On creating Startup, custom services do not resolves

Describe the bug

I have a library for strongly typed IConfiguration wrapper, it works fine on 2.2, but in 3.0.0 GenericWebHostBuilder.UseStartup does not resolve custom services, already added to IServiceCollection to HostBuilder/WebHostBuilder at the moment Startup created using ActivatorUtilities.

For now used GenericWebHostBuilder.HostServiceProvider. It can resolve only IHostingEnvironment and IConfiguration.

To Reproduce

Complete example: https://github.com/phema-team/Phema.Configuration/tree/master/examples/Phema.Configuration.Example Steps to reproduce the behavior:

1. Use builder.ConfigureServices((c, s) => s.AddSomeService())
2. Use builder.ConfigureWebHostDefaults (call builder.ConfigureWebHost) and add Startup
3. In Startup add SomeService to constructor

Expected behavior

All services added previously to IServiceCollection can be resolved in Startup creation

Screenshots

Additional context

I think we should use in GenericWebHostBuilder.UseStartup for creating Startup all previously registered services passing IServiceProvider built from IServiceCollection parameter to GenericWebHostBuilder.HostServiceProvider. Logic the same, if IHostingEnvironment/IConfiguration resolve from WebHostBuilderContext, else try to resolve from already added services

I added pull request with potential fix https://github.com/aspnet/AspNetCore/pull/9296

[Tratcher]

And the official announcement: https://github.com/aspnet/Announcements/issues/353

[Tratcher]

This issue is closed, please follow the announcement issue instead.