Improve HostBuilder and WebApplicationBuilder ServiceCollection integration

[halter73]

Today WebApplicationBuilder has some hacky logic to synchronize the WebApplicationBuilder.Services IServiceCollection and the HostBuilder's IServiceCollection in case any custom services have been added via HostFactoryResolver. This logic can be found here.

The synchronization is not perfect and can lead to bugs like the following throwing even though the equivalent would work in Startup.ConfigureServices when using the HostBuilder directly.

builder.Services.BuildServiceProvider().GetRequiredService<IHostApplicationLifetime>();

We should look into adding an API to HostBuilder to share an IServiceCollection with the WebApplicationBuilder.

Related: #61634

Tagging subscribers to this area: @eerhardt, @maryamariyan
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Issue Details

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Today WebApplicationBuilder has some hacky logic to synchronize the WebApplicationBuilder.Services IServiceCollection and the HostBuilder's IServiceCollection in case any custom services have been added via HostFactoryResolver. This logic can be found here.

The synchronization is not perfect and can lead to bugs like the following throwing even though it would work in Startup.ConfigureServices when using the HostBuilder directly.

builder.Services.BuildServiceProvider().GetRequiredService<IHostApplicationLifetime>();

We should look into adding an API to HostBuilder to share an IServiceCollection with the WebApplicationBuilder.

Related: #61634

Author:	halter73
Assignees:	-
Labels:	api-suggestion, area-Extensions-Hosting
Milestone:	-

[eerhardt]

@halter73 - Do you have an idea of what the API would look like? Can you update the issue to use the API proposal template?

https://github.com/dotnet/runtime/issues/new?assignees=&labels=api-suggestion&template=02_api_proposal.yml&title=%5BAPI+Proposal%5D%3A+

[halter73]

This should be addressed by the API proposed in #61634.