Add script to check format of changed dart files (#160007)

The script is modeled after a similar script in the engine (see engine's
[format.dart](https://github.com/flutter/engine/blob/main/ci/bin/format.dart)).

It identifies the files that have been changed and checks if their
formatting is correct. It also offers an option to correct formatting
(`--fix`) and an option to check the formatting of all files in the
repro (not just changed ones, `--all-files`).

When we are enforcing dart format this script will be called as part of
presubmit.

dev/bots/analyze.dart

@@ -2246,6 +2246,7 @@ const Set<String> kExecutableAllowlist = <String>{
   'dev/tools/gen_keycodes/bin/gen_keycodes',
   'dev/tools/repackage_gradle_wrapper.sh',
   'dev/tools/bin/engine_hash.sh',
+  'dev/tools/format.sh',
 
   'packages/flutter_tools/bin/macos_assemble.sh',
   'packages/flutter_tools/bin/tool_backend.sh',

dev/tools/bin/format.dart

@@ -0,0 +1,256 @@
+// Copyright 2014 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:io';
+
+import 'package:args/args.dart';
+import 'package:path/path.dart' as path;
+import 'package:process_runner/process_runner.dart';
+
+Future<int> main(List<String> arguments) async {
+  final ArgParser parser = ArgParser();
+  parser.addFlag('help', help: 'Print help.', abbr: 'h');
+  parser.addFlag('fix',
+      abbr: 'f',
+      help: 'Instead of just checking for formatting errors, fix them in place.');
+  parser.addFlag('all-files',
+      abbr: 'a',
+      help: 'Instead of just checking for formatting errors in changed files, '
+          'check for them in all files.');
+
+  late final ArgResults options;
+  try {
+    options = parser.parse(arguments);
+  } on FormatException catch (e) {
+    stderr.writeln('ERROR: $e');
+    _usage(parser, exitCode: 0);
+  }
+
+  if (options['help'] as bool) {
+    _usage(parser, exitCode: 0);
+  }
+
+  final File script = File.fromUri(Platform.script).absolute;
+  final Directory flutterRoot = script.parent.parent.parent.parent;
+
+  final bool result = (await DartFormatChecker(
+    flutterRoot: flutterRoot,
+    allFiles: options['all-files'] as bool,
+  ).check(fix: options['fix'] as bool)) == 0;
+
+  exit(result ? 0 : 1);
+}
+
+void _usage(ArgParser parser, {int exitCode = 1}) {
+  stderr.writeln('format.dart [--help] [--fix] [--all-files]');
+  stderr.writeln(parser.usage);
+  exit(exitCode);
+}
+
+class DartFormatChecker {
+  DartFormatChecker({
+    required this.flutterRoot,
+    required this.allFiles,
+  }) : processRunner = ProcessRunner(
+    defaultWorkingDirectory: flutterRoot,
+  );
+
+  final Directory flutterRoot;
+  final bool allFiles;
+  final ProcessRunner processRunner;
+
+  Future<int> check({required bool fix}) async {
+    final String baseGitRef = await _getDiffBaseRevision();
+    final List<String> filesToCheck = await _getFileList(
+      types: <String>['*.dart'],
+      allFiles: allFiles,
+      baseGitRef: baseGitRef,
+    );
+    return _checkFormat(
+      filesToCheck: filesToCheck,
+      fix: fix,
+    );
+  }
+
+  Future<String> _getDiffBaseRevision() async {
+    String upstream = 'upstream';
+    final String upstreamUrl = await _runGit(
+      <String>['remote', 'get-url', upstream],
+      processRunner,
+      failOk: true,
+    );
+    if (upstreamUrl.isEmpty) {
+      upstream = 'origin';
+    }
+    await _runGit(<String>['fetch', upstream, 'main'], processRunner);
+    String result = '';
+    try {
+      // This is the preferred command to use, but developer checkouts often do
+      // not have a clear fork point, so we fall back to just the regular
+      // merge-base in that case.
+      result = await _runGit(
+        <String>['merge-base', '--fork-point', 'FETCH_HEAD', 'HEAD'],
+        processRunner,
+      );
+    } on ProcessRunnerException {
+      result = await _runGit(<String>['merge-base', 'FETCH_HEAD', 'HEAD'], processRunner);
+    }
+    return result.trim();
+  }
+
+  Future<String> _runGit(
+      List<String> args,
+      ProcessRunner processRunner, {
+        bool failOk = false,
+      }) async {
+    final ProcessRunnerResult result = await processRunner.runProcess(
+      <String>['git', ...args],
+      failOk: failOk,
+    );
+    return result.stdout;
+  }
+
+  Future<List<String>> _getFileList({
+    required List<String> types,
+    required bool allFiles,
+    required String baseGitRef,
+  }) async {
+    String output;
+    if (allFiles) {
+      output = await _runGit(<String>[
+        'ls-files',
+        '--',
+        ...types,
+      ], processRunner);
+    } else {
+      output = await _runGit(<String>[
+        'diff',
+        '-U0',
+        '--no-color',
+        '--diff-filter=d',
+        '--name-only',
+        baseGitRef,
+        '--',
+        ...types,
+      ], processRunner);
+    }
+    return output.split('\n').where((String line) => line.isNotEmpty).toList();
+  }
+
+  Future<int> _checkFormat({
+    required List<String> filesToCheck,
+    required bool fix,
+  }) async {
+    final List<String> cmd = <String>[
+      path.join(flutterRoot.path, 'bin', 'dart'),
+      'format',
+      '--set-exit-if-changed',
+      '--show=none',
+      if (!fix) '--output=show',
+      if (fix) '--output=write',
+    ];
+    final List<WorkerJob> jobs = <WorkerJob>[];
+    for (final String file in filesToCheck) {
+      jobs.add(WorkerJob(<String>[...cmd, file]));
+    }
+    final ProcessPool dartFmt = ProcessPool(
+      processRunner: processRunner,
+      printReport: _namedReport('dart format'),
+    );
+
+    Iterable<WorkerJob> incorrect;
+    if (!fix) {
+      final Stream<WorkerJob> completedJobs = dartFmt.startWorkers(jobs);
+      final List<WorkerJob> diffJobs = <WorkerJob>[];
+      await for (final WorkerJob completedJob in completedJobs) {
+        if (completedJob.result.exitCode == 1) {
+          diffJobs.add(
+            WorkerJob(
+              <String>[
+                'git',
+                'diff',
+                '--no-index',
+                '--no-color',
+                '--ignore-cr-at-eol',
+                '--',
+                completedJob.command.last,
+                '-',
+              ],
+              stdinRaw: _codeUnitsAsStream(completedJob.result.stdoutRaw),
+            ),
+          );
+        }
+      }
+      final ProcessPool diffPool = ProcessPool(
+        processRunner: processRunner,
+        printReport: _namedReport('diff'),
+      );
+      final List<WorkerJob> completedDiffs = await diffPool.runToCompletion(diffJobs);
+      incorrect = completedDiffs.where((WorkerJob job) => job.result.exitCode != 0);
+    } else {
+      final List<WorkerJob> completedJobs = await dartFmt.runToCompletion(jobs);
+      incorrect = completedJobs.where((WorkerJob job) => job.result.exitCode == 1);
+    }
+
+    _clearOutput();
+
+    if (incorrect.isNotEmpty) {
+      final bool plural = incorrect.length > 1;
+      if (fix) {
+        stdout.writeln('Fixing ${incorrect.length} dart file${plural ? 's' : ''}'
+            ' which ${plural ? 'were' : 'was'} formatted incorrectly.');
+      } else {
+        stderr.writeln('Found ${incorrect.length} Dart file${plural ? 's' : ''}'
+            ' which ${plural ? 'were' : 'was'} formatted incorrectly.');
+        final String fileList = incorrect.map(
+          (WorkerJob job) => job.command[job.command.length - 2]
+        ).join(' ');
+        stdout.writeln();
+        stdout.writeln('To fix, run `dart format $fileList` or:');
+        stdout.writeln();
+        stdout.writeln('git apply <<DONE');
+        for (final WorkerJob job in incorrect) {
+          stdout.write(job.result.stdout
+              .replaceFirst('b/-', 'b/${job.command[job.command.length - 2]}')
+              .replaceFirst('b/-', 'b/${job.command[job.command.length - 2]}')
+              .replaceFirst(RegExp('\\+Formatted \\d+ files? \\(\\d+ changed\\) in \\d+.\\d+ seconds.\n'), '')
+          );
+        }
+        stdout.writeln('DONE');
+        stdout.writeln();
+      }
+    } else {
+      stdout.writeln('All dart files formatted correctly.');
+    }
+    return incorrect.length;
+  }
+}
+
+ProcessPoolProgressReporter _namedReport(String name) {
+  return (int total, int completed, int inProgress, int pending, int failed) {
+    final String percent =
+    total == 0 ? '100' : ((100 * completed) ~/ total).toString().padLeft(3);
+    final String completedStr = completed.toString().padLeft(3);
+    final String totalStr = total.toString().padRight(3);
+    final String inProgressStr = inProgress.toString().padLeft(2);
+    final String pendingStr = pending.toString().padLeft(3);
+    final String failedStr = failed.toString().padLeft(3);
+
+    stdout.write('$name Jobs: $percent% done, '
+        '$completedStr/$totalStr completed, '
+        '$inProgressStr in progress, '
+        '$pendingStr pending, '
+        '$failedStr failed.${' ' * 20}\r');
+  };
+}
+
+void _clearOutput() {
+  stdout.write('\r${' ' * 100}\r');
+}
+
+Stream<List<int>> _codeUnitsAsStream(List<int>? input) async* {
+  if (input != null) {
+    yield input;
+  }
+}

dev/tools/format.bat

@@ -0,0 +1,22 @@
+@ECHO off
+REM Copyright 2014 The Flutter Authors. All rights reserved.
+REM Use of this source code is governed by a BSD-style license that can be
+REM found in the LICENSE file.
+
+SETLOCAL ENABLEDELAYEDEXPANSION
+
+FOR %%i IN ("%~dp0..\..") DO SET FLUTTER_ROOT=%%~fi
+
+REM Test if Git is available on the Host
+where /q git || ECHO Error: Unable to find git in your PATH. && EXIT /B 1
+
+SET tools_dir=%FLUTTER_ROOT%\dev\tools
+
+SET dart=%FLUTTER_ROOT%\bin\dart.bat
+
+cd "%tools_dir%"
+
+REM Do not use the CALL command in the next line to execute Dart. CALL causes
+REM Windows to re-read the line from disk after the CALL command has finished
+REM regardless of the ampersand chain.
+"%dart%" pub get > NUL && "%dart%" "%tools_dir%\bin\format.dart" %* & exit /B !ERRORLEVEL!

dev/tools/format.sh

@@ -0,0 +1,37 @@
+#!/usr/bin/env bash
+# Copyright 2014 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.
+
+set -e
+
+# Needed because if it is set, cd may print the path it changed to.
+unset CDPATH
+
+# On Mac OS, readlink -f doesn't work, so follow_links traverses the path one
+# link at a time, and then cds into the link destination and find out where it
+# ends up.
+#
+# The function is enclosed in a subshell to avoid changing the working directory
+# of the caller.
+function follow_links() (
+  cd -P "$(dirname -- "$1")"
+  file="$PWD/$(basename -- "$1")"
+  while [[ -h "$file" ]]; do
+    cd -P "$(dirname -- "$file")"
+    file="$(readlink -- "$file")"
+    cd -P "$(dirname -- "$file")"
+    file="$PWD/$(basename -- "$file")"
+  done
+  echo "$file"
+)
+
+SCRIPT_DIR=$(follow_links "$(dirname -- "${BASH_SOURCE[0]}")")
+FLUTTER_DIR="$(cd "$SCRIPT_DIR/../.."; pwd -P)"
+DART="${FLUTTER_DIR}/bin/dart"
+
+cd "$SCRIPT_DIR"
+"$DART" pub get > /dev/null
+"$DART" \
+  bin/format.dart \
+  "$@"

