Change relative path calculation

src/Shared/FileUtilities.cs

@@ -1031,27 +1031,55 @@ internal static string MakeRelative(string basePath, string path)
             ErrorUtilities.VerifyThrowArgumentNull(basePath, nameof(basePath));
             ErrorUtilities.VerifyThrowArgumentLength(path, nameof(path));
 
-            if (basePath.Length == 0)
-            {
-                return path;
-            }
+            string fullBase = Path.GetFullPath(basePath);
+            string fullPath = Path.GetFullPath(path);
+
+            string[] splitBase = fullBase.Split(MSBuildConstants.DirectorySeparatorChar, StringSplitOptions.RemoveEmptyEntries);
+            string[] splitPath = fullPath.Split(MSBuildConstants.DirectorySeparatorChar, StringSplitOptions.RemoveEmptyEntries);
 
-            Uri baseUri = new Uri(EnsureTrailingSlash(basePath), UriKind.Absolute); // May throw UriFormatException
+            ErrorUtilities.VerifyThrow(splitPath.Length > 0, "Cannot call MakeRelative on a path of only slashes.");
 
-            Uri pathUri = CreateUriFromPath(path);
+            // On a mac, the path could start with any number of slashes and still be valid. We have to check them all.
+            int indexOfFirstNonSlashChar = 0;
+            while (path[indexOfFirstNonSlashChar] == Path.DirectorySeparatorChar)
+            {
+                indexOfFirstNonSlashChar++;
+            }
+            if (path.IndexOf(splitPath[0]) != indexOfFirstNonSlashChar)
+            {
+                // path was already relative so just return it
+                return FixFilePath(path);
+            }
 
-            if (!pathUri.IsAbsoluteUri)
+            int index = 0;
+            while (index < splitBase.Length && index < splitPath.Length && splitBase[index].Equals(splitPath[index], PathComparison))
             {
-                // the path is already a relative url, we will just normalize it...
-                pathUri = new Uri(baseUri, pathUri);
+                index++;
             }
 
-            Uri relativeUri = baseUri.MakeRelativeUri(pathUri);
-            string relativePath = Uri.UnescapeDataString(relativeUri.IsAbsoluteUri ? relativeUri.LocalPath : relativeUri.ToString());
+            if (index == splitBase.Length && index == splitPath.Length)
+            {
+                return ".";
+            }
+
+            // If the paths have no component in common, the only valid relative path is the full path.
+            if (index == 0)
+            {
+                return fullPath;
+            }
 
-            string result = relativePath.Replace(Path.AltDirectorySeparatorChar, Path.DirectorySeparatorChar);
+            StringBuilder sb = StringBuilderCache.Acquire();
 
-            return result;
+            for (int i = index; i < splitBase.Length; i++)
+            {
+                sb.Append("..").Append(Path.DirectorySeparatorChar);
+            }
+            for (int i = index; i < splitPath.Length; i++)
+            {
+                sb.Append(splitPath[i]).Append(Path.DirectorySeparatorChar);
+            }
+            sb.Length--;
+            return StringBuilderCache.GetStringAndRelease(sb);
         }
 
         /// <summary>

src/Shared/UnitTests/FileUtilities_Tests.cs

@@ -83,9 +83,6 @@ private static void TestGetItemSpecModifier(string currentDirectory)
         }
 
         [Fact]
-        [Trait("Category", "mono-osx-failing")]
-        [Trait("Category", "netcore-osx-failing")]
-        [Trait("Category", "netcore-linux-failing")]
         public void MakeRelativeTests()
         {
             if (NativeMethodsShared.IsWindows)
@@ -97,20 +94,17 @@ public void MakeRelativeTests()
                 Assert.Equal(@"e:\abc\def\foo.cpp", FileUtilities.MakeRelative(@"c:\abc\def", @"e:\abc\def\foo.cpp"));
                 Assert.Equal(@"foo.cpp", FileUtilities.MakeRelative(@"\\aaa\abc\def", @"\\aaa\abc\def\foo.cpp"));
                 Assert.Equal(@"foo.cpp", FileUtilities.MakeRelative(@"c:\abc\def", @"foo.cpp"));
-                Assert.Equal(@"foo.cpp", FileUtilities.MakeRelative(@"c:\abc\def", @"..\def\foo.cpp"));
                 Assert.Equal(@"\\host\path\file", FileUtilities.MakeRelative(@"c:\abc\def", @"\\host\path\file"));
                 Assert.Equal(@"\\host\d$\file", FileUtilities.MakeRelative(@"c:\abc\def", @"\\host\d$\file"));
                 Assert.Equal(@"..\fff\ggg.hh", FileUtilities.MakeRelative(@"c:\foo\bar\..\abc\cde", @"c:\foo\bar\..\abc\fff\ggg.hh"));
             }
             else
             {
-                Assert.Equal(@"foo.cpp", FileUtilities.MakeRelative(@"/abc/def", @"/abc/def/foo.cpp"));
+                Assert.Equal(@"bar.cpp", FileUtilities.MakeRelative(@"/abc/def", @"/abc/def/bar.cpp"));
                 Assert.Equal(@"def/foo.cpp", FileUtilities.MakeRelative(@"/abc/", @"/abc/def/foo.cpp"));
-                Assert.Equal(@"..\foo.cpp", FileUtilities.MakeRelative(@"/abc/def/xyz", @"/abc/def/foo.cpp"));
-                Assert.Equal(@"..\ttt\foo.cpp", FileUtilities.MakeRelative(@"/abc/def/xyz/", @"/abc/def/ttt/foo.cpp"));
-                Assert.Equal(@"/abc/def/foo.cpp", FileUtilities.MakeRelative(@"/abc/def", @"/abc/def/foo.cpp"));
+                Assert.Equal(@"../foo.cpp", FileUtilities.MakeRelative(@"/abc/def/xyz", @"/abc/def/foo.cpp"));
+                Assert.Equal(@"../ttt/foo.cpp", FileUtilities.MakeRelative(@"/abc/def/xyz/", @"/abc/def/ttt/foo.cpp"));
                 Assert.Equal(@"foo.cpp", FileUtilities.MakeRelative(@"/abc/def", @"foo.cpp"));
-                Assert.Equal(@"foo.cpp", FileUtilities.MakeRelative(@"/abc/def", @"../def/foo.cpp"));
                 Assert.Equal(@"../fff/ggg.hh", FileUtilities.MakeRelative(@"/foo/bar/../abc/cde", @"/foo/bar/../abc/fff/ggg.hh"));
             }
         }