application/vnd.foo+json disables problem details

[sylveon]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When you make a request using an Accept header that uses the json suffix, for example application/vnd.foo+json, this disables problem details, despite the requested output format being json.

Expected Behavior

Problem details should not be disabled

Steps To Reproduce

1. Create a minimal API project with the following code:

var builder = WebApplication.CreateSlimBuilder(args);
builder.Services.AddProblemDetails();

var app = builder.Build();
app.UseStatusCodePages();
app.MapPost("/hello", () => TypedResults.Ok());
app.Run();

2. Run curl http://localhost:5182/hello -H "Accept: application/vnd.foo+json"
3. Observe curl prints Status Code: 405; Method Not Allowed instead of {"type":"https://tools.ietf.org/html/rfc9110#section-15.5.6","title":"Method Not Allowed","status":405}

Exceptions (if any)

N/A

.NET Version

9.0.100-preview.7.24407.12

Anything else?

ASP.NET Core version: 8.0 I think? My TFM is net8.0
IDE: VSCode 1.92.2

> dotnet --info   
.NET SDK:
 Version:           9.0.100-preview.7.24407.12
 Commit:            d672b8a045
 Workload version:  9.0.100-manifests.baed1e37
 MSBuild version:   17.12.0-preview-24374-02+48e81c6f1

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.26100
 OS Platform: Windows
 RID:         win-x64
 Base Path:   C:\Program Files\dotnet\sdk\9.0.100-preview.7.24407.12\

.NET workloads installed:
Configured to use loose manifests when installing new manifests.
There are no installed workloads to display.

Host:
  Version:      9.0.0-preview.7.24405.7
  Architecture: x64
  Commit:       static

.NET SDKs installed:
  9.0.100-preview.7.24407.12 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.32 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.0-preview.7.24406.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]       
  Microsoft.NETCore.App 6.0.18 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.32 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.0-preview.7.24405.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 6.0.18 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.32 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.33 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.7 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 9.0.0-preview.7.24405.2 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

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

Environment variables:
  Not set

global.json file:
  Not found

Learn more:
  https://aka.ms/dotnet/info

Download .NET:
  https://aka.ms/dotnet/download

For context, I am currently implementing https://github.com/swiftlang/swift-package-manager/blob/main/Documentation/PackageRegistry/Registry.md, which uses a custom Accept header for API versioning, but requires problem details responses for any error.