Doctor summary

Doctor summary (to see all details, run flutter doctor -v):
[✓] Flutter (Channel stable, 1.22.1, on Linux, locale en_US.UTF-8)
[✓] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
[✓] Android Studio (version 4.0)
[✓] VS Code (version 1.50.0)
[✓] Connected device (1 available)

Steps to Reproduce

1. Create TextField as follows:

      TextField(
              maxLength: 5,
            ),

or

      TextField(
              maxLength: 5,
              inputFormatters: [LengthLimitingTextInputFormatter(5)],
            ),

2. Start typing some text

Expected results:

• TextField allows to enter only maxLength characters

Actual results:

• it's possible to enter more than maxLength characters

Looks like it's related to the following change introduced in flutter 1.22 - https://github.com/flutter/flutter/pull/63754/files

packages/flutter/lib/src/services/text_formatter.dart

  ///
  /// ### Composing text behaviors
  ///
  /// There is no guarantee for the final value before the composing ends.
  /// So while the value is composing, the constraint of [maxLength] will be
  /// temporary lifted until the composing ends.
  ///
  /// In addition, if the current value already reached the [maxLength],
  /// composing is not allowed.