Modify ViewBag in Controller will cause RuntimeBinderException in 6.0.0-preview4

Describe the bug

If I add some “ViewBag” code in MVC Controller will cause RuntimeBinderException in 6.0.0-preview4.

RuntimeBinderException: 'System.Dynamic.DynamicObject' does not contain a definition for 'OK'

It could be a hot reload bug.

To Reproduce

I recorded all steps in video here: https://youtu.be/JDX7nM7Fh7c (Only 85 seconds without any sound/voice)

Exceptions (if any)

Microsoft.CSharp.RuntimeBinder.RuntimeBinderException: 'System.Dynamic.DynamicObject' does not contain a definition for 'OK'
   at CallSite.Target(Closure , CallSite , Object , String )
   at System.Dynamic.UpdateDelegates.UpdateAndExecute2[T0,T1,TRet](CallSite site, T0 arg0, T1 arg1) in System.Linq.Expressions.dll:token 0x6001062+0x11d
   at Projects.Controllers.HomeController.Index() in Projects.dll:token 0x600006b+0x58
   at lambda_method1(Closure , Object , Object[] )
   at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.SyncActionResultExecutor.Execute(IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000fa1+0x0
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeActionMethodAsync() in Microsoft.AspNetCore.Mvc.Core.dll:token 0x600099f+0x2e
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x600099c+0x33a
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeNextActionFilterAsync() in Microsoft.AspNetCore.Mvc.Core.dll:token 0x600099d+0xa
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Rethrow(ActionExecutedContextSealed context) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x60009a1+0x15
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x600099c+0x39a
   at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.InvokeInnerFilterAsync() in Microsoft.AspNetCore.Mvc.Core.dll:token 0x60009a0+0xa
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000a7f+0x6a
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000a74+0x15
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000a6b+0x835
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.InvokeFilterPipelineAsync() in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000a68+0xa
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000a77+0x77
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Awaited|17_0(ResourceInvoker invoker, Task task, IDisposable scope) in Microsoft.AspNetCore.Mvc.Core.dll:token 0x6000a77+0xfb
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|6_0(Endpoint endpoint, Task requestTask, ILogger logger) in Microsoft.AspNetCore.Routing.dll:token 0x60000aa+0x5e
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context) in Microsoft.AspNetCore.Authorization.Policy.dll:token 0x600000b+0x16b
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddleware.Invoke(HttpContext context) in Microsoft.AspNetCore.Diagnostics.dll:token 0x60000aa+0x82

Further technical details

• ASP.NET Core version:

  Microsoft.AspNetCore.App 6.0.0-preview.4.21253.5
  

• Include the output of dotnet --info

  .NET SDK (reflecting any global.json):
  Version:   6.0.100-preview.4.21255.9
  Commit:    950e4949a7
  
  Runtime Environment:
  OS Name:     Windows
  OS Version:  10.0.19042
  OS Platform: Windows
  RID:         win10-x64
  Base Path:   C:\Program Files\dotnet\sdk\6.0.100-preview.4.21255.9\
  
  Host (useful for support):
  Version: 6.0.0-preview.4.21253.7
  Commit:  bfd6048a60
  
  .NET SDKs installed:
  3.1.100 [C:\Program Files\dotnet\sdk]
  3.1.115 [C:\Program Files\dotnet\sdk]
  3.1.201 [C:\Program Files\dotnet\sdk]
  3.1.301 [C:\Program Files\dotnet\sdk]
  3.1.302 [C:\Program Files\dotnet\sdk]
  3.1.402 [C:\Program Files\dotnet\sdk]
  3.1.409 [C:\Program Files\dotnet\sdk]
  5.0.104 [C:\Program Files\dotnet\sdk]
  5.0.203 [C:\Program Files\dotnet\sdk]
  5.0.300 [C:\Program Files\dotnet\sdk]
  6.0.100-preview.4.21255.9 [C:\Program Files\dotnet\sdk]
  
  .NET runtimes installed:
  Microsoft.AspNetCore.All 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 6.0.0-preview.4.21253.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.28 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 6.0.0-preview.4.21253.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.1.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.8 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.9 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 3.1.15 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.4 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 5.0.6 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 6.0.0-preview.4.21254.5 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  
  To install additional .NET runtimes or SDKs:
  https://aka.ms/dotnet-download
  

• The IDE (VS / VS Code/ VS4Mac) you’re running on, and its version

  Version: 1.56.2 (user setup)
  Commit: 054a9295330880ed74ceaedda236253b4f39a335
  Date: 2021-05-12T17:13:13.157Z
  Electron: 12.0.4
  Chrome: 89.0.4389.114
  Node.js: 14.16.0
  V8: 8.9.255.24-electron.0
  OS: Windows_NT x64 10.0.19042
  

[pranavkm]

@doggy8088, thanks for trying this out with the newest builds. We’ll use https://github.com/dotnet/roslyn/issues/56592 to track addressing this as it’s not specific to MVC. In the meanwhile, you could consider using ViewData instead to pass contents to your views. We generally recommend it over ViewBag anyway since it’s ever so slightly better performing.

[doggy8088]

@mkArtakMSFT I tried 6.0.100-rc.1.21458.32. The issue still there. ☹