[SuperEditor][iOS] Fix exception when moving floating cursor between …

…paragraphs (Resolves #1449) (#1471)

super_editor/lib/src/default_editor/document_ime/document_ime_communication.dart

@@ -69,6 +69,11 @@ class DocumentImeInputClient extends TextInputConnectionDecorator with TextInput
   /// For the list of selectors, see [MacOsSelectors].
   final void Function(String selectorName) onPerformSelector;
 
+  /// Whether the floating cursor is being displayed.
+  ///
+  /// This value is updated on [updateFloatingCursor].
+  bool _isFloatingCursorVisible = false;
+
   void _onContentChange() {
     if (!attached) {
       return;
@@ -187,6 +192,18 @@ class DocumentImeInputClient extends TextInputConnectionDecorator with TextInput
       return;
     }
 
+    if (_isFloatingCursorVisible && textEditingDeltas.every((e) => e is TextEditingDeltaNonTextUpdate)) {
+      // On iOS, dragging the floating cursor generates non-text deltas to update the selection.
+      //
+      // When dragging the floating cursor between paragraphs, we receive a non-text delta for the previously
+      // selected paragraph when our selection already changed to another paragraph. If the previously selected
+      // paragraph is bigger than the newly selected paragraph, a mapping error occurs, because we try
+      // to select an offset bigger than the paragraph's length.
+      //
+      // As we already change the selection when the floating cursor moves, we ignore these deltas.
+      return;
+    }
+
     editorImeLog.fine("Received edit deltas from platform: ${textEditingDeltas.length} deltas");
     for (final delta in textEditingDeltas) {
       editorImeLog.fine("$delta");
@@ -277,10 +294,14 @@ class DocumentImeInputClient extends TextInputConnectionDecorator with TextInput
   void updateFloatingCursor(RawFloatingCursorPoint point) {
     switch (point.state) {
       case FloatingCursorDragState.Start:
+        _isFloatingCursorVisible = true;
+        _floatingCursorController?.offset = point.offset;
+        break;
       case FloatingCursorDragState.Update:
         _floatingCursorController?.offset = point.offset;
         break;
       case FloatingCursorDragState.End:
+        _isFloatingCursorVisible = false;
         _floatingCursorController?.offset = null;
         break;
     }

super_editor/test/super_editor/supereditor_floating_cursor_test.dart

@@ -1,10 +1,13 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:flutter_test/flutter_test.dart';
+import 'package:flutter_test_robots/flutter_test_robots.dart';
 import 'package:flutter_test_runners/flutter_test_runners.dart';
 import 'package:super_editor/src/core/document.dart';
 import 'package:super_editor/src/core/document_selection.dart';
 import 'package:super_editor/src/default_editor/text.dart';
 import 'package:super_editor/src/infrastructure/blinking_caret.dart';
+import 'package:super_editor/src/test/ime.dart';
 import 'package:super_editor/src/test/super_editor_test/supereditor_inspector.dart';
 import 'package:super_editor/src/test/super_editor_test/supereditor_robot.dart';
 
@@ -175,6 +178,50 @@ void main() {
           ),
         );
       });
+
+      testWidgetsOnIos('moves selection between paragraphs', (tester) async {
+        final testContext = await tester //
+            .createDocument()
+            .fromMarkdown('''
+This is the first paragraph
+
+Second paragraph''') //
+            .pump();
+
+        // Place the caret at the end of the first paragraph.
+        await tester.placeCaretInParagraph(testContext.document.nodes.first.id, 27);
+
+        // Show the floating cursor.
+        await tester.startFloatingCursorGesture();
+        await tester.pump();
+
+        // Move the floating cursor down to the next paragraph.
+        await tester.updateFloatingCursorGesture(const Offset(0, 30));
+        await tester.pump();
+
+        // Simulate iOS IME generating deltas as a result of moving the floating cursor.
+        // At this point, the selection already changed to the second paragraph, which is
+        // smaller than the selection offset reported in the delta.
+        await tester.ime.sendDeltas([
+          const TextEditingDeltaNonTextUpdate(
+            oldText: 'This is the first paragraph',
+            selection: TextSelection.collapsed(offset: 27),
+            composing: TextRange.empty,
+          )
+        ], getter: imeClientGetter);
+        await tester.pump();
+
+        // Ensure the selection changed to the end of the second paragraph.
+        expect(
+          SuperEditorInspector.findDocumentSelection(),
+          DocumentSelection.collapsed(
+            position: DocumentPosition(
+              nodeId: testContext.document.nodes.last.id,
+              nodePosition: const TextNodePosition(offset: 16, affinity: TextAffinity.upstream),
+            ),
+          ),
+        );
+      });
     });
   });
 }