An OpenAPI-enabled HTTP API in .NET 5, in two files, using top-level statements programming style

api.cs

using System;
using Microsoft.AspNetCore.Builder;
using Microsoft.AspNetCore.Hosting;
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Hosting;
using Microsoft.Extensions.Logging;
using Carter;
using Carter.Response;
using Carter.OpenApi;
using Microsoft.OpenApi.Models;

Host.CreateDefaultBuilder(args)
    .ConfigureWebHostDefaults(webBuilder =>
    {
        webBuilder
            .ConfigureServices((services) => 
            {
                services.AddSwaggerGen(setup => 
                {
                    setup.SwaggerDoc("Swashbuckle", new OpenApiInfo
                    {
                        Version = "v1",
                        Title = "Swashbuckle"
                    });
                });
                services.AddControllers();
                services.AddCarter(options =>
                {
                    options.OpenApi.DocumentTitle = "Carter"; 
                    options.OpenApi.ServerUrls = new[] { "https://localhost:5001" };
                });
            })
            .Configure((app) =>
            {
                app.UseSwagger(setup => 
                {
                    setup.RouteTemplate = "/openapi/{documentName}";
                });

                app.UseSwaggerUI(setup => 
                {
                    setup.SwaggerEndpoint("/openapi/Swashbuckle", "Swashbuckle");
                    setup.SwaggerEndpoint("/openapi", "Carter");
                });
                app.UseHttpsRedirection();
                app.UseRouting();
                app.UseEndpoints(endpoints =>
                {
                    endpoints.MapControllers();
                    endpoints.MapCarter();
                });
            });
    })
.Build()
    .Run();

[Route("ServerTime")]
[ApiController]
public class TimeController : ControllerBase
{
    [HttpGet]
    public ActionResult<TimeResponse> GetServerTime() => 
        Ok(new TimeResponse(DateTime.Now));
}

public record TimeResponse(DateTime ServerTime);

public class TimeModule : CarterModule
{
    public TimeModule()
    {
        this.Get<GetServerTimeResponse>("/GetServerTime", async(request, response) =>
            await response.AsJson(new TimeResponse(DateTime.Now)));
    }
}

public class GetServerTimeResponse : RouteMetaData
{
    public override string OperationId => "GetServerTime";

    public override RouteMetaDataResponse[] Responses { get; } =
    {
        new RouteMetaDataResponse
        {
            Code = 200,
            Description = $"A {nameof(TimeResponse)}",
            Response = typeof(TimeResponse)
        }
    };
}

api.csproj

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>net5.0</TargetFramework>
    <LangVersion>Preview</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Carter" Version="5.2.0" />
    <PackageReference Include="Swashbuckle.AspNetCore" Version="5.6.3" />
  </ItemGroup>


</Project>