Skip version (dotnet/corefx#28835)

Signed-off-by: dotnet-bot-corefx-mirror <[email protected]>

Author: Anipik

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

@@ -115,6 +115,25 @@ internal static bool AreRootsEqual(string first, string second, StringComparison
         /// </summary>
         /// <param name="rootLength">The length of the root of the given path</param>
         internal static string RemoveRelativeSegments(string path, int rootLength)
+        {
+            Span<char> initialBuffer = stackalloc char[260 /* PathInternal.MaxShortPath */];
+            ValueStringBuilder sb = new ValueStringBuilder(initialBuffer);
+
+            if (RemoveRelativeSegments(path.AsSpan(), rootLength, ref sb))
+            {
+                path = sb.ToString();
+            }
+
+            sb.Dispose();
+            return path;
+        }
+
+        /// <summary>
+        /// Try to remove relative segments from the given path (without combining with a root).
+        /// </summary>
+        /// <param name="rootLength">The length of the root of the given path</param>
+        /// <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;
@@ -126,15 +145,12 @@ internal static string RemoveRelativeSegments(string path, int rootLength)
             if (PathInternal.IsDirectorySeparator(path[skip - 1]))
                 skip--;
 
-            Span<char> initialBuffer = stackalloc char[260 /* PathInternal.MaxShortPath */];
-            ValueStringBuilder sb = new ValueStringBuilder(initialBuffer);
-
             // Remove "//", "/./", and "/../" from the path by copying each character to the output, 
             // except the ones we're removing, such that the builder contains the normalized path 
             // at the end.
             if (skip > 0)
             {
-                sb.Append(path.AsSpan(0, skip));
+                sb.Append(path.Slice(0, skip));
             }
 
             for (int i = skip; i < path.Length; i++)
@@ -182,7 +198,7 @@ internal static string RemoveRelativeSegments(string path, int rootLength)
 
                         i += 2;
                         continue;
-                    }
+                   }
                 }
 
                 // Normalize the directory separator if needed
@@ -198,11 +214,16 @@ internal static string RemoveRelativeSegments(string path, int rootLength)
             // If we haven't changed the source path, return the original
             if (!flippedSeparator && sb.Length == path.Length)
             {
-                sb.Dispose();
-                return path;
+                return false;
+            }
+
+            // We may have eaten the trailing separator from the root when we started and not replaced it
+            if (skip != rootLength && sb.Length < rootLength)
+            {
+                sb.Append(path[rootLength - 1]);
             }
 
-            return sb.Length < rootLength ? path.Substring(0, rootLength) : sb.ToString();
+            return true;
         }
     }
 }