Trackpad mode crash fix (#30475)

Fixes a crash that happened when attempting to select text in trackpad mode on iOS.

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

diff --git a/packages/flutter/lib/src/widgets/editable_text.dart b/packages/flutter/lib/src/widgets/editable_text.dart
index d728cea..3b98b0e 100644
--- a/packages/flutter/lib/src/widgets/editable_text.dart
+++ b/packages/flutter/lib/src/widgets/editable_text.dart
@@ -914,6 +914,10 @@
   void updateFloatingCursor(RawFloatingCursorPoint point) {
     switch(point.state){
       case FloatingCursorDragState.Start:
+        if (_floatingCursorResetController.isAnimating) {
+          _floatingCursorResetController.stop();
+          _onFloatingCursorResetTick();
+        }
         final TextPosition currentTextPosition = TextPosition(offset: renderEditable.selection.baseOffset);
         _startCaretRect = renderEditable.getLocalRectForCaret(currentTextPosition);
         renderEditable.setFloatingCursor(point.state, _startCaretRect.center - _floatingCursorOffset, currentTextPosition);

packages/flutter/test/widgets/editable_text_cursor_test.dart

diff --git a/packages/flutter/test/widgets/editable_text_cursor_test.dart b/packages/flutter/test/widgets/editable_text_cursor_test.dart
index 6e00f92..ba232dd 100644
--- a/packages/flutter/test/widgets/editable_text_cursor_test.dart
+++ b/packages/flutter/test/widgets/editable_text_cursor_test.dart
@@ -476,6 +476,72 @@
     expect(controller.selection.baseOffset, 10);
   });
 
+  // Regression test for https://github.com/flutter/flutter/pull/30475.
+  testWidgets('Trying to select with the floating cursor does not crash', (WidgetTester tester) async {
+    const String text = 'hello world this is fun and cool and awesome!';
+    controller.text = text;
+    final FocusNode focusNode = FocusNode();
+
+    await tester.pumpWidget(
+      MediaQuery(
+        data: const MediaQueryData(devicePixelRatio: 1),
+        child: Directionality(
+          textDirection: TextDirection.ltr,
+          child: FocusScope(
+            node: focusScopeNode,
+            autofocus: true,
+            child: EditableText(
+              backgroundCursorColor: Colors.grey,
+              controller: controller,
+              focusNode: focusNode,
+              style: textStyle,
+              cursorColor: cursorColor,
+            ),
+          ),
+        ),
+      ),
+    );
+
+    await tester.tap(find.byType(EditableText));
+    final RenderEditable renderEditable = findRenderEditable(tester);
+    renderEditable.selection = const TextSelection(baseOffset: 29, extentOffset: 29);
+
+    expect(controller.selection.baseOffset, 29);
+
+    final EditableTextState editableTextState = tester.firstState(find.byType(EditableText));
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.Start));
+
+    expect(controller.selection.baseOffset, 29);
+
+    // Sets the origin.
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.Update,
+      offset: const Offset(20, 20)));
+
+    expect(controller.selection.baseOffset, 29);
+
+    // Moves the cursor right a few characters.
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.Update,
+      offset: const Offset(-250, 20)));
+
+    // But we have not yet set the offset because the user is not done placing the cursor.
+    expect(controller.selection.baseOffset, 29);
+
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.End));
+    // Immediately start a new floating cursor, in the same way as happens when
+    // the user tries to select text in trackpad mode.
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.Start));
+    await tester.pumpAndSettle();
+
+    // Set and move the second cursor like a selection. Previously, the second
+    // Update here caused a crash.
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.Update,
+      offset: const Offset(20, 20)));
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.Update,
+      offset: const Offset(-250, 20)));
+    editableTextState.updateFloatingCursor(RawFloatingCursorPoint(state: FloatingCursorDragState.End));
+    await tester.pumpAndSettle();
+  });
+
   testWidgets('autofocus sets cursor to the end of text', (WidgetTester tester) async {
     const String text = 'hello world';
     final FocusScopeNode focusScopeNode = FocusScopeNode();