Add [Obsolete] attribute to WebHost class and IWebHost interface with proper diagnostic codes, convert sample apps to HostBuilder pattern

[Copilot]

Part of #20964, #27528, and #63017

Pattern transformation applied:

// Before (deprecated)
public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
    WebHost.CreateDefaultBuilder(args)
        .UseStartup<Startup>();

// After (recommended)
public static IHostBuilder CreateHostBuilder(string[] args) =>
    Host.CreateDefaultBuilder(args)
        .ConfigureWebHostDefaults(webBuilder =>
        {
            webBuilder.UseStartup<Startup>();
        });

Diagnostic IDs

Add ASPDEPR008 and ASPDEPR009. I grouped a bunch of APIs with ASPDEPR008, the ones that are closely related to WebHost and IWebHost. And ASPDEPR009 is for the Windows Service APIs that use IWebHost. Listed all the APIs below and the specific obsoletion messages used.

ASPDEPR008

"IWebHost is obsolete. Use IHost instead. For more information, visit https://aka.ms/aspnet/deprecate/008.":
public interface IWebHost { }
IWebHost IWebHostBuilder.Build();
public IWebHost TestServer.Host { get; }
public static TestServer WebHostBuilderExtensions.GetTestServer(this IWebHost host) { }
public static HttpClient WebHostBuilderExtensions.GetTestClient(this IWebHost host) { }

"WebHost is obsolete. Use HostBuilder or WebApplicationBuilder instead. For more information, visit https://aka.ms/aspnet/deprecate/008.":
public static class WebHost { }

"WebHostExtensions is obsolete. Use Host.CreateDefaultBuilder or WebApplication.CreateBuilder instead. For more information, visit https://aka.ms/aspnet/deprecate/008.":
public static class WebHostExtensions { }

"IWebHost, which this method uses, is obsolete. Use one of the ctors that takes an IServiceProvider instead. For more information, visit https://aka.ms/aspnet/deprecate/008.":
public TestServer(IWebHostBuilder builder) { }
public TestServer(IWebHostBuilder builder, IFeatureCollection featureCollection) { }

"WebHost, which this method uses, is obsolete. Use one of the overloads that takes an IServiceProvider instead. For more information, visit https://aka.ms/aspnet/deprecate/008.":
protected virtual TestServer WebApplicationFactory.CreateServer(IWebHostBuilder builder) { }

ASPDEPR009

"Use UseWindowsService and AddHostedService instead. For more information, visit https://aka.ms/aspnet/deprecate/009.":
public class WebHostService { }
public static class WebHostWindowsServiceExtensions { }

[BrennanConroy]

@copilot I meant https://github.com/dotnet/aspnetcore/blob/main/src/DefaultBuilder/src/WebHost.cs

[Copilot]

@copilot I meant https://github.com/dotnet/aspnetcore/blob/main/src/DefaultBuilder/src/WebHost.cs

You're absolutely right! I applied the [Obsolete] attribute to the correct WebHost class in /src/DefaultBuilder/src/WebHost.cs (the public static class that provides convenience methods) rather than the internal implementation. I've also reverted the changes to the wrong files and added appropriate pragma warning suppressions for test code and samples. All builds and tests are now passing. (commit 4c94381)

[BrennanConroy]

@copilot can you convert the sample apps to HostBuilder?
e.g.

Before:

public static void Main(string[] args)
    {
        CreateWebHostBuilder(args).Build().Run();
    }

    public static IWebHostBuilder CreateWebHostBuilder(string[] args) =>
        WebHost.CreateDefaultBuilder(args)
            .UseStartup<Startup>();

After:

public static void Main(string[] args)
    {
        CreateHostBuilder(args).Build().Run();
    }

    public static IHostBuilder CreateHostBuilder(string[] args) =>
        Host.CreateDefaultBuilder(args)
            .ConfigureWebHostDefaults(webBuilder =>
            {
                webBuilder.UseStartup<Startup>();
            });

[Copilot]

@copilot can you convert the sample apps to HostBuilder?
e.g.

...

