fix #856: picking .app files on macOS

.app files on macOS are actually directories. But, they are treated as
files by the file picker and therefore can only be selected via
'FilePicker.platform.pickFiles()'. When picking .app files,
'createPlatformFile()' tries to get the size of the .app file which
throws an exception because directories don't have an inherent size.

lib/src/platform_file.dart

@@ -54,7 +54,8 @@ class PlatformFile {
   /// File content as stream
   final Stream<List<int>>? readStream;
 
-  /// The file size in bytes.
+  /// The file size in bytes. Defaults to `0` if the file size could not be
+  /// determined.
   final int size;
 
   /// File extension for this file.

lib/src/utils.dart

@@ -39,7 +39,7 @@ Future<PlatformFile> createPlatformFile(
       name: basename(file.path),
       path: file.path,
       readStream: readStream,
-      size: await file.length(),
+      size: file.existsSync() ? file.lengthSync() : 0,
     );
 
 Future<String?> runExecutableWithArguments(

test/common.dart

@@ -1,27 +1,33 @@
 import 'dart:io';
 
 setUpTestFiles(
-  String imageTestFile,
-  String pdfTestFile,
-  String yamlTestFile,
+  String appTestFilePath,
+  String imageTestFilePath,
+  String pdfTestFilePath,
+  String yamlTestFilePath,
 ) {
+  // .app files on macOS are actually directories but they are treated as files
+  Directory(appTestFilePath).createSync();
+
   File(
     './test/test_files/franz-michael-schneeberger-unsplash.jpg',
-  ).copySync(imageTestFile);
+  ).copySync(imageTestFilePath);
   File(
     './test/test_files/test.pdf',
-  ).copySync(pdfTestFile);
+  ).copySync(pdfTestFilePath);
   File(
     './test/test_files/test.yml',
-  ).copySync(yamlTestFile);
+  ).copySync(yamlTestFilePath);
 }
 
 tearDownTestFiles(
-  String imageTestFile,
-  String pdfTestFile,
-  String yamlTestFile,
+  String appTestFilePath,
+  String imageTestFilePath,
+  String pdfTestFilePath,
+  String yamlTestFilePath,
 ) {
-  File(imageTestFile).deleteSync();
-  File(pdfTestFile).deleteSync();
-  File(yamlTestFile).deleteSync();
+  Directory(appTestFilePath).deleteSync();
+  File(imageTestFilePath).deleteSync();
+  File(pdfTestFilePath).deleteSync();
+  File(yamlTestFilePath).deleteSync();
 }

test/file_picker_utils_test.dart

@@ -1,23 +1,60 @@
 @TestOn('linux || mac-os')
 
+import 'dart:io';
 import 'package:file_picker/src/utils.dart';
 import 'package:flutter_test/flutter_test.dart';
 
 import 'common.dart';
 
 void main() {
+  final appTestFilePath = '/tmp/test_utils.app';
   final imageTestFile = '/tmp/test_utils.jpg';
   final pdfTestFile = '/tmp/test_utils.pdf';
   final yamlTestFile = '/tmp/test_utils.yml';
 
   setUpAll(
-    () => setUpTestFiles(imageTestFile, pdfTestFile, yamlTestFile),
+    () => setUpTestFiles(
+        appTestFilePath, imageTestFile, pdfTestFile, yamlTestFile),
   );
 
   tearDownAll(
-    () => tearDownTestFiles(imageTestFile, pdfTestFile, yamlTestFile),
+    () => tearDownTestFiles(
+        appTestFilePath, imageTestFile, pdfTestFile, yamlTestFile),
   );
 
+  group('createPlatformFile()', () {
+    test('should return an instance of PlatformFile', () async {
+      final imageFile = File(imageTestFile);
+      final bytes = imageFile.readAsBytesSync();
+      final readStream = imageFile.openRead();
+
+      final platformFile =
+          await createPlatformFile(imageFile, bytes, readStream);
+
+      expect(platformFile.bytes, equals(bytes));
+      expect(platformFile.name, equals('test_utils.jpg'));
+      expect(platformFile.readStream, equals(readStream));
+      expect(platformFile.size, equals(bytes.length));
+    });
+
+    test(
+        'should not throw an exception when picking .app files on macOS (.app files on macOS are actually directories but they are treated as files, similar to .exe files on Windows)',
+        () async {
+      final appFile = File(appTestFilePath);
+
+      final platformFile = await createPlatformFile(appFile, null, null);
+
+      expect(platformFile.bytes, equals(null));
+      expect(platformFile.name, equals('test_utils.app'));
+      expect(platformFile.readStream, equals(null));
+      expect(
+        platformFile.size,
+        equals(0),
+        reason: 'Expect size to be 0 because .app files are directories.',
+      );
+    });
+  });
+
   group('filePathsToPlatformFiles()', () {
     test('should transform a list of file paths into a list of PlatformFiles',
         () async {