Add System.Private.CoreLib shared sources (#12162)

Taken from corefx commit 5956ad35864352b38c53aa8c2d1ce012c96b168d. Subsequent updates will happen via a mirroring bot.

1 files changed, 102 insertions, 0 deletions

diff --git a/netcore/System.Private.CoreLib/shared/System/IO/PathInternal.Unix.cs b/netcore/System.Private.CoreLib/shared/System/IO/PathInternal.Unix.cs
new file mode 100644
index 00000000000..fae309be565
--- /dev/null
+++ b/netcore/System.Private.CoreLib/shared/System/IO/PathInternal.Unix.cs
@@ -0,0 +1,102 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Diagnostics;
+using System.Text;
+using System.Runtime.InteropServices;
+
+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 = "/";
+
+        // There is only one invalid path character in Unix
+        private const char InvalidPathChar = '\0';
+
+        internal const string ParentDirectoryPrefix = @"../";
+
+        internal static int GetRootLength(ReadOnlySpan<char> path)
+        {
+            return path.Length > 0 && IsDirectorySeparator(path[0]) ? 1 : 0;
+        }
+
+        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(DirectorySeparatorChar == AltDirectorySeparatorChar);
+            return c == DirectorySeparatorChar;
+        }
+
+        /// <summary>
+        /// Normalize separators in the given path. Compresses forward slash runs.
+        /// </summary>
+        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 !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;
+        }
+    }
+}