[TextPainter] Don't invalidate layout cache for paint only changes (#89515)

packages/flutter/test/painting/text_painter_test.dart

@@ -152,7 +152,16 @@ void main() {
 
   test('TextPainter error test', () {
     final TextPainter painter = TextPainter(textDirection: TextDirection.ltr);
-    expect(() { painter.paint(MockCanvas(), Offset.zero); }, anyOf(throwsFlutterError, throwsAssertionError));
+    Object? e;
+    try {
+      painter.paint(MockCanvas(), Offset.zero);
+    } catch (exception) {
+      e = exception;
+    }
+    expect(
+      e.toString(),
+      contains('TextPainter.paint called when text geometry was not yet calculated'),
+    );
   });
 
   test('TextPainter requires textDirection', () {

packages/flutter/test/widgets/text_test.dart

@@ -1261,7 +1261,7 @@ void main() {
   testWidgets('Text uses TextStyle.overflow', (WidgetTester tester) async {
     const TextOverflow overflow = TextOverflow.fade;
 
-    await tester.pumpWidget( const Text(
+    await tester.pumpWidget(const Text(
       'Hello World',
       textDirection: TextDirection.ltr,
       style: TextStyle(overflow: overflow),
@@ -1272,6 +1272,42 @@ void main() {
     expect(richText.overflow, overflow);
     expect(richText.text.style!.overflow, overflow);
   });
+
+  testWidgets(
+    'Text can be hit-tested without layout or paint being called in a frame',
+    (WidgetTester tester) async {
+      // Regression test for https://github.com/flutter/flutter/issues/85108.
+      await tester.pumpWidget(
+        const Opacity(
+          opacity: 1.0,
+          child: Text(
+            'Hello World',
+            textDirection: TextDirection.ltr,
+            style: TextStyle(color: Color(0xFF123456)),
+          ),
+        ),
+      );
+
+      // The color changed and the opacity is set to 0:
+      //  * 0 opacity will prevent RenderParagraph.paint from being called.
+      //  * Only changing the color will prevent RenderParagraph.performLayout
+      //    from being called.
+      //  The underlying TextPainter should not evict its layout cache in this
+      //  case, for hit-testing.
+      await tester.pumpWidget(
+        const Opacity(
+          opacity: 0.0,
+          child: Text(
+            'Hello World',
+            textDirection: TextDirection.ltr,
+            style: TextStyle(color: Color(0x87654321)),
+          ),
+        ),
+      );
+
+      await tester.tap(find.text('Hello World'));
+      expect(tester.takeException(), isNull);
+  });
 }
 
 Future<void> _pumpTextWidget({