LocalPath: normalize current directory to .

CHANGELOG.md

@@ -25,7 +25,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - On Windows, `AbsolutePath / LocalPath` now resolves a path relative to the current directory of another drive against the current directory of that drive, so the result is always absolute: e.g. `C:\base / D:x` is `D:\x` if the current directory of drive `D:` is its root. Previously, the result was `D:x`, which is not absolute.
 - On Windows, `LocalPath.ResolveToCurrentDirectory` now resolves `\x` against the drive of the current directory, and `D:x` against the current directory of drive `D:`.
 - **Breaking:** `LocalPath.StartsWith` and `AbsolutePath.StartsWith` now compare whole path segments instead of raw strings, which makes them exact inverses of `IsPrefixOf` as originally intended in [#43](https://github.com/ForNeVeR/TruePath/issues/43). For example, `new LocalPath("/foo1").StartsWith(new LocalPath("/foo"))` is now `false`, where it used to be `true`.
-- `LocalPath.IsPrefixOf` now treats an empty path — the normalized form of `""`, `"."` and `"a/.."`, and the parent of any single-segment relative path — as the current directory, so it is a prefix of every path of kind `PathKind.Relative` that does not begin with a `..` reference.
+- **Breaking:** path normalization now represents the current directory as `.` instead of an empty string: `PathStrings.Normalize` returns `"."` for `""`, `"."` and `"a/.."`, and so do `LocalPath.Value` and `ToString()` (and `LocalPath.Parent` of a single-segment relative path is `.`). As a consequence, `LocalPath.FileName` of such a path is `.`, the same way it is `..` for `..`, and `GetExtensionWithDot` returns `.` for it.
+- `LocalPath.IsPrefixOf` now treats the current directory path `.` — the normalized form of `""`, `"."` and `"a/.."`, and the parent of any single-segment relative path — as the current directory, so it is a prefix of every path of kind `PathKind.Relative` that does not begin with a `..` reference.
 - The platform-default path comparers (`LocalPath.PlatformDefaultComparer`, `AbsolutePath.PlatformDefaultComparer`) are now case-insensitive on iOS and tvOS as well, matching the .NET runtime.
 
 ### Fixed
@@ -35,7 +36,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - `LocalPath.IsPrefixOf` and `StartsWith` now compare path strings ordinally. Previously they used the current culture, which ignores collation-ignorable characters, so a path could be reported as a prefix of an unrelated one.
 - Path normalization no longer drops the root separator when a rooted path ends with `..`: `C:\base\..` is now normalized to `C:\` (was `C:`, a path relative to the current directory of drive `C:`), and `/base/..` to `/` (was an empty path, i.e. the current directory). This affects `PathStrings.Normalize`, `LocalPath` and `AbsolutePath`.
 - [#95](https://github.com/ForNeVeR/TruePath/issues/95): Path normalization now drops a `..` directly after the root, since the root has no parent: `/..` is normalized to `/`, and `C:\..\x` to `C:\x`, the same as `Path.GetFullPath` does. Thanks to @sinthu-14 for help!
-- `LocalPath.RelativeTo` no longer throws an exception when either path is empty (i.e. designates the current directory).
+- `LocalPath.RelativeTo` no longer throws an exception when either path designates the current directory.
 - On .NET Standard 2.0 (e.g., .NET Framework), `LocalPath.RelativeTo` and `AbsolutePath.RelativeTo` now use a port of the .NET runtime's `Path.GetRelativePath`, and return the same results as on .NET 8+ (except for the stream syntax, see [#235](https://github.com/ForNeVeR/TruePath/issues/235)). Previously, the result was wrong for a destination equal to or above the base path, and for names containing `%XX` sequences.
 
