universal_spell_check

Spell checking for Flutter TextFields on every platform.

Flutter's built-in spell check (SpellCheckConfiguration + DefaultSpellCheckService) only works on Android and iOS. Web, macOS, Windows and Linux get nothing. This is flutter/flutter#40682. This package adds a SpellCheckService that works on all six platforms and plugs straight into the existing Flutter API.

Platform	Engine	Notes
Android	Flutter DefaultSpellCheckService	Uses the system spell checker service
iOS	Flutter DefaultSpellCheckService	Uses UITextChecker
macOS 10.15+	NSSpellChecker (Swift)	Every language macOS has a dictionary for
Windows 8+	ISpellChecker (C++)	Every language pack installed on Windows
Linux	Enchant-2 (C), loaded with dlopen	Needs libenchant-2-2 plus e.g. hunspell-en-us. Without them it reports unavailable and does not crash
Web	Pure-Dart Hunspell engine	Bundled en_US dictionary. Any other Hunspell dictionary can be loaded from assets or a URL

With the default SpellCheckBackend.auto, a desktop OS that cannot check a locale falls back to the Hunspell engine if a dictionary exists for it (en_US ships in the package).

Install

dependencies:
  universal_spell_check: ^0.1.0

Usage

import 'package:universal_spell_check/universal_spell_check.dart';

TextField(
  spellCheckConfiguration: UniversalSpellCheck.configuration(),
  // Right-click (desktop/web) or long-press menu with suggestions + "Ignore":
  contextMenuBuilder: UniversalSpellCheck.contextMenuBuilder,
)

On the web, call this once at startup so right-click opens Flutter's menu (with suggestions) and not the browser's:

await UniversalSpellCheck.useFlutterContextMenuOnWeb();

Using only the service

TextField(
  spellCheckConfiguration: SpellCheckConfiguration(
    spellCheckService: UniversalSpellCheckService.instance,
    misspelledTextStyle: UniversalSpellCheck.misspelledTextStyle,
  ),
)

Options

final service = UniversalSpellCheckService(
  backend: SpellCheckBackend.auto,      // auto | native | hunspell
  hunspellDictionaries: {
    'en': const HunspellSource.bundledEnUS(),
    'de': const HunspellSource.asset('assets/de_DE.aff', 'assets/de_DE.dic'),
    'fr': HunspellSource.url(Uri.parse('https://example.com/fr.aff'),
                             Uri.parse('https://example.com/fr.dic')),
  },
  maxSuggestions: 5,
  useIsolate: true,                     // Hunspell off the UI isolate (native)
  ignoredWords: ['Flutter'],
);

await service.availability(const Locale('de', 'DE')); // which engine, which dictionary
await service.warmUp(const Locale('en', 'US'));        // parse the dictionary early
service.ignoreWord('Manish');

Create a service once, for example in a State or as a global. Do not create one inside build().

The Hunspell engine on its own

final dict = HunspellDictionary.parse(affText, dicText);
final hunspell = Hunspell(dict);
hunspell.check('colour');          // false with en_US
hunspell.suggest('recieve');       // [receive, relieve]

final checker = HunspellSpellChecker(const HunspellSource.bundledEnUS());
await checker.check('I recieve teh mail'); // List<SpellCheckRange>

Supported .aff features: SET, FLAG (char/long/num/UTF-8), AF, PFX/SFX (conditions, strip, cross product, continuation classes), TRY, KEY, REP, MAP, ICONV/OCONV, KEEPCASE, NOSUGGEST, FORBIDDENWORD, NEEDAFFIX, ONLYINCOMPOUND, COMPOUNDRULE, COMPOUNDMIN, WORDCHARS, BREAK.

Limitations

• Web: browsers give web apps no way to query their own spell checker, so the web uses the bundled Hunspell engine. Dart on the web has no isolates, so the engine runs on the main thread and yields between chunks of work. Parsing en_US takes a few hundred milliseconds, once. The dictionary adds about 540 KB to the web build (about 190 KB gzipped).
• Desktop suggestions: Flutter itself only opens its spell-check toolbar when you tap a word on Android/iOS. On desktop and web, use contextMenuBuilder (right-click) to show suggestions.
• Hunspell coverage: there is no morphological analysis, no COMPOUNDFLAG-style compounding (only COMPOUNDRULE), no CHECKSHARPS and no PHONE table. The order of suggestions can differ from C Hunspell. en_US is fully supported.
• Ignore list: it lasts for the session only, and it is not written to the OS dictionary.
• Screenshots: the example's integration_test/screenshot_test.dart regenerates the macOS images from the real NSSpellChecker.
• Windows/Linux: the native code is written against the documented APIs, but this release was built and run only on macOS and the web. The Linux C code was syntax-checked against real GLib headers.

Dictionary license

dictionaries/en_US.* comes from SCOWL (wordlist.aspell.net, 2020.12.07, size 60) and uses its own permissive license, in dictionaries/LICENSE-en_US.txt. The package code is MIT.