Microsoft.Extensions.ApiDescription.Server ignores minimal API endpoints

[bachratyg]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When using the Microsoft.Extensions.ApiDescription.Server package to generate openapi spec at build minimal routes are not present in the output.

ApiDescription.Server will stop the host right after HostBuilder.Build (at https://github.com/dotnet/runtime/blob/v6.0.8/src/libraries/Microsoft.Extensions.HostFactoryResolver/src/HostFactoryResolver.cs#L344). However minimal endpoints have not been added to the host at this point.

Expected Behavior

Same (equivalent) output from ApiDescription that would be emitted by Swagger at runtime

Steps To Reproduce

a.csproj

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

  <PropertyGroup>
    <TargetFramework>net6.0</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <OpenApiGenerateDocumentsOnBuild>true</OpenApiGenerateDocumentsOnBuild>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Swashbuckle.AspNetCore" Version="6.2.3" />
    <PackageReference Include="Microsoft.Extensions.ApiDescription.Server" Version="6.0.8" PrivateAssets="all" />
  </ItemGroup>

</Project>

Program.cs

using Microsoft.AspNetCore.Mvc;

var builder = WebApplication.CreateBuilder(args);

builder.Services.AddControllers();
builder.Services.AddEndpointsApiExplorer();
builder.Services.AddSwaggerGen();

var app = builder.Build();
app.MapControllers();
app.MapGet("/qwer", () => "Hello!");
app.MapSwagger();
app.UseSwaggerUI();
app.Run();

[ApiController]
public class MyController : ControllerBase
{
    [HttpGet("/asdf")]
    [Produces("text/plain")]
    public string HelloThere() => "Hi!";
}

Start with dotnet run.
Compare obj\a.json (generated by ApiDescription.Server) to https://localhost:5001/swagger/v1/swagger.json (generated by Swagger).
The first does not contain the /qwer endpoint. Diff included for convenience.

diff

 {
   "openapi": "3.0.1",
   "info": {
-    "title": "a, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null",
+    "title": "a",
     "version": "1.0"
   },
   "paths": {
+    "/qwer": {
+      "get": {
+        "tags": [
+          "a"
+        ],
+        "responses": {
+          "200": {
+            "description": "Success",
+            "content": {
+              "text/plain": {
+                "schema": {
+                  "type": "string"
+                }
+              }
+            }
+          }
+        }
+      }
+    },
    "/asdf": {
      "get": {
        "tags": [
          "My"
        ],
        "responses": {
          "200": {
            "description": "Success",
            "content": {
              "text/plain": {
                "schema": {
                  "type": "string"
                }
              }
            }
          }
        }
      }
    }
  },
  "components": { }
}

Exceptions (if any)

No exception

.NET Version

6.0.400

Anything else?

dotnet --info

.NET SDK (reflecting any global.json):
 Version:   6.0.400
 Commit:    7771abd614

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.19044
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\6.0.400\

Host:
  Version:      7.0.0-preview.7.22375.6
  Architecture: x64
  Commit:       eecb028078

.NET SDKs installed:
  6.0.400 [C:\Program Files\dotnet\sdk]
  7.0.100-preview.7.22377.5 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.0-preview.7.22376.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.0-preview.7.22375.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 5.0.17 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 7.0.0-preview.7.22377.1 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  arm64 [C:\Program Files\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\arm64\InstallLocation]
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

[davidfowl]

This is how we fixed it in swashbuckle https://github.com/domaindrivendev/Swashbuckle.AspNetCore/blob/2434c2834cf46628710aaac69c21bb1e8c1c9c6d/src/Swashbuckle.AspNetCore.Cli/HostingApplication.cs#L18 🙈

[bachratyg]

👀 If I understand the Swashbuckle solution correctly this also allows all IHostedServices to start. Considering GenericWebHostService is an IHostedService and processes IStartupFilters that could add more APIs this is a good thing but there may be other IHostedServices configured e.g. some background process that polls an external resource. Also some log emit is possible (to file, database, whatever's configured) if log filtering allows it. During build. Not fun.

[captainsafia]

Triage: marking as a candidate for a bug fix in rc2.