Skip reformatting and calling onChanged for composing region only changes. (#70883)

packages/flutter/lib/src/widgets/editable_text.dart

@@ -69,12 +69,21 @@ const int _kObscureShowLatestCharCursorTicks = 3;
 /// text field. If you build a text field with a controller that already has
 /// [text], the text field will use that text as its initial value.
 ///
-/// The [text] or [selection] properties can be set from within a listener
-/// added to this controller. If both properties need to be changed then the
-/// controller's [value] should be set instead.
+/// The [value] (as well as [text] and [selection]) of this controller can be
+/// updated from within a listener added to this controller. Be aware of
+/// infinite loops since the listener will also be notified of the changes made
+/// from within itself. Modifying the composing region from within a listener
+/// can also have a bad interaction with some input methods. Gboard, for
+/// example, will try to restore the composing region of the text if it was
+/// modified programmatically, creating an infinite loop of communications
+/// between the framework and the input method. Consider using
+/// [TextInputFormatter]s instead for as-you-type text modification.
 ///
-/// Remember to [dispose] of the [TextEditingController] when it is no longer needed.
-/// This will ensure we discard any resources used by the object.
+/// If both the [text] or [selection] properties need to be changed, set the
+/// controller's [value] instead.
+///
+/// Remember to [dispose] of the [TextEditingController] when it is no longer
+/// needed. This will ensure we discard any resources used by the object.
 /// {@tool dartpad --template=stateful_widget_material}
 /// This example creates a [TextField] with a [TextEditingController] whose
 /// change listener forces the entered text to be lower case and keeps the
@@ -2183,14 +2192,18 @@ class EditableTextState extends State<EditableText> with AutomaticKeepAliveClien
   late final _WhitespaceDirectionalityFormatter _whitespaceFormatter = _WhitespaceDirectionalityFormatter(textDirection: _textDirection);
 
   void _formatAndSetValue(TextEditingValue value) {
-    // Check if the new value is the same as the current local value, or is the same
-    // as the pre-formatting value of the previous pass (repeat call).
-    final bool textChanged = _value.text != value.text || _value.composing != value.composing;
+    // Only apply input formatters if the text has changed (including uncommited
+    // text in the composing region), or when the user committed the composing
+    // text.
+    // Gboard is very persistent in restoring the composing region. Applying
+    // input formatters on composing-region-only changes (except clearing the
+    // current composing region) is very infinite-loop-prone: the formatters
+    // will keep trying to modify the composing region while Gboard will keep
+    // trying to restore the original composing region.
+    final bool textChanged = _value.text != value.text
+                          || (!_value.composing.isCollapsed && value.composing.isCollapsed);
 
     if (textChanged) {
-      // Only format when the text has changed and there are available formatters.
-      // Pass through the formatter regardless of repeat status if the input value is
-      // different than the stored value.
       value = widget.inputFormatters?.fold<TextEditingValue>(
         value,
         (TextEditingValue newValue, TextInputFormatter formatter) => formatter.formatEditUpdate(_value, newValue),

packages/flutter/test/widgets/editable_text_test.dart

@@ -5835,12 +5835,15 @@ void main() {
     expect(formatter.formatCallCount, 3);
     state.updateEditingValue(const TextEditingValue(text: '0123', selection: TextSelection.collapsed(offset: 2))); // No text change, does not format
     expect(formatter.formatCallCount, 3);
-    state.updateEditingValue(const TextEditingValue(text: '0123', selection: TextSelection.collapsed(offset: 2), composing: TextRange(start: 1, end: 2))); // Composing change triggers reformat
-    expect(formatter.formatCallCount, 4);
+
+    // Composing changes should not trigger reformat, as it could cause infinite loops on some IMEs.
+    state.updateEditingValue(const TextEditingValue(text: '0123', selection: TextSelection.collapsed(offset: 2), composing: TextRange(start: 1, end: 2)));
+    expect(formatter.formatCallCount, 3);
     expect(formatter.lastOldValue.composing, const TextRange(start: -1, end: -1));
-    expect(formatter.lastNewValue.composing, const TextRange(start: 1, end: 2)); // The new composing was registered in formatter.
+    expect(formatter.lastNewValue.composing, const TextRange(start: -1, end: -1)); // The new composing was registered in formatter.
+    // Clearing composing region should trigger reformat.
     state.updateEditingValue(const TextEditingValue(text: '01234', selection: TextSelection.collapsed(offset: 2))); // Formats, with oldValue containing composing region.
-    expect(formatter.formatCallCount, 5);
+    expect(formatter.formatCallCount, 4);
     expect(formatter.lastOldValue.composing, const TextRange(start: 1, end: 2));
     expect(formatter.lastNewValue.composing, const TextRange(start: -1, end: -1));
 
@@ -5851,10 +5854,8 @@ void main() {
       '[2]: normal aaaa',
       '[3]: 012, 0123',
       '[3]: normal aaaaaa',
-      '[4]: 0123, 0123',
+      '[4]: 0123, 01234',
       '[4]: normal aaaaaaaa',
-      '[5]: 0123, 01234',
-      '[5]: normal aaaaaaaaaa',
     ];
 
     expect(formatter.log, referenceLog);