From 6858a365523981bddfe670e61e4470a70e290487 Mon Sep 17 00:00:00 2001
From: YoshiRulz <OSSYoshiRulz@gmail.com>
Date: Sun, 31 Jan 2021 10:02:45 +1000
Subject: [PATCH] Fix Unix implementation of GetRelativePath; expand on docs

---
 .../tools/MultiDiskBundler/MultiDiskBundler.cs      |  2 +-
 src/BizHawk.Common/Extensions/PathExtensions.cs     | 13 ++++++++++---
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/BizHawk.Client.EmuHawk/tools/MultiDiskBundler/MultiDiskBundler.cs b/src/BizHawk.Client.EmuHawk/tools/MultiDiskBundler/MultiDiskBundler.cs
index 79cd66b069..1a00d10eb4 100644
--- a/src/BizHawk.Client.EmuHawk/tools/MultiDiskBundler/MultiDiskBundler.cs
+++ b/src/BizHawk.Client.EmuHawk/tools/MultiDiskBundler/MultiDiskBundler.cs
@@ -213,7 +213,7 @@ namespace BizHawk.Client.EmuHawk
 						new XElement("LoadAssets",
 							names.Select(n => new XElement(
 								"Asset",
-								new XAttribute("FileName", OSTailoredCode.IsUnixHost ? PathExtensions.GetRelativePath(n, basePath) : PathExtensions.GetRelativePath(basePath, n))
+								new XAttribute("FileName", PathExtensions.GetRelativePath(basePath, n))
 							))
 						)
 					);
diff --git a/src/BizHawk.Common/Extensions/PathExtensions.cs b/src/BizHawk.Common/Extensions/PathExtensions.cs
index 4aaa40dcd1..e7c04b4ed5 100644
--- a/src/BizHawk.Common/Extensions/PathExtensions.cs
+++ b/src/BizHawk.Common/Extensions/PathExtensions.cs
@@ -50,11 +50,15 @@ namespace BizHawk.Common.PathExtensions
 
 		/// <exception cref="ArgumentException">running on Windows host, and unmanaged call failed</exception>
 		/// <exception cref="FileNotFoundException">running on Windows host, and either path is not a regular file or directory</exception>
-		/// <remarks>Algorithm for Windows taken from https://stackoverflow.com/a/485516/7467292</remarks>
+		/// <remarks>
+		/// always returns a relative path, even if it means going up first<br/>
+		/// algorithm for Windows taken from https://stackoverflow.com/a/485516/7467292<br/>
+		/// the parameter names seem backwards, but those are the names used in the Win32 API we're calling
+		/// </remarks>
 		public static string? GetRelativePath(string? fromPath, string? toPath)
 		{
 			if (fromPath == null || toPath == null) return null;
-			if (OSTailoredCode.IsUnixHost) return fromPath.MakeRelativeTo(toPath);
+			if (OSTailoredCode.IsUnixHost) return toPath.MakeRelativeTo(fromPath);
 
 			//TODO merge this with the Windows implementation in MakeRelativeTo
 			static FileAttributes GetPathAttribute(string path1)
@@ -87,7 +91,10 @@ namespace BizHawk.Common.PathExtensions
 		public static string MakeProgramRelativePath(this string path) => Path.Combine(PathUtils.ExeDirectoryPath, path);
 
 		/// <returns>the relative path which is equivalent to <paramref name="absolutePath"/> when the CWD is <paramref name="basePath"/>, or <see langword="null"/> if either path is <see langword="null"/></returns>
-		/// <remarks>returned string omits trailing slash; implementation calls <see cref="IsSubfolderOf"/> for you</remarks>
+		/// <remarks>
+		/// only returns a relative path if <paramref name="absolutePath"/> is a child of <paramref name="basePath"/> (uses <see cref="IsSubfolderOf"/>), otherwise returns <paramref name="absolutePath"/><br/>
+		/// returned string omits trailing slash
+		/// </remarks>
 		public static string? MakeRelativeTo(this string? absolutePath, string? basePath)
 		{
 			if (absolutePath == null || basePath == null) return null;