Deprecating WebHostBuilder, IWebHost, and WebHost

[BrennanConroy]

Discussion for announcement aspnet/Announcements#526

[julealgon]

Why not deprecate HostBuilder as well? Don't you want everyone to move to the new HostApplicationBuilder-based API?

I don't see a point in maintaining anything other than the new HostApplicationBuilder approach. It is superior to the previous method in every way. Having both available is quite confusing.

[martincostello]

FWIW, I would have had to refactor a lot more tests in some projects if that had been deprecated too 😅

[davidfowl]

The new interface IHostApplicationBuilder exists in .NET 9 only so it's tough to deprecate HostBuilder and IHostBuilder because many people have never used IHostApplicationBuilder. Going forward though we'll recommand HostApplicationBuilder and IHostApplicationBuilder

[julealgon]

Fair enough. Thanks @davidfowl .

[Lanayx]

The After example seems to be misleading:

using var host = new HostBuilder()
    .ConfigureWebHost(webHostBuilder =>
    {
        webHostBuilder
            .UseTestServer() // If using TestServer
            .UseContentRoot(Directory.GetCurrentDirectory())
            .UseStartup()
            .UseKestrel(); // <--- This line should be deleted
    })
    .Build();
await host.StartAsync();

var testServer = host.GetTestServer();

While .UseKestrel worked fine in Before version, in After version it leads to the following exception

System.InvalidCastException
Unable to cast object of type 'Microsoft.AspNetCore.Server.Kestrel.Core.KestrelServerImpl' to type 'Microsoft.AspNetCore.TestHost.TestServer'.

Once .UseKestrel is removed, everything works fine in new version. Remarkably, the advise to use ChatGPT worked - it didn't include that line while doing conversion.