Update copyDirectory to allow links to not be followed (#144040)

In other words, copy links within a directory as links rather than copying them as files/directories. 

Fixes https://github.com/flutter/flutter/issues/144032.

packages/flutter_tools/lib/src/base/file_system.dart

@@ -109,12 +109,19 @@ String getDisplayPath(String fullPath, FileSystem fileSystem) {
 ///
 /// Skips files if [shouldCopyFile] returns `false`.
 /// Does not recurse over directories if [shouldCopyDirectory] returns `false`.
+///
+/// If [followLinks] is false, then any symbolic links found are reported as
+/// [Link] objects, rather than as directories or files, and are not recursed into.
+///
+/// If [followLinks] is true, then working links are reported as directories or
+/// files, depending on what they point to.
 void copyDirectory(
   Directory srcDir,
   Directory destDir, {
   bool Function(File srcFile, File destFile)? shouldCopyFile,
   bool Function(Directory)? shouldCopyDirectory,
   void Function(File srcFile, File destFile)? onFileCopied,
+  bool followLinks = true,
 }) {
   if (!srcDir.existsSync()) {
     throw Exception('Source directory "${srcDir.path}" does not exist, nothing to copy');
@@ -124,7 +131,7 @@ void copyDirectory(
     destDir.createSync(recursive: true);
   }
 
-  for (final FileSystemEntity entity in srcDir.listSync()) {
+  for (final FileSystemEntity entity in srcDir.listSync(followLinks: followLinks)) {
     final String newPath = destDir.fileSystem.path.join(destDir.path, entity.basename);
     if (entity is Link) {
       final Link newLink = destDir.fileSystem.link(newPath);
@@ -145,6 +152,7 @@ void copyDirectory(
         destDir.fileSystem.directory(newPath),
         shouldCopyFile: shouldCopyFile,
         onFileCopied: onFileCopied,
+        followLinks: followLinks,
       );
     } else {
       throw Exception('${entity.path} is neither File nor Directory, was ${entity.runtimeType}');

packages/flutter_tools/test/general.shard/base/file_system_test.dart

@@ -88,6 +88,106 @@ void main() {
       expect(sourceMemoryFs.directory(sourcePath).listSync().length, 3);
     });
 