 ## [1.12.0] - 2026-03-14

TruePath.Tests/LocalPathTests.cs

@@ -33,18 +33,36 @@ public void RootedPathAboveRootHasNoParent(string relativePath)
     }
 
     [Theory]
-    [InlineData(".", "")]
+    [InlineData("", ".")]
+    [InlineData(".", ".")]
+    [InlineData("a/..", ".")]
     [InlineData("..", "..")]
     [InlineData("../..", "../..")]
     [InlineData(".../...", ".../...")]
-    [InlineData(".../..", "")]
+    [InlineData(".../..", ".")]
     public void ConstructionTest(string pathString, string expectedValue)
     {
         var path = new LocalPath(pathString);
         Assert.Equal(expectedValue.Replace('/', Path.DirectorySeparatorChar), path.Value);
     }
 
     [Theory]
+    [InlineData("")]
+    [InlineData(".")]
+    [InlineData("./.")]
+    [InlineData("a/..")]
+    public void CurrentDirectoryValue(string pathString)
+    {
+        var path = new LocalPath(pathString);
+
+        Assert.Equal(".", path.Value);
+        Assert.Equal(".", path.ToString());
+        Assert.Equal(PathKind.Relative, path.Kind);
+        Assert.Equal(".", path.FileName);
+    }
+
+    [Theory]
+    [InlineData("", "..")]
     [InlineData(".", "..")]
     [InlineData("..", "../..")]
     [InlineData("../..", "../../..")]
@@ -187,16 +205,16 @@ public void IsPrefixOfRequiresWholeSegmentRegardlessOfCase()
     }
 
     [Fact]
-    public void EmptyParentIsPrefixOfDescendantPath()
+    public void CurrentDirectoryParentIsPrefixOfDescendantPath()
     {
         var parent = new LocalPath("foo").Parent;
         Assert.NotNull(parent);
-        Assert.Equal("", parent.Value.Value);
+        Assert.Equal(".", parent.Value.Value);
         Assert.True(parent.Value.IsPrefixOf(new LocalPath("bar")));
     }
 
     [Fact]
-    public void EmptyParentIsNotPrefixOfPathEscapingUpwards()
+    public void CurrentDirectoryParentIsNotPrefixOfPathEscapingUpwards()
     {
         var parent = new LocalPath("foo").Parent;
         Assert.NotNull(parent);
@@ -296,7 +314,10 @@ public void ResolveToCurrentDirectoryForDriveRelativePathsOnWindows()
     [InlineData("a", "a/b", "b")]
     [InlineData("a/b", "a", "..")]
     [InlineData("a/c", "a/b", "../b")]
-    [InlineData("a", "a", "")]
+    [InlineData("a", "a", ".")]
+    [InlineData("", "a", "a")]
+    [InlineData("a", "", "..")]
+    [InlineData("", "", ".")]
     public void RelativeToForRelativePaths(string from, string to, string expected)
     {
         var relativePath = new LocalPath(to).RelativeTo(new LocalPath(from));
@@ -513,7 +534,10 @@ public void AppendMatrixOnWindows()
             ("", "D:x", "D:x", "D:x"),
             ("", "C:x", "C:x", "C:x"),
             ("", "c:x", "c:x", "c:x"),
-            ("", "", "", ""),
+            ("", "", ".", ""),
+            (".", "x", "x", @".\x"),
+            ("x", ".", "x", @"x\."),
+            ("C:", ".", "C:", @"C:\."),
         ];
 
         var failures = new List<string>();
@@ -548,6 +572,9 @@ public void AppendMatrixOnUnix()
             ("base", "C:x", "base/C:x"),
             ("C:", "x", "C:/x"),
             ("", "x", "x"),
+            ("", "", "."),
+            (".", "x", "x"),
+            ("x", ".", "x"),
         ];
 
         var failures = new List<string>();

TruePath.Tests/NormalizationTests.cs

@@ -20,7 +20,7 @@ public void NormalizedPathDoesNotEndWithDirSeparator(List<string> pathParts)
         var normalizedPath = PathStrings.Normalize(sourcePath);
 
         testOutputHelper.WriteLine($"{sourcePath} => {normalizedPath}");
-        Assert.True(normalizedPath == ""
+        Assert.True(normalizedPath == "."
             || normalizedPath == Path.DirectorySeparatorChar.ToString()
             || normalizedPath is [_, ':', _]
             || normalizedPath[^1] != Path.DirectorySeparatorChar);

TruePath.Tests/PathExtensionsTests.cs

@@ -7,6 +7,7 @@ namespace TruePath.Tests;
 public class PathExtensionsTests
 {
     [Theory]
+    [InlineData(".", ".")]
     [InlineData("..", ".")]
     [InlineData("foo/bar.txt", ".txt")]
     [InlineData("/foo/bar.txt", ".txt")]
@@ -44,6 +45,7 @@ public void GetExtensionWithoutDotTests(string path, string expected)
     }
 
     [Theory]
+    [InlineData(".", "")]
     [InlineData("..", ".")]
     [InlineData("foo/bar.txt", "bar")]
     [InlineData("/foo/bar.txt", "bar")]
@@ -62,6 +64,7 @@ public void GetFilenameWithoutExtensionTests(string path, string expected)
     }
 
     [Theory]
+    [InlineData(".")]
     [InlineData("..")]
     [InlineData("file.txt")]
     [InlineData("file..txt")]

TruePath.Tests/PathStringsTests.cs

@@ -45,11 +45,15 @@ public void SeparatorsAreDeduplicated(string input, string expected)
     }
 
     [Theory]
-    [InlineData(".", "")]
+    [InlineData("", ".")]
+    [InlineData(".", ".")]
+    [InlineData("./.", ".")]
+    [InlineData("./", ".")]
     [InlineData("./foo", "foo")]
     [InlineData("..", "..")]
     [InlineData("./..", "..")]
-    [InlineData("a/..", "")]
+    [InlineData("a/..", ".")]
+    [InlineData("a/../", ".")]
     [InlineData("a/../..", "..")]
     [InlineData("a/../../.", "..")]
     [InlineData("a/../../..", "../..")]
@@ -68,7 +72,7 @@ public void SeparatorsAreDeduplicated(string input, string expected)
     [InlineData("../../../foo", "../../../foo")]
     [InlineData("../foo/..", "..")]
     [InlineData("...", "...")]
-    [InlineData(".../..", "")]
+    [InlineData(".../..", ".")]
     [InlineData(".../...", ".../...")]
     [InlineData(".../../...", "...")]
     [InlineData("foo/bar/../file.ext", "foo/file.ext")]

TruePath/LocalPath.cs

@@ -13,7 +13,7 @@ namespace TruePath;
 /// <para>A path pointing to a place in the local file system.</para>
 /// <para>It may be either absolute or relative.</para>
 /// <para>
-/// An <b>empty</b> path designates the <b>current directory</b>. Normalizing an empty string, <c>.</c> or
+/// The path <c>.</c> designates the <b>current directory</b>. Normalizing an empty string, <c>.</c> or
 /// <c>a/..</c> produces it, and so does <see cref="Parent"/> of a relative path consisting of a single segment
 /// (e.g. the parent of <c>foo</c>).
 /// </para>
@@ -80,7 +80,6 @@ public PathKind Kind
     {
         get
         {
-            if (Value.Length == 0) return PathKind.Relative;
             if (!PathStrings.IsDriveBasedSystem) return Value[0] == Separator ? PathKind.Absolute : PathKind.Relative;
 
             if (HasDriveLetter)
@@ -140,8 +139,8 @@ public PathKind Kind
 
     /// <inheritdoc cref="IPath.Parent"/>
     /// <remarks>
-    /// The parent of a relative path consisting of a single segment is the <b>empty</b> path (the current
-    /// directory), not <see langword="null"/>. Similarly, on Windows, the parent of a bare drive (<c>C:</c>, the
+    /// The parent of a relative path consisting of a single segment is <c>.</c> (the current directory), not
+    /// <see langword="null"/>. Similarly, on Windows, the parent of a bare drive (<c>C:</c>, the
     /// current directory of that drive) is <c>C:..</c>.
     /// </remarks>
     public LocalPath? Parent
@@ -154,7 +153,9 @@ public LocalPath? Parent
             {
                 // For C:foo, the rest after the drive letter is a relative path, and follows the same rules.
                 var relativePart = kind == PathKind.DriveCurrentDirectoryRelative ? Value[2..] : Value;
-                if (relativePart == "" || relativePart == ".." || relativePart.EndsWith($"{Separator}.."))
+                if (IsCurrentDirectory(relativePart.AsSpan())
+                    || relativePart == ".."
+                    || relativePart.EndsWith($"{Separator}.."))
                     return this / "..";
             }
 
