Clean-up duplicated PathInternal files

src/libraries/Common/src/System/IO/PathInternal.Unix.cs

@@ -1,44 +1,97 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
-using System;
 using System.Diagnostics;
 using System.Text;
+using System.Diagnostics.CodeAnalysis;
 
 namespace System.IO
 {
     /// <summary>Contains internal path helpers that are shared between many projects.</summary>
     internal static partial class PathInternal
     {
+        internal const char DirectorySeparatorChar = '/';
+        internal const char AltDirectorySeparatorChar = '/';
+        internal const char VolumeSeparatorChar = '/';
+        internal const char PathSeparator = ':';
+        internal const string DirectorySeparatorCharAsString = "/";
+        internal const string ParentDirectoryPrefix = @"../";
+
         internal static int GetRootLength(ReadOnlySpan<char> path)
         {
             return path.Length > 0 && IsDirectorySeparator(path[0]) ? 1 : 0;
         }
 
-        internal static bool EndsInDirectorySeparator(ReadOnlySpan<char> path)
-            => path.Length > 0 && IsDirectorySeparator(path[path.Length - 1]);
-
-        internal static ReadOnlySpan<char> TrimEndingDirectorySeparator(ReadOnlySpan<char> path) =>
-            EndsInDirectorySeparator(path) && !IsRoot(path) ?
-                path.Slice(0, path.Length - 1) :
-                path;
-
-        internal static bool IsRoot(ReadOnlySpan<char> path)
-            => path.Length == GetRootLength(path);
-
         internal static bool IsDirectorySeparator(char c)
         {
             // The alternate directory separator char is the same as the directory separator,
             // so we only need to check one.
-            Debug.Assert(Path.DirectorySeparatorChar == Path.AltDirectorySeparatorChar);
-            return c == Path.DirectorySeparatorChar;
+            Debug.Assert(DirectorySeparatorChar == AltDirectorySeparatorChar);
+            return c == DirectorySeparatorChar;
         }
 
-        internal static bool IsPartiallyQualified(string path)
+        /// <summary>
+        /// Normalize separators in the given path. Compresses forward slash runs.
+        /// </summary>
+        [return: NotNullIfNotNull("path")]
+        internal static string? NormalizeDirectorySeparators(string? path)
+        {
+            if (string.IsNullOrEmpty(path))
+                return path;
+
+            // Make a pass to see if we need to normalize so we can potentially skip allocating
+            bool normalized = true;
+
+            for (int i = 0; i < path.Length; i++)
+            {
+                if (IsDirectorySeparator(path[i])
+                    && (i + 1 < path.Length && IsDirectorySeparator(path[i + 1])))
+                {
+                    normalized = false;
+                    break;
+                }
+            }
+
+            if (normalized)
+                return path;
+
+            StringBuilder builder = new StringBuilder(path.Length);
+
+            for (int i = 0; i < path.Length; i++)
+            {
+                char current = path[i];
+
+                // Skip if we have another separator following
+                if (IsDirectorySeparator(current)
+                    && (i + 1 < path.Length && IsDirectorySeparator(path[i + 1])))
+                    continue;
+
+                builder.Append(current);
+            }
+
+            return builder.ToString();
+        }
+
+        internal static bool IsPartiallyQualified(ReadOnlySpan<char> path)
         {
             // This is much simpler than Windows where paths can be rooted, but not fully qualified (such as Drive Relative)
             // As long as the path is rooted in Unix it doesn't use the current directory and therefore is fully qualified.
-            return string.IsNullOrEmpty(path) || path[0] != Path.DirectorySeparatorChar;
+            return !Path.IsPathRooted(path);
+        }
+
+        /// <summary>
+        /// Returns true if the path is effectively empty for the current OS.
+        /// For unix, this is empty or null. For Windows, this is empty, null, or
+        /// just spaces ((char)32).
+        /// </summary>
+        internal static bool IsEffectivelyEmpty(string? path)
+        {
+            return string.IsNullOrEmpty(path);
+        }
+
+        internal static bool IsEffectivelyEmpty(ReadOnlySpan<char> path)
+        {
+            return path.IsEmpty;
         }
     }
 }