Default new Razor Components project loads empty page, then get Failed to reconnect to the server. [Retry?] message.

[Eilon]

Describe the bug

Default new Razor Components project loads empty page, then eventually times out with Failed to reconnect to the server. [Retry?] message.

To Reproduce

Steps to reproduce the behavior:

1. Dev16 Preview 4.1
2. File/New Project/Razor Components
3. F5
4. Browser opens with empty page
5. Then eventually get Failed to reconnect to the server. [Retry?] message:
   
6. Clicking Retry doesn't seem to do anything

Expected behavior

A page should show up

Additional context

dotnet --info:

C:\Users\elipton>dotnet --info
.NET Core SDK (reflecting any global.json):
 Version:   3.0.100-preview4-010745
 Commit:    7b46750b5c

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17763
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100-preview4-010745\

Host (useful for support):
  Version: 3.0.0-preview4-27513-07
  Commit:  f9965e5a7e

.NET Core SDKs installed:
  2.1.504 [C:\Program Files\dotnet\sdk]
  2.1.600-preview-009472 [C:\Program Files\dotnet\sdk]
  2.1.600-preview-009497 [C:\Program Files\dotnet\sdk]
  2.1.600 [C:\Program Files\dotnet\sdk]
  2.2.200-preview-009748 [C:\Program Files\dotnet\sdk]
  2.2.200-preview-009804 [C:\Program Files\dotnet\sdk]
  2.2.200 [C:\Program Files\dotnet\sdk]
  3.0.100-preview4-010745 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  <trimmed>
  Microsoft.AspNetCore.App 2.2.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview4-19162-05 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.8 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.2.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview4-27513-07 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview4-27511-44 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

And here's what's relevant in the CSPROJ:

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Components.Server" Version="3.0.0-preview4-19162-05" />
    <PackageReference Include="Microsoft.AspNetCore.Mvc.NewtonsoftJson" Version="3.0.0-preview4-19162-05" />
  </ItemGroup>

[Eilon]

Saw this in the console log, don't know if relevant:

Microsoft.Hosting.Lifetime: Information: Application started. Press Ctrl+C to shut down.
Microsoft.Hosting.Lifetime: Information: Hosting environment: Development
Microsoft.Hosting.Lifetime: Information: Content root path: C:\Users\elipton\source\repos\WebApplication57\WebApplication57
Microsoft.AspNetCore.Hosting.Internal.GenericWebHostService: Information: Request starting HTTP/2.0 GET https://localhost:44339/  
Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker: Information: Route matched with {page = "/Index"}. Executing page /Index
Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker: Information: Executing an implicit handler method - ModelState is Valid
Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker: Information: Executed an implicit handler method, returned result Microsoft.AspNetCore.Mvc.RazorPages.PageResult.
Microsoft.AspNetCore.Components.Browser.Rendering.RemoteRenderer: Warning: Unhandled exception rendering component: Unable to set property 'AppAssembly' on object of type 'Microsoft.AspNetCore.Components.Routing.Router'. The error was: Unable to cast object of type 'System.String' to type 'System.Reflection.Assembly'.

System.InvalidOperationException: Unable to set property 'AppAssembly' on object of type 'Microsoft.AspNetCore.Components.Routing.Router'. The error was: Unable to cast object of type 'System.String' to type 'System.Reflection.Assembly'. ---> System.InvalidCastException: Unable to cast object of type 'System.String' to type 'System.Reflection.Assembly'.
   at Microsoft.AspNetCore.Components.Reflection.MemberAssignment.PropertySetter`2.SetValue(Object target, Object value)
   at Microsoft.AspNetCore.Components.ParameterCollectionExtensions.SetParameterProperties(ParameterCollection& parameterCollection, Object target)
   --- End of inner exception stack trace ---
   at Microsoft.AspNetCore.Components.ParameterCollectionExtensions.SetParameterProperties(ParameterCollection& parameterCollection, Object target)
   at Microsoft.AspNetCore.Components.Routing.Router.SetParametersAsync(ParameterCollection parameters)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.SetDirectParameters(ParameterCollection parameters)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewComponentFrame(DiffContext& diffContext, Int32 frameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InitializeNewSubtree(DiffContext& diffContext, Int32 frameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.InsertNewFrame(DiffContext& diffContext, Int32 newFrameIndex)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.AppendDiffEntriesForRange(DiffContext& diffContext, Int32 oldStartIndex, Int32 oldEndIndexExcl, Int32 newStartIndex, Int32 newEndIndexExcl)
   at Microsoft.AspNetCore.Components.RenderTree.RenderTreeDiffBuilder.ComputeDiff(Renderer renderer, RenderBatchBuilder batchBuilder, Int32 componentId, ArrayRange`1 oldTree, ArrayRange`1 newTree)
   at Microsoft.AspNetCore.Components.Rendering.ComponentState.RenderIntoBatch(RenderBatchBuilder batchBuilder, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.Rendering.Renderer.RenderInExistingBatch(RenderQueueEntry renderQueueEntry)
   at Microsoft.AspNetCore.Components.Rendering.Renderer.ProcessRenderQueue()
   at Microsoft.AspNetCore.Components.Rendering.Renderer.AddToRenderQueue(Int32 componentId, RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.RenderHandle.Render(RenderFragment renderFragment)
   at Microsoft.AspNetCore.Components.ComponentBase.StateHasChanged()
   at Microsoft.AspNetCore.Components.ComponentBase.CallOnParametersSetAsync()
   at Microsoft.AspNetCore.Components.ComponentBase.RunInitAndSetParametersAsync()
Microsoft.AspNetCore.Mvc.RazorPages.Infrastructure.PageActionInvoker: Information: Executed page /Index in 174.8417ms
Microsoft.AspNetCore.Hosting.Internal.GenericWebHostService: Information: Request finished in 337.5319ms 200 text/html; charset=utf-8

But if it's not relevant, there still definitely shouldn't be some exception there.

[rynowak]

This is related to ref-assemblies. Ref assemblies don't include non-public members, and components currently recommend using non-public members for component properties.

  {
    "Kind": "Components.Component",
    "Name": "Microsoft.AspNetCore.Components.Routing.Router",
    "AssemblyName": "Microsoft.AspNetCore.Components",
    "Documentation": null,
    "TagOutputHint": null,
    "TagMatchingRules": [
      {
        "TagName": "Router",
        "ParentTag": null,
        "TagStructure": 0,
        "Attributes": [],
        "Diagnostics": []
      }
    ],
    "BoundAttributes": [], // There should be something here!
    "AllowedChildTags": [],
    "Diagnostics": [],
    "Metadata": {
      "Runtime.Name": "Components.IComponent",
      "Common.TypeName": "Microsoft.AspNetCore.Components.Routing.Router"
    }
  },

The parameters of the component are not being discovered, and the compiler behaves differently depending on the declared type of a parameter (tag helpers). Since the parameters aren't being found, all parameters are treated like string-likes. So <Router AppAssembly="typeof(Program).Assembly" /> passes a string, not an Assembly` object.

This means that recent builds are complete blocked from using any components we ship in the box.

[rynowak]

@SteveSandersonMS - lets discuss this this week.