Blazor WebAssembly hot reload support broken when changing environment from Development

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

When launching Blazor WASM standalone application via dotnet watch (behind the scenes launching a dev server to host it) hot reload support is broken when host environment is changed to anything else than Development. In the browser’s console it reports:

Error: System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.AspNetCore.Components.WebAssembly.HotReload.WebAssemblyHotReload.ApplyHotReloadDelta(String moduleIdString, Byte[] metadataDelta, