Fix windows creation of relative symlinks to directories (#931)

* Fix windows creation of relative symlinks to directories

* Add additional unit tests

* Fix windows test failure

Author: jmschonfeld

Sources/FoundationEssentials/FileManager/FileManager+SymbolicLinks.swift

@@ -59,7 +59,8 @@ extension _FileManagerImpl {
     ) throws {
 #if os(Windows)
         var bIsDirectory = false
-        _ = fileManager.fileExists(atPath: destPath, isDirectory: &bIsDirectory)
+        let absoluteDestPath = URL(filePath: destPath, relativeTo: URL(filePath: path, directoryHint: .notDirectory)).path
+        _ = fileManager.fileExists(atPath: absoluteDestPath, isDirectory: &bIsDirectory)
 
         try path.withNTPathRepresentation { lpSymlinkFileName in
             try destPath.withFileSystemRepresentation {

Tests/FoundationEssentialsTests/FileManager/FileManagerTests.swift

@@ -412,9 +412,13 @@ final class FileManagerTests : XCTestCase {
     func testCreateSymbolicLinkAtPath() throws {
         try FileManagerPlayground {
             "foo"
+            Directory("dir") {}
         }.test {
             try $0.createSymbolicLink(atPath: "bar", withDestinationPath: "foo")
             XCTAssertEqual(try $0.destinationOfSymbolicLink(atPath: "bar"), "foo")
+
+            try $0.createSymbolicLink(atPath: "dir_link", withDestinationPath: "dir")
+            XCTAssertEqual(try $0.destinationOfSymbolicLink(atPath: "dir_link"), "dir")
 
             XCTAssertThrowsError(try $0.createSymbolicLink(atPath: "bar", withDestinationPath: "foo")) {
                 XCTAssertEqual(($0 as? CocoaError)?.code, .fileWriteFileExists)
@@ -426,6 +430,41 @@ final class FileManagerTests : XCTestCase {
                 XCTAssertEqual(($0 as? CocoaError)?.code, .fileReadUnknown)
             }
         }
+
+        try FileManagerPlayground {
+            Directory("dir") {
+                Directory("other_dir") {
+                    "file"
+                }
+            }
+        }.test {
+            // Create a relative symlink to other_dir from within dir (tests windows special dir symlink handling)
+            try $0.createSymbolicLink(atPath: "dir/link", withDestinationPath: "other_dir")
+
+            // Ensure it is created successfully
+            XCTAssertEqual(try $0.destinationOfSymbolicLink(atPath: "dir/link"), "other_dir")
+            XCTAssertEqual(try $0.contentsOfDirectory(atPath: "dir/link"), ["file"])
+            
+            do {
+                // Second symlink creation with an absolute path
+                let absolute = URL(filePath: "dir/link2", relativeTo: URL(filePath: $0.currentDirectoryPath, directoryHint: .isDirectory)).path
+                try $0.createSymbolicLink(atPath: absolute, withDestinationPath: "other_dir")
+                
+                // Ensure it is created successfully
+                XCTAssertEqual(try $0.destinationOfSymbolicLink(atPath: "dir/link2"), "other_dir")
+                XCTAssertEqual(try $0.contentsOfDirectory(atPath: "dir/link2"), ["file"])
+            }
+            
+            do {
+                // And lastly a symlink to an absolute path
+                let absolute = URL(filePath: "dir/other_dir", relativeTo: URL(filePath: $0.currentDirectoryPath, directoryHint: .isDirectory)).path
+                try $0.createSymbolicLink(atPath: "dir/link3", withDestinationPath: absolute)
+                
+                // Ensure it is created successfully
+                XCTAssertEqual(try $0.destinationOfSymbolicLink(atPath: "dir/link3"), absolute.withFileSystemRepresentation { String(cString: $0!) })
+                XCTAssertEqual(try $0.contentsOfDirectory(atPath: "dir/link3"), ["file"])
+            }
+        }
     }
 
     func testMoveItemAtPathToPath() throws {