expose IME composing range in QuillController

Author: rk54rk

lib/src/controller/quill_controller.dart

@@ -1,5 +1,6 @@
 import 'dart:math' as math;
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart' show ClipboardData, Clipboard;
 import 'package:flutter/widgets.dart';
 import 'package:meta/meta.dart';
@@ -48,6 +49,20 @@ class QuillController extends ChangeNotifier {
         selection: const TextSelection.collapsed(offset: 0),
       );
 
+  // Expose current IME composing range for filtering out intermediate edits.
+  final ValueNotifier<TextRange> _composingRangeNotifier =
+      ValueNotifier<TextRange>(TextRange.empty);
+
+  /// Current IME (Chinese/Japanese etc input method) composing range.
+  /// This can be used to filter out intermediate edits that happen during IME composition.
+  ValueListenable<TextRange> get composing => _composingRangeNotifier;
+
+  @internal
+  void setComposingRange(TextRange range) {
+    if (_composingRangeNotifier.value == range) return;
+    _composingRangeNotifier.value = range;
+  }
+
   final QuillControllerConfig config;
 
   /// Document managed by this controller.

lib/src/editor/raw_editor/raw_editor_state_text_input_client_mixin.dart

@@ -19,8 +19,11 @@ mixin RawEditorStateTextInputClientMixin on EditorState
 
   set _lastKnownRemoteTextEditingValue(TextEditingValue? value) {
     __lastKnownRemoteTextEditingValue = value;
-    if (composingRange.value != value?.composing) {
-      composingRange.value = value?.composing ?? TextRange.empty;
+    final newRange = value?.composing ?? TextRange.empty;
+    if (composingRange.value != newRange) {
+      composingRange.value = newRange;
+      // Forward composing range to the controller
+      widget.controller.setComposingRange(newRange);
     }
   }