GetRelative paths accepts paths shorter than the base directory (#72166)

Author: AnakinRaW

src/Compilers/Core/Portable/FileSystem/PathUtilities.cs

@@ -562,7 +562,8 @@ public static string GetRelativePath(string directory, string fullPath)
             int index = 0;
 
             // find index where full path diverges from base path
-            for (; index < directoryPathParts.Length; index++)
+            var maxSearchIndex = Math.Min(directoryPathParts.Length, fullPathParts.Length);
+            for (; index < maxSearchIndex; index++)
             {
                 if (!PathsEqual(directoryPathParts[index], fullPathParts[index]))
                 {
@@ -593,6 +594,8 @@ public static string GetRelativePath(string directory, string fullPath)
                 relativePath = CombinePathsUnchecked(relativePath, fullPathParts[i]);
             }
 
+            relativePath = TrimTrailingSeparators(relativePath);
+
             return relativePath;
         }
 

src/Workspaces/CoreTest/UtilityTest/FilePathUtilitiesTests.cs

@@ -99,5 +99,27 @@ public void GetRelativePath_WithBaseDirectoryMatchingIncompletePortionOfFullPath
 
             Assert.Equal(expected: @"..\Beta2\Gamma", actual: result);
         }
+
+        [ConditionalTheory(typeof(WindowsOnly)), WorkItem(72043, "https://github.com/dotnet/roslyn/issues/72043")]
+        [InlineData(@"C:\Alpha", @"C:\", @"..")]
+        [InlineData(@"C:\Alpha\Beta", @"C:\", @"..\..")]
+        [InlineData(@"C:\Alpha\Beta", @"C:\Gamma", @"..\..\Gamma")]
+        public void GetRelativePath_WithFullPathShorterThanBasePath_Windows(string baseDirectory, string fullPath, string expected)
+        {
+            var result = PathUtilities.GetRelativePath(baseDirectory, fullPath);
+
+            Assert.Equal(expected, result);
+        }
+
+        [ConditionalTheory(typeof(UnixLikeOnly)), WorkItem(72043, "https://github.com/dotnet/roslyn/issues/72043")]
+        [InlineData("/Alpha", "/", "..")]
+        [InlineData("/Alpha/Beta", "/", "../..")]
+        [InlineData("/Alpha/Beta", "/Gamma", "../../Gamma")]
+        public void GetRelativePath_WithFullPathShorterThanBasePath_Unix(string baseDirectory, string fullPath, string expected)
+        {
+            var result = PathUtilities.GetRelativePath(baseDirectory, fullPath);
+
+            Assert.Equal(expected, result);
+        }
     }
 }