Treat a dotfile as having no extension in RemoveExtension and ChangeExtension [patch]

Semantics.Paths/Implementations/AbsoluteFilePath.cs

@@ -52,7 +52,7 @@ public FileName FileNameWithoutExtension
 		get
 		{
 			return _cachedFileNameWithoutExtension ??= FileName.Create<FileName>(
-				Path.GetFileNameWithoutExtension(WeakString) ?? "");
+				Path.GetFileName(WeakStringWithoutExtension));
 		}
 	}
 
@@ -65,19 +65,14 @@ public AbsoluteFilePath ChangeExtension(FileExtension newExtension)
 	{
 		Ensure.NotNull(newExtension);
 
-		string newPath = Path.ChangeExtension(WeakString, newExtension.WeakString);
-		return Create<AbsoluteFilePath>(newPath);
+		return Create<AbsoluteFilePath>(WeakStringWithExtension(newExtension));
 	}
 
 	/// <summary>
 	/// Removes the file extension from this path.
 	/// </summary>
 	/// <returns>A new <see cref="AbsoluteFilePath"/> without an extension.</returns>
-	public AbsoluteFilePath RemoveExtension()
-	{
-		string pathWithoutExtension = Path.ChangeExtension(WeakString, null) ?? "";
-		return Create<AbsoluteFilePath>(pathWithoutExtension);
-	}
+	public AbsoluteFilePath RemoveExtension() => Create<AbsoluteFilePath>(WeakStringWithoutExtension);
 
 	/// <summary>
 	/// Determines whether this file is inside the specified parent directory.

Semantics.Paths/Implementations/RelativeFilePath.cs

@@ -52,7 +52,7 @@ public FileName FileNameWithoutExtension
 		get
 		{
 			return _cachedFileNameWithoutExtension ??= FileName.Create<FileName>(
-				Path.GetFileNameWithoutExtension(WeakString) ?? "");
+				Path.GetFileName(WeakStringWithoutExtension));
 		}
 	}
 
@@ -65,19 +65,14 @@ public RelativeFilePath ChangeExtension(FileExtension newExtension)
 	{
 		Ensure.NotNull(newExtension);
 
-		string newPath = Path.ChangeExtension(WeakString, newExtension.WeakString);
-		return Create<RelativeFilePath>(newPath);
+		return Create<RelativeFilePath>(WeakStringWithExtension(newExtension));
 	}
 
 	/// <summary>
 	/// Removes the file extension from this path.
 	/// </summary>
 	/// <returns>A new <see cref="RelativeFilePath"/> without an extension.</returns>
-	public RelativeFilePath RemoveExtension()
-	{
-		string pathWithoutExtension = Path.ChangeExtension(WeakString, null) ?? "";
-		return Create<RelativeFilePath>(pathWithoutExtension);
-	}
+	public RelativeFilePath RemoveExtension() => Create<RelativeFilePath>(WeakStringWithoutExtension);
 
 	/// <summary>
 	/// Converts this relative file path to an absolute file path representation.

Semantics.Paths/SemanticFilePath.cs

@@ -67,6 +67,42 @@ public FileExtension FullFileExtension
 	/// <returns>The index just past the last directory separator, or 0 if there is none.</returns>
 	private static int FileNameStart(string path) => path.LastIndexOfAny(['/', '\\']) + 1;
 
+	/// <summary>
+	/// Gets the path with its <see cref="FileExtension"/> removed, so a dotfile such as <c>.bashrc</c>,
+	/// which has no extension, keeps its whole name. A trailing dot after the name (<c>file.</c>) is
+	/// removed too, as <see cref="Path.ChangeExtension(string, string)"/> removes it.
+	/// </summary>
+	private protected string WeakStringWithoutExtension
+	{
+		get
+		{
+			string path = WeakString;
+			int length = path.Length - FileExtension.WeakString.Length;
+			if (length == path.Length && length - 1 > FileNameStart(path) && path[length - 1] == '.')
+			{
+				length--;
+			}
+
+			return path.Substring(0, length);
+		}
+	}
+
+	/// <summary>
+	/// Gets the path with its <see cref="FileExtension"/> replaced by <paramref name="newExtension"/>, or
+	/// with <paramref name="newExtension"/> appended when the path has none, as a dotfile does.
+	/// </summary>
+	/// <param name="newExtension">The new extension, with or without its leading period.</param>
+	/// <returns>The path with the new extension.</returns>
+	private protected string WeakStringWithExtension(FileExtension newExtension)
+	{
+		Ensure.NotNull(newExtension);
+
+		string extension = newExtension.WeakString;
+		return extension.Length > 0 && extension[0] == '.'
+			? WeakStringWithoutExtension + extension
+			: $"{WeakStringWithoutExtension}.{extension}";
+	}
+
 	/// <summary>
 	/// Gets the filename portion of the path
 	/// </summary>

