[DonoT review] Removing rootlength variable from removeRelative segments

src/System.Private.CoreLib/shared/System/IO/Path.Unix.cs

@@ -35,7 +35,7 @@ public static string GetFullPath(string path)
 
             // We would ideally use realpath to do this, but it resolves symlinks, requires that the file actually exist,
             // and turns it into a full path, which we only want if fullCheck is true.
-            string collapsedString = PathInternal.RemoveRelativeSegments(path, PathInternal.GetRootLength(path));
+            string collapsedString = PathInternal.RemoveRelativeSegments(path);
 
             Debug.Assert(collapsedString.Length < path.Length || collapsedString.ToString() == path,
                 "Either we've removed characters, or the string should be unmodified from the input path.");

src/System.Private.CoreLib/shared/System/IO/Path.Windows.cs

@@ -130,7 +130,7 @@ public static string GetFullPath(string path, string basePath)
             // them properly. As such we need to manually remove segments and not use GetFullPath().
 
             return PathInternal.IsDevice(combinedPath.AsSpan())
-                ? PathInternal.RemoveRelativeSegments(combinedPath, PathInternal.GetRootLength(combinedPath.AsSpan()))
+                ? PathInternal.RemoveRelativeSegments(combinedPath)
                 : GetFullPath(combinedPath);
         }
 

src/System.Private.CoreLib/shared/System/IO/PathInternal.cs

@@ -115,11 +115,11 @@ internal static bool AreRootsEqual(string first, string second, StringComparison
         /// Try to remove relative segments from the given path (without combining with a root).
         /// </summary>
         /// <param name="path">Input path</param>
-        /// <param name="rootLength">The length of the root of the given path</param>
-        internal static string RemoveRelativeSegments(string path, int rootLength)
+        internal static string RemoveRelativeSegments(string path)
         {
             Span<char> initialBuffer = stackalloc char[260 /* PathInternal.MaxShortPath */];
             ValueStringBuilder sb = new ValueStringBuilder(initialBuffer);
+            int rootLength = GetRootLength(path.AsSpan());
 
             if (RemoveRelativeSegments(path.AsSpan(), rootLength, ref sb))
             {
@@ -139,14 +139,13 @@ internal static string RemoveRelativeSegments(string path, int rootLength)
         /// <returns>"true" if the path was modified</returns>
         internal static bool RemoveRelativeSegments(ReadOnlySpan<char> path, int rootLength, ref ValueStringBuilder sb)
         {
-            Debug.Assert(rootLength > 0);
             bool flippedSeparator = false;
 
             int skip = rootLength;
             // We treat "\.." , "\." and "\\" as a relative segment. We want to collapse the first separator past the root presuming
             // the root actually ends in a separator. Otherwise the first segment for RemoveRelativeSegments
             // in cases like "\\?\C:\.\" and "\\?\C:\..\", the first segment after the root will be ".\" and "..\" which is not considered as a relative segment and hence not be removed.
-            if (PathInternal.IsDirectorySeparator(path[skip - 1]))
+            if (skip > 0 && PathInternal.IsDirectorySeparator(path[skip - 1]))
                 skip--;
 
             // Remove "//", "/./", and "/../" from the path by copying each character to the output,