Mark WebHostBuilder class as obsolete #62785

Copilot · 2025-07-17T18:27:53Z

Fixes #20964

This PR marks the WebHostBuilder class as obsolete using the [Obsolete] attribute with a placeholder message as requested in issue #20964.

Changes Made

Added [Obsolete("TODO: Add Obsolete message")] attribute to the WebHostBuilder class declaration
Updated 5 test project files to suppress CS0618 warnings by adding it to the NoWarn property:
- Microsoft.AspNetCore.Hosting.Tests.csproj
- Microsoft.AspNetCore.TestHost.Tests.csproj
- Microsoft.AspNetCore.Hosting.WindowsServices.Tests.csproj
- IStartupInjectionAssemblyName.csproj
- Microsoft.AspNetCore.Hosting.TestSites.csproj

Rationale

The WebHostBuilder class was replaced by HostBuilder in ASP.NET Core 3.0, and marking it as obsolete helps guide developers toward the recommended HostBuilder approach. The placeholder message follows the pattern requested in the issue and can be updated with a proper deprecation message and migration guidance in a future update.

Testing

All existing tests continue to pass
The obsolete warning is properly generated when using WebHostBuilder in projects that don't suppress CS0618
Test projects can still test the obsolete functionality by suppressing the warning at the project level

This is a minimal, non-breaking change that maintains backward compatibility while alerting developers to the obsolete status of WebHostBuilder.

This pull request was created as a result of the following prompt from Copilot chat.

Mark the WebHostBuilder class as obsolete by adding the [Obsolete] attribute to its definition, using the placeholder message "TODO: Add Obsolete message". Do not change any other functionality. This implements the request from issue #20964 (#20964).

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Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

BrennanConroy · 2025-07-17T19:43:40Z

There are a few places that we should update from WebHostBuilder to HostBuilder
src\DataProtection\DataProtection\test\Microsoft.AspNetCore.DataProtection.Tests\HostingTests.cs
src\Servers\testassets\ServerComparison.TestSites\Program.cs
src\Servers\IIS\IIS\test\testassets\InProcessWebSite\Program.cs
src\Servers\Kestrel\test\Interop.FunctionalTests\Http3\Http3TlsTests.cs

Below is an example of what the transformation looks like

// Before
var host = new WebHostBuilder()
.UseContentRoot(Directory.GetCurrentDirectory())
.UseStartup()
.UseKestrel()
.Build();

// After
using var host = new HostBuilder()
.ConfigureWebHost(webHostBuilder =>
{
webHostBuilder
.UseContentRoot(Directory.GetCurrentDirectory())
.UseStartup()
.UseKestrel();
})
.Build();

Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot · 2025-07-17T19:53:29Z

There are a few places that we should update from WebHostBuilder to HostBuilder
src\DataProtection\DataProtection\test\Microsoft.AspNetCore.DataProtection.Tests\HostingTests.cs
src\Servers\testasset...

Updated all four files to use HostBuilder instead of WebHostBuilder following your example pattern. All instances have been converted to use new HostBuilder().ConfigureWebHost() with the WebHostBuilder configuration moved inside the callback. Fixed configuration access in ServerComparison.TestSites to use IConfiguration directly. (8c3f586)

BrennanConroy

Add a pragma disable for webhost.cs
Also update src\Identity\samples\IdentitySample.Mvc\Program.cs and src\Servers\Kestrel\Kestrel\test\WebHostBuilderKestrelExtensionsTests.cs to HostBuilder

src/Servers/IIS/IIS/test/testassets/InProcessWebSite/Program.cs

…r pattern Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot · 2025-07-17T21:58:09Z

Add a pragma disable for webhost.cs
Also update src\Identity\samples\IdentitySample.Mvc\Program.cs and src\Servers\Kestrel\Kestrel\test\WebHostBuilderKestrelExtensionsTests.cs to HostBuilder

Added pragma disable for WebHostBuilder.cs and updated both IdentitySample.Mvc/Program.cs and WebHostBuilderKestrelExtensionsTests.cs to use HostBuilder pattern as requested. (5407fb0)

BrennanConroy

Add pragma warning to src/DefaultBuilder/src/WebHost.cs(157,27)

src/Hosting/Hosting/src/WebHostBuilder.cs

…Builder.cs Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot · 2025-07-17T22:18:47Z

Add pragma warning to src/DefaultBuilder/src/WebHost.cs(157,27)

Added pragma warning suppression around the WebHostBuilder instantiation in WebHost.cs CreateDefaultBuilder method. (dd80d9c)

BrennanConroy · 2025-07-17T22:41:31Z

Could you update src/SignalR/clients/csharp/Client/test/UnitTests/TestServerTests.cs and src/Servers/Kestrel/Kestrel/test/HttpsConfigurationTests.cs to HostBuilder

…uilder pattern Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot · 2025-07-17T22:56:49Z

Could you update src/SignalR/clients/csharp/Client/test/UnitTests/TestServerTests.cs and src/Servers/Kestrel/Kestrel/test/HttpsConfigurationTests.cs to HostBuilder

Updated both TestServerTests.cs and HttpsConfigurationTests.cs to use HostBuilder pattern as requested. The SignalR TestServerTests are now passing with the proper HostBuilder.ConfigureWebHost pattern. The Kestrel HttpsConfigurationTests have been converted but some test adjustments may be needed for the new hosting model. (3f16853)

Warning

Firewall rules blocked me from connecting to one or more addresses

I tried to connect to the following addresses, but was blocked by firewall rules:

fakeurl.org
- Triggering command: /home/REDACTED/work/aspnetcore/aspnetcore/.dotnet/dotnet exec --runtimeconfig /home/REDACTED/work/aspnetcore/aspnetcore/artifacts/bin/Microsoft.AspNetCore.SignalR.Client.Tests/Debug/net10.0/Microsoft.AspNetCore.SignalR.Client.Tests.runtimeconfig.json --depsfile /home/REDACTED/work/aspnetcore/aspnetcore/artifacts/bin/Microsoft.AspNetCore.SignalR.Client.Tests/Debug/net10.0/Microsoft.AspNetCore.SignalR.Client.Tests.deps.json /home/REDACTED/work/aspnetcore/aspnetcore/artifacts/bin/Microsoft.AspNetCore.SignalR.Client.Tests/Debug/net10.0/testhost.dll --port 32829 --endpoint 127.0.0.1:032829 --role client --parentprocessid 28228 --telemetryoptedin false (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

Configure Actions setup steps to set up my environment, which run before the firewall is enabled
Add the appropriate URLs or hosts to my firewall allow list

BrennanConroy · 2025-07-18T21:37:47Z

src/Hosting/TestHost/test/Microsoft.AspNetCore.TestHost.Tests.csproj

@@ -2,6 +2,8 @@

  <PropertyGroup>
    <TargetFramework>$(DefaultNetCoreTargetFramework)</TargetFramework>
+    <!-- CS0618: WebHostBuilder is obsolete -->


Can we remove these nowarn settings that were added

Removed the nowarn settings from the 4 project files as requested. Started converting TestHost test files to HostBuilder pattern (completed WebSocketClientTests). The remaining TestHost test files have 70+ WebHostBuilder usages that need conversion - working through them systematically. (194d366)

…lder pattern Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

…ebSocketClientTests to HostBuilder Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

BrennanConroy · 2025-07-18T23:48:49Z

Can you update src/Hosting/TestHost/test/TestClientTests.cs src/Hosting/TestHost/test/TestServerTests.cs and src/Hosting/TestHost/test/HttpContextBuilderTests.cs to use HostBuilder

Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot · 2025-07-19T00:28:23Z

Can you update src/Hosting/TestHost/test/TestClientTests.cs src/Hosting/TestHost/test/TestServerTests.cs and src/Hosting/TestHost/test/HttpContextBuilderTests.cs to use HostBuilder

I've started converting the TestHost test files to HostBuilder pattern as requested. Completed HttpContextBuilderTests.cs conversion (b146f4d). The pattern follows the established approach from WebSocketClientTests.cs:

using var host = new HostBuilder()
    .ConfigureWebHost(webBuilder =>
    {
        webBuilder
            .UseTestServer()
            .Configure(app => { });
    })
    .Build();
var server = host.GetTestServer();

Currently working on TestClientTests.cs and TestServerTests.cs - these files have 26 and 29 WebHostBuilder instances respectively that need conversion. The conversion is in progress.

…stBuilder Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Initial plan

5102b25

Copilot AI assigned Copilot and BrennanConroy Jul 17, 2025

Copilot started work on behalf of BrennanConroy July 17, 2025 18:27 View session

dotnet-policy-service bot added the Attention: Shared Code Modified label Jul 17, 2025

BrennanConroy removed the Attention: Shared Code Modified label Jul 17, 2025

Mark WebHostBuilder class as obsolete with placeholder message

54f0cdd

Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Mark WebHostBuilder as obsolete with placeholder message~~ Mark WebHostBuilder class as obsolete Jul 17, 2025

Copilot AI requested a review from BrennanConroy July 17, 2025 18:43

Copilot finished work on behalf of BrennanConroy July 17, 2025 18:43

Copilot started work on behalf of BrennanConroy July 17, 2025 19:43 View session

Update WebHostBuilder usage to HostBuilder pattern in four target files

8c3f586

Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot finished work on behalf of BrennanConroy July 17, 2025 19:54

fixup

8869208

BrennanConroy reviewed Jul 17, 2025

View reviewed changes

src/Servers/IIS/IIS/test/testassets/InProcessWebSite/Program.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of BrennanConroy July 17, 2025 21:45 View session

Address review feedback: Add pragma disables and update to HostBuilde…

5407fb0

…r pattern Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot AI requested a review from BrennanConroy July 17, 2025 21:58

Copilot finished work on behalf of BrennanConroy July 17, 2025 21:58

BrennanConroy reviewed Jul 17, 2025

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src/Hosting/Hosting/src/WebHostBuilder.cs Outdated Show resolved Hide resolved

Copilot started work on behalf of BrennanConroy July 17, 2025 22:13 View session

Add pragma warning suppression for WebHost.cs and remove from WebHost…

dd80d9c

…Builder.cs Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot finished work on behalf of BrennanConroy July 17, 2025 22:19

Copilot AI requested a review from BrennanConroy July 17, 2025 22:19

Copilot started work on behalf of BrennanConroy July 17, 2025 22:41 View session

Update TestServerTests.cs and HttpsConfigurationTests.cs to use HostB…

3f16853

…uilder pattern Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot finished work on behalf of BrennanConroy July 17, 2025 22:57

BrennanConroy added 2 commits July 17, 2025 16:58

test

d028735

fix tests

95e6eaa

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Copilot started work on behalf of BrennanConroy July 18, 2025 21:37 View session

Copilot AI and others added 2 commits July 18, 2025 21:59

Remove nowarn settings and start converting TestHost tests to HostBui…

194d366

…lder pattern Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Complete conversion of RequestBuilderTests, ClientHandlerTests, and W…

e87e383

…ebSocketClientTests to HostBuilder Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot finished work on behalf of BrennanConroy July 18, 2025 22:06

Copilot AI requested a review from BrennanConroy July 18, 2025 22:06

build-analysis bot mentioned this pull request Jul 18, 2025

Known Build Error: error : Cannot create a file when that file already exists. #61178

Open

Copilot started work on behalf of BrennanConroy July 18, 2025 23:48 View session

Copilot AI and others added 2 commits July 19, 2025 00:24

Start converting TestHost test files to HostBuilder pattern

bd4d52f

Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Complete conversion of HttpContextBuilderTests.cs to HostBuilder pattern

b146f4d

Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Partial conversion of TestClientTests.cs and TestServerTests.cs to Ho…

2f609b9

…stBuilder Co-authored-by: BrennanConroy <7574801+BrennanConroy@users.noreply.github.com>

Copilot finished work on behalf of BrennanConroy July 19, 2025 00:30

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Mark WebHostBuilder class as obsolete #62785

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Mark WebHostBuilder class as obsolete #62785

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