dart format causes lines to exceed 80 character limit in Dart 3.7

[felangel]

Description

Running dart format with Dart 3.7 reformats code such that some lines exceed the 80 character limit and trigger the lines_longer_than_80_chars lint. I would expect the new formatter to adhere to the max line length configured (by default 80 characters).

Reproduction Steps

pubspec.yaml

name: example
publish_to: none

environment:
  sdk: ^3.7.0

dev_dependencies:
  mocktail: ^1.0.0
  test: ^1.0.0

analysis_options.yaml

linter:
  rules:
    - lines_longer_than_80_chars
formatter:
    page_width: 80

main.dart

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

import 'package:mocktail/mocktail.dart';
import 'package:test/test.dart';

class BuildProcess {
  Stream<List<int>> get stdout => throw UnimplementedError();
}

class MockBuildProcess extends Mock implements BuildProcess {}

void main() {
  group('Root Group', () {
    group('Nested Group', () {
      test('Test', () {
        final buildProcess = MockBuildProcess();
        when(() => buildProcess.stdout).thenAnswer(
          (_) => Stream.fromIterable(
            [
              '[  +10 ms] Generating /Users/bryanoltman/Documents/sandbox/notification_extension/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java',
              '[  +50 ms] executing: [/Users/bryanoltman/Documents/sandbox/notification_extension/ios/] /usr/bin/arch -arm64e xcrun xcodebuild -list',
              '[+32333 ms] Command line invocation:',
              '[   +6 ms] Exit code 0 from: mkfifo /var/folders/64/dj6krpq1093dmx08dy4r1cwh0000gn/T/flutter_tools.WDvaE9/flutter_ios_build_temp_dirUAyStV/pipe_to_stdout',
              '[+62601 ms] Running Xcode build... (completed in 62.6s)',
              '[        ]  └─Compiling, linking and signing...',
              '[+5925 ms] Command line invocation:',
              '/Applications/Xcode.app/Contents/Developer/usr/bin/xcodebuild -configuration Release VERBOSE_SCRIPT_LOGGING=YES -workspace Runner.xcworkspace -scheme Runner -sdk iphoneos -destination generic/platform=iOS SCRIPT_OUTPUT_STREAM_FILE=/var/folders/64/dj6krpq1093dmx08dy4r1cwh0000gn/T/flutter_tools.WDvaE9/flutter_ios_build_temp_dirUAyStV/pipe_to_stdout -resultBundlePath /var/folders/64/dj6krpq1093dmx08dy4r1cwh0000gn/T/flutter_tools.WDvaE9/flutter_ios_build_temp_dirUAyStV/temporary_xcresult_bundle -resultBundleVersion 3 FLUTTER_SUPPRESS_ANALYTICS=true COMPILER_INDEX_STORE_ENABLE=NO -archivePath /Users/bryanoltman/Documents/sandbox/notification_extension/build/ios/archive/Runner archive',
            ]
            .map((line) => 'prefix$line${Platform.lineTerminator}')
            .map(utf8.encode),
          ),
        );
      });
    });
  });
}

1. Run dart format

$ dart format .
Formatted main.dart
Formatted 1 file (1 changed) in 0.12 seconds.

1. Observe the reformatted code now exceeds 80 characters

$ dart analyze .           
Analyzing ....                         0.5s

   info • main.dart:29:81 • The line length exceeds the 80-character limit. Try breaking the line across multiple lines. • lines_longer_than_80_chars

1 issue found.

The diff from running dart format:

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

import 'package:mocktail/mocktail.dart';
import 'package:test/test.dart';

class BuildProcess {
  Stream<List<int>> get stdout => throw UnimplementedError();
}

class MockBuildProcess extends Mock implements BuildProcess {}

void main() {
  group('Root Group', () {
    group('Nested Group', () {
      test('Test', () {
        final buildProcess = MockBuildProcess();
        when(() => buildProcess.stdout).thenAnswer(
          (_) => Stream.fromIterable(
            [
              '[  +10 ms] Generating /Users/bryanoltman/Documents/sandbox/notification_extension/android/app/src/main/java/io/flutter/plugins/GeneratedPluginRegistrant.java',
              '[  +50 ms] executing: [/Users/bryanoltman/Documents/sandbox/notification_extension/ios/] /usr/bin/arch -arm64e xcrun xcodebuild -list',
              '[+32333 ms] Command line invocation:',
              '[   +6 ms] Exit code 0 from: mkfifo /var/folders/64/dj6krpq1093dmx08dy4r1cwh0000gn/T/flutter_tools.WDvaE9/flutter_ios_build_temp_dirUAyStV/pipe_to_stdout',
              '[+62601 ms] Running Xcode build... (completed in 62.6s)',
              '[        ]  └─Compiling, linking and signing...',
              '[+5925 ms] Command line invocation:',
              '/Applications/Xcode.app/Contents/Developer/usr/bin/xcodebuild -configuration Release VERBOSE_SCRIPT_LOGGING=YES -workspace Runner.xcworkspace -scheme Runner -sdk iphoneos -destination generic/platform=iOS SCRIPT_OUTPUT_STREAM_FILE=/var/folders/64/dj6krpq1093dmx08dy4r1cwh0000gn/T/flutter_tools.WDvaE9/flutter_ios_build_temp_dirUAyStV/pipe_to_stdout -resultBundlePath /var/folders/64/dj6krpq1093dmx08dy4r1cwh0000gn/T/flutter_tools.WDvaE9/flutter_ios_build_temp_dirUAyStV/temporary_xcresult_bundle -resultBundleVersion 3 FLUTTER_SUPPRESS_ANALYTICS=true COMPILER_INDEX_STORE_ENABLE=NO -archivePath /Users/bryanoltman/Documents/sandbox/notification_extension/build/ios/archive/Runner archive',
-            ]
-            .map((line) => 'prefix$line${Platform.lineTerminator}')
-            .map(utf8.encode),
+            ].map((line) => 'prefix$line${Platform.lineTerminator}').map(utf8.encode),
          ),
        );
      });
    });
  });
}
}

$ dart --version
Dart SDK version: 3.7.0 (stable) (Wed Feb 5 04:53:58 2025 -0800) on "macos_arm64"

[felangel]

Tagging @munificent since I believe you were heavily involved in the new Dart formatter changes.

[ChunhThanhDe]

I had the same issue and reported it on Flutter, hope it will be fixed soon

flutter/flutter#163827