Double Page Declaration Causes Object Reference Not Set Error

[CheetahChrome]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

If a user accidently adds an extra page declaration such as

Razor Page Duplication

@page "/additionalinfo"
@page "/additionalinfo" 
@using BPG.Model

...

A runtime exception is thrown.

---

Exception on Page

NullReferenceException: Object reference not set to an instance of an object.

StackTrace

BlazorProvingGroundServerApp.Pages.Pages__Host.ExecuteAsync() in _Host.cshtml
-
@namespace BlazorProvingGroundServerApp.Pages
@addTagHelper *, Microsoft.AspNetCore.Mvc.TagHelpers
@{
    Layout = "_Layout";
}
<component type="typeof(App)" render-mode="ServerPrerendered" />

Expected Behavior

(This falls into a user doing a Garbage in, garbage out scenario...) But, this should be caught, if at runtime, then a more robust error describing multiple page declarations found. Or if at compile time, at least as a warning, or better an error.

Steps To Reproduce

1. Create a component page.
2. Duplicate the @page line.

Exceptions (if any)

NullReferenceException: Object reference not set to an instance of an object.
Microsoft.AspNetCore.Components.Routing.Router.Refresh(bool isNavigationIntercepted)

.NET Version

.Net 6

Anything else?

No response

[ghost]

Thanks for contacting us.

We're moving this issue to the .NET 7 Planning milestone for future evaluation / consideration. We would like to keep this around to collect more feedback, which can help us with prioritizing this work. We will re-evaluate this issue, during our next planning meeting(s).
If we later determine, that the issue has no community involvement, or it's very rare and low-impact issue, we will close it - so that the team can focus on more important and high impact issues.
To learn more about what to expect next and how this issue will be handled you can read more about our triage process here.

[geogreg1]

Here is what appears to be a variation or related issue: duplicate page in the RCL causes an an exception to be thrown when router code is modified even though the duplicate page is not being consumed. https://stackoverflow.com/questions/72310618/adding-an-additional-assembly-to-app-razor-router-in-blazor-causes-host-cshtml

[mkArtakMSFT]

Thanks for contacting us. We believe that having different page attributes works. Having duplicate page attributes is just not a scenario that we support, and we don't plan to spend resources to improve the experience with duplicate page attributes.