Startup fails when static method is passed to WebHostBuilder.Configure

[nil4]

using System;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;

static class Program {
    static void Main(string[] args) => new WebHostBuilder()
        .UseKestrel()
        .Configure(ConfigureApplication)
        .Build().Run();

    static void ConfigureApplication(IApplicationBuilder app) {}
}

Expected: the application starts up and ConfigureApplication is called.

Actual: the application crashes on startup with stack trace:

Unhandled Exception: System.NullReferenceException: Object reference not set to an instance of an object.
   at System.Object.GetType()
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.ResolveApplicationName()
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.BuildHostingServices()
   at Microsoft.AspNetCore.Hosting.WebHostBuilder.Build()
   at Program.Main(String[] args) in D:\projects\Repro\Program.cs:line 6

In WebHostBuilder.ResolveApplicationName, _startup.ConfigureDelegate.Target is assumed to be non-null. This assumption is invalid for static methods.

[nil4]

Pull request #713 resolves this issue by using _startup.ConfigureDelegate.GetMethodInfo().DeclaringType instead.

[khellang]

Doesn't #714 get rind of this code completely?

[davidfowl]

Nope, we still determine the application name https://github.com/aspnet/Hosting/blob/dev/src/Microsoft.AspNetCore.Hosting/WebHostBuilderExtensions.cs#L82

[nil4]

PR #716 resolves this issue. /cc @davidfowl @Tratcher