I've converted 12 sample apps from the WebHost.CreateDefaultBuilder pattern to the Host.CreateDefaultBuilder pattern as requested. The conversion follows the exact pattern you provided:

Converted files:

• Security sample apps (8): Cookies, SocialSample, DynamicSchemes, PathSchemeSelection, StaticFilesAuth, CustomPolicyProvider, ClaimsTransformation, Identity.ExternalClaims
• DefaultBuilder sample: SampleApp DirectWebHost method
• Test assets (3): CreateDefaultBuilderApp, CreateDefaultBuilderOfTApp, DependencyInjectionApp
• Components test asset: ComponentsApp.Server

Pattern applied:

• Changed CreateWebHostBuilder to CreateHostBuilder
• Changed IWebHostBuilder to IHostBuilder
• Wrapped configuration in ConfigureWebHostDefaults(webBuilder => { ... })
• Updated using statements to replace Microsoft.AspNetCore with Microsoft.Extensions.Hosting

All builds and tests pass successfully. (commit ac4fcb6)

[BrennanConroy]

@copilot let's mark IWebHost as obsolete now

[Copilot]

@copilot let's mark IWebHost as obsolete now

I've marked the IWebHost interface as obsolete with the message "IWebHost is obsolete. Use IHost instead." and added appropriate pragma warning suppressions to framework code that still needs to use it for backward compatibility. The obsolete attribute properly generates compiler warnings for consumers while maintaining compatibility. (commit 410ec79)

[BrennanConroy]

@copilot Disable the warning in https://github.com/dotnet/aspnetcore/blob/main/src/Servers/Kestrel/shared/test/TransportTestHelpers/IWebHostPortExtensions.cs

[Copilot]

@copilot I updated one of the obsoletions to use ASPDEPR008 diagnostic code, could you update the appropriate pragma disables to use ASPDEPR008 instead of CS0618

Updated the WebHost obsolete attribute to use ASPDEPR008 diagnostic code and replaced the appropriate CS0618 pragma disables with ASPDEPR008 in files that use WebHost methods. All builds and tests pass successfully. (commit fc1770f)

[BrennanConroy]

@copilot
Add disabling ASPDEPR008 to src/Servers/IIS/IIS/test/testassets/InProcessWebSite/Program.cs

Also, update anymore warning disables with the rest of the diagnostic ID changes.

[Copilot]

@copilot
Add disabling ASPDEPR008 to src/Servers/IIS/IIS/test/testassets/InProcessWebSite/Program.cs

...

Added ASPDEPR008 suppression to InProcessWebSite/Program.cs and updated all pragma disables to use the correct diagnostic IDs: ASPDEPR008 for WebHost/IWebHost related obsoletions and ASPDEPR004 for WindowsService related obsoletions. Also added project-level warning suppressions for test projects that legitimately test obsolete functionality. (commit 650081c)

[Copilot]

Pull Request Overview

This PR adds obsolete attributes to WebHost class and IWebHost interface with proper diagnostic codes, and converts sample apps to use the HostBuilder pattern. The goal is to deprecate the legacy WebHost pattern in favor of the more modern Host.CreateDefaultBuilder approach.

• Adds ASPDEPR008 and ASPDEPR009 diagnostic codes to mark WebHost and related APIs as obsolete
• Converts sample applications from WebHost.CreateDefaultBuilder to Host.CreateDefaultBuilder pattern
• Adds pragma warning suppressions to test code that still needs to use deprecated APIs

Reviewed Changes

Copilot reviewed 53 out of 53 changed files in this pull request and generated no comments.

File	Description
Various sample Program.cs files	Converted from WebHost pattern to Host.CreateDefaultBuilder pattern
Test files	Added pragma warning suppressions for ASPDEPR008 to continue testing deprecated APIs
WebHost-related source files	Added Obsolete attributes with appropriate diagnostic IDs
WebApplicationFactory.cs	Added obsolete attributes to methods using IWebHost

[martincostello]

@BrennanConroy Maybe it's just because it's a TODO that hasn't been actioned yet, but if I visit this link I get this message: