How to walk "up" a folder structure

[nils-a]

I want to walk a folder structure "up". I.e. given a folder I want to check it's parent, then that parent and so on. Until I found the root ..

Given the following script:

///////////////////////////////////////////////////////////////////////////////
// ARGUMENTS
///////////////////////////////////////////////////////////////////////////////

var startDir = Argument("start", System.IO.Path.GetTempPath());

///////////////////////////////////////////////////////////////////////////////
// TASKS
///////////////////////////////////////////////////////////////////////////////

Task("Default")
.Does(() => {
   var dir = Context.MakeAbsolute(Directory(startDir).Path);
   Information("FYI: Root is: "+System.IO.Path.GetPathRoot(dir.FullPath));
   Information("Staring loop...");
   var i = 0;

   do {
      Information("Checking: " + dir.FullPath);
      var parent = dir.Combine("..").Collapse();
      if(!Context.FileSystem.Exist(parent)){
         Information("Found root at: "+dir);
         break;
      }

      dir = parent;
   } while (i++ < 100); // to be sure...

   if(i >= 100) {
      Warning($"Tried  {i} loops. Aborting.");
   }

});

RunTarget("Default");

on windows the output looks something like:

========================================
Default
========================================
FYI: Root is: D:\
Staring loop...
Checking: D:/_dev/test1
Checking: D:/_dev
Checking: D:/
[...]
Checking: D:/
Checking: D:/
Tried  101 loops. Aborting.

and on linux the output is something like:

========================================
Default
========================================
FYI: Root is: /
Staring loop...
Checking: /home/nils/dev/test1
Checking: /home/nils/dev
Checking: /home/nils
Checking: /home
Checking: .
[...]
Checking: .
Checking: .
Tried  101 loops. Aborting.

Of cause I could walk System.IO.Path.GetDirectoryName() until the result is null, but that's not very Cake, is it?

[nils-a]

Related to #2763 and #3349

[nils-a]

After reading #3349 a bit I came up with the following "helper" :

internal DirectoryPath GetParent(DirectoryPath path) {
   path = MakeAbsolute(path); // to be sure. I's no use splitting the segments of "."

   if(path.Segments.Length == 1) {
      // one segment on Windows is e.g. "C:/" 
      // on all other systems one segment is e.g "/home"
      if(IsRunningOnWindows()) {
         // no more parents
         return null;
      } else { 
         // root ("/") is not really a segment for Cake, 
         // so we return that directly.
         return new DirectoryPath("/");
      }  
   }
   if(path.Segments.Length == 0) {
      return null;
   }

   var segments = path.Segments.Take(path.Segments.Length - 1);
   return new DirectoryPath(string.Join(path.Separator.ToString(), segments));
}

the code from above then changes:

[...]
var parent = GetParent(dir);
if(parent == null){
[...]