[Bug]: Calling `WithFallbackConverter` results in a stack overflow

[meld-cp]

Describe the bug 🐞

Calling WithFallbackConverter results in a StackOverflow

Step to reproduce

Try to run:

var app = RxAppBuilder.CreateReactiveUIBuilder()
	.WithWpf()
	.WithFallbackConverter( new DefaultFallbackConverter() )
	.BuildApp()
;

Reproduction repository

https://github.com/reactiveui/ReactiveUI

Expected behavior

A default fallback converter being used and no stack overflow

Screenshots 🖼️

No response

IDE

Visual Studio 2022

Operating system

Windows

Version

No response

Device

No response

ReactiveUI Version

23.1.1

Additional information ℹ️

WPF Stacktrace:

[System.StackOverflowException unhandled]
ReactiveUI!ReactiveUI.Helpers.ArgumentExceptionHelper.ThrowIfNull(object argument, string paramName) Line 25
	at /_/src/ReactiveUI/Helpers/ArgumentExceptionHelper.cs(25)
ReactiveUI!ReactiveUI.Builder.BuilderMixins.WithFallbackConverter(ReactiveUI.Builder.IReactiveUIBuilder builder, ReactiveUI.IBindingFallbackConverter converter) Line 1278
	at /_/src/ReactiveUI/Mixins/BuilderMixins.cs(1278)
ReactiveUI!ReactiveUI.Builder.BuilderMixins.WithFallbackConverter(ReactiveUI.Builder.IReactiveUIBuilder builder, ReactiveUI.IBindingFallbackConverter converter) Line 1279
	at /_/src/ReactiveUI/Mixins/BuilderMixins.cs(1279)
[The 1 frame(s) above this were repeated 32060 times]
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler)
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.InvokeImpl()
WindowsBase.dll!MS.Internal.CulturePreservingExecutionContext.CallbackWrapper(object obj)
System.Private.CoreLib.dll!System.Threading.ExecutionContext.RunInternal(System.Threading.ExecutionContext executionContext, System.Threading.ContextCallback callback, object state)
WindowsBase.dll!MS.Internal.CulturePreservingExecutionContext.Run(MS.Internal.CulturePreservingExecutionContext executionContext, System.Threading.ContextCallback callback, object state)
WindowsBase.dll!System.Windows.Threading.DispatcherOperation.Invoke()
WindowsBase.dll!System.Windows.Threading.Dispatcher.ProcessQueue()
WindowsBase.dll!System.Windows.Threading.Dispatcher.WndProcHook(nint hwnd, int msg, nint wParam, nint lParam, ref bool handled)
WindowsBase.dll!MS.Win32.HwndWrapper.WndProc(nint hwnd, int msg, nint wParam, nint lParam, ref bool handled)
WindowsBase.dll!MS.Win32.HwndSubclass.DispatcherCallbackOperation(object o)
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.InternalRealCall(System.Delegate callback, object args, int numArgs)
WindowsBase.dll!System.Windows.Threading.ExceptionWrapper.TryCatchWhen(object source, System.Delegate callback, object args, int numArgs, System.Delegate catchHandler)
WindowsBase.dll!System.Windows.Threading.Dispatcher.LegacyInvokeImpl(System.Windows.Threading.DispatcherPriority priority, System.TimeSpan timeout, System.Delegate method, object args, int numArgs)
WindowsBase.dll!System.Windows.Threading.Dispatcher.Invoke(System.Windows.Threading.DispatcherPriority priority, System.Delegate method, object arg)
WindowsBase.dll!MS.Win32.HwndSubclass.SubclassWndProc(nint hwnd, int msg, nint wParam, nint lParam)
[Native to Managed Transition]
[Managed to Native Transition]
WindowsBase.dll!System.Windows.Threading.Dispatcher.PushFrameImpl(System.Windows.Threading.DispatcherFrame frame)
PresentationFramework.dll!System.Windows.Application.RunDispatcher(object ignore)
PresentationFramework.dll!System.Windows.Application.RunInternal(System.Windows.Window window)
MyApp.dll!MyApp.Wpf.App.Main()

[glennawatson]

This has been fixed in #4301.

The root cause was that WithFallbackConverter, WithConverter, WithSetMethodConverter, and WithConvertersFrom were only defined on the concrete ReactiveUIBuilder class -- not on the IReactiveUIBuilder interface. The extension methods in BuilderMixins call builder.WithFallbackConverter(...) on IReactiveUIBuilder, which resolved back to the extension method itself rather than dispatching to the concrete implementation, causing infinite recursion.

The fix adds all converter registration methods to the IReactiveUIBuilder interface so the extension methods correctly delegate to the implementation.

This should be available in the next release.