Custom IServiceProviderFactory in ASP.NET Core - asp.net-core

Question

I wrote a custom IServiceProviderFactory and installed it in Program.cs of a new app like this:
public static IHostBuilder CreateHostBuilder(string[] args) =>
Host.CreateDefaultBuilder(args)
.UseServiceProviderFactory(new PropertyInjectingContainerFactory())
.ConfigureWebHostDefaults(webBuilder =>
{
webBuilder.UseStartup<Startup>();
});
It does lead to the correct configure function in Startup.cs getting called:
public void ConfigureContainer(PropertyInjectingContainerFactory.Builder builder)
{
builder.AddInjectAttribute<InjectDependencyAttribute>();
}
However, my created container only ever resolves two services: IConfiguration and IHost.
Everything else is resolved by the default container apparantly (for instance a service like ILogger<T> on a controller). What do I do wrong?
Here's the code for my custom factory - and please understand that I probably should be using an existing third-party container, but I also want to understand how this all fits together.
public class PropertyInjectingContainerFactory : IServiceProviderFactory<PropertyInjectingContainerFactory.Builder>
{
public Builder CreateBuilder(IServiceCollection services)
{
return new Builder(services);
}
public IServiceProvider CreateServiceProvider(Builder containerBuilder)
{
return containerBuilder.CreateServiceProvider();
}
public class Builder
{
internal readonly IServiceCollection services;
internal List<Type> attributeTypes = new List<Type>();
public Builder(IServiceCollection services)
{
this.services = services;
}
public Builder AddInjectAttribute<A>()
where A : Attribute
{
attributeTypes.Add(typeof(A));
return this;
}
public IServiceProvider CreateServiceProvider()
=> new PropertyInjectingServiceProvider(services.BuildServiceProvider(), attributeTypes.ToArray());
}
class PropertyInjectingServiceProvider : IServiceProvider
{
private readonly IServiceProvider services;
private readonly Type[] injectAttributes;
public PropertyInjectingServiceProvider(IServiceProvider services, Type[] injectAttributes)
{
this.services = services;
this.injectAttributes = injectAttributes;
}
// This function is only called for `IConfiguration` and `IHost` - why?
public object GetService(Type serviceType)
{
var service = services.GetService(serviceType);
InjectProperties(service);
return service;
}
private void InjectProperties(Object target)
{
var type = target.GetType();
var candidateProperties = type.GetProperties(System.Reflection.BindingFlags.Public);
var props = from p in candidateProperties
where injectAttributes.Any(a => p.GetCustomAttributes(a, true).Any())
select p;
foreach (var prop in props)
{
prop.SetValue(target, services.GetService(prop.PropertyType));
}
}
}
}