script/tool/lib/src/format_command.dart - mirrors/packages - Git at Google

 // Copyright 2013 The Flutter Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.

 import 'dart:convert';
 import 'dart:io' as io;

 import 'package:file/file.dart';
 import 'package:http/http.dart' as http;
 import 'package:meta/meta.dart';

 import 'common/core.dart';
 import 'common/output_utils.dart';
 import 'common/package_command.dart';

 /// In theory this should be 8191, but in practice that was still resulting in
 /// "The input line is too long" errors. This was chosen as a value that worked
 /// in practice via trial and error, but may need to be adjusted based on
 /// further experience.
 @visibleForTesting
 const int windowsCommandLineMax = 8000;

 /// This value is picked somewhat arbitrarily based on checking `ARG_MAX` on a
 /// macOS and Linux machine. If anyone encounters a lower limit in pratice, it
 /// can be lowered accordingly.
 @visibleForTesting
 const int nonWindowsCommandLineMax = 1000000;

 const int _exitClangFormatFailed = 3;
 const int _exitFlutterFormatFailed = 4;
 const int _exitJavaFormatFailed = 5;
 const int _exitGitFailed = 6;
 const int _exitDependencyMissing = 7;

 final Uri _googleFormatterUrl = Uri.https('github.com',
     '/google/google-java-format/releases/download/google-java-format-1.3/google-java-format-1.3-all-deps.jar');

 /// A command to format all package code.
 class FormatCommand extends PackageCommand {
   /// Creates an instance of the format command.
   FormatCommand(
     super.packagesDir, {
     super.processRunner,
     super.platform,
   }) {
     argParser.addFlag('fail-on-change', hide: true);
     argParser.addOption('clang-format',
         defaultsTo: 'clang-format', help: 'Path to "clang-format" executable.');
     argParser.addOption('java',
         defaultsTo: 'java', help: 'Path to "java" executable.');
   }

   @override
   final String name = 'format';

   @override
   final String description =
       'Formats the code of all packages (Java, Objective-C, C++, and Dart).\n\n'
       'This command requires "git", "flutter" and "clang-format" v5 to be in '
       'your path.';

   @override
   Future<void> run() async {
     final String googleFormatterPath = await _getGoogleFormatterPath();

     // This class is not based on PackageLoopingCommand because running the
     // formatters separately for each package is an order of magnitude slower,
     // due to the startup overhead of the formatters.
     final Iterable<String> files =
         await _getFilteredFilePaths(getFiles(), relativeTo: packagesDir);
     await _formatDart(files);
     await _formatJava(files, googleFormatterPath);
     await _formatCppAndObjectiveC(files);

     if (getBoolArg('fail-on-change')) {
       final bool modified = await _didModifyAnything();
       if (modified) {
         throw ToolExit(exitCommandFoundErrors);
       }
     }
   }

   Future<bool> _didModifyAnything() async {
     final io.ProcessResult modifiedFiles = await processRunner.run(
       'git',
       <String>['ls-files', '--modified'],
       workingDir: packagesDir,
       logOnError: true,
     );
     if (modifiedFiles.exitCode != 0) {
       printError('Unable to determine changed files.');
       throw ToolExit(_exitGitFailed);
     }

     print('\n\n');

     final String stdout = modifiedFiles.stdout as String;
     if (stdout.isEmpty) {
       print('All files formatted correctly.');
       return false;
     }

     print('These files are not formatted correctly (see diff below):');
     LineSplitter.split(stdout).map((String line) => '  $line').forEach(print);

     print('\nTo fix run the repository tooling `format` command: '
         'https://github.com/flutter/packages/blob/main/script/tool/README.md#format-code\n'
         'or copy-paste this command into your terminal:');

     final io.ProcessResult diff = await processRunner.run(
       'git',
       <String>['diff'],
       workingDir: packagesDir,
       logOnError: true,
     );
     if (diff.exitCode != 0) {
       printError('Unable to determine diff.');
       throw ToolExit(_exitGitFailed);
     }
     print('patch -p1 <<DONE');
     print(diff.stdout);
     print('DONE');
     return true;
   }

   Future<void> _formatCppAndObjectiveC(Iterable<String> files) async {
     final Iterable<String> clangFiles = _getPathsWithExtensions(
         files, <String>{'.h', '.m', '.mm', '.cc', '.cpp'});
     if (clangFiles.isNotEmpty) {
       final String clangFormat = await _findValidClangFormat();

       print('Formatting .cc, .cpp, .h, .m, and .mm files...');
       final int exitCode = await _runBatched(
           clangFormat, <String>['-i', '--style=file'],
           files: clangFiles);
       if (exitCode != 0) {
         printError(
             'Failed to format C, C++, and Objective-C files: exit code $exitCode.');
         throw ToolExit(_exitClangFormatFailed);
       }
     }
   }

   Future<String> _findValidClangFormat() async {
     final String clangFormatArg = getStringArg('clang-format');
     if (await _hasDependency(clangFormatArg)) {
       return clangFormatArg;
     }

     // There is a known issue where "chromium/depot_tools/clang-format"
     // fails with "Problem while looking for clang-format in Chromium source tree".
     // Loop through all "clang-format"s in PATH until a working one is found,
     // for example "/usr/local/bin/clang-format" or a "brew" installed version.
     for (final String clangFormatPath in await _whichAll('clang-format')) {
       if (await _hasDependency(clangFormatPath)) {
         return clangFormatPath;
       }
     }
     printError('Unable to run "clang-format". Make sure that it is in your '
         'path, or provide a full path with --clang-format.');
     throw ToolExit(_exitDependencyMissing);
   }

   Future<void> _formatJava(
       Iterable<String> files, String googleFormatterPath) async {
     final Iterable<String> javaFiles =
         _getPathsWithExtensions(files, <String>{'.java'});
     if (javaFiles.isNotEmpty) {
       final String java = getStringArg('java');
       if (!await _hasDependency(java)) {
         printError(
             'Unable to run "java". Make sure that it is in your path, or '
             'provide a full path with --java.');
         throw ToolExit(_exitDependencyMissing);
       }

       print('Formatting .java files...');
       final int exitCode = await _runBatched(
           java, <String>['-jar', googleFormatterPath, '--replace'],
           files: javaFiles);
       if (exitCode != 0) {
         printError('Failed to format Java files: exit code $exitCode.');
         throw ToolExit(_exitJavaFormatFailed);
       }
     }
   }

   Future<void> _formatDart(Iterable<String> files) async {
     final Iterable<String> dartFiles =
         _getPathsWithExtensions(files, <String>{'.dart'});
     if (dartFiles.isNotEmpty) {
       print('Formatting .dart files...');
       final int exitCode =
           await _runBatched('dart', <String>['format'], files: dartFiles);
       if (exitCode != 0) {
         printError('Failed to format Dart files: exit code $exitCode.');
         throw ToolExit(_exitFlutterFormatFailed);
       }
     }
   }

   /// Given a stream of [files], returns the paths of any that are not in known
   /// locations to ignore, relative to [relativeTo].
   Future<Iterable<String>> _getFilteredFilePaths(
     Stream<File> files, {
     required Directory relativeTo,
   }) async {
     // Returns a pattern to check for [directories] as a subset of a file path.
     RegExp pathFragmentForDirectories(List<String> directories) {
       String s = path.separator;
       // Escape the separator for use in the regex.
       if (s == r'\') {
         s = r'\\';
       }
       return RegExp('(?:^|$s)${path.joinAll(directories)}$s');
     }

     final String fromPath = relativeTo.path;

     // Dart files are allowed to have a pragma to disable auto-formatting. This
     // was added because Hixie hurts when dealing with what dartfmt does to
     // artisanally-formatted Dart, while Stuart gets really frustrated when
     // dealing with PRs from newer contributors who don't know how to make Dart
     // readable. After much discussion, it was decided that files in the plugins
     // and packages repos that really benefit from hand-formatting (e.g. files
     // with large blobs of hex literals) could be opted-out of the requirement
     // that they be autoformatted, so long as the code's owner was willing to
     // bear the cost of this during code reviews.
     // In the event that code ownership moves to someone who does not hold the
     // same views as the original owner, the pragma can be removed and the file
     // auto-formatted.
     const String handFormattedExtension = '.dart';
     const String handFormattedPragma = '// This file is hand-formatted.';

     return files
         .where((File file) {
           // See comment above near [handFormattedPragma].
           return path.extension(file.path) != handFormattedExtension ||
               !file.readAsLinesSync().contains(handFormattedPragma);
         })
         .map((File file) => path.relative(file.path, from: fromPath))
         .where((String path) =>
             // Ignore files in build/ directories (e.g., headers of frameworks)
             // to avoid useless extra work in local repositories.
             !path.contains(
                 pathFragmentForDirectories(<String>['example', 'build'])) &&
             // Ignore files in Pods, which are not part of the repository.
             !path.contains(pathFragmentForDirectories(<String>['Pods'])) &&
             // Ignore .dart_tool/, which can have various intermediate files.
             !path.contains(pathFragmentForDirectories(<String>['.dart_tool'])))
         .toList();
   }

   Iterable<String> _getPathsWithExtensions(
       Iterable<String> files, Set<String> extensions) {
     return files.where(
         (String filePath) => extensions.contains(path.extension(filePath)));
   }

   Future<String> _getGoogleFormatterPath() async {
     final String javaFormatterPath = path.join(
         path.dirname(path.fromUri(platform.script)),
         'google-java-format-1.3-all-deps.jar');
     final File javaFormatterFile =
         packagesDir.fileSystem.file(javaFormatterPath);

     if (!javaFormatterFile.existsSync()) {
       print('Downloading Google Java Format...');
       final http.Response response = await http.get(_googleFormatterUrl);
       javaFormatterFile.writeAsBytesSync(response.bodyBytes);
     }

     return javaFormatterPath;
   }

   /// Returns true if [command] can be run successfully.
   Future<bool> _hasDependency(String command) async {
     // Some versions of Java accept both -version and --version, but some only
     // accept -version.
     final String versionFlag = command == 'java' ? '-version' : '--version';
     try {
       final io.ProcessResult result =
           await processRunner.run(command, <String>[versionFlag]);
       if (result.exitCode != 0) {
         return false;
       }
     } on io.ProcessException {
       // Thrown when the binary is missing entirely.
       return false;
     }
     return true;
   }

   /// Returns all instances of [command] executable found on user path.
   Future<List<String>> _whichAll(String command) async {
     try {
       final io.ProcessResult result =
           await processRunner.run('which', <String>['-a', command]);

       if (result.exitCode != 0) {
         return <String>[];
       }

       final String stdout = (result.stdout as String).trim();
       if (stdout.isEmpty) {
         return <String>[];
       }
       return LineSplitter.split(stdout).toList();
     } on io.ProcessException {
       return <String>[];
     }
   }

   /// Runs [command] on [arguments] on all of the files in [files], batched as
   /// necessary to avoid OS command-line length limits.
   ///
   /// Returns the exit code of the first failure, which stops the run, or 0
   /// on success.
   Future<int> _runBatched(
     String command,
     List<String> arguments, {
     required Iterable<String> files,
   }) async {
     final int commandLineMax =
         platform.isWindows ? windowsCommandLineMax : nonWindowsCommandLineMax;

     // Compute the max length of the file argument portion of a batch.
     // Add one to each argument's length for the space before it.
     final int argumentTotalLength =
         arguments.fold(0, (int sum, String arg) => sum + arg.length + 1);
     final int batchMaxTotalLength =
         commandLineMax - command.length - argumentTotalLength;

     // Run the command in batches.
     final List<List<String>> batches =
         _partitionFileList(files, maxStringLength: batchMaxTotalLength);
     for (final List<String> batch in batches) {
       batch.sort(); // For ease of testing.
       final int exitCode = await processRunner.runAndStream(
           command, <String>[...arguments, ...batch],
           workingDir: packagesDir);
       if (exitCode != 0) {
         return exitCode;
       }
     }
     return 0;
   }

   /// Partitions [files] into batches whose max string length as parameters to
   /// a command (including the spaces between them, and between the list and
   /// the command itself) is no longer than [maxStringLength].
   List<List<String>> _partitionFileList(Iterable<String> files,
       {required int maxStringLength}) {
     final List<List<String>> batches = <List<String>>[<String>[]];
     int currentBatchTotalLength = 0;
     for (final String file in files) {
       final int length = file.length + 1 /* for the space */;
       if (currentBatchTotalLength + length > maxStringLength) {
         // Start a new batch.
         batches.add(<String>[]);
         currentBatchTotalLength = 0;
       }
       batches.last.add(file);
       currentBatchTotalLength += length;
     }
     return batches;
   }
 }
	// Copyright 2013 The Flutter Authors. All rights reserved.
	// Use of this source code is governed by a BSD-style license that can be
	// found in the LICENSE file.

	import 'dart:convert';
	import 'dart:io' as io;

	import 'package:file/file.dart';
	import 'package:http/http.dart' as http;
	import 'package:meta/meta.dart';

	import 'common/core.dart';
	import 'common/output_utils.dart';
	import 'common/package_command.dart';

	/// In theory this should be 8191, but in practice that was still resulting in
	/// "The input line is too long" errors. This was chosen as a value that worked
	/// in practice via trial and error, but may need to be adjusted based on
	/// further experience.
	@visibleForTesting
	const int windowsCommandLineMax = 8000;

	/// This value is picked somewhat arbitrarily based on checking `ARG_MAX` on a
	/// macOS and Linux machine. If anyone encounters a lower limit in pratice, it
	/// can be lowered accordingly.
	@visibleForTesting
	const int nonWindowsCommandLineMax = 1000000;

	const int _exitClangFormatFailed = 3;
	const int _exitFlutterFormatFailed = 4;
	const int _exitJavaFormatFailed = 5;
	const int _exitGitFailed = 6;
	const int _exitDependencyMissing = 7;

	final Uri _googleFormatterUrl = Uri.https('github.com',
	'/google/google-java-format/releases/download/google-java-format-1.3/google-java-format-1.3-all-deps.jar');

	/// A command to format all package code.
	class FormatCommand extends PackageCommand {
	/// Creates an instance of the format command.
	FormatCommand(
	super.packagesDir, {
	super.processRunner,
	super.platform,
	}) {
	argParser.addFlag('fail-on-change', hide: true);
	argParser.addOption('clang-format',
	defaultsTo: 'clang-format', help: 'Path to "clang-format" executable.');
	argParser.addOption('java',
	defaultsTo: 'java', help: 'Path to "java" executable.');
	}

	@override
	final String name = 'format';

	@override
	final String description =
	'Formats the code of all packages (Java, Objective-C, C++, and Dart).\n\n'
	'This command requires "git", "flutter" and "clang-format" v5 to be in '
	'your path.';

	@override
	Future<void> run() async {
	final String googleFormatterPath = await _getGoogleFormatterPath();

	// This class is not based on PackageLoopingCommand because running the
	// formatters separately for each package is an order of magnitude slower,
	// due to the startup overhead of the formatters.
	final Iterable<String> files =
	await _getFilteredFilePaths(getFiles(), relativeTo: packagesDir);
	await _formatDart(files);
	await _formatJava(files, googleFormatterPath);
	await _formatCppAndObjectiveC(files);

	if (getBoolArg('fail-on-change')) {
	final bool modified = await _didModifyAnything();
	if (modified) {
	throw ToolExit(exitCommandFoundErrors);
	}
	}
	}

	Future<bool> _didModifyAnything() async {
	final io.ProcessResult modifiedFiles = await processRunner.run(
	'git',
	<String>['ls-files', '--modified'],
	workingDir: packagesDir,
	logOnError: true,
	);
	if (modifiedFiles.exitCode != 0) {
	printError('Unable to determine changed files.');
	throw ToolExit(_exitGitFailed);
	}

	print('\n\n');

	final String stdout = modifiedFiles.stdout as String;
	if (stdout.isEmpty) {
	print('All files formatted correctly.');
	return false;
	}

	print('These files are not formatted correctly (see diff below):');
	LineSplitter.split(stdout).map((String line) => ' $line').forEach(print);

	print('\nTo fix run the repository tooling `format` command: '
	'https://github.com/flutter/packages/blob/main/script/tool/README.md#format-code\n'
	'or copy-paste this command into your terminal:');

	final io.ProcessResult diff = await processRunner.run(
	'git',
	<String>['diff'],
	workingDir: packagesDir,
	logOnError: true,
	);
	if (diff.exitCode != 0) {
	printError('Unable to determine diff.');
	throw ToolExit(_exitGitFailed);
	}
	print('patch -p1 <<DONE');
	print(diff.stdout);
	print('DONE');
	return true;
	}

	Future<void> _formatCppAndObjectiveC(Iterable<String> files) async {
	final Iterable<String> clangFiles = _getPathsWithExtensions(
	files, <String>{'.h', '.m', '.mm', '.cc', '.cpp'});
	if (clangFiles.isNotEmpty) {
	final String clangFormat = await _findValidClangFormat();

	print('Formatting .cc, .cpp, .h, .m, and .mm files...');
	final int exitCode = await _runBatched(
	clangFormat, <String>['-i', '--style=file'],
	files: clangFiles);
	if (exitCode != 0) {
	printError(
	'Failed to format C, C++, and Objective-C files: exit code $exitCode.');
	throw ToolExit(_exitClangFormatFailed);
	}
	}
	}

	Future<String> _findValidClangFormat() async {
	final String clangFormatArg = getStringArg('clang-format');
	if (await _hasDependency(clangFormatArg)) {
	return clangFormatArg;
	}

	// There is a known issue where "chromium/depot_tools/clang-format"
	// fails with "Problem while looking for clang-format in Chromium source tree".
	// Loop through all "clang-format"s in PATH until a working one is found,
	// for example "/usr/local/bin/clang-format" or a "brew" installed version.
	for (final String clangFormatPath in await _whichAll('clang-format')) {
	if (await _hasDependency(clangFormatPath)) {
	return clangFormatPath;
	}
	}
	printError('Unable to run "clang-format". Make sure that it is in your '
	'path, or provide a full path with --clang-format.');
	throw ToolExit(_exitDependencyMissing);
	}

	Future<void> _formatJava(
	Iterable<String> files, String googleFormatterPath) async {
	final Iterable<String> javaFiles =
	_getPathsWithExtensions(files, <String>{'.java'});
	if (javaFiles.isNotEmpty) {
	final String java = getStringArg('java');
	if (!await _hasDependency(java)) {
	printError(
	'Unable to run "java". Make sure that it is in your path, or '
	'provide a full path with --java.');
	throw ToolExit(_exitDependencyMissing);
	}

	print('Formatting .java files...');
	final int exitCode = await _runBatched(
	java, <String>['-jar', googleFormatterPath, '--replace'],
	files: javaFiles);
	if (exitCode != 0) {
	printError('Failed to format Java files: exit code $exitCode.');
	throw ToolExit(_exitJavaFormatFailed);
	}
	}
	}

	Future<void> _formatDart(Iterable<String> files) async {
	final Iterable<String> dartFiles =
	_getPathsWithExtensions(files, <String>{'.dart'});
	if (dartFiles.isNotEmpty) {
	print('Formatting .dart files...');
	final int exitCode =
	await _runBatched('dart', <String>['format'], files: dartFiles);
	if (exitCode != 0) {
	printError('Failed to format Dart files: exit code $exitCode.');
	throw ToolExit(_exitFlutterFormatFailed);
	}
	}
	}

	/// Given a stream of [files], returns the paths of any that are not in known
	/// locations to ignore, relative to [relativeTo].
	Future<Iterable<String>> _getFilteredFilePaths(
	Stream<File> files, {
	required Directory relativeTo,
	}) async {
	// Returns a pattern to check for [directories] as a subset of a file path.
	RegExp pathFragmentForDirectories(List<String> directories) {
	String s = path.separator;
	// Escape the separator for use in the regex.
	if (s == r'\') {
	s = r'\\';
	}
	return RegExp('(?:^\|$s)${path.joinAll(directories)}$s');
	}

	final String fromPath = relativeTo.path;

	// Dart files are allowed to have a pragma to disable auto-formatting. This
	// was added because Hixie hurts when dealing with what dartfmt does to
	// artisanally-formatted Dart, while Stuart gets really frustrated when
	// dealing with PRs from newer contributors who don't know how to make Dart
	// readable. After much discussion, it was decided that files in the plugins
	// and packages repos that really benefit from hand-formatting (e.g. files
	// with large blobs of hex literals) could be opted-out of the requirement
	// that they be autoformatted, so long as the code's owner was willing to
	// bear the cost of this during code reviews.
	// In the event that code ownership moves to someone who does not hold the
	// same views as the original owner, the pragma can be removed and the file
	// auto-formatted.
	const String handFormattedExtension = '.dart';
	const String handFormattedPragma = '// This file is hand-formatted.';

	return files
	.where((File file) {
	// See comment above near [handFormattedPragma].
	return path.extension(file.path) != handFormattedExtension \|\|
	!file.readAsLinesSync().contains(handFormattedPragma);
	})
	.map((File file) => path.relative(file.path, from: fromPath))
	.where((String path) =>
	// Ignore files in build/ directories (e.g., headers of frameworks)
	// to avoid useless extra work in local repositories.
	!path.contains(
	pathFragmentForDirectories(<String>['example', 'build'])) &&
	// Ignore files in Pods, which are not part of the repository.
	!path.contains(pathFragmentForDirectories(<String>['Pods'])) &&
	// Ignore .dart_tool/, which can have various intermediate files.
	!path.contains(pathFragmentForDirectories(<String>['.dart_tool'])))
	.toList();
	}

