[io_file] Add the ability to get file metadata on Windows.

pkgs/io_file/example/io_file_example.dart

@@ -2,9 +2,25 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-import 'package:io_file/posix_file_system.dart';
+import 'package:io_file/io_file.dart';
+import 'package:io_file/windows_file_system.dart';
+
+import 'package:path/path.dart' as p;
+
+bool isHidden(String path) {
+  if (fileSystem case final WindowsFileSystem fs) {
+    return fs.metadata(path).isHidden;
+  } else {
+    // On POSIX, convention is that files and directories starting with a period
+    // are hidden (except for the special files representing the current working
+    // directory and parent directory).
+    //
+    // In addition, macOS has the UF_HIDDEN flag.
+    final name = p.basename(path);
+    return name.startsWith('.') && name != '.' && name != '..';
+  }
+}
 
 void main() {
-  // TODO(brianquinlan): Create a better example.
-  PosixFileSystem().rename('foo.txt', 'bar.txt');
+  isHidden('somefile');
 }

pkgs/io_file/lib/src/file_system.dart

@@ -5,10 +5,22 @@
 import 'dart:convert';
 import 'dart:typed_data';
 
+import 'package:meta/meta.dart' show sealed;
+
 // TODO(brianquinlan): When we switch to using exception types outside of
 // `dart:io` then change the doc strings to use reference syntax rather than
 // code syntax e.g. `PathExistsException` => [PathExistsException].
 
+/// Information about a directory, link, etc. stored in the [FileSystem].
+abstract interface class Metadata {
+  // TODO(brianquinlan): Document all public fields.
+
+  bool get isFile;
+  bool get isDirectory;
+  bool get isLink;
+  int get size;
+}
+
 /// The modes in which a File can be written.
 class WriteMode {
   /// Open the file for writing such that data can only be appended to the end
@@ -34,26 +46,18 @@ class WriteMode {
 }
 
 /// An abstract representation of a file system.
-base class FileSystem {
-  /// Checks whether two paths refer to the same object in the file system.
-  ///
-  /// Throws `PathNotFoundException` if either path doesn't exist.
-  ///
-  /// Links are resolved before determining if the paths refer to the same
-  /// object. Throws `PathNotFoundException` if either path requires resolving
-  /// a broken link.
-  bool same(String path1, String path2) {
-    throw UnsupportedError('same');
-  }
-
+///
+/// TODO(brianquinlan): Far now, this class is not meant to be implemented,
+/// extended outside of this package. Clarify somewhere that people implementing
+/// this class should reach out to be.
+@sealed
+abstract class FileSystem {
   /// Create a directory at the given path.
   ///
   /// If the directory already exists, then `PathExistsException` is thrown.
   ///
   /// If the parent path does not exist, then `PathNotFoundException` is thrown.
-  void createDirectory(String path) {
-    throw UnsupportedError('createDirectory');
-  }
+  void createDirectory(String path);
 
   /// Creates a temporary directory and returns its path.
   ///
@@ -82,9 +86,13 @@ base class FileSystem {
   ///   fileSystem.createTemporaryDirectory(prefix: 'myproject');
   /// }
   /// ```
-  String createTemporaryDirectory({String? parent, String? prefix}) {
-    throw UnsupportedError('createTemporaryDirectory');
-  }
+  String createTemporaryDirectory({String? parent, String? prefix});
+
+  /// Metadata for the file system object at [path].
+  ///
+  /// If `path` represents a symbolic link then metadata for the link is
+  /// returned.
+  Metadata metadata(String path);
 
   /// Deletes the directory at the given path.
   ///
@@ -97,17 +105,13 @@ base class FileSystem {
   /// - On Windows, if `path` is a symbolic link to a directory then the
   ///   symbolic link is deleted. Otherwise, a `FileSystemException` is thrown.
   /// - On POSIX, a `FileSystemException` is thrown.
-  void removeDirectory(String path) {
-    throw UnsupportedError('removeDirectory');
-  }
+  void removeDirectory(String path);
 
   /// Deletes the directory at the given path and its contents.
   ///
   /// If the directory (or its subdirectories) contains any symbolic links then
   /// those links are deleted but their targets are not.
-  void removeDirectoryTree(String path) {
-    throw UnsupportedError('removeDirectoryTree');
-  }
+  void removeDirectoryTree(String path);
 
   /// Renames, and possibly moves a file system object from one path to another.
   ///
@@ -125,14 +129,19 @@ base class FileSystem {
   // If `newPath` identifies an existing file or link, that entity is removed
   // first. If `newPath` identifies an existing directory, the operation
   // fails and raises [PathExistsException].
-  void rename(String oldPath, String newPath) {
-    throw UnsupportedError('rename');
-  }
+  void rename(String oldPath, String newPath);
 
   /// Reads the entire file contents as a list of bytes.
-  Uint8List readAsBytes(String path) {
-    throw UnsupportedError('readAsBytes');
-  }
+  Uint8List readAsBytes(String path);
+
+  /// Checks whether two paths refer to the same object in the file system.
+  ///
+  /// Throws `PathNotFoundException` if either path doesn't exist.
+  ///
+  /// Links are resolved before determining if the paths refer to the same
+  /// object. Throws `PathNotFoundException` if either path requires resolving
+  /// a broken link.
+  bool same(String path1, String path2);
 
   /// The directory path used to store temporary files.
   ///
@@ -156,9 +165,7 @@ base class FileSystem {
     String path,
     Uint8List data, [
     WriteMode mode = WriteMode.failExisting,
-  ]) {
-    throw UnsupportedError('writeAsBytes');
-  }
+  ]);
 
   /// Write the string to a file.
   ///
@@ -177,7 +184,5 @@ base class FileSystem {
     WriteMode mode = WriteMode.failExisting,
     Encoding encoding = utf8,
     String? lineTerminator,
-  ]) {
-    throw UnsupportedError('writeAsString');
-  }
+  ]);
 }

pkgs/io_file/lib/src/vm_posix_file_system.dart

@@ -64,7 +64,7 @@ external int write(int fd, Pointer<Uint8> buf, int count);
 
 /// A [FileSystem] implementation for POSIX systems (e.g. Android, iOS, Linux,
 /// macOS).
-base class PosixFileSystem extends FileSystem {
+final class PosixFileSystem extends FileSystem {
   @override
   bool same(String path1, String path2) => ffi.using((arena) {
     final stat1 = arena<libc.Stat>();
@@ -111,6 +111,11 @@ base class PosixFileSystem extends FileSystem {
         return path.cast<ffi.Utf8>().toDartString();
       });
 
+  @override
+  Metadata metadata(String path) {
+    throw UnimplementedError();
+  }
+
   @override
   void removeDirectory(String path) => ffi.using((arena) {
     if (libc.unlinkat(
@@ -124,6 +129,11 @@ base class PosixFileSystem extends FileSystem {
     }
   });
 
+  @override
+  void removeDirectoryTree(String path) {
+    throw UnimplementedError();
+  }
+
   @override
   void rename(String oldPath, String newPath) => ffi.using((arena) {
     // See https://pubs.opengroup.org/onlinepubs/000095399/functions/rename.html