Introduce `MaxLengthEnforcement` (#68086)

packages/flutter/lib/src/cupertino/text_field.dart

@@ -260,6 +260,7 @@ class CupertinoTextField extends StatefulWidget {
     this.expands = false,
     this.maxLength,
     this.maxLengthEnforced = true,
+    this.maxLengthEnforcement,
     this.onChanged,
     this.onEditingComplete,
     this.onSubmitted,
@@ -292,6 +293,10 @@ class CupertinoTextField extends StatefulWidget {
        smartQuotesType = smartQuotesType ?? (obscureText ? SmartQuotesType.disabled : SmartQuotesType.enabled),
        assert(enableSuggestions != null),
        assert(maxLengthEnforced != null),
+       assert(
+         maxLengthEnforced || maxLengthEnforcement == null,
+         'maxLengthEnforced is deprecated, use only maxLengthEnforcement',
+       ),
        assert(scrollPadding != null),
        assert(dragStartBehavior != null),
        assert(selectionHeightStyle != null),
@@ -402,6 +407,7 @@ class CupertinoTextField extends StatefulWidget {
     this.expands = false,
     this.maxLength,
     this.maxLengthEnforced = true,
+    this.maxLengthEnforcement,
     this.onChanged,
     this.onEditingComplete,
     this.onSubmitted,
@@ -434,6 +440,10 @@ class CupertinoTextField extends StatefulWidget {
        smartQuotesType = smartQuotesType ?? (obscureText ? SmartQuotesType.disabled : SmartQuotesType.enabled),
        assert(enableSuggestions != null),
        assert(maxLengthEnforced != null),
+       assert(
+         maxLengthEnforced || maxLengthEnforcement == null,
+         'maxLengthEnforced is deprecated, use only maxLengthEnforcement',
+       ),
        assert(scrollPadding != null),
        assert(dragStartBehavior != null),
        assert(selectionHeightStyle != null),
@@ -619,12 +629,13 @@ class CupertinoTextField extends StatefulWidget {
   /// The maximum number of characters (Unicode scalar values) to allow in the
   /// text field.
   ///
-  /// If set, a character counter will be displayed below the
-  /// field, showing how many characters have been entered and how many are
-  /// allowed. After [maxLength] characters have been input, additional input
-  /// is ignored, unless [maxLengthEnforced] is set to false. The TextField
-  /// enforces the length with a [LengthLimitingTextInputFormatter], which is
-  /// evaluated after the supplied [inputFormatters], if any.
+  /// After [maxLength] characters have been input, additional input
+  /// is ignored, unless [maxLengthEnforcement] is set to
+  /// [MaxLengthEnforcement.none].
+  ///
+  /// The TextField enforces the length with a
+  /// [LengthLimitingTextInputFormatter], which is evaluated after the supplied
+  /// [inputFormatters], if any.
   ///
   /// This value must be either null or greater than zero. If set to null
   /// (the default), there is no limit to the number of characters allowed.
@@ -635,14 +646,23 @@ class CupertinoTextField extends StatefulWidget {
   /// {@macro flutter.services.lengthLimitingTextInputFormatter.maxLength}
   final int? maxLength;
 
+  /// If [maxLength] is set, [maxLengthEnforced] indicates whether or not to
+  /// enforce the limit.
+  ///
   /// If true, prevents the field from allowing more than [maxLength]
   /// characters.
-  ///
-  /// If [maxLength] is set, [maxLengthEnforced] indicates whether or not to
-  /// enforce the limit, or merely provide a character counter and warning when
-  /// [maxLength] is exceeded.
   final bool maxLengthEnforced;
 
+  /// Determines how the [maxLength] limit should be enforced.
+  ///
+  /// If [MaxLengthEnforcement.none] is set, additional input beyond [maxLength]
+  /// will not be enforced by the limit.
+  ///
+  /// {@macro flutter.services.textFormatter.effectiveMaxLengthEnforcement}
+  ///
+  /// {@macro flutter.services.textFormatter.maxLengthEnforcement}
+  final MaxLengthEnforcement? maxLengthEnforcement;
+
   /// {@macro flutter.widgets.editableText.onChanged}
   final ValueChanged<String>? onChanged;
 
@@ -761,6 +781,7 @@ class CupertinoTextField extends StatefulWidget {
     properties.add(DiagnosticsProperty<bool>('expands', expands, defaultValue: false));
     properties.add(IntProperty('maxLength', maxLength, defaultValue: null));
     properties.add(FlagProperty('maxLengthEnforced', value: maxLengthEnforced, ifTrue: 'max length enforced'));
+    properties.add(EnumProperty<MaxLengthEnforcement>('maxLengthEnforcement', maxLengthEnforcement, defaultValue: null));
     properties.add(DoubleProperty('cursorWidth', cursorWidth, defaultValue: 2.0));
     properties.add(DoubleProperty('cursorHeight', cursorHeight, defaultValue: null));
     properties.add(DiagnosticsProperty<Radius>('cursorRadius', cursorRadius, defaultValue: null));
@@ -783,6 +804,9 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with Restoratio
   FocusNode? _focusNode;
   FocusNode get _effectiveFocusNode => widget.focusNode ?? (_focusNode ??= FocusNode());
 
+  MaxLengthEnforcement get _effectiveMaxLengthEnforcement => widget.maxLengthEnforcement
+    ?? LengthLimitingTextInputFormatter.inferredDefaultMaxLengthEnforcement;
+
   bool _showSelectionHandles = false;
 
   late _CupertinoTextFieldSelectionGestureDetectorBuilder _selectionGestureDetectorBuilder;
@@ -1030,7 +1054,11 @@ class _CupertinoTextFieldState extends State<CupertinoTextField> with Restoratio
     final Offset cursorOffset = Offset(_iOSHorizontalCursorOffsetPixels / MediaQuery.of(context).devicePixelRatio, 0);
     final List<TextInputFormatter> formatters = <TextInputFormatter>[
       ...?widget.inputFormatters,
-      if (widget.maxLength != null && widget.maxLengthEnforced) LengthLimitingTextInputFormatter(widget.maxLength)
+      if (widget.maxLength != null && widget.maxLengthEnforced)
+        LengthLimitingTextInputFormatter(
+          widget.maxLength,
+          maxLengthEnforcement: _effectiveMaxLengthEnforcement,
+        ),
     ];
     final CupertinoThemeData themeData = CupertinoTheme.of(context);
 

packages/flutter/lib/src/material/text_field.dart

@@ -302,10 +302,11 @@ class TextField extends StatefulWidget {
   /// [TextField.noMaxLength] then only the current length is displayed.
   ///
   /// After [maxLength] characters have been input, additional input
-  /// is ignored, unless [maxLengthEnforced] is set to false. The text field
-  /// enforces the length with a [LengthLimitingTextInputFormatter], which is
-  /// evaluated after the supplied [inputFormatters], if any. The [maxLength]
-  /// value must be either null or greater than zero.
+  /// is ignored, unless [maxLengthEnforcement] is set to
+  /// [MaxLengthEnforcement.none].
+  /// The text field enforces the length with a [LengthLimitingTextInputFormatter],
+  /// which is evaluated after the supplied [inputFormatters], if any.
+  /// The [maxLength] value must be either null or greater than zero.
   ///
   /// If [maxLengthEnforced] is set to false, then more than [maxLength]
   /// characters may be entered, and the error counter and divider will
@@ -356,6 +357,7 @@ class TextField extends StatefulWidget {
     this.expands = false,
     this.maxLength,
     this.maxLengthEnforced = true,
+    this.maxLengthEnforcement,
     this.onChanged,
     this.onEditingComplete,
     this.onSubmitted,
@@ -391,6 +393,10 @@ class TextField extends StatefulWidget {
        assert(enableSuggestions != null),
        assert(enableInteractiveSelection != null),
        assert(maxLengthEnforced != null),
+       assert(
+         maxLengthEnforced || maxLengthEnforcement == null,
+         'maxLengthEnforced is deprecated, use only maxLengthEnforcement',
+       ),
        assert(scrollPadding != null),
        assert(dragStartBehavior != null),
        assert(selectionHeightStyle != null),
@@ -568,9 +574,11 @@ class TextField extends StatefulWidget {
   /// to [TextField.noMaxLength] then only the current character count is displayed.
   ///
   /// After [maxLength] characters have been input, additional input
-  /// is ignored, unless [maxLengthEnforced] is set to false. The text field
-  /// enforces the length with a [LengthLimitingTextInputFormatter], which is
-  /// evaluated after the supplied [inputFormatters], if any.
+  /// is ignored, unless [maxLengthEnforcement] is set to
+  /// [MaxLengthEnforcement.none].
+  ///
+  /// The text field enforces the length with a [LengthLimitingTextInputFormatter],
+  /// which is evaluated after the supplied [inputFormatters], if any.
   ///
   /// This value must be either null, [TextField.noMaxLength], or greater than 0.
   /// If null (the default) then there is no limit to the number of characters
@@ -580,7 +588,8 @@ class TextField extends StatefulWidget {
   /// Whitespace characters (e.g. newline, space, tab) are included in the
   /// character count.
   ///
-  /// If [maxLengthEnforced] is set to false, then more than [maxLength]
+  /// If [maxLengthEnforced] is set to false or [maxLengthEnforcement] is
+  /// [MaxLengthEnforcement.none], then more than [maxLength]
   /// characters may be entered, but the error counter and divider will switch
   /// to the [decoration]'s [InputDecoration.errorStyle] when the limit is
   /// exceeded.
@@ -588,14 +597,21 @@ class TextField extends StatefulWidget {
   /// {@macro flutter.services.lengthLimitingTextInputFormatter.maxLength}
   final int? maxLength;
 
-  /// If true, prevents the field from allowing more than [maxLength]
-  /// characters.
-  ///
   /// If [maxLength] is set, [maxLengthEnforced] indicates whether or not to
   /// enforce the limit, or merely provide a character counter and warning when
   /// [maxLength] is exceeded.
+  ///
+  /// If true, prevents the field from allowing more than [maxLength]
+  /// characters.
   final bool maxLengthEnforced;
 
