Exception thrown when attempting to use model members in sections in a Razor Page

[DamianEdwards]

Repro

1. Create a new Razor Pages project in Visual Studio
2. Open the Index.cshtml.cs model class file
3. Add a property to be accessed from the page's CSHTML file: public string Message { get; set; } = "Hello";
4. Open the Index.cshtml page file
5. Attempt to render the value of Model.Message inside the "Scripts" section:

   @section Scripts {
      <h1>@Model.Message</h1>
   }

Expected Result

The message is rendered in the HTML OK.

Actual Result

InvalidCastException: Unable to cast object of type 'Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary`1[System.Object]' to type 'Microsoft.AspNetCore.Mvc.ViewFeatures.ViewDataDictionary`1[WebApplication26.Pages.IndexModel]'.

@rynowak @NTaylorMullen

[Eilon]

@rynowak - please reassign as appropriate.

[rynowak]

Razor generates a property like the following. Code here

public ViewDataDictionary<TModel> ViewData => (ViewDataDictionary<TModel>)PageContext?.ViewData;

It's this cast operation that's blowing up.

When we're executing the Layout, we'll set ViewContext.ViewData here to the appropriate type for the Layout page, which will be ViewDataDictionary<object>.

I'm not sure why it's the same ViewContext. We should be providing a different ViewContext to the Layout.

[rynowak]

#6310 will accomplish the bulk of what we need to do. I'll do a follow up afterwards to add a test

[rynowak]

Fixed by: 2992f8e
Test Added: c1dd95b