Using MapGroup() with MapControllers() results in incorrect path in Swagger

Is there an existing issue for this?

[X] I have searched the existing issues

Describe the bug

When doing this:

app.MapGroup("prefix").MapControllers();

Assuming there is a FooController, the generated OpenAPI spec incorrectly says the path is /Foo instead of /prefix/Foo:

  ...
  paths": {
    "/Foo": {
      "get": {
        "tags": [
          "Foo"
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "string"
                }
              },
              "application/json": {
                "schema": {
                  "type": "string"
                }
              },
              "text/json": {
                "schema": {
                  "type": "string"
                }
              }
            }
          }
        }
      }
    },
    ...

Trying to curl both /Foo and /prefix/Foo shows that the wrong path was generated in the OpenAPI spec:

$ curl -f http://localhost:5147/Foo
curl: (22) The requested URL returned error: 404
$ curl -f http://localhost:5147/prefix/Foo
It works!

Interestingly, this problem only happens with MapControllers() and minimal API endpoints created using MapGet() for example don't experience this problem. See the steps to reproduce to see what I mean.

Expected Behavior

The OpenAPI spec should generate the correct path when using MapGroup() with MapControllers().

Steps To Reproduce

Program.cs

using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.ApiExplorer;

var builder = WebApplication.CreateBuilder(args);
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();
builder.Services.AddControllers();

var app = builder.Build();
app.UseRouting();
app.UseEndpoints(endpoints =>
{
    endpoints.MapGroup("prefix").MapGet("/Bar", () => "It works!\n");
});
app.MapGroup("prefix").MapControllers();

app.UseSwagger();
app.UseSwaggerUI();

// Print relative paths
var p = app.Services.GetService<IApiDescriptionGroupCollectionProvider>()!;
foreach (var group in p.ApiDescriptionGroups.Items)
{
    foreach (var api in group.Items)
    {
        Console.WriteLine(api.RelativePath);
    }
}

app.Run();

[ApiController]
[Route("[controller]")]
public class FooController : Controller
{
    [HttpGet]
    public string Get() => "It works!\n";
}

$ dotnet run
Building...
prefix/Bar
Foo
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: http://localhost:5147
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
info: Microsoft.Hosting.Lifetime[0]
      Content root path: /home/brian/projects/SwaggerBugExample/SwaggerBugExample

$ curl -f http://localhost:5147/swagger/v1/swagger.json
{
  "openapi": "3.0.1",
  "info": {
    "title": "SwaggerBugExample",
    "version": "1.0"
  },
  "paths": {
    "/Foo": {
      "get": {
        "tags": [
          "Foo"
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "string"
                }
              },
              "application/json": {
                "schema": {
                  "type": "string"
                }
              },
              "text/json": {
                "schema": {
                  "type": "string"
                }
              }
            }
          }
        }
      }
    },
    "/prefix/Bar": {
      "get": {
        "tags": [
          "SwaggerBugExample"
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "string"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": { }

$ curl -f http://localhost:5147/Foo
curl: (22) The requested URL returned error: 404
$ curl -f http://localhost:5147/prefix/Foo
It works!
$ curl -f http://localhost:5147/prefix/Bar
It works!

dotnet / aspnetcore