+  /// Determines how the [maxLength] limit should be enforced.
+  ///
+  /// {@macro flutter.services.textFormatter.effectiveMaxLengthEnforcement}
+  ///
+  /// {@macro flutter.services.textFormatter.maxLengthEnforcement}
+  final MaxLengthEnforcement? maxLengthEnforcement;
+
   /// {@macro flutter.widgets.editableText.onChanged}
   ///
   /// See also:
@@ -810,6 +826,7 @@ class TextField extends StatefulWidget {
     properties.add(DiagnosticsProperty<bool>('expands', expands, defaultValue: false));
     properties.add(IntProperty('maxLength', maxLength, defaultValue: null));
     properties.add(FlagProperty('maxLengthEnforced', value: maxLengthEnforced, defaultValue: true, ifFalse: 'maxLength not enforced'));
+    properties.add(EnumProperty<MaxLengthEnforcement>('maxLengthEnforcement', maxLengthEnforcement, defaultValue: null));
     properties.add(EnumProperty<TextInputAction>('textInputAction', textInputAction, defaultValue: null));
     properties.add(EnumProperty<TextCapitalization>('textCapitalization', textCapitalization, defaultValue: TextCapitalization.none));
     properties.add(EnumProperty<TextAlign>('textAlign', textAlign, defaultValue: TextAlign.start));
@@ -835,6 +852,9 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
   FocusNode? _focusNode;
   FocusNode get _effectiveFocusNode => widget.focusNode ?? (_focusNode ??= FocusNode());
 
+  MaxLengthEnforcement get _effectiveMaxLengthEnforcement => widget.maxLengthEnforcement
+    ?? LengthLimitingTextInputFormatter.inferredDefaultMaxLengthEnforcement;
+
   bool _isHovering = false;
 
   bool get needsCounter => widget.maxLength != null
@@ -1095,7 +1115,11 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
     final FocusNode focusNode = _effectiveFocusNode;
     final List<TextInputFormatter> formatters = <TextInputFormatter>[
       ...?widget.inputFormatters,
-      if (widget.maxLength != null && widget.maxLengthEnforced) LengthLimitingTextInputFormatter(widget.maxLength)
+      if (widget.maxLength != null && widget.maxLengthEnforced)
+        LengthLimitingTextInputFormatter(
+          widget.maxLength,
+          maxLengthEnforcement: _effectiveMaxLengthEnforcement,
+        ),
     ];
 
     TextSelectionControls? textSelectionControls = widget.selectionControls;
@@ -1226,6 +1250,16 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
       },
     );
 
+    final int? semanticsMaxValueLength;
+    if (widget.maxLengthEnforced &&
+      _effectiveMaxLengthEnforcement != MaxLengthEnforcement.none &&
+      widget.maxLength != null &&
+      widget.maxLength! > 0) {
+      semanticsMaxValueLength = widget.maxLength;
+    } else {
+      semanticsMaxValueLength = null;
+    }
+
     return MouseRegion(
       cursor: effectiveMouseCursor,
       onEnter: (PointerEnterEvent event) => _handleHover(true),
@@ -1236,9 +1270,7 @@ class _TextFieldState extends State<TextField> with RestorationMixin implements
           animation: controller, // changes the _currentLength
           builder: (BuildContext context, Widget? child) {
             return Semantics(
-              maxValueLength: widget.maxLengthEnforced && widget.maxLength != null && widget.maxLength! > 0
-                  ? widget.maxLength
-                  : null,
+              maxValueLength: semanticsMaxValueLength,
               currentValueLength: _currentLength,
               onTap: () {
                 if (!_effectiveController.selection.isValid)

packages/flutter/lib/src/material/text_form_field.dart

@@ -163,6 +163,7 @@ class TextFormField extends FormField<String> {
     )
     bool autovalidate = false,
     bool maxLengthEnforced = true,
+    MaxLengthEnforcement? maxLengthEnforcement,
     int? maxLines = 1,
     int? minLines,
     bool expands = false,
@@ -202,6 +203,10 @@ class TextFormField extends FormField<String> {
          'autovalidate and autovalidateMode should not be used together.'
        ),
        assert(maxLengthEnforced != null),
+       assert(
+         maxLengthEnforced || maxLengthEnforcement == null,
+         'maxLengthEnforced is deprecated, use only maxLengthEnforcement',
+       ),
        assert(scrollPadding != null),
        assert(maxLines == null || maxLines > 0),
        assert(minLines == null || minLines > 0),
@@ -259,6 +264,7 @@ class TextFormField extends FormField<String> {
            smartQuotesType: smartQuotesType ?? (obscureText ? SmartQuotesType.disabled : SmartQuotesType.enabled),
            enableSuggestions: enableSuggestions,
            maxLengthEnforced: maxLengthEnforced,
+           maxLengthEnforcement: maxLengthEnforcement,
            maxLines: maxLines,
            minLines: minLines,
            expands: expands,

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

@@ -11,6 +11,49 @@ import 'package:flutter/foundation.dart';
 import 'text_editing.dart';
 import 'text_input.dart';
 
+/// {@template flutter.services.textFormatter.maxLengthEnforcement}
+/// ### [MaxLengthEnforcement.enforced] versus
+/// [MaxLengthEnforcement.truncateAfterCompositionEnds]
+///
+/// Both [MaxLengthEnforcement.enforced] and
+/// [MaxLengthEnforcement.truncateAfterCompositionEnds] make sure the final
+/// length of the text does not exceed the max length specified. The difference
+/// is that [MaxLengthEnforcement.enforced] truncates all text while
+/// [MaxLengthEnforcement.truncateAfterCompositionEnds] allows composing text to
+/// exceed the limit. Allowing this "placeholder" composing text to exceed the
+/// limit may provide a better user experience on some platforms for entering
+/// ideographic characters (e.g. CJK characters) via composing on phonetic
+/// keyboards.
+///
+/// Some input methods (Gboard on Android for example) initiate text composition
+/// even for Latin characters, in which case the best experience may be to
+/// truncate those composing characters with [MaxLengthEnforcement.enforced].
+///
+/// In fields that strictly support only a small subset of characters, such as
+/// verification code fields, [MaxLengthEnforcement.enforced] may provide the
+/// best experience.
+/// {@endtemplate}
+///
+/// See also:
+///
+///  * [TextField.maxLengthEnforcement] which is used in conjunction with
+///  [TextField.maxLength] to limit the length of user input. [TextField] also
+///  provides a character counter to provide visual feedback.
+enum MaxLengthEnforcement {
+  /// No enforcement applied to the editing value. It's possible to exceed the
+  /// max length.
+  none,
+
+  /// Keep the length of the text input from exceeding the max length even when
+  /// the text has an unfinished composing region.
+  enforced,
+
+  /// Users can still input text if the current value is composing even after
+  /// reaching the max length limit. After composing ends, the value will be
+  /// truncated.
+  truncateAfterCompositionEnds,
+}
+
 /// A [TextInputFormatter] can be optionally injected into an [EditableText]
 /// to provide as-you-type validation and formatting of the text being edited.
 ///
@@ -322,8 +365,10 @@ class LengthLimitingTextInputFormatter extends TextInputFormatter {
   ///
   /// The [maxLength] must be null, -1 or greater than zero. If it is null or -1
   /// then no limit is enforced.
-  LengthLimitingTextInputFormatter(this.maxLength)
-    : assert(maxLength == null || maxLength == -1 || maxLength > 0);
+  LengthLimitingTextInputFormatter(
+    this.maxLength, {
+    this.maxLengthEnforcement,
+  }) : assert(maxLength == null || maxLength == -1 || maxLength > 0);
 
   /// The limit on the number of user-perceived characters that this formatter
   /// will allow.
@@ -363,6 +408,47 @@ class LengthLimitingTextInputFormatter extends TextInputFormatter {
   /// composing is not allowed.
   final int? maxLength;
 
+  /// Determines how the [maxLength] limit should be enforced.
+  ///
+  /// Defaults to [MaxLengthEnforcement.enforced].
+  ///
+  /// {@macro flutter.services.textFormatter.maxLengthEnforcement}
+  final MaxLengthEnforcement? maxLengthEnforcement;
+
+  /// Return an effective [MaxLengthEnforcement] according the target platform.
+  ///
+  /// {@template flutter.services.textFormatter.effectiveMaxLengthEnforcement}
+  /// ### Platform specific behaviors
+  ///
+  /// Different platforms follow different behaviors by default, according to
+  /// their native behavior.
+  ///  * Android, Windows: [MaxLengthEnforcement.enforced]. The native behavior
+  ///    of these platforms is enforced. The composing will be handled by the
+  ///    IME while users are entering CJK characters.
+  ///  * iOS: [MaxLengthEnforcement.truncateAfterCompositionEnds]. iOS has no
+  ///    default behavior and it requires users implement the behavior
+  ///    themselves. Allow the composition to exceed to avoid breaking CJK input.
+  ///  * Web, macOS, linux, fuchsia:
+  ///    [MaxLengthEnforcement.truncateAfterCompositionEnds]. These platforms
+  ///    allow the composition to exceed by default.
+  /// {@endtemplate}
+  static MaxLengthEnforcement get inferredDefaultMaxLengthEnforcement {
+    if (kIsWeb) {
+      return MaxLengthEnforcement.truncateAfterCompositionEnds;
+    } else {
+      switch (defaultTargetPlatform) {
+        case TargetPlatform.android:
+        case TargetPlatform.windows:
+          return MaxLengthEnforcement.enforced;
+        case TargetPlatform.iOS:
+        case TargetPlatform.macOS:
+        case TargetPlatform.linux:
+        case TargetPlatform.fuchsia:
+          return MaxLengthEnforcement.truncateAfterCompositionEnds;
+      }
+    }
+  }
+
   /// Truncate the given TextEditingValue to maxLength user-perceived
   /// characters.
   ///
@@ -376,13 +462,19 @@ class LengthLimitingTextInputFormatter extends TextInputFormatter {
       iterator.expandNext(maxLength);
     }
     final String truncated = iterator.current;
+
     return TextEditingValue(
       text: truncated,
       selection: value.selection.copyWith(
         baseOffset: math.min(value.selection.start, truncated.length),
         extentOffset: math.min(value.selection.end, truncated.length),
       ),
-      composing: TextRange.empty,
+      composing: !value.composing.isCollapsed && truncated.length > value.composing.start
+        ? TextRange(
+            start: value.composing.start,
+            end: math.min(value.composing.end, truncated.length),
+          )
+        : TextRange.empty,
     );
   }
 
@@ -393,20 +485,43 @@ class LengthLimitingTextInputFormatter extends TextInputFormatter {
   ) {
     final int? maxLength = this.maxLength;
 
-    if (maxLength == null || maxLength == -1 || newValue.text.characters.length <= maxLength)
+    if (maxLength == null ||
+      maxLength == -1 ||
+      newValue.text.characters.length <= maxLength) {
       return newValue;
+    }
 
     assert(maxLength > 0);
 
-    // If already at the maximum and tried to enter even more, keep the old
-    // value.
-    if (oldValue.text.characters.length == maxLength && !oldValue.composing.isValid) {
+    switch (maxLengthEnforcement ?? inferredDefaultMaxLengthEnforcement) {
+      case MaxLengthEnforcement.none:
+        return newValue;
+      case MaxLengthEnforcement.enforced:
+        // If already at the maximum and tried to enter even more, and has no
+        // selection, keep the old value.
+        if (oldValue.text.characters.length == maxLength && !oldValue.selection.isValid) {
+          return oldValue;
+        }
+
+        // Enforced to return a truncated value.
+        return truncate(newValue, maxLength);
+      case MaxLengthEnforcement.truncateAfterCompositionEnds:
+        // If already at the maximum and tried to enter even more, and the old
+        // value is not composing, keep the old value.
+        if (oldValue.text.characters.length == maxLength &&
+          !oldValue.composing.isValid) {
           return oldValue;
         }
 
         // Temporarily exempt `newValue` from the maxLength limit if it has a
-    // composing text going, until the composing is finished.
-    return newValue.composing.isValid ? newValue : truncate(newValue, maxLength);
+        // composing text going and no enforcement to the composing value, until
+        // the composing is finished.
+        if (newValue.composing.isValid) {
+          return newValue;
+        }
+
+        return truncate(newValue, maxLength);
+    }
   }
 }
 

packages/flutter/test/cupertino/text_field_test.dart

@@ -4302,4 +4302,126 @@ void main() {
 
     expect(formatters.isEmpty, isTrue);
   });
+
+  group('MaxLengthEnforcement', () {
+    const int maxLength = 5;
+
+    Future<void> setupWidget(
+      WidgetTester tester,
+      MaxLengthEnforcement? enforcement,
+    ) async {
+
+      final Widget widget = CupertinoApp(
+        home: Center(
+          child: CupertinoTextField(
+            maxLength: maxLength,
+            maxLengthEnforcement: enforcement,
+          ),
+        ),
+      );
+
+      await tester.pumpWidget(widget);
+      await tester.pumpAndSettle();
+    }
+
+    testWidgets('using none enforcement.', (WidgetTester tester) async {
+      const MaxLengthEnforcement enforcement = MaxLengthEnforcement.none;
+
+      await setupWidget(tester, enforcement);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.text, 'abc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcdef');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcdef');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    testWidgets('using enforced.', (WidgetTester tester) async {
+      const MaxLengthEnforcement enforcement = MaxLengthEnforcement.enforced;
+
+      await setupWidget(tester, enforcement);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.text, 'abc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+    });
+
+    testWidgets('using truncateAfterCompositionEnds.', (WidgetTester tester) async {
+      const MaxLengthEnforcement enforcement = MaxLengthEnforcement.truncateAfterCompositionEnds;
+
+      await setupWidget(tester, enforcement);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.text, 'abc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcdef');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    testWidgets('using default behavior for different platforms.', (WidgetTester tester) async {
+      await setupWidget(tester, null);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊'));
+      expect(state.currentTextEditingValue.text, '侬好啊');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊旁友', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.text, '侬好啊旁友');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊旁友们', composing: TextRange(start: 3, end: 6)));
+      if (kIsWeb ||
+        defaultTargetPlatform == TargetPlatform.iOS ||
+        defaultTargetPlatform == TargetPlatform.macOS ||
+        defaultTargetPlatform == TargetPlatform.linux ||
+        defaultTargetPlatform == TargetPlatform.fuchsia
+      ) {
+        expect(state.currentTextEditingValue.text, '侬好啊旁友们');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+      } else {
+        expect(state.currentTextEditingValue.text, '侬好啊旁友');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+      }
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊旁友'));
+      expect(state.currentTextEditingValue.text, '侬好啊旁友');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+  });
 }

packages/flutter/test/material/text_field_test.dart

@@ -2196,7 +2196,7 @@ void main() {
             TextFormField(
               key: textFieldKey,
               maxLength: 3,
-              maxLengthEnforced: false,
+              maxLengthEnforcement: MaxLengthEnforcement.none,
               decoration: InputDecoration(
                 counterText: '',
                 errorText: errorText,
@@ -3671,7 +3671,7 @@ void main() {
       child: TextField(
         controller: textController,
         maxLength: 10,
-        maxLengthEnforced: false,
+        maxLengthEnforcement: MaxLengthEnforcement.none,
       ),
     ));
 
@@ -3688,7 +3688,7 @@ void main() {
         decoration: const InputDecoration(errorStyle: testStyle),
         controller: textController,
         maxLength: 10,
-        maxLengthEnforced: false,
+        maxLengthEnforcement: MaxLengthEnforcement.none,
       ),
     ));
 
@@ -3718,7 +3718,7 @@ void main() {
         decoration: const InputDecoration(errorStyle: testStyle),
         controller: textController,
         maxLength: 10,
-        maxLengthEnforced: false,
+        maxLengthEnforcement: MaxLengthEnforcement.none,
       ),
     ));
 
@@ -3748,7 +3748,7 @@ void main() {
         decoration: const InputDecoration(errorStyle: testStyle),
         controller: textController,
         maxLength: 10,
-        maxLengthEnforced: false,
+        maxLengthEnforcement: MaxLengthEnforcement.none,
       ),
     ));
 
@@ -7504,7 +7504,7 @@ void main() {
       autocorrect: false,
       maxLines: 10,
       maxLength: 100,
-      maxLengthEnforced: false,
+      maxLengthEnforcement: MaxLengthEnforcement.none,
       smartDashesType: SmartDashesType.disabled,
       smartQuotesType: SmartQuotesType.disabled,
       enabled: false,
@@ -7532,7 +7532,7 @@ void main() {
       'smartQuotesType: disabled',
       'maxLines: 10',
       'maxLength: 100',
-      'maxLength not enforced',
+      'maxLengthEnforcement: none',
       'textInputAction: done',
       'textAlign: end',
       'textDirection: ltr',
@@ -8745,4 +8745,125 @@ void main() {
     // The label will always float above the content.
     expect(tester.getTopLeft(find.text('Label')).dy, 12.0);
   });
+
+  group('MaxLengthEnforcement', () {
+    const int maxLength = 5;
+
+    Future<void> setupWidget(
+      WidgetTester tester,
+      MaxLengthEnforcement? enforcement,
+    ) async {
+      final Widget widget = MaterialApp(
+        home: Material(
+          child: TextField(
+            maxLength: maxLength,
+            maxLengthEnforcement: enforcement,
+          ),
+        ),
+      );
+
+      await tester.pumpWidget(widget);
+      await tester.pumpAndSettle();
+    }
+
+    testWidgets('using none enforcement.', (WidgetTester tester) async {
+      const MaxLengthEnforcement enforcement = MaxLengthEnforcement.none;
+
+      await setupWidget(tester, enforcement);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.text, 'abc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcdef');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcdef');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    testWidgets('using enforced.', (WidgetTester tester) async {
+      const MaxLengthEnforcement enforcement = MaxLengthEnforcement.enforced;
+
+      await setupWidget(tester, enforcement);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.text, 'abc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+    });
+
+    testWidgets('using truncateAfterCompositionEnds.', (WidgetTester tester) async {
+      const MaxLengthEnforcement enforcement = MaxLengthEnforcement.truncateAfterCompositionEnds;
+
+      await setupWidget(tester, enforcement);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.text, 'abc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcdef');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    testWidgets('using default behavior for different platforms.', (WidgetTester tester) async {
+      await setupWidget(tester, null);
+
+      final EditableTextState state = tester.state(find.byType(EditableText));
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊'));
+      expect(state.currentTextEditingValue.text, '侬好啊');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊旁友', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.text, '侬好啊旁友');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊旁友们', composing: TextRange(start: 3, end: 6)));
+      if (kIsWeb ||
+        defaultTargetPlatform == TargetPlatform.iOS ||
+        defaultTargetPlatform == TargetPlatform.macOS ||
+        defaultTargetPlatform == TargetPlatform.linux ||
+        defaultTargetPlatform == TargetPlatform.fuchsia
+      ) {
+        expect(state.currentTextEditingValue.text, '侬好啊旁友们');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+      } else {
+        expect(state.currentTextEditingValue.text, '侬好啊旁友');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+      }
+
+      state.updateEditingValue(const TextEditingValue(text: '侬好啊旁友'));
+      expect(state.currentTextEditingValue.text, '侬好啊旁友');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+  });
 }

packages/flutter/test/widgets/editable_text_test.dart

@@ -6500,9 +6500,13 @@ void main() {
     expect(state.currentTextEditingValue.composing, TextRange.empty);
   });
 
-  // Regression test for https://github.com/flutter/flutter/issues/65374.
-  testWidgets('Length formatter will not cause crash while the TextEditingValue is composing', (WidgetTester tester) async {
-    final TextInputFormatter formatter = LengthLimitingTextInputFormatter(5);
+  group('Length formatter', () {
+    const int maxLength = 5;
+
+    Future<void> setupWidget(
+      WidgetTester tester,
+      LengthLimitingTextInputFormatter formatter,
+    ) async {
       final Widget widget = MaterialApp(
         home: EditableText(
           backgroundCursorColor: Colors.grey,
@@ -6516,59 +6520,264 @@ void main() {
       );
 
       await tester.pumpWidget(widget);
+      await tester.pumpAndSettle();
+    }
+
+    // Regression test for https://github.com/flutter/flutter/issues/65374.
+    testWidgets('will not cause crash while the TextEditingValue is composing', (WidgetTester tester) async {
+      await setupWidget(
+        tester,
+        LengthLimitingTextInputFormatter(
+          maxLength,
+          maxLengthEnforcement: MaxLengthEnforcement.truncateAfterCompositionEnds,
+        ),
+      );
 
       final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
-    state.updateEditingValue(const TextEditingValue(text: '12345'));
+      state.updateEditingValue(const TextEditingValue(text: 'abcde'));
       expect(state.currentTextEditingValue.composing, TextRange.empty);
-    state.updateEditingValue(const TextEditingValue(text: '12345', composing: TextRange(start: 2, end: 4)));
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 2, end: 4)));
       expect(state.currentTextEditingValue.composing, const TextRange(start: 2, end: 4));
 
       // Formatter will not update format while the editing value is composing.
-    state.updateEditingValue(const TextEditingValue(text: '123456', composing: TextRange(start: 2, end: 5)));
-    expect(state.currentTextEditingValue.text, '123456');
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 2, end: 5)));
+      expect(state.currentTextEditingValue.text, 'abcdef');
       expect(state.currentTextEditingValue.composing, const TextRange(start: 2, end: 5));
 
       // After composing ends, formatter will update.
-    state.updateEditingValue(const TextEditingValue(text: '123456'));
-    expect(state.currentTextEditingValue.text, '12345');
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef'));
+      expect(state.currentTextEditingValue.text, 'abcde');
       expect(state.currentTextEditingValue.composing, TextRange.empty);
     });
 
-  testWidgets('Length formatter handles composing text correctly, continued', (WidgetTester tester) async {
-    final TextInputFormatter formatter = LengthLimitingTextInputFormatter(5);
-    final Widget widget = MaterialApp(
-      home: EditableText(
-        backgroundCursorColor: Colors.grey,
-        controller: controller,
-        focusNode: focusNode,
-        inputFormatters: <TextInputFormatter>[formatter],
-        style: textStyle,
-        cursorColor: cursorColor,
-        selectionControls: materialTextSelectionControls,
+    testWidgets('handles composing text correctly, continued', (WidgetTester tester) async {
+      await setupWidget(
+        tester,
+        LengthLimitingTextInputFormatter(
+          maxLength,
+          maxLengthEnforcement: MaxLengthEnforcement.truncateAfterCompositionEnds,
         ),
       );
 
-    await tester.pumpWidget(widget);
       final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
 
       // Initially we're at maxLength with no composing text.
-    controller.text = '12345' ;
-    assert(state.currentTextEditingValue == const TextEditingValue(text: '12345'));
+      controller.text = 'abcde' ;
+      assert(state.currentTextEditingValue == const TextEditingValue(text: 'abcde'));
 
       // Should be able to change the editing value if the new value is still shorter
       // than maxLength.
-    state.updateEditingValue(const TextEditingValue(text: '12345', composing: TextRange(start: 2, end: 4)));
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 2, end: 4)));
       expect(state.currentTextEditingValue.composing, const TextRange(start: 2, end: 4));
 
       // Reset.
-    controller.text = '12345' ;
-    assert(state.currentTextEditingValue == const TextEditingValue(text: '12345'));
+      controller.text = 'abcde' ;
+      assert(state.currentTextEditingValue == const TextEditingValue(text: 'abcde'));
 
       // The text should not change when trying to insert when the text is already
       // at maxLength.
       state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 5, end: 6)));
-    expect(state.currentTextEditingValue.text, '12345');
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    // Regression test for https://github.com/flutter/flutter/issues/68086.
+    testWidgets('enforced composing truncated', (WidgetTester tester) async {
+      await setupWidget(
+        tester,
+        LengthLimitingTextInputFormatter(
+          maxLength,
+          maxLengthEnforcement: MaxLengthEnforcement.enforced,
+        ),
+      );
+
+      final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+
+      // Initially we're at maxLength with no composing text.
+      state.updateEditingValue(const TextEditingValue(text: 'abcde'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // When it's not longer than `maxLength`, it can still start composing.
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      // `newValue` will be truncated if `composingMaxLengthEnforced`.
+      state.updateEditingValue(const TextEditingValue(text: 'abcdef', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, 'abcde');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      // Reset the value.
+      state.updateEditingValue(const TextEditingValue(text: 'abcde'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Change the value in order to take effects on web test.
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start composing with a longer value, it should be the same state.
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友们', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    // Regression test for https://github.com/flutter/flutter/issues/68086.
+    testWidgets('default truncate behaviors with different platforms', (WidgetTester tester) async {
+      await setupWidget(tester, LengthLimitingTextInputFormatter(maxLength));
+
+      final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+
+      // Initially we're at maxLength with no composing text.
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // When it's not longer than `maxLength`, it can still start composing.
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友们', composing: TextRange(start: 3, end: 6)));
+      if (kIsWeb ||
+        defaultTargetPlatform == TargetPlatform.iOS ||
+        defaultTargetPlatform == TargetPlatform.macOS ||
+        defaultTargetPlatform == TargetPlatform.linux ||
+        defaultTargetPlatform == TargetPlatform.fuchsia
+      ) {
+        // `newValue` will will not be truncated on couple platforms.
+        expect(state.currentTextEditingValue.text, '你好啊朋友们');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 6));
+      } else {
+        // `newValue` on other platforms will be truncated.
+        expect(state.currentTextEditingValue.text, '你好啊朋友');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+      }
+
+      // Reset the value.
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start composing with a longer value, it should be the same state.
+      state.updateEditingValue(const TextEditingValue(text: '你好啊朋友们', composing: TextRange(start: 3, end: 6)));
+      expect(state.currentTextEditingValue.text, '你好啊朋友');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    // Regression test for https://github.com/flutter/flutter/issues/68086.
+    testWidgets('composing range removed if it\'s overflowed the truncated value\'s length', (WidgetTester tester) async {
+      await setupWidget(
+        tester,
+        LengthLimitingTextInputFormatter(
+          maxLength,
+          maxLengthEnforcement: MaxLengthEnforcement.enforced,
+        ),
+      );
+
+      final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+
+      // Initially we're not at maxLength with no composing text.
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start composing.
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      // Reset the value.
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start composing with a range already overflowed the truncated length.
+      state.updateEditingValue(const TextEditingValue(text: 'abcdefgh', composing: TextRange(start: 5, end: 7)));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    // Regression test for https://github.com/flutter/flutter/issues/68086.
+    testWidgets('composing range removed with different platforms', (WidgetTester tester) async {
+      await setupWidget(tester, LengthLimitingTextInputFormatter(maxLength));
+
+      final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+
+      // Initially we're not at maxLength with no composing text.
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start composing.
+      state.updateEditingValue(const TextEditingValue(text: 'abcde', composing: TextRange(start: 3, end: 5)));
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+
+      // Reset the value.
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start composing with a range already overflowed the truncated length.
+      state.updateEditingValue(const TextEditingValue(text: 'abcdefgh', composing: TextRange(start: 5, end: 7)));
+      if (kIsWeb ||
+        defaultTargetPlatform == TargetPlatform.iOS ||
+        defaultTargetPlatform == TargetPlatform.macOS ||
+        defaultTargetPlatform == TargetPlatform.linux ||
+        defaultTargetPlatform == TargetPlatform.fuchsia
+      ) {
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 5, end: 7));
+      } else {
         expect(state.currentTextEditingValue.composing, TextRange.empty);
+      }
+    });
+
+    testWidgets('composing range handled correctly when it\'s overflowed', (WidgetTester tester) async {
+      const String string = '👨‍👩‍👦0123456';
+
+      await setupWidget(tester, LengthLimitingTextInputFormatter(maxLength));
+
+      final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+
+      // Initially we're not at maxLength with no composing text.
+      state.updateEditingValue(const TextEditingValue(text: string));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Clearing composing range if collapsed.
+      state.updateEditingValue(const TextEditingValue(text: string, composing: TextRange(start: 10, end: 10)));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Clearing composing range if overflowed.
+      state.updateEditingValue(const TextEditingValue(text: string, composing: TextRange(start: 10, end: 11)));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
+
+    // Regression test for https://github.com/flutter/flutter/issues/68086.
+    testWidgets('typing in the middle with different platforms.', (WidgetTester tester) async {
+      await setupWidget(tester, LengthLimitingTextInputFormatter(maxLength));
+
+      final EditableTextState state = tester.state<EditableTextState>(find.byType(EditableText));
+
+      // Initially we're not at maxLength with no composing text.
+      state.updateEditingValue(const TextEditingValue(text: 'abc'));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      // Start typing in the middle.
+      state.updateEditingValue(const TextEditingValue(text: 'abDEc', composing: TextRange(start: 3, end: 4)));
+      expect(state.currentTextEditingValue.text, 'abDEc');
+      expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 4));
+
+      // Keep typing when the value has exceed the limitation.
+      state.updateEditingValue(const TextEditingValue(text: 'abDEFc', composing: TextRange(start: 3, end: 5)));
+      if (kIsWeb ||
+        defaultTargetPlatform == TargetPlatform.iOS ||
+        defaultTargetPlatform == TargetPlatform.macOS ||
+        defaultTargetPlatform == TargetPlatform.linux ||
+        defaultTargetPlatform == TargetPlatform.fuchsia
+      ) {
+        expect(state.currentTextEditingValue.text, 'abDEFc');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 5));
+      } else {
+        expect(state.currentTextEditingValue.text, 'abDEc');
+        expect(state.currentTextEditingValue.composing, const TextRange(start: 3, end: 4));
+      }
+
+      // Reset the value according to the limit.
+      state.updateEditingValue(const TextEditingValue(text: 'abDEc'));
+      expect(state.currentTextEditingValue.text, 'abDEc');
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+
+      state.updateEditingValue(const TextEditingValue(text: 'abDEFc', composing: TextRange(start: 4, end: 5)));
+      expect(state.currentTextEditingValue.composing, TextRange.empty);
+    });
   });
 
   group('callback errors', () {

packages/flutter/test/widgets/form_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:flutter_test/flutter_test.dart';
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 
 void main() {
   testWidgets('onSaved callback is called', (WidgetTester tester) async {
@@ -848,7 +849,7 @@ void main() {
     expect(() => builder(), throwsAssertionError);
   });
 
-  // Regression test for https://github.com/flutter/flutter/issues/65374.
+  // Regression test for https://github.com/flutter/flutter/issues/63753.
   testWidgets('Validate form should return correct validation if the value is composing', (WidgetTester tester) async {
     final GlobalKey<FormState> formKey = GlobalKey<FormState>();
     String? fieldValue;
@@ -864,6 +865,7 @@ void main() {
                 key: formKey,
                 child: TextFormField(
                   maxLength: 5,
+                  maxLengthEnforcement: MaxLengthEnforcement.truncateAfterCompositionEnds,
                   onSaved: (String? value) { fieldValue = value; },
                   validator: (String? value) => (value != null && value.length > 5) ? 'Exceeded' : null,
                 ),