Semantics.Test/Paths/DotfileExtensionTests.cs

@@ -0,0 +1,92 @@
+// Copyright (c) 2023-2026 ktsu-dev contributors
+
+namespace ktsu.Semantics.Test.Paths;
+
+using ktsu.Semantics.Paths;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+
+/// <summary>
+/// Issue #325: a dotfile (<c>.bashrc</c>) has no extension, so <c>RemoveExtension</c> leaves it alone
+/// and <c>ChangeExtension</c> appends to it, instead of treating the whole name as an extension.
+/// </summary>
+[TestClass]
+public sealed class DotfileExtensionTests
+{
+	private static FileExtension Bak => FileExtension.Create<FileExtension>(".bak");
+
+	// Absolute and relative dotfiles from the issue, iterated inside each test rather than passed
+	// through [DataRow]: a public test method taking a string trips CA1062.
+	private static readonly string[] AbsoluteDotfiles =
+	[
+		TestPaths.Absolute("home", "user", ".bashrc"),
+		TestPaths.Absolute(".profile"),
+	];
+
+	private static readonly string[] RelativeDotfiles =
+	[
+		TestPaths.Relative(".gitignore"),
+		TestPaths.Relative("src", ".editorconfig"),
+	];
+
+	[TestMethod]
+	public void AbsoluteFilePath_Dotfile_RemoveExtension_KeepsName()
+	{
+		foreach (string path in AbsoluteDotfiles)
+		{
+			Assert.AreEqual(path, AbsoluteFilePath.Create<AbsoluteFilePath>(path).RemoveExtension().WeakString);
+		}
+	}
+
+	[TestMethod]
+	public void AbsoluteFilePath_Dotfile_ChangeExtension_Appends()
+	{
+		foreach (string path in AbsoluteDotfiles)
+		{
+			Assert.AreEqual(path + ".bak", AbsoluteFilePath.Create<AbsoluteFilePath>(path).ChangeExtension(Bak).WeakString);
+		}
+	}
+
+	[TestMethod]
+	public void RelativeFilePath_Dotfile_RemoveExtension_KeepsName()
+	{
+		foreach (string path in RelativeDotfiles)
+		{
+			Assert.AreEqual(path, RelativeFilePath.Create<RelativeFilePath>(path).RemoveExtension().WeakString);
+		}
+	}
+
+	[TestMethod]
+	public void RelativeFilePath_Dotfile_ChangeExtension_Appends()
+	{
+		foreach (string path in RelativeDotfiles)
+		{
+			Assert.AreEqual(path + ".bak", RelativeFilePath.Create<RelativeFilePath>(path).ChangeExtension(Bak).WeakString);
+		}
+	}
+
+	[TestMethod]
+	public void Dotfile_FileNameWithoutExtension_IsWholeName()
+	{
+		Assert.AreEqual(".bashrc", AbsoluteFilePath.Create<AbsoluteFilePath>(TestPaths.Absolute("home", "user", ".bashrc")).FileNameWithoutExtension.WeakString);
+		Assert.AreEqual(".gitignore", RelativeFilePath.Create<RelativeFilePath>(".gitignore").FileNameWithoutExtension.WeakString);
+	}
+
+	[TestMethod]
+	public void DotfileWithExtension_RemoveAndChangeExtension_TouchOnlyTheExtension()
+	{
+		RelativeFilePath path = RelativeFilePath.Create<RelativeFilePath>(TestPaths.Relative("src", ".config.json"));
+
+		Assert.AreEqual(TestPaths.Relative("src", ".config"), path.RemoveExtension().WeakString);
+		Assert.AreEqual(TestPaths.Relative("src", ".config.bak"), path.ChangeExtension(Bak).WeakString);
+		Assert.AreEqual(".config", path.FileNameWithoutExtension.WeakString);
+	}
+
+	[TestMethod]
+	public void DotInDirectoryName_IsNotAnExtension()
+	{
+		RelativeFilePath path = RelativeFilePath.Create<RelativeFilePath>(TestPaths.Relative("app.v2", "README"));
+
+		Assert.AreEqual(path.WeakString, path.RemoveExtension().WeakString);
+		Assert.AreEqual(TestPaths.Relative("app.v2", "README.bak"), path.ChangeExtension(Bak).WeakString);
+	}
+}