is null

Question

When I start my application that only has one AppDomain, AppDomain.CurrentDomain.SetupInformation.PrivateBinPath is null. Even though I have probing paths set in MyApp.exe.config as shown below.

I would have expeceted that AppDomain.CurrentDomain.SetupInformation.PrivateBinPath contains the string "Dir1;Dir2;Dir3".

How can I access the probing path as configured in the MyApp.exe.config?

<?xml version="1.0" encoding="utf-8"?>

<configuration>
  <appSettings>
    <add key="Foo" value="Bar" />
  </appSettings>
  <startup>
    <!-- supportedRuntime version="v1.1.4322" / -->
  </startup>

  <runtime>
    <gcConcurrent enabled="true" />
    <assemblyBinding xmlns="urn:schemas-microsoft-com:asm.v1">
      <publisherPolicy apply="yes" />

      <!-- Please add your subdirectories to the probing path! -->
      <probing privatePath="Dir1;Dir2;Dir3" />
    </assemblyBinding>
  </runtime>
  <system.windows.forms jitDebugging="true" />
</configuration>

Update

As Hans Passant pointed out the comment below, SetupInformation.PrivateBinPath is not set for the primary appdomain. So the above doesn't work. What would be your suggestion to simulate the way fusion searches for assemblies in the probing path or at least take <probing privatePath="" /> from the current application configuration into account? The best thing I can come up with is to read <probing privatePath="" /> from App.config manually when the current domain is the primary appdomain (AppDomain.CurrentDomain.IsDefaultAppDomain() is true). Is there a better way?

Update 2

Here some additional background information what this is needed for: This problem occured in AppDomainAssemblyTypeScanner.GetAssemblyDirectories() of the Nancy framework.

Nancy autodiscovers and loads 3rd party modules and other "plugins". By default this is supposed to be done same way as normally linked assemblies would be loaded (i.e. as fusion would do it) by looking through the probing paths. Assemblies are loaded using Assembly.Load (as opposed to Assembly.LoadFrom) so as I understand it, all the dependent assemblies of the loaded assemblies must be reachable in the probing path of the application/appdomain too.

Answer 1

How can I access the probing path as configured in the MyApp.exe.config

To remain compatible what fusion will do, you can read the config file in effect to get the current probing paths:

private static string GetProbingPath()
{
    var configFile = XElement.Load(AppDomain.CurrentDomain.SetupInformation.ConfigurationFile);
    var probingElement = (
        from runtime 
            in configFile.Descendants("runtime")
        from assemblyBinding 
            in runtime.Elements(XName.Get("assemblyBinding", "urn:schemas-microsoft-com:asm.v1"))
        from probing 
            in assemblyBinding.Elements(XName.Get("probing", "urn:schemas-microsoft-com:asm.v1"))
        select probing)
        .FirstOrDefault();

    return probingElement?.Attribute("privatePath").Value;
}

Supposing the config file sample in your question it returns: "Dir1;Dir2;Dir3"