Not all default services are added to WebApplicationBuilder.Services

[halter73]

HostBuilder adds some default services in CreateServiceProvider() that are not added to WebApplicationBuilder.Services until after build.

var builder = WebApplication.CreateBuilder();
// System.InvalidOperationException: No service for type IHost has been registered.
builder.Services.BuildServiceProvider().GetRequiredService<IHost>(); 

Before #34455 was merged, these services never showed up in WebApplicationBuilder.Services even after build. Because CreateServiceProvider() is called in HostBuilder.Build(), we cannot access these service descriptors any earlier without new public API.

[davidfowl]

The scenarios that could be broken here are limited to a couple of default services provided by the HostBuilder. The only potential problem we're aware of so far is a customer trying to replace a built in service only if it wasn't already provided using TryAdd* on the IServiceCollection for one of the built in services. With our current implementation, if the user calls builder.Services.TryAddSingleton<IHostLifetime, MyHostLifetime>(), it will override the default ConsoleLifetime with MyHostLifetime becaues the service collection didn't get a chance to observe the IHostLifetime that comes by default.

This is the case for the default services linked above.

@rafikiassumanimsft I marked this as pri3 as we think the impact is very low.

We've moved this issue to the Backlog milestone. This means that it is not going to be worked on for the coming release. We will reassess the backlog following the current release and consider this item at that time. To learn more about our issue management process and to have better expectation regarding different types of issues you can read our Triage Process.

[nvmkpk]

This is an issue for a nuget package that I am working on. My package when referenced by a web application project, replaces the console window with a wpf window for better viewing of the application logs. It requires replacing ConsoleLifetime with a custom implementation that handles WPF UI and hides the logs on the console. The very least change that will fix the issue is to use TryAdd... when adding the ConsoleLifetime service in HostBuilder.AddLifetime. I hope this will get fixed in .net 7 timeframe.