Optional parameter is not cleared when navigating to same page with a different set of parameters

[ThomasBleijendaal]

When navigating to a page which has two @page directives with one or two parameters, the optional one is not always cleared when navigating to this page when the optional parameter should have be set to its default.

In the documentation it is said to use two @page directives for support for optional parameters.

To Reproduce:

Start with the sample app of Razor Components, and add a new page:

@page "/node/{Id:int}"
@page "/node/{ParentId:int}/{Id:int}"

@functions {
    [Parameter]
    private int? ParentId { get; set; } = null;

    [Parameter]
    private int Id { get; set; }
}

update NavMenu.cshtml to include:

<NavLink href="node/1">First click me</NavLink>
<NavLink href="node/2/3">Then click me</NavLink>
<NavLink href="node/4">And finally click me</NavLink>

Start the app.

Navigating to node/1 works: ParentId is null and Id is 1.
Navigating to node/2/3 works: ParentId is 2 and Id is 3.
Navigating to node/4 works but gives: ParentId stays 2, and Id is 4.

Expected behavior

When navigating to node/4 I expect ParentId to be null again and Id to be 4. ParentId is a Parameter, and should be set to null when the route does not provide the information.

Additional context

 Version:   3.0.100-preview-010184
 Commit:    c57bde4593

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.17134
 OS Platform: Windows
 RID:         win10-x64
 Base Path:   C:\Program Files\dotnet\sdk\3.0.100-preview-010184\

Host (useful for support):
  Version: 3.0.0-preview-27324-5
  Commit:  63a01b08e5

.NET Core SDKs installed:
  1.0.0-preview2-003121 [C:\Program Files\dotnet\sdk]
  1.0.0-preview2-003131 [C:\Program Files\dotnet\sdk]
  1.0.0 [C:\Program Files\dotnet\sdk]
  1.0.4 [C:\Program Files\dotnet\sdk]
  1.1.0 [C:\Program Files\dotnet\sdk]
  2.0.0 [C:\Program Files\dotnet\sdk]
  2.0.3 [C:\Program Files\dotnet\sdk]
  2.1.2 [C:\Program Files\dotnet\sdk]
  2.1.4 [C:\Program Files\dotnet\sdk]
  2.1.100 [C:\Program Files\dotnet\sdk]
  2.1.200 [C:\Program Files\dotnet\sdk]
  2.1.201 [C:\Program Files\dotnet\sdk]
  2.1.202 [C:\Program Files\dotnet\sdk]
  2.1.300-preview1-008174 [C:\Program Files\dotnet\sdk]
  2.1.300-rc1-008673 [C:\Program Files\dotnet\sdk]
  2.1.300 [C:\Program Files\dotnet\sdk]
  2.1.302 [C:\Program Files\dotnet\sdk]
  2.1.400 [C:\Program Files\dotnet\sdk]
  2.1.401 [C:\Program Files\dotnet\sdk]
  2.1.403 [C:\Program Files\dotnet\sdk]
  2.1.500 [C:\Program Files\dotnet\sdk]
  2.1.503 [C:\Program Files\dotnet\sdk]
  2.1.600-preview-009472 [C:\Program Files\dotnet\sdk]
  3.0.100-preview-010184 [C:\Program Files\dotnet\sdk]

.NET Core runtimes installed:
  Microsoft.AspNetCore.All 2.1.0-preview1-final [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.0-rc1-final [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.All 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.All]
  Microsoft.AspNetCore.App 2.1.0-preview1-final [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.0-rc1-final [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 3.0.0-preview-19075-0444 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 1.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.0.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.0.4 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 1.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.3 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.0.9 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.0-preview1-26216-03 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.0-rc1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.2 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.3-servicing-26724-03 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.6 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 2.1.7 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 3.0.0-preview-27324-5 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 3.0.0-preview-27325-3 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]```

[Andrzej-W]

This is very old bug and it was tracked somewhere. It was fixed but then reverted. See this #6864. Hopefully both problems will be solved in preview 3.

[mkArtakMSFT]

@SteveSandersonMS, is this fixed already?

[SteveSandersonMS]

@mkArtakMSFT We fixed it in 0.7.0, but then we had to revert the fix just prior to the 0.7.0 release because it caused a bad regression elsewhere. We don't yet have a design for what the replacement fix should be. It should remain on the backlog, but it's not at the top of the priority list in my opinion.

[mkArtakMSFT]

Thanks @SteveSandersonMS. Can you please dupe this one with that one you reference and close this issue?

[mkArtakMSFT]

@SteveSandersonMS, I assume you meant 0.8.0 there, did you?

[SteveSandersonMS]

Yes, 0.8.0. Thanks!

The change where we originally fixed this was #4797, but then we reverted it in #6931.

I've searched and can't find another issue on the backlog tracking making a further long-term fix, so perhaps this issue can be that one for us now :)

Putting on backlog.