	Iterable<String> _getPathsWithExtensions(
	Iterable<String> files, Set<String> extensions) {
	return files.where(
	(String filePath) => extensions.contains(path.extension(filePath)));
	}

	Future<String> _getGoogleFormatterPath() async {
	final String javaFormatterPath = path.join(
	path.dirname(path.fromUri(platform.script)),
	'google-java-format-1.3-all-deps.jar');
	final File javaFormatterFile =
	packagesDir.fileSystem.file(javaFormatterPath);

	if (!javaFormatterFile.existsSync()) {
	print('Downloading Google Java Format...');
	final http.Response response = await http.get(_googleFormatterUrl);
	javaFormatterFile.writeAsBytesSync(response.bodyBytes);
	}

	return javaFormatterPath;
	}

	/// Returns true if [command] can be run successfully.
	Future<bool> _hasDependency(String command) async {
	// Some versions of Java accept both -version and --version, but some only
	// accept -version.
	final String versionFlag = command == 'java' ? '-version' : '--version';
	try {
	final io.ProcessResult result =
	await processRunner.run(command, <String>[versionFlag]);
	if (result.exitCode != 0) {
	return false;
	}
	} on io.ProcessException {
	// Thrown when the binary is missing entirely.
	return false;
	}
	return true;
	}

	/// Returns all instances of [command] executable found on user path.
	Future<List<String>> _whichAll(String command) async {
	try {
	final io.ProcessResult result =
	await processRunner.run('which', <String>['-a', command]);

	if (result.exitCode != 0) {
	return <String>[];
	}

	final String stdout = (result.stdout as String).trim();
	if (stdout.isEmpty) {
	return <String>[];
	}
	return LineSplitter.split(stdout).toList();
	} on io.ProcessException {
	return <String>[];
	}
	}

	/// Runs [command] on [arguments] on all of the files in [files], batched as
	/// necessary to avoid OS command-line length limits.
	///
	/// Returns the exit code of the first failure, which stops the run, or 0
	/// on success.
	Future<int> _runBatched(
	String command,
	List<String> arguments, {
	required Iterable<String> files,
	}) async {
	final int commandLineMax =
	platform.isWindows ? windowsCommandLineMax : nonWindowsCommandLineMax;

	// Compute the max length of the file argument portion of a batch.
	// Add one to each argument's length for the space before it.
	final int argumentTotalLength =
	arguments.fold(0, (int sum, String arg) => sum + arg.length + 1);
	final int batchMaxTotalLength =
	commandLineMax - command.length - argumentTotalLength;

	// Run the command in batches.
	final List<List<String>> batches =
	_partitionFileList(files, maxStringLength: batchMaxTotalLength);
	for (final List<String> batch in batches) {
	batch.sort(); // For ease of testing.
	final int exitCode = await processRunner.runAndStream(
	command, <String>[...arguments, ...batch],
	workingDir: packagesDir);
	if (exitCode != 0) {
	return exitCode;
	}
	}
	return 0;
	}

	/// Partitions [files] into batches whose max string length as parameters to
	/// a command (including the spaces between them, and between the list and
	/// the command itself) is no longer than [maxStringLength].
	List<List<String>> _partitionFileList(Iterable<String> files,
	{required int maxStringLength}) {
	final List<List<String>> batches = <List<String>>[<String>[]];
	int currentBatchTotalLength = 0;
	for (final String file in files) {
	final int length = file.length + 1 /* for the space */;
	if (currentBatchTotalLength + length > maxStringLength) {
	// Start a new batch.
	batches.add(<String>[]);
	currentBatchTotalLength = 0;
	}
	batches.last.add(file);
	currentBatchTotalLength += length;
	}
	return batches;
	}
	}