@@ -219,7 +220,7 @@ public override bool Equals(object? obj)
     /// <inheritdoc cref="IPath{TPath}.IsPrefixOf(TPath)"/>
     /// <remarks>
     /// <para>
-    /// An <b>empty</b> path designates the current directory. It is a prefix of every relative path that stays
+    /// The path <c>.</c> designates the current directory. It is a prefix of every relative path that stays
     /// at or below that directory, which means every relative path that does not begin with a <c>..</c>
     /// reference.
     /// </para>
@@ -237,7 +238,7 @@ public override bool Equals(object? obj)
     /// <para>
     /// On Windows, paths relative to the current directory of a drive (such as <c>C:Windows</c>) are only related
     /// if they have the same drive letter. A bare drive (<c>C:</c>) designates that drive's current directory, and
-    /// behaves the same way as the empty path does for relative paths.
+    /// behaves the same way as <c>.</c> does for relative paths.
     /// </para>
     /// <para>
     /// Note that <c>C:\</c> will <i>not</i> be considered as a prefix of <c>C:Folder</c>, even though they
@@ -280,10 +281,7 @@ public bool IsPrefixOf(LocalPath other)
 
     private static bool IsSegmentPrefix(ReadOnlySpan<char> prefix, ReadOnlySpan<char> path)
     {
-        // The empty path is the current directory, so every path at or below it has it as a prefix - but one
-        // starting with a ".." reference points outside it. Normalization only ever keeps such references at the
-        // very start of a path, so testing the first segment is enough.
-        if (prefix.Length == 0) return !StartsWithParentDirectoryReference(path);
+        if (IsCurrentDirectory(prefix)) return !StartsWithParentDirectoryReference(path);
 
         if (!path.StartsWith(prefix, PlatformDefaultPathComparer.DefaultStringComparison))
             return false;
@@ -292,6 +290,13 @@ private static bool IsSegmentPrefix(ReadOnlySpan<char> prefix, ReadOnlySpan<char
                path[prefix.Length] == Separator;
     }
 
+    /// <summary>
+    /// Whether a normalized relative path (or its part left after stripping a drive letter or the leading <c>..</c>
+    /// references) designates the directory it is relative to.
+    /// </summary>
+    private static bool IsCurrentDirectory(ReadOnlySpan<char> value) =>
+        value.Length == 0 || value is ".";
+
     private static bool IsSameDrive(string a, string b) => char.ToUpperInvariant(a[0]) == char.ToUpperInvariant(b[0]);
 
     /// <summary>
@@ -307,7 +312,7 @@ private static bool IsSegmentPrefix(ReadOnlySpan<char> prefix, ReadOnlySpan<char
     /// If either path is not absolute, it is first <b>resolved</b> against the current directory, the same way
     /// <see cref="ResolveToCurrentDirectory"/> does, so the result may depend on the current directory (or a
     /// drive-specific current directory on Windows). Two relative paths are resolved against the same directory, so
-    /// <c>a/b</c> relative to <c>a</c> is <c>b</c>. An empty path designates the current directory.
+    /// <c>a/b</c> relative to <c>a</c> is <c>b</c>. The path <c>.</c> designates the current directory.
     /// </para>
     /// <para>
     /// If the resolved paths have different roots (on Windows, e.g. paths on different drives), there's no relative
@@ -317,13 +322,10 @@ private static bool IsSegmentPrefix(ReadOnlySpan<char> prefix, ReadOnlySpan<char
     /// </remarks>
     public LocalPath RelativeTo(LocalPath basePath)
     {
-        // An empty value means the current directory, but GetRelativePath doesn't work for empty strings.
-        var relativeTo = basePath.Value.Length == 0 ? "." : basePath.Value;
-        var path = Value.Length == 0 ? "." : Value;
 #if NET8_0_OR_GREATER
-        return new(Path.GetRelativePath(relativeTo, path));
+        return new(Path.GetRelativePath(basePath.Value, Value));
 #else
-        return new(PathPolyfills.GetRelativePath(relativeTo, path));
+        return new(PathPolyfills.GetRelativePath(basePath.Value, Value));
 #endif
     }
 
