Fix Directory.current setter compatibility with IOOverrides

The `Directory.current` setter has a `dynamic` parameter so that it
can accept either `String` or `Directory` arguments. (This is
asymmetric with the getter, which always returns a `Directory`.)

The corresponding `IOOverrides` callback, however, assumes that the
argument is always a `String`, and `Directory.current` passed its
`dynamic` argument through unchanged.  Consequently, overriding
the `Directory.current` setter would result in a `TypeError` when
setting `Directory.current` to a `Directory` object.

Changing `IOOverrides.setCurrentDirectory` to use a `dynamic`
parameter would be a breaking change, so instead make the
`Directory.current` setter check the argument's runtime type before
passing it along.

Bug: https://github.com/dart-lang/sdk/issues/52140
Change-Id: I3c5bba6b442b314c798bd7949dfeb5eb6251dc6e
CoreLibraryReviewExempt: No API changes and VM-only.
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/336604
Reviewed-by: Brian Quinlan <bquinlan@google.com>
Reviewed-by: Lasse Nielsen <lrn@google.com>
Auto-Submit: James Lin <jamesdlin@gmail.com>
Commit-Queue: Brian Quinlan <bquinlan@google.com>

sdk/lib/io/directory.dart

@@ -162,13 +162,26 @@ abstract interface class Directory implements FileSystemEntity {
   /// operations and multiple isolates. Changing the working directory,
   /// while asynchronous operations are pending or when other isolates
   /// are working with the file system, can lead to unexpected results.
-  static void set current(path) {
+  static void set current(dynamic path) {
+    // Disallow implicit casts to avoid bugs like
+    // <https://github.com/dart-lang/sdk/issues/52140>.
+    //
+    // This can be removed if `strict-casts` is enabled.
+    path as Object?;
+
     final IOOverrides? overrides = IOOverrides.current;
     if (overrides == null) {
       _Directory.current = path;
       return;
     }
-    overrides.setCurrentDirectory(path);
+
+    // IOOverrides.setCurrentDirectory accepts only a [String].
+    overrides.setCurrentDirectory(switch (path) {
+      String s => s,
+      Directory d => d.path,
+      _ => throw ArgumentError('${Error.safeToString(path)} is not a String or'
+          ' Directory'),
+    });
   }
 
   /// Creates the directory if it doesn't exist.

sdk/lib/io/directory_impl.dart

@@ -45,23 +45,18 @@ class _Directory extends FileSystemEntity implements Directory {
     return new _Directory(result);
   }
 
-  static void set current(path) {
-    late Uint8List _rawPath;
-    if (path is _Directory) {
+  static void set current(Object? path) {
+    var _rawPath = switch (path) {
       // For our internal Directory implementation, go ahead and use the raw
       // path.
-      _rawPath = path._rawPath;
-    } else if (path is Directory) {
-      // FIXME(bkonyi): package:file passes in instances of classes which do
-      // not have _path defined, so we will fallback to using the existing
-      // path String for now.
-      _rawPath = FileSystemEntity._toUtf8Array(path.path);
-    } else if (path is String) {
-      _rawPath = FileSystemEntity._toUtf8Array(path);
-    } else {
-      throw new ArgumentError('${Error.safeToString(path)} is not a String or'
-          ' Directory');
-    }
+      _Directory d => d._rawPath,
+      // Fall back to the String-based path.
+      Directory d => FileSystemEntity._toUtf8Array(d.path),
+      String s => FileSystemEntity._toUtf8Array(s),
+      _ => throw ArgumentError('${Error.safeToString(path)} is not a String or'
+          ' Directory')
+    };
+
     if (!_EmbedderConfig._mayChdir) {
       throw new UnsupportedError(
           "This embedder disallows setting Directory.current");

tests/standalone/io/io_override_test.dart

@@ -12,13 +12,16 @@ import "package:expect/expect.dart";
 
 class DirectoryMock extends FileSystemEntity implements Directory {
   static final _mockUri = Uri.parse('http:///mockdir/');
-  final String path = "/mockdir";
+  final String path;
 
-  DirectoryMock(String path);
+  DirectoryMock(this.path);
+
+  static DirectoryMock _currentDirectory = DirectoryMock("");
 
   static DirectoryMock createDirectory(String path) => new DirectoryMock(path);
-  static DirectoryMock getCurrent() => new DirectoryMock("");
-  static void setCurrent(String path) {}
+  static DirectoryMock getCurrent() => _currentDirectory;
+  static void setCurrent(String path) =>
+      _currentDirectory = DirectoryMock(path);
   static DirectoryMock getSystemTemp() => new DirectoryMock("");
   Uri get uri => _mockUri;
 
@@ -207,6 +210,15 @@ Future<Null> ioOverridesRunTest() async {
     () async {
       Expect.isTrue(new Directory("directory") is DirectoryMock);
       Expect.isTrue(Directory.current is DirectoryMock);
+
+      const mockDirectoryPath1 = "/mockDirectory1";
+      const mockDirectoryPath2 = "/mockDirectory2";
+
+      Directory.current = mockDirectoryPath1;
+      Expect.isTrue(Directory.current.path == mockDirectoryPath1);
+      Directory.current = Directory(mockDirectoryPath2);
+      Expect.isTrue(Directory.current.path == mockDirectoryPath2);
+
       Expect.identical(Uri.base, DirectoryMock._mockUri);
       Expect.isTrue(Directory.systemTemp is DirectoryMock);
       Expect.isTrue(new File("file") is FileMock);