From 68659055cbd2c1664308dd9ab07277014b8d0580 Mon Sep 17 00:00:00 2001
From: YoshiRulz <OSSYoshiRulz@gmail.com>
Date: Sun, 31 Jan 2021 10:53:16 +1000
Subject: [PATCH] Add Unix implementation matching docs for GetRelativePath,
 add tests

---
 src/BizHawk.Common/Extensions/PathExtensions.cs |  8 ++++++--
 .../Common.PathExtensions/PathExtensionTests.cs | 17 +++++++++++++----
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/src/BizHawk.Common/Extensions/PathExtensions.cs b/src/BizHawk.Common/Extensions/PathExtensions.cs
index e7c04b4ed5..e03f11057e 100644
--- a/src/BizHawk.Common/Extensions/PathExtensions.cs
+++ b/src/BizHawk.Common/Extensions/PathExtensions.cs
@@ -58,7 +58,11 @@ namespace BizHawk.Common.PathExtensions
 		public static string? GetRelativePath(string? fromPath, string? toPath)
 		{
 			if (fromPath == null || toPath == null) return null;
-			if (OSTailoredCode.IsUnixHost) return toPath.MakeRelativeTo(fromPath);
+			if (OSTailoredCode.IsUnixHost)
+			{
+				var realpathOutput = OSTailoredCode.SimpleSubshell("realpath", $"--relative-to=\"{fromPath}\" \"{toPath}\"", $"invalid path {toPath}, invalid path {fromPath}, or missing realpath binary");
+				return !realpathOutput.StartsWith("../") && realpathOutput != "." && realpathOutput != ".." ? $"./{realpathOutput}" : realpathOutput;
+			}
 
 			//TODO merge this with the Windows implementation in MakeRelativeTo
 			static FileAttributes GetPathAttribute(string path1)
@@ -101,7 +105,7 @@ namespace BizHawk.Common.PathExtensions
 			if (!absolutePath.IsSubfolderOf(basePath)) return absolutePath;
 			if (!OSTailoredCode.IsUnixHost) return absolutePath.Replace(basePath, ".").RemoveSuffix(Path.DirectorySeparatorChar);
 #if true // Unix implementation using realpath
-			var realpathOutput = OSTailoredCode.SimpleSubshell("realpath", $"--relative-to=\"{basePath}\" \"{absolutePath}\"", $"invalid path {absolutePath}, invalid path {basePath}, or missing realpath binary");
+			var realpathOutput = OSTailoredCode.SimpleSubshell("realpath", $"--relative-base=\"{basePath}\" \"{absolutePath}\"", $"invalid path {absolutePath}, invalid path {basePath}, or missing realpath binary");
 			return !realpathOutput.StartsWith("../") && realpathOutput != "." && realpathOutput != ".." ? $"./{realpathOutput}" : realpathOutput;
 #else // for some reason there were two Unix implementations in the codebase before me? --yoshi
 			// alt. #1
diff --git a/src/BizHawk.Tests/PlatformTests/Common.PathExtensions/PathExtensionTests.cs b/src/BizHawk.Tests/PlatformTests/Common.PathExtensions/PathExtensionTests.cs
index 297500a9ac..faa302efac 100644
--- a/src/BizHawk.Tests/PlatformTests/Common.PathExtensions/PathExtensionTests.cs
+++ b/src/BizHawk.Tests/PlatformTests/Common.PathExtensions/PathExtensionTests.cs
@@ -58,16 +58,25 @@ namespace BizHawk.Tests.Common.PathExtensions
 			Assert.AreEqual(expectedIsSubfolder, childPath.IsSubfolderOf(parentPath));
 		}
 
-#if false // don't bother, GetRelativePath simply calls MakeRelativeTo on Unix
-		public void TestGetRelativePathUnix() {}
-#endif
+		[TestMethod]
+		[DataRow("./share", "/usr/share", "/usr")]
+		[DataRow(".", "/usr", "/usr")]
+		[DataRow("..", "/usr", "/usr/share")]
+		[DataRow("../bin", "/usr/bin", "/usr/share")]
+		[DataRow("../../etc", "/etc", "/usr/share")]
+		public void TestGetRelativePathUnix(string expectedRelPath, string toPath, string fromPath) // swapped here instead of in data
+		{
+			PlatformTestUtils.OnlyRunOnRealUnix();
+
+			Assert.AreEqual(expectedRelPath, PE.GetRelativePath(fromPath: fromPath, toPath: toPath));
+		}
 
 		[TestMethod]
 		[DataRow("./share", "/usr/share", "/usr")]
 		[DataRow(".", "/usr", "/usr")]
 		[DataRow("/usr", "/usr", "/usr/share")] // not `..`
 		[DataRow("/usr/bin", "/usr/bin", "/usr/share")] // not `../bin`
-		[DataRow("/bin", "/bin", "/usr/share")] // not `../../bin`
+		[DataRow("/etc", "/etc", "/usr/share")] // not `../../etc`
 		public void TestMakeRelativeToUnix(string expectedRelPath, string absolutePath, string basePath)
 		{
 			PlatformTestUtils.OnlyRunOnRealUnix();