Suggest the Characters API when completing callbacks for handling user-generated text

[InMatrix]

This is a feature request for the Dart Analyzer to augment its current completion behavior for certain known callbacks in Flutter that handle user-generated text (e.g., https://api.flutter.dev/flutter/material/TextField/onChanged.html).

Background

The characters package was recently introduced to address Dart String's limitations of manipulating extended grapheme clusters (dart-lang/language#34). However, it requires the user to get out of their way to look for it and add it to their projects. This barrier is likely to cause continued use of the String API in cases where the characters package ought to be used to avoid breaking emojis and non-English text.

Request

As part of a larger plan to make the Characters API more discoverable when writing text manipulation code, the Dart Analyzer could suggest the API when autocompleting the callback template for handling user entered text. For example everything in this snippet after the user autocompletes on onChanged can potentially be populated for them:

TextField(
  onChanged: (String value) {
  // Converting String to Characters to handle emojis 
  // and non-English characters more robustly.
  var myText = value.characters;     
  // Do something with myText 
  }
)

This request, if accepted, depends on exposing the Characters package in Flutter's public API as tracked here: flutter/flutter#55593.

[InMatrix]

The dependency flutter/flutter#55593 has been satisfied. Is there any chance to increase the priority of this issue?

[bwilkerson]

I'm guessing that String.characters is an extension method. If that's the case then another aspect of this would be to improve analyzer's ability to suggest extension methods, which at the moment is very limited.

@devoncarew For the priority question.

[bwilkerson]

If we do something here, we should consider adding an annotation that can be used to mark such APIs so that the system is more general.

[InMatrix]

If we do something here, we should consider adding an annotation that can be used to mark such APIs so that the system is more general.

I like the idea. It will allow anyone writing a text input widget to take advantage of this auto completion feature.