ASPNETCORE_HOSTINGSTARTUPASSEMBLIES not working for Blazor wasm development server

[kallebysantos]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

Previous I remember that I was working in a dotnet new blazorwasm project and did setup the ASPNETCORE_HOSTINGSTARTUPASSEMBLIES for my tailwindcss compiler package.

It was working well, until an user come out saying the following error (issue #15):

crit: Microsoft.AspNetCore.Hosting.Diagnostics[11]
      Hosting startup assembly exception
      System.InvalidOperationException: Startup assembly Tailwind.Hosting failed to execute. See the inner exception for more details.
       ---> System.IO.FileNotFoundException: Could not load file or assembly 'Tailwind.Hosting, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.

      File name: 'Tailwind.Hosting, Culture=neutral, PublicKeyToken=null'
         at System.Reflection.RuntimeAssembly.InternalLoad(AssemblyName assemblyName, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext, RuntimeAssembly requestingAssembly, Boolean throwOnFileNotFound)
         at System.Reflection.Assembly.Load(AssemblyName assemblyRef)
         at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.ExecuteHostingStartups()
         --- End of inner exception stack trace ---

After trying to launch my old project I could see that is not working anymore, I'm not sure if was a sdk version update breaking change. But seems not possible to fit a Hosting Startup Assembly to the Dev Server.

I did also setup a blank solution with a minimal hosted assembly with "Hello world" message and its only working for dotnet web projects while throws on blazorwasm.

---

I know that after publish a blazorwasm it will generate client side only code. But in my case I just need theses Startup Assemblies while development from dotnet watch run command.

Expected Behavior

After run: dotnet run -c Development or dotnet watch run, it should also load the ASPNETCORE_HOSTINGSTARTUPASSEMBLIES

Steps To Reproduce

Add any startup assembly to launchSettings.json then execute with dotnet run -c Development

Exceptions (if any)

crit: Microsoft.AspNetCore.Hosting.Diagnostics[11]
      Hosting startup assembly exception
      System.InvalidOperationException: Startup assembly Tailwind.Hosting failed to execute. See the inner exception for more details.
       ---> System.IO.FileNotFoundException: Could not load file or assembly 'Tailwind.Hosting, Culture=neutral, PublicKeyToken=null'. The system cannot find the file specified.

      File name: 'Tailwind.Hosting, Culture=neutral, PublicKeyToken=null'
         at System.Reflection.RuntimeAssembly.InternalLoad(AssemblyName assemblyName, StackCrawlMark& stackMark, AssemblyLoadContext assemblyLoadContext, RuntimeAssembly requestingAssembly, Boolean throwOnFileNotFound)
         at System.Reflection.Assembly.Load(AssemblyName assemblyRef)
         at Microsoft.AspNetCore.Hosting.GenericWebHostBuilder.ExecuteHostingStartups()
         --- End of inner exception stack trace ---

.NET Version

10, 9 and 8

Anything else?

The Startup library mentioned
Project that I was working before

[javiercn]

@kallebysantos thanks for contacting us.

We don't do anything with hosting startup assemblies. Maybe other folks can give you a hint.

I would say, however, that this is not a supported way of extending our dev server (in fact there isn't one).

[MackinnonBuck]

Thanks for reaching out, @kallebysantos. This scenario isn't supported for the Blazor WebAssembly dev server. Going to close this out as not a direction.