Different output in Unix between Path.GetPathRoot overloads for redundant segments

[carlossanlop]

While working on this issue (PR), I found a bug in the string overload for Path.GetPathRoot (Unix):

using System;
using System.IO;
namespace ConsoleAppCore
{
    class Program
    {
        static void Main()
        {
            string original = "/home/../folder/../..";
            string expected = "/";
            ReadOnlySpan<char> actualSpan = Path.GetPathRoot(original.AsSpan());
            string actualString = Path.GetPathRoot(original);
            Console.WriteLine($"Expected:      '{expected}'");
            Console.WriteLine($"Actual string: '{actualString}'");          // This returns '/'
            Console.WriteLine($"Actual span:   '{actualSpan.ToString()}'"); // This returns ''
        }
    }
}

I also found that running the same code in Windows will yield the behavior below, which is why I originally opened this issue, but @jkotas kindly pointed out it's expected behavior - the string method overload normalizes, while the span overload does not:

            Console.WriteLine($"Actual span:   '{actualSpan.ToString()}'"); // This returns '/'
            Console.WriteLine($"Actual string: '{actualString}'");          // This returns '\'

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[carlossanlop]

Assigning to myself to investigate and fix since it's blocking my redundant segments PR.

[jkotas]

FWIW, this is by design. From https://docs.microsoft.com/en-us/dotnet/api/system.io.path.getpathroot?view=netcore-3.1#System_IO_Path_GetPathRoot_System_ReadOnlySpan_System_Char__ :

Unlike the string overload, this method doesn't normalize directory separators.

[carlossanlop]

Thanks, @jkotas. I assume the behavior is different because we wanted to prevent introducing a breaking change in the old string overload method, and the new method had the behavior corrected to prevent normalization. I found a couple of places in our own code where the string overload of GetPathRoot is being used to normalize a path.

[carlossanlop]

I'm reopening this issue because I reviewed my notes more closely and realized the actual bug is in Unix. I edited the original description with the details.