[leak-scan] VisualState.StateTriggers — removal skips trigger detachment #38243

using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using Microsoft.Maui.Controls;
using Xunit;

public sealed class LeakTest
{
	const int N = 30;

	enum Scenario
	{
		Control,
		Leaky,
		Mitigation
	}

	[Fact]
	public void VisualState_StateTriggers_Clear_Leaks()
	{
		var control = CreateVictims(Scenario.Control);
		var leaky = CreateVictims(Scenario.Leaky);
		var mitigation = CreateVictims(Scenario.Mitigation);

		for (var i = 0; i < 7; i++)
		{
			GC.Collect();
			GC.WaitForPendingFinalizers();
			GC.Collect();
		}

		Assert.Equal(0, CountAlive(control));
		Assert.Equal(N, CountAlive(leaky));
		Assert.Equal(0, CountAlive(mitigation));
	}

	[System.Runtime.CompilerServices.MethodImpl(
		System.Runtime.CompilerServices.MethodImplOptions.NoInlining)]
	static List<WeakReference<byte[]>> CreateVictims(Scenario scenario)
	{
		var references = new List<WeakReference<byte[]>>(N);
		var sendAttached = typeof(StateTriggerBase).GetMethod(
			"SendAttached", BindingFlags.Instance | BindingFlags.NonPublic)!;
		var sendDetached = typeof(StateTriggerBase).GetMethod(
			"SendDetached", BindingFlags.Instance | BindingFlags.NonPublic)!;

		for (var i = 0; i < N; i++)
		{
			var payload = new byte[1024 * 1024];
			references.Add(new WeakReference<byte[]>(payload));

			if (scenario == Scenario.Control)
				continue;

			var trigger = new SharedPublisherTrigger(payload);
			var state = new VisualState { Name = "Probe" };
			state.StateTriggers.Add(trigger);
			var group = new VisualStateGroup();
			group.States.Add(state);
			VisualStateManager.SetVisualStateGroups(
				new Label(), new VisualStateGroupList { group });

			sendAttached.Invoke(trigger, null);
			if (scenario == Scenario.Mitigation)
				sendDetached.Invoke(trigger, null);

			state.StateTriggers.Clear();
		}

		return references;
	}

	static int CountAlive(IEnumerable<WeakReference<byte[]>> references)
		=> references.Count(reference => reference.TryGetTarget(out _));

	sealed class SharedPublisherTrigger : StateTriggerBase
	{
		readonly byte[] _payload;

		public SharedPublisherTrigger(byte[] payload) => _payload = payload;

		protected override void OnAttached() => SharedPublisher.Changed += OnChanged;

		protected override void OnDetached() => SharedPublisher.Changed -= OnChanged;

		void OnChanged(object? sender, EventArgs e) => GC.KeepAlive(_payload);
	}

	static class SharedPublisher
	{
		public static event EventHandler? Changed;
	}
}