PathStrings: guard drive-letter normalization by platform

TruePath.Tests/PathStringsTests.cs

@@ -128,6 +128,35 @@ public void WindowsSpecificDotFoldersAreTraversed(string input, string expected)
         }
     }
 
+    [Theory]
+    [InlineData("C:/", "C:")]
+    [InlineData("C:/../file", "file")]
+    public void Normalize_DriveLetterCheckDisabled_TreatsColonAsRegularPathCharacter(string input, string expected)
+    {
+        var actual = PathStrings.Normalize(input, driveBasedSystem: false);
+
+        Assert.Equal(NormalizeSeparators(expected), actual);
+    }
+
+    [Theory]
+    [InlineData("C:/", "C:/")]
+    [InlineData("C:/../file", "C:/../file")]
+    public void Normalize_DriveLetterCheckEnabled_PreservesWindowsDrivePrefix(string input, string expected)
+    {
+        var actual = PathStrings.Normalize(input, driveBasedSystem: true);
+
+        Assert.Equal(NormalizeSeparators(expected), actual);
+    }
+
+    [Fact]
+    public void Normalize_DriveLetterHandling_MatchesCurrentPlatform()
+    {
+        var actual = PathStrings.Normalize("C:/../file");
+        var expected = RuntimeInformation.IsOSPlatform(OSPlatform.Windows) ? "C:/../file" : "file";
+
+        Assert.Equal(NormalizeSeparators(expected), actual);
+    }
+
     private static string NormalizeSeparators(string path) =>
         path.Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
 }

TruePath/LocalPath.cs

@@ -15,8 +15,8 @@ namespace TruePath;
 ///     (e.g. the parent of <c>foo</c>).
 /// </para>
 /// <para>
-///     Always stored in a normalized form. Read the documentation on <see cref="TruePath.PathStrings.Normalize"/> to
-///     know what form of normalization the path uses.
+///     Always stored in a normalized form. Read the documentation on <see cref="TruePath.PathStrings.Normalize(string)"/>
+///     to know what form of normalization the path uses.
 /// </para>
 /// </summary>
 public readonly struct LocalPath(string value) : IEquatable<LocalPath>, IComparable<LocalPath>, IPath, IPath<LocalPath>

TruePath/PathStrings.cs

@@ -1,9 +1,12 @@
-// SPDX-FileCopyrightText: 2024 TruePath contributors <https://github.com/ForNeVeR/TruePath>
+// SPDX-FileCopyrightText: 2024-2026 TruePath contributors <https://github.com/ForNeVeR/TruePath>
 //
 // SPDX-License-Identifier: MIT
 
 using System.Buffers;
+using System.Runtime.InteropServices;
+#if NET8_0_OR_GREATER
 using System.Runtime.CompilerServices;
+#endif
 
 namespace TruePath;
 
@@ -46,12 +49,15 @@ public static class PathStrings
     ///     Note that this operation will never perform any file IO, and is purely string manipulation.
     /// </para>
     /// </summary>
+    public static string Normalize(string path) =>
+        Normalize(path, driveBasedSystem: RuntimeInformation.IsOSPlatform(OSPlatform.Windows));
+
 #if NET8_0_OR_GREATER
     [SkipLocalsInit] // is necessary to prevent the CLR from filling stackalloc with zeros.
 #endif
-    public static string Normalize(string path)
+    internal static string Normalize(string path, bool driveBasedSystem)
     {
-        bool containsDriveLetter = SourceContainsDriveLetter(path.AsSpan());
+        bool containsDriveLetter = driveBasedSystem && SourceContainsDriveLetter(path.AsSpan());
 
         int written = 0;