import 'package:flutter/material.dart';

void main() {
  runApp(const MaterialApp(home: Scaffold(body: BugReport())));
}

class BugReport extends StatefulWidget {
  const BugReport({super.key});

  @override
  State<BugReport> createState() => _BugReportState();
}

class _BugReportState extends State<BugReport> {
  static const int _length = 50;

  List<PopupMenuEntry<int>> _buildItems(BuildContext context) {
    return List<PopupMenuEntry<int>>.generate(_length, (int index) {
      return PopupMenuItem<int>(value: index, child: Text('$index'));
    });
  }

  @override
  Widget build(BuildContext context) {
    final Size screenSize = MediaQuery.of(context).size;
    return Padding(
      padding: const EdgeInsets.all(50),
      child: Align(
        alignment: Alignment.bottomCenter,
        child: PopupMenuButton(
          itemBuilder: _buildItems,
          constraints: BoxConstraints(maxHeight: screenSize.height / 4),
          initialValue: _length - 1,
          child: const Row(
            mainAxisSize: MainAxisSize.min,
            children: [
              Text('Click here to open popup menu '),
              Icon(Icons.ads_click),
            ],
          ),
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';
import 'package:flutter_test/flutter_test.dart';

void main() {
  testWidgets('PopupMenuButton properly positions a constrained-size popup', (WidgetTester tester) async {
    final Size windowSize = tester.view.physicalSize / tester.view.devicePixelRatio;
    const int length = 50;
    await tester.pumpWidget(
      MaterialApp(
        home: Scaffold(
          body: Padding(
            padding: const EdgeInsets.all(50),
            child: Align(
              alignment: Alignment.bottomCenter,
              child: PopupMenuButton<int>(
                itemBuilder: (BuildContext context) {
                  return List<PopupMenuEntry<int>>.generate(length, (int index) {
                    return PopupMenuItem<int>(value: index, child: Text('item #$index'));
                  });
                },
                constraints: BoxConstraints(maxHeight: windowSize.height / 3),
                popUpAnimationStyle: AnimationStyle.noAnimation,
                initialValue: length - 1,
                child: const Text('click here'),
              ),
            ),
          ),
        ),
      ),
    );
    await tester.tap(find.text('click here'));
    await tester.pump();

    // Set up finders and verify basic widget structure
    final Finder findButton = find.byType(PopupMenuButton<int>);
    final Finder findLastItem = find.text('item #49');
    final Finder findListBody = find.byType(ListBody);
    final Finder findListViewport = find.ancestor(
      of: findListBody,
      matching: find.byType(SingleChildScrollView),
    );
    expect(findButton, findsOne);
    expect(findLastItem, findsOne);
    expect(findListBody, findsOne);
    expect(findListViewport, findsOne);

    // The button and the list viewport should overlap
    final RenderBox button = tester.renderObject<RenderBox>(findButton);
    final Rect buttonBounds = button.localToGlobal(Offset.zero) & button.size;
    final RenderBox listViewport = tester.renderObject<RenderBox>(findListViewport);
    final Rect listViewportBounds = listViewport.localToGlobal(Offset.zero) & listViewport.size;
    expect(listViewportBounds.topLeft.dy, lessThanOrEqualTo(windowSize.height));
    expect(listViewportBounds.bottomRight.dy, lessThanOrEqualTo(windowSize.height));
    expect(listViewportBounds, overlaps(buttonBounds));
  });
}

Matcher overlaps(Rect other) => OverlapsMatcher(other);

class OverlapsMatcher extends Matcher {
  OverlapsMatcher(this.other);

  final Rect other;

  @override
  Description describe(Description description) {
    return description.add("<Rect that overlaps with $other>");
  }

  @override
  bool matches(Object? item, Map matchState) => item is Rect && item.overlaps(other);

  @override
  Description describeMismatch(dynamic item, Description mismatchDescription,
      Map matchState, bool verbose) {
    return mismatchDescription.add("does not overlap");
  }
}