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Autofac + ASP.NET Core 6 + Hot Reload/Debug = crash

One of the cool things in .NET 6 is the concept of hot reload if doing something like dotnet watch run. This extends into ASP.NET to things like Razor pages. If your like me, wants a specific IoC container – like Autofac, you might run into problems with this and even running the debugger. The reason they behave the same is that the hot reload feature is actually leveraging edit&continue, a feature of the debugging facilities of the .NET Core infrastructure.

The problem I ran into was with .NET 6 preview 7 that it didn’t know how to resolve the constructor for an internal class in one of the Microsofts Razor assemblies. When calling MapControllers() on the endpoints:

app.UseEndpoints(endpoints => endpoints.MapControllers());

It would crash with the following:

Autofac.Core.DependencyResolutionException: An exception was thrown while activating Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionEndpointDataSourceFactory -> Microsoft.AspNetCore.Mvc.Infrastructure.DefaultActionDescriptorCollectionProvider -> λ:Microsoft.AspNetCore.Mvc.Infrastructure.IActionDescriptorChangeProvider[] -> Microsoft.AspNetCore.Mvc.HotReload.HotReloadService -> Microsoft.AspNetCore.Mvc.Razor.RazorHotReload.
       ---> Autofac.Core.DependencyResolutionException: None of the constructors found with 'Autofac.Core.Activators.Reflection.DefaultConstructorFinder' on type 'Microsoft.AspNetCore.Mvc.Razor.RazorHotReload' can be invoked with the available services and parameters:

My workaround for this is basically to just explicitly add razor pages, even though I’m not using it:

public void ConfigureServices(IServiceCollection services)
{
    services.AddRazorPages();
}

With that in place, I was able to debug and also use hot reloading for my code.

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