Missing public API to generate config entries procedurally

[ratijas]

Situation

My mod manages a list of things of type T, each of which has an associated config entry. The list is fixed at compile time, but the things are not bound to individual class fields, nor should they.

BepInEx and LethalConfig both support creation of config entries on the fly:

using BepInEx;
using BepInEx.Configuration;

class Thing {
    public string Name;
    public ConfigEntry<int> Weight;
}

Thing[] Things;
foreach (var t in Things)
{
    t.Weight = Config.Bind("Section", t.Name, 0);
}

using LethalConfig;
using LethalConfig.ConfigItems;
using LethalConfig.ConfigItems.Options;

foreach (var t in Things)
{
    var slider = new IntSliderConfigItem(t.Weight.Entry, new IntSliderOptions
    {
        RequiresRestart = false,
        CanModifyCallback = CanModifyWeightsNow,
    });
    LethalConfigManager.AddConfigItem(slider);
}

Problem

CSync doesn't provide an equivalent API. The only supported option is to write a class with field annotated with a certain attribute:

[PublicAPI]
public class SyncedConfig2<T> : ISyncedConfig where T : SyncedConfig2<T>
{
    // [...]
    private static Lazy<FieldInfo[]> SyncedEntryFields = new(
        () => AccessTools.GetDeclaredFields(typeof(T))
            .Where(field => field.GetCustomAttribute<SyncedEntryFieldAttribute>() is not null)
            .Where(field => typeof(SyncedEntryBase).IsAssignableFrom(field.FieldType))
            .ToArray()
    );

    internal void PopulateEntryContainer()
    {
        if (Interlocked.Exchange(ref _entryContainerPopulated, 1) != 0) return;
        foreach (var fieldInfo in SyncedEntryFields.Value)
        {
            var entryBase = (SyncedEntryBase)fieldInfo.GetValue(this);
            EntryContainer.Add(entryBase.BoxedEntry.ToSyncedEntryIdentifier(), entryBase);
        }
    }
    // [...]
}

This requires fields to be declared in advanced for every entry in the list, which is not the most maintainable solution.

Expected behavior

Provide public API for adding entries to the EntryContainer programmatically.

Workaround

Since we mods are patching the whole game by forcefully exposing their entire codebase, why mods themselves should be any different? After all, why not…

<PackageReference Include="Sigurd.BepInEx.CSync" Version="5.0.1" Publicize="true" />

foreach (var t in Things)
{
    // This is basically what ConfigFile.PopulateEntryContainer does
    SyncedEntryBase entryBase = t.Weight;
    EntryContainer.Add(entryBase.BoxedEntry.ToSyncedEntryIdentifier(), entryBase);
}

ConfigManager.Register(this);

oh well, can't have any privacy \s

[ratijas]

Not sure if it is related to my modifications (probably not, since they only do what the base CSync would do anyway), but today during a run I started getting these red errors in logs each time I'd attempt to modify and Apply a value via LethalConfig:

[Error  :   BepInEx] System.NullReferenceException: Object reference not set to an instance of an object
  at Unity.Collections.LowLevel.Unsafe.UnsafeList`1[T].get_Item (System.Int32 index) [0x00000] in <d0c0081e1ce74649912b55aa702cd13d>:0
  at Unity.Collections.NativeList`1[T].get_Item (System.Int32 index) [0x00000] in <d0c0081e1ce74649912b55aa702cd13d>:0
  at Unity.Netcode.NetworkList`1[T].set_Item (System.Int32 index, T value) [0x00023] in <895801699cfc4b4ab52267f31e2a4998>:0
  at CSync.Lib.ConfigSyncBehaviour+<>c__DisplayClass18_0.<OnNetworkSpawn>b__0 (System.Object _, BepInEx.Configuration.SettingChangedEventArgs args) [0x00014] in /home/runner/work/CSync/CSync/CSync/CSync/Lib/ConfigSyncBehaviour.cs:70
  at BepInEx.Configuration.ConfigFile.OnSettingChanged (System.Object sender, BepInEx.Configuration.ConfigEntryBase changedEntryBase) [0x00048] in <fe49c90fe8e24102b42489c11910c71c>:0

My modpack is pretty vanilla, no other mods depend on CSync. However, I am not 100% sure if other players had any extra mods installed (I played with random people whom I never met before).

Possible cause is Late Company and people late-joining while in orbit?

Another possible cause is LethalConfig, because that's what I use to change the config at runtime. I get those CSync errors every time I click Apply or otherwise change config values in a LethalConfig's button Click handler.

[ratijas]

I tried registering synced config entry fields legitimately (via attributes), it didn't make any difference.

CSync breaks after host quits the game (back to the main menu).