Automatically create the layer when setting hints in PaintingContext (#130364)

Fixes https://github.com/flutter/flutter/issues/92722

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

@@ -397,8 +397,16 @@ class PaintingContext extends ClipContext {
   /// If this hint is not set, the compositor will apply its own heuristics to
   /// decide whether the current layer is complex enough to benefit from
   /// caching.
+  ///
+  /// Calling this ensures a [Canvas] is available. Only draw calls on the
+  /// current canvas will be hinted; the hint is not propagated to new canvases
+  /// created after a new layer is added to the painting context (e.g. with
+  /// [addLayer] or [pushLayer]).
   void setIsComplexHint() {
-    _currentLayer?.isComplexHint = true;
+    if (_currentLayer == null) {
+      _startRecording();
+    }
+    _currentLayer!.isComplexHint = true;
   }
 
   /// Hints that the painting in the current layer is likely to change next frame.
@@ -407,8 +415,16 @@ class PaintingContext extends ClipContext {
   /// cache will not be used in the future. If this hint is not set, the
   /// compositor will apply its own heuristics to decide whether the current
   /// layer is likely to be reused in the future.
+  ///
+  /// Calling this ensures a [Canvas] is available. Only draw calls on the
+  /// current canvas will be hinted; the hint is not propagated to new canvases
+  /// created after a new layer is added to the painting context (e.g. with
+  /// [addLayer] or [pushLayer]).
   void setWillChangeHint() {
-    _currentLayer?.willChangeHint = true;
+    if (_currentLayer == null) {
+      _startRecording();
+    }
+    _currentLayer!.willChangeHint = true;
   }
 
   /// Adds a composited leaf layer to the recording.

packages/flutter/test/rendering/painting_context_test.dart

+// Copyright 2014 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/rendering.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+import 'rendering_tester.dart';
+
+void main() {
+  TestRenderingFlutterBinding.ensureInitialized();
+
+  test('PaintingContext.setIsComplexHint', () {
+    final ContainerLayer layer = ContainerLayer();
+    final PaintingContext context = PaintingContext(layer, Rect.zero);
+    expect(layer.hasChildren, isFalse);
+    context.setIsComplexHint();
+    expect(layer.hasChildren, isTrue);
+    expect(layer.firstChild, isA<PictureLayer>());
+    expect((layer.firstChild! as PictureLayer).isComplexHint, isTrue);
+  });
+
+  test('PaintingContext.setWillChangeHint', () {
+    final ContainerLayer layer = ContainerLayer();
+    final PaintingContext context = PaintingContext(layer, Rect.zero);
+    expect(layer.hasChildren, isFalse);
+    context.setWillChangeHint();
+    expect(layer.hasChildren, isTrue);
+    expect(layer.firstChild, isA<PictureLayer>());
+    expect((layer.firstChild! as PictureLayer).willChangeHint, isTrue);
+  });
+}