dev/tools/pubspec.yaml

@@ -12,6 +12,7 @@ dependencies:
   meta: 1.15.0
   path: 1.9.1
   process: 5.0.3
+  process_runner: 4.2.0
   pub_semver: 2.1.4
   yaml: 3.1.2
 
@@ -63,4 +64,4 @@ dev_dependencies:
   web_socket_channel: 3.0.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
   webkit_inspection_protocol: 1.2.1 # THIS LINE IS AUTOGENERATED - TO UPDATE USE "flutter update-packages --force-upgrade"
 
-# PUBSPEC CHECKSUM: f620
+# PUBSPEC CHECKSUM: 2d6b

dev/tools/test/format_test.dart

@@ -0,0 +1,94 @@
+// Copyright 2014 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:io' as io;
+
+import 'package:path/path.dart' as path;
+import 'package:test/test.dart';
+
+class FileContentPair {
+  FileContentPair({required this.name, required this.original, required this.formatted});
+
+  final String name;
+  final String original;
+  final String formatted;
+}
+
+final FileContentPair dartContentPair = FileContentPair(
+  name: 'format_test.dart',
+  original: 'enum \n\nfoo {\n  entry1,\n  entry2,\n}',
+  formatted: 'enum foo { entry1, entry2 }\n',
+);
+
+class TestFileFixture {
+  TestFileFixture(this.filePairs, this.baseDir) {
+    for (final FileContentPair filePair in filePairs) {
+      final io.File file = io.File(path.join(baseDir.path, filePair.name));
+      file.writeAsStringSync(filePair.original);
+      files.add(file);
+    }
+  }
+
+  final List<io.File> files = <io.File>[];
+  final io.Directory baseDir;
+  final List<FileContentPair> filePairs;
+
+  void gitAdd() {
+    final List<String> args = <String>['add'];
+    for (final io.File file in files) {
+      args.add(file.path);
+    }
+
+    io.Process.runSync('git', args);
+  }
+
+  void gitRemove() {
+    final List<String> args = <String>['rm', '-f'];
+    for (final io.File file in files) {
+      args.add(file.path);
+    }
+    io.Process.runSync('git', args);
+  }
+
+  Iterable<FileContentPair> getFileContents() {
+    final List<FileContentPair> results = <FileContentPair>[];
+    for (int i = 0; i < files.length; i++) {
+      final io.File file = files[i];
+      final FileContentPair filePair = filePairs[i];
+      final String content = file.readAsStringSync().replaceAll('\r\n', '\n');
+      results.add(
+        FileContentPair(name: filePair.name, original: content, formatted: filePair.formatted),
+      );
+    }
+    return results;
+  }
+}
+
+void main() {
+  final io.File script = io.File(path.current).absolute;
+  final io.Directory flutterRoot = script.parent.parent;
+  final String formatterPath = path.join(
+    flutterRoot.path,
+    'dev',
+    'tools',
+    'format.${io.Platform.isWindows ? 'bat' : 'sh'}',
+  );
+
+  test('Can fix Dart formatting errors', () {
+    final TestFileFixture fixture = TestFileFixture(<FileContentPair>[
+      dartContentPair,
+    ], flutterRoot);
+    try {
+      fixture.gitAdd();
+      io.Process.runSync(formatterPath, <String>['--fix'], workingDirectory: flutterRoot.path);
+
+      final Iterable<FileContentPair> files = fixture.getFileContents();
+      for (final FileContentPair pair in files) {
+        expect(pair.original, equals(pair.formatted));
+      }
+    } finally {
+      fixture.gitRemove();
+    }
+  });
+}