[leak-scan] BackButtonBehavior.Command — strong CanExecuteChanged subscription retains the behavior #37635

using System;
using System.Collections.Generic;
using System.Collections.ObjectModel;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Windows.Input;
using Microsoft.Maui.Controls;
using Xunit;

public sealed class LeakTest
{
	const int N = 30;

	[Fact]
	public void BackButtonBehavior_Command_Leaks()
	{
		var command = new TestCommand();
		var control = CreateBackButtonBehaviorCohort(null, mitigate: false);
		var leaky = CreateBackButtonBehaviorCohort(command, mitigate: false);
		var mitigation = CreateBackButtonBehaviorCohort(command, mitigate: true);

		AssertCohorts(control, leaky, mitigation, command);
	}

	[Fact]
	public void TableView_Root_Leaks()
	{
		var root = new TableRoot();
		var control = CreateTableViewCohort(null, mitigate: false);
		var leaky = CreateTableViewCohort(root, mitigate: false);
		var mitigation = CreateTableViewCohort(root, mitigate: true);

		AssertCohorts(control, leaky, mitigation, root);
	}

	[Fact]
	public void IndicatorView_ItemsSource_Leaks()
	{
		var items = new ObservableCollection<int>();
		var control = CreateIndicatorViewCohort(null, mitigate: false);
		var leaky = CreateIndicatorViewCohort(items, mitigate: false);
		var mitigation = CreateIndicatorViewCohort(items, mitigate: true);

		AssertCohorts(control, leaky, mitigation, items);
	}

	[Fact]
	public void Picker_ItemsSource_Leaks()
	{
		var items = new ObservableCollection<int>();
		var control = CreatePickerCohort(null, mitigate: false);
		var leaky = CreatePickerCohort(items, mitigate: false);
		var mitigation = CreatePickerCohort(items, mitigate: true);

		AssertCohorts(control, leaky, mitigation, items);
	}

	static void AssertCohorts(
		WeakReference[] control,
		WeakReference[] leaky,
		WeakReference[] mitigation,
		object root)
	{
		ForceGc();

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

	[MethodImpl(MethodImplOptions.NoInlining)]
	static WeakReference[] CreateBackButtonBehaviorCohort(TestCommand? command, bool mitigate)
	{
		var references = new WeakReference[N];
		for (var i = 0; i < N; i++)
		{
			var payload = new Payload();
			var behavior = new BackButtonBehavior { BindingContext = payload };
			if (command is not null)
				behavior.Command = command;
			if (mitigate)
				behavior.Command = null;
			references[i] = new WeakReference(payload);
		}
		return references;
	}

	[MethodImpl(MethodImplOptions.NoInlining)]
	static WeakReference[] CreateTableViewCohort(TableRoot? root, bool mitigate)
	{
		var references = new WeakReference[N];
		for (var i = 0; i < N; i++)
		{
			var payload = new Payload();
			var view = new TableView { BindingContext = payload };
			if (root is not null)
				view.Root = root;
			if (mitigate)
				view.Root = null!;
			references[i] = new WeakReference(payload);
		}
		return references;
	}

	[MethodImpl(MethodImplOptions.NoInlining)]
	static WeakReference[] CreateIndicatorViewCohort(ObservableCollection<int>? items, bool mitigate)
	{
		var references = new WeakReference[N];
		for (var i = 0; i < N; i++)
		{
			var payload = new Payload();
			var view = new IndicatorView { BindingContext = payload };
			if (items is not null)
				view.ItemsSource = items;
			if (mitigate)
				view.ItemsSource = null;
			references[i] = new WeakReference(payload);
		}
		return references;
	}

	[MethodImpl(MethodImplOptions.NoInlining)]
	static WeakReference[] CreatePickerCohort(ObservableCollection<int>? items, bool mitigate)
	{
		var references = new WeakReference[N];
		for (var i = 0; i < N; i++)
		{
			var payload = new Payload();
			var picker = new Picker { BindingContext = payload };
			if (items is not null)
				picker.ItemsSource = items;
			if (mitigate)
				picker.ItemsSource = null;
			references[i] = new WeakReference(payload);
		}
		return references;
	}

	static int CountAlive(IEnumerable<WeakReference> references) =>
		references.Count(reference => reference.IsAlive);

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

	sealed class Payload
	{
		readonly byte[] _bytes = new byte[1024 * 1024];
	}

	sealed class TestCommand : ICommand
	{
		public event EventHandler? CanExecuteChanged;

		public bool CanExecute(object? parameter) => true;

		public void Execute(object? parameter)
		{
		}

		public void RaiseCanExecuteChanged() => CanExecuteChanged?.Invoke(this, EventArgs.Empty);
	}
}