Error when running Blazor app before running any other .NET Core 3.0 app: Unable to generate deps.json, it may have been already generated

If you create a Blazor app after installing the .NET Core 3.0 Preview 2 SDK and you have a clean NuGet package cache you get an error when running the app: “Unable to generate deps.json, it may have been already generated”.

Blazor apps rely on a DotNetCliToolReference to run, but they also target .NET Standard:

<Project Sdk="Microsoft.NET.Sdk.Web">

  <PropertyGroup>
    <TargetFramework>netstandard2.0</TargetFramework>
    <RunCommand>dotnet</RunCommand>
    <RunArguments>blazor serve</RunArguments> 
    <LangVersion>7.3</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.AspNetCore.Blazor" Version="0.8.0-preview-19104-04" />
    <PackageReference Include="Microsoft.AspNetCore.Blazor.Build" Version="0.8.0-preview-19104-04" PrivateAssets="all" />

    <DotNetCliToolReference Include="Microsoft.AspNetCore.Blazor.Cli" Version="0.8.0-preview-19104-04" />
  </ItemGroup>

</Project>

It appears that the problem is that the Microsoft.NetCore.App package doesn’t get restored, which then causes the Blazor app to fail at runtime. If you create any other .NET Core app before trying to run the Blazor app, the Microsoft.NetCore.App package is then already restored and the app runs fine. At the very least the error message doesn’t really help you understand what is going on here.

Repro steps:

• Install .NET Core 3.0 Preview 2
• dotnet new -i Microsoft.AspNetCore.Blazor.Templates::0.8.0-preview-19104-04
• dotnet nuget locals all -c
• dotnet new blazor -o BlazorApp1
• cd BlazorApp1
• dotnet run

Expected result:

• Blazor app runs successfully

Actual result:

• Unable to generate deps.json, it may have been already generated. You can specify the “-d” option before the tool name for diagnostic output (for example, “dotnet -d <toolname>”: C:\Program Files\dotnet\sdk\3.0.100-preview-010184\Sdks\Microsoft.NET.Sdk\targets\GenerateDeps\GenerateDeps.proj

To workaround the issue you can create any .NET Core app, which will result in the missing Microsoft.AspNetCore.App package to get successfully restored.

Workaround:

• cd ..
• dotnet new console -o ConsoleApp1
• cd BlazorApp1
• dotnet run

[alierdogan70]

This worked for me. Thank you.

To workaround the issue you can create any .NET Core app, which will result in the missing Microsoft.AspNetCore.App package to get successfully restored.

Workaround:

• cd ..
• dotnet new console -o ConsoleApp1
• cd BlazorApp1
• dotnet run

[nguerrera]

I took a look at this yesterday with @wli3, and we think this will be fixed when the targeting packs are bundled in the .NET Core SDK. This will be in Preview 3 for Windows.

I just checked. It stops reproducing

Closing as fixed.