.NET 9 Blazor Web App template - build is broken

[GummiGerken]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Each time I make a code change to a page using @rendermode InteractiveWebAssembly I get an error about blazor.boot.json. Testing the browser for this files shows it is returned as an empty file.

If I clean my solution then rebuild, this issue goes away until I make another change to the Blazor WASM code.

Expected Behavior

I should not have to clean my solution every time I make a change to a .razor page in the .Client project.

Steps To Reproduce

• Create an app with the Blazor Web App template
• Add BugDemo.Client/Pages/RandomPage.razor
• Add some C# code
• Debug
• Make changes to your C# code
• Debug again. It'll fail because Blazor.boot.json is empty.
• Clean project
• Debug again. It'll work until more change are made

DEMO REPO

Exceptions (if any)

blazor.boot.json SyntaxError: Unexpected end of JSON input SyntaxError: Unexpected end of JSON input

.NET Version

9.0.101

Anything else?

• Tested on my Windows work computer and Mac running Parallels. Same result both places.
• ASP.NET Core version: 9
• IDE: Visual Studio Version 17.12.3

dotnet --info

.NET SDK:
 Version:           9.0.101
 Commit:            eedb237549
 Workload version:  9.0.100-manifests.4a280210
 MSBuild version:   17.12.12+1cce77968

Runtime Environment:
 OS Name:     Windows
 OS Version:  10.0.22631
 OS Platform: Windows
 RID:         win-arm64
 Base Path:   C:\Program Files\dotnet\sdk\9.0.101\

.NET workloads installed:
 [maccatalyst]
   Installation Source: VS 17.12.35527.113
   Manifest Version:    18.1.9163/9.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.maccatalyst\18.1.9163\WorkloadManifest.json
   Install Type:              Msi

 [aspire]
   Installation Source: VS 17.12.35527.113
   Manifest Version:    8.2.2/8.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\8.0.100\microsoft.net.sdk.aspire\8.2.2\WorkloadManifest.json
   Install Type:              Msi

 [maui-windows]
   Installation Source: VS 17.12.35527.113
   Manifest Version:    9.0.0/9.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.maui\9.0.0\WorkloadManifest.json
   Install Type:              Msi

 [ios]
   Installation Source: VS 17.12.35527.113
   Manifest Version:    18.1.9163/9.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.ios\18.1.9163\WorkloadManifest.json
   Install Type:              Msi

 [android]
   Installation Source: VS 17.12.35527.113
   Manifest Version:    35.0.7/9.0.100
   Manifest Path:       C:\Program Files\dotnet\sdk-manifests\9.0.100\microsoft.net.sdk.android\35.0.7\WorkloadManifest.json
   Install Type:              Msi

Configured to use loose manifests when installing new manifests.

Host:
  Version:      9.0.0
  Architecture: arm64
  Commit:       9d5a6a9aa4

.NET SDKs installed:
  9.0.101 [C:\Program Files\dotnet\sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App]
  Microsoft.WindowsDesktop.App 6.0.36 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 7.0.20 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 8.0.11 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]
  Microsoft.WindowsDesktop.App 9.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

Other architectures found:
  x64   [C:\Program Files\dotnet\x64]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x64\InstallLocation]
  x86   [C:\Program Files (x86)\dotnet]
    registered at [HKLM\SOFTWARE\dotnet\Setup\InstalledVersions\x86\InstallLocation]

Environment variables:
  Not set

global.json file:
  Not found

[javiercn]

@GummiGerken thanks for contacting us.

We believe this is a known issue. See the comment on #59565 (comment) on how to work around it.