+    testWithoutContext('test directory copy with followLinks: true', () async {
+      final Signals signals = Signals.test();
+      final LocalFileSystem fileSystem = LocalFileSystem.test(
+        signals: signals,
+      );
+      final Directory tempDir = fileSystem.systemTempDirectory.createTempSync('flutter_copy_directory.');
+      try {
+        final String sourcePath = io.Platform.isWindows ? r'some\origin' : 'some/origin';
+        final Directory sourceDirectory = tempDir.childDirectory(sourcePath)..createSync(recursive: true);
+        final File sourceFile1 = sourceDirectory.childFile('some_file.txt')..writeAsStringSync('file 1');
+        sourceDirectory.childLink('absolute_linked.txt').createSync(sourceFile1.absolute.path);
+        final DateTime writeTime = sourceFile1.lastModifiedSync();
+        final Directory sourceSubDirectory = sourceDirectory.childDirectory('dir1').childDirectory('dir2')..createSync(recursive: true);
+        sourceSubDirectory.childFile('another_file.txt').writeAsStringSync('file 2');
+        final String subdirectorySourcePath = io.Platform.isWindows ? r'dir1\dir2' : 'dir1/dir2';
+        sourceDirectory.childLink('relative_linked_sub_dir').createSync(subdirectorySourcePath);
+        sourceDirectory.childDirectory('empty_directory').createSync(recursive: true);
+
+        final String targetPath = io.Platform.isWindows ? r'some\non-existent\target' : 'some/non-existent/target';
+        final Directory targetDirectory = tempDir.childDirectory(targetPath);
+
+        copyDirectory(sourceDirectory, targetDirectory);
+
+        expect(targetDirectory.existsSync(), true);
+        expect(targetDirectory.childFile('some_file.txt').existsSync(), true);
+        expect(targetDirectory.childFile('some_file.txt').readAsStringSync(), 'file 1');
+        expect(targetDirectory.childFile('absolute_linked.txt').readAsStringSync(), 'file 1');
+        expect(targetDirectory.childLink('absolute_linked.txt').existsSync(), false);
+        expect(targetDirectory.childDirectory('dir1').childDirectory('dir2').existsSync(), true);
+        expect(targetDirectory.childDirectory('dir1').childDirectory('dir2').childFile('another_file.txt').existsSync(), true);
+        expect(targetDirectory.childDirectory('dir1').childDirectory('dir2').childFile('another_file.txt').readAsStringSync(), 'file 2');
+        expect(targetDirectory.childDirectory('relative_linked_sub_dir').existsSync(), true);
+        expect(targetDirectory.childLink('relative_linked_sub_dir').existsSync(), false);
+        expect(targetDirectory.childDirectory('relative_linked_sub_dir').childFile('another_file.txt').existsSync(), true);
+        expect(targetDirectory.childDirectory('relative_linked_sub_dir').childFile('another_file.txt').readAsStringSync(), 'file 2');
+        expect(targetDirectory.childDirectory('empty_directory').existsSync(), true);
+
+        // Assert that the copy operation hasn't modified the original file in some way.
+        expect(sourceDirectory.childFile('some_file.txt').lastModifiedSync(), writeTime);
+        // There's still 5 things in the original directory as there were initially.
+        expect(sourceDirectory.listSync().length, 5);
+      } finally {
+        tryToDelete(tempDir);
+      }
+    });
+
+    testWithoutContext('test directory copy with followLinks: false', () async {
+      final Signals signals = Signals.test();
+      final LocalFileSystem fileSystem = LocalFileSystem.test(
+        signals: signals,
+      );
+      final Directory tempDir = fileSystem.systemTempDirectory.createTempSync('flutter_copy_directory.');
+      try {
+        final String sourcePath = io.Platform.isWindows ? r'some\origin' : 'some/origin';
+        final Directory sourceDirectory = tempDir.childDirectory(sourcePath)..createSync(recursive: true);
+        final File sourceFile1 = sourceDirectory.childFile('some_file.txt')..writeAsStringSync('file 1');
+        sourceDirectory.childLink('absolute_linked.txt').createSync(sourceFile1.absolute.path);
+        final DateTime writeTime = sourceFile1.lastModifiedSync();
+        final Directory sourceSubDirectory = sourceDirectory.childDirectory('dir1').childDirectory('dir2')..createSync(recursive: true);
+        sourceSubDirectory.childFile('another_file.txt').writeAsStringSync('file 2');
+        final String subdirectorySourcePath = io.Platform.isWindows ? r'dir1\dir2' : 'dir1/dir2';
+        sourceDirectory.childLink('relative_linked_sub_dir').createSync(subdirectorySourcePath);
+        sourceDirectory.childDirectory('empty_directory').createSync(recursive: true);
+
+        final String targetPath = io.Platform.isWindows ? r'some\non-existent\target' : 'some/non-existent/target';
+        final Directory targetDirectory = tempDir.childDirectory(targetPath);
+
+        copyDirectory(sourceDirectory, targetDirectory, followLinks: false);
+
+        expect(targetDirectory.existsSync(), true);
+        expect(targetDirectory.childFile('some_file.txt').existsSync(), true);
+        expect(targetDirectory.childFile('some_file.txt').readAsStringSync(), 'file 1');
+        expect(targetDirectory.childFile('absolute_linked.txt').readAsStringSync(), 'file 1');
+        expect(targetDirectory.childLink('absolute_linked.txt').existsSync(), true);
+        expect(
+          targetDirectory.childLink('absolute_linked.txt').targetSync(),
+          sourceFile1.absolute.path,
+        );
+        expect(targetDirectory.childDirectory('dir1').childDirectory('dir2').existsSync(), true);
+        expect(targetDirectory.childDirectory('dir1').childDirectory('dir2').childFile('another_file.txt').existsSync(), true);
+        expect(targetDirectory.childDirectory('dir1').childDirectory('dir2').childFile('another_file.txt').readAsStringSync(), 'file 2');
+        expect(targetDirectory.childDirectory('relative_linked_sub_dir').existsSync(), true);
+        expect(targetDirectory.childLink('relative_linked_sub_dir').existsSync(), true);
+        expect(
+          targetDirectory.childLink('relative_linked_sub_dir').targetSync(),
+          subdirectorySourcePath,
+        );
+        expect(targetDirectory.childDirectory('relative_linked_sub_dir').childFile('another_file.txt').existsSync(), true);
+        expect(targetDirectory.childDirectory('relative_linked_sub_dir').childFile('another_file.txt').readAsStringSync(), 'file 2');
+        expect(targetDirectory.childDirectory('empty_directory').existsSync(), true);
+
+        // Assert that the copy operation hasn't modified the original file in some way.
+        expect(sourceDirectory.childFile('some_file.txt').lastModifiedSync(), writeTime);
+        // There's still 5 things in the original directory as there were initially.
+        expect(sourceDirectory.listSync().length, 5);
+      } finally {
+        tryToDelete(tempDir);
+      }
+    });
+
     testWithoutContext('Skip files if shouldCopyFile returns false', () {
       final MemoryFileSystem fileSystem = MemoryFileSystem.test();
       final Directory origin = fileSystem.directory('/origin');