@@ -346,8 +348,8 @@ public LocalPath RelativeTo(LocalPath basePath)
     ///     <item>
     ///         <see cref="PathKind.Relative"/> (<c>x</c>): <paramref name="b"/> is appended after a separator, so
     ///         <c>C:\base / x</c> is <c>C:\base\x</c>. No separator is added after a bare drive: <c>C: / x</c> is
-    ///         <c>C:x</c>. Appending an empty path returns the base path unchanged, and appending to an empty path
-    ///         returns <paramref name="b"/>.
+    ///         <c>C:x</c>. Appending <c>.</c> (the current directory) returns the base path unchanged, and appending
+    ///         to <c>.</c> returns <paramref name="b"/>.
     ///     </item>
     ///     <item>
     ///         <see cref="PathKind.DriveRootRelative"/> (<c>\x</c>): the drive of the base path is kept, if there is
@@ -408,8 +410,8 @@ private static string Append(LocalPath basePath, LocalPath b)
     private static string Join(LocalPath basePath, string relativePath)
     {
         var baseValue = basePath.Value;
-        if (relativePath.Length == 0) return baseValue;
-        if (baseValue.Length == 0) return relativePath;
+        if (IsCurrentDirectory(relativePath.AsSpan())) return baseValue;
+        if (baseValue == ".") return relativePath;
 
         // A bare drive (C:) designates the current directory of the drive, and C:x is a path relative to it.
         var isBareDrive = baseValue.Length == 2 && basePath.HasDriveLetter;

TruePath/PathExtensions.cs

@@ -78,8 +78,8 @@ public static string GetFilenameWithoutExtension(this IPath path) =>
     /// </returns>
     /// <exception cref="ArgumentException">
     ///     <para>
-    ///         Thrown if the <paramref name="path"/> has no file name to change: it is empty (which designates the
-    ///         current directory), it consists of a root or a drive designator (Windows) alone, such as <c>C:\</c>,
+    ///         Thrown if the <paramref name="path"/> has no file name to change: it designates the current directory
+    ///         (<c>.</c>), it consists of a root or a drive designator (Windows) alone, such as <c>C:\</c>,
     ///         <c>/</c> or <c>C:</c>, or its last segment is a parent directory reference (<c>..</c>).
     ///     </para>
     ///     <para>
@@ -139,8 +139,8 @@ public static TPath WithExtension<TPath>(this TPath path, string? extension) whe
     /// </returns>
     /// <exception cref="ArgumentException">
     ///     <para>
-    ///     Thrown if the <paramref name="path"/> has no file name to change: it is empty (which designates the
-    ///     current directory), it consists of a root or a drive designator alone, such as <c>C:\</c>, <c>/</c>
+    ///     Thrown if the <paramref name="path"/> has no file name to change: it designates the current directory
+    ///     (<c>.</c>), it consists of a root or a drive designator alone, such as <c>C:\</c>, <c>/</c>
     ///     or <c>C:</c>, or its last segment is a parent directory reference (<c>..</c>).
     ///     </para>
     ///     <para>
@@ -197,8 +197,8 @@ public static AbsolutePath WithExtension(this AbsolutePath path, string? extensi
     /// </returns>
     /// <exception cref="ArgumentException">
     ///     <para>
-    ///     Thrown if the <paramref name="path"/> has no file name to change: it is empty (which designates the
-    ///     current directory), it consists of a root or a drive designator alone, such as <c>C:\</c>, <c>/</c>
+    ///     Thrown if the <paramref name="path"/> has no file name to change: it designates the current directory
+    ///     (<c>.</c>), it consists of a root or a drive designator alone, such as <c>C:\</c>, <c>/</c>
     ///     or <c>C:</c>, or its last segment is a parent directory reference (<c>..</c>).
     ///     </para>
     ///     <para>

TruePath/PathKind.cs

@@ -29,8 +29,8 @@ public enum PathKind
     Absolute,
 
     /// <summary>
-    /// A path relative to the current directory: e.g. <c>Windows</c>, <c>..\Windows</c>, or the empty path (the
-    /// current directory itself).
+    /// A path relative to the current directory: e.g. <c>Windows</c>, <c>..\Windows</c>, or <c>.</c> (the current
+    /// directory itself).
     /// </summary>
     /// <remarks>
     /// On Unix, every path not starting with <c>/</c> is of this kind, including <c>C:foo</c> and <c>\foo</c>.