iOS selection handles are invisible (#31332)

Fix a bug where text selection handles were invisible in iOS

packages/flutter/lib/src/painting/text_painter.dart

@@ -654,4 +654,4 @@ class TextPainter {
     final List<int> indices = _paragraph.getWordBoundary(position.offset);
     return TextRange(start: indices[0], end: indices[1]);
   }
-}
\ No newline at end of file
+}

packages/flutter/lib/src/rendering/editable.dart

@@ -302,15 +302,25 @@ class RenderEditable extends RenderBox {
       TextPosition(offset: _selection.start, affinity: _selection.affinity),
       Rect.zero,
     );
-
-    _selectionStartInViewport.value = visibleRegion.contains(startOffset + effectiveOffset);
+    // TODO(justinmc): https://github.com/flutter/flutter/issues/31495
+    // Check if the selection is visible with an approximation because a
+    // difference between rounded and unrounded values causes the caret to be
+    // reported as having a slightly (< 0.5) negative y offset. This rounding
+    // happens in paragraph.cc's layout and TextPainer's
+    // _applyFloatingPointHack. Ideally, the rounding mismatch will be fixed and
+    // this can be changed to be a strict check instead of an approximation.
+    const double visibleRegionSlop = 0.5;
+    _selectionStartInViewport.value = visibleRegion
+      .inflate(visibleRegionSlop)
+      .contains(startOffset + effectiveOffset);
 
     final Offset endOffset =  _textPainter.getOffsetForCaret(
       TextPosition(offset: _selection.end, affinity: _selection.affinity),
       Rect.zero,
     );
-
-    _selectionEndInViewport.value = visibleRegion.contains(endOffset + effectiveOffset);
+    _selectionEndInViewport.value = visibleRegion
+      .inflate(visibleRegionSlop)
+      .contains(endOffset + effectiveOffset);
   }
 
   static const int _kLeftArrowCode = 21;

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

@@ -612,7 +612,6 @@ class _TextSelectionHandleOverlayState
       point.dy.clamp(0.0, viewport.height),
     );
 
-
     return CompositedTransformFollower(
       link: widget.layerLink,
       showWhenUnlinked: false,

packages/flutter/test/cupertino/text_field_test.dart

@@ -2091,4 +2091,39 @@ void main() {
     final EditableText editableText = tester.firstWidget(find.byType(EditableText));
     expect(editableText.cursorColor, const Color(0xFFF44336));
   });
+
+  testWidgets('iOS shows selection handles', (WidgetTester tester) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    const String testText = 'lorem ipsum';
+    final TextEditingController controller = TextEditingController(text: testText);
+
+    await tester.pumpWidget(
+      CupertinoApp(
+        theme: const CupertinoThemeData(),
+        home: Center(
+          child: CupertinoTextField(
+            controller: controller,
+          ),
+        ),
+      ),
+    );
+
+    final RenderEditable renderEditable =
+      tester.state<EditableTextState>(find.byType(EditableText)).renderEditable;
+
+    await tester.tapAt(textOffsetToPosition(tester, 5));
+    renderEditable.selectWord(cause: SelectionChangedCause.longPress);
+    await tester.pumpAndSettle();
+
+    final List<Widget> transitions =
+      find.byType(FadeTransition).evaluate().map((Element e) => e.widget).toList();
+    expect(transitions.length, 2);
+    final FadeTransition left = transitions[0];
+    final FadeTransition right = transitions[1];
+
+    expect(left.opacity.value, equals(1.0));
+    expect(right.opacity.value, equals(1.0));
+
+    debugDefaultTargetPlatformOverride = null;
+  });
 }

packages/flutter/test/material/text_field_test.dart

@@ -5676,4 +5676,71 @@ void main() {
     );
     expect(topLeft.dx, equals(383)); // Should be same as equivalent in 'Caret center position'
   });
+
+  testWidgets('selection handles are rendered and not faded away', (WidgetTester tester) async {
+    const String testText = 'lorem ipsum';
+    final TextEditingController controller = TextEditingController(text: testText);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: TextField(
+            controller: controller,
+          ),
+        ),
+      ),
+    );
+
+    final RenderEditable renderEditable =
+      tester.state<EditableTextState>(find.byType(EditableText)).renderEditable;
+
+    await tester.tapAt(const Offset(20, 10));
+    renderEditable.selectWord(cause: SelectionChangedCause.longPress);
+    await tester.pumpAndSettle();
+
+    final List<Widget> transitions =
+      find.byType(FadeTransition).evaluate().map((Element e) => e.widget).toList();
+    // On Android, an empty app contains a single FadeTransition. The following
+    // two are the left and right text selection handles, respectively.
+    expect(transitions.length, 3);
+    final FadeTransition left = transitions[1];
+    final FadeTransition right = transitions[2];
+
+    expect(left.opacity.value, equals(1.0));
+    expect(right.opacity.value, equals(1.0));
+  });
+
+  testWidgets('iOS selection handles are rendered and not faded away', (WidgetTester tester) async {
+    debugDefaultTargetPlatformOverride = TargetPlatform.iOS;
+    const String testText = 'lorem ipsum';
+    final TextEditingController controller = TextEditingController(text: testText);
+
+    await tester.pumpWidget(
+      MaterialApp(
+        home: Material(
+          child: TextField(
+            controller: controller,
+          ),
+        ),
+      ),
+    );
+
+    final RenderEditable renderEditable =
+      tester.state<EditableTextState>(find.byType(EditableText)).renderEditable;
+
+    await tester.tapAt(const Offset(20, 10));
+    renderEditable.selectWord(cause: SelectionChangedCause.longPress);
+    await tester.pumpAndSettle();
+
+    final List<Widget> transitions =
+      find.byType(FadeTransition).evaluate().map((Element e) => e.widget).toList();
+    expect(transitions.length, 2);
+    final FadeTransition left = transitions[0];
+    final FadeTransition right = transitions[1];
+
+    expect(left.opacity.value, equals(1.0));
+    expect(right.opacity.value, equals(1.0));
+
+    debugDefaultTargetPlatformOverride = null;
+  });
 }