[mono][ios] ToFrozenSet crashes on iOS devices with 8.0.3 release

[ivanpovazan]

Description

With 8.0.3+ servicing release if an iOS app uses ToFrozenSet directly (or through some dependency CommunityToolkit) the app crashes with something like:

at System.Collections.Frozen.SmallFrozenSet`1.GSW[[UIKit.UIView, Microsoft.iOS, Version=17.2.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]].Store(FrozenSet`1 )
   at System.Collections.Frozen.FrozenSetInternalBase`2[[UIKit.UIView, Microsoft.iOS, Version=17.2.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065],[System.Collections.Frozen.SmallFrozenSet`1.GSW[[UIKit.UIView, Microsoft.iOS, Version=17.2.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]], System.Collections.Immutable, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a]]..ctor(IEqualityComparer`1 )
   at System.Collections.Frozen.SmallFrozenSet`1[[UIKit.UIView, Microsoft.iOS, Version=17.2.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065]]..ctor(HashSet`1 )
   at System.Collections.Frozen.FrozenSet.CreateFromSet[UIView](HashSet`1 )
   at System.Collections.Frozen.FrozenSet.ToFrozenSet[UIView](IEnumerable`1 , IEqualityComparer`1 )
   at CommunityToolkit.Maui.Core.Views.AlertView.get_Children()
   at CommunityToolkit.Maui.Core.Views.AlertView.Initialize()
   at CommunityToolkit.Maui.Core.Views.Alert.Show()
   at CommunityToolkit.Maui.Alerts.Toast.ShowPlatform(CancellationToken token)
   at CommunityToolkit.Maui.Alerts.Toast.Show(CancellationToken token)
   at KinesiaOne.ViewModels.SettingsPageViewModel.VersionTapped()

Regression

Yes, this is a regression compared to 8.0.2 servicing release, and is caused by this backport: #97850

Analysis

The problem seems to be related to the fact that the problematic backport actually needs #94787 also to be backported in order to work properly.
@kotlarmilos could you issue the backport?

This is not reproducible on the main (.NET9) branch because we have the both changes (linked above) merged in.

Known workarounds

• Use interpreter as described here: [BUG] Toast.Show crashing on iOS Release builds CommunityToolkit/Maui#1752 (comment)
• Use .NET9 release

Reported as issue

Originally reported in various places:
CommunityToolkit/Maui#1752
CommunityToolkit/Maui#1768
MudBlazor/MudBlazor#6558

[dotnet-policy-service]

Tagging subscribers to 'os-ios': @steveisok, @akoeplinger, @kotlarmilos
See info in area-owners.md if you want to be subscribed.

[ivanpovazan]

Smaller repro with a full AOTed console app (that crashes with 8.0.3 release):

using System;
using System.Collections.Generic;
using System.Collections.Frozen;

namespace HelloWorld
{
    internal class Program
    {
        private static void Main(string[] args)
        {
            try
            {
                var people = new List<Person>()
                { 
                    new Person("John") 
                };

                foreach (var frozenPerson in people.ToFrozenSet())
                {
                    Console.WriteLine($"Element in frozen set has: {frozenPerson.Name} name");
                }
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex);
            }
        }
    }

    class Person
    {
        public Person(string name) => Name = name;
        public string Name { get; set; }
    }
}

[jkotas]

FWIW, CommunityToolkit should not be using FrozenSet in the first place. I have filled CommunityToolkit/Maui#1829 on it.

[plppp2001]

FWIW, CommunityToolkit should not be using FrozenSet in the first place. I have filled CommunityToolkit/Maui#1829 on it.

Yeah exactly. Agreed.

[lambdageek]

Fixed in .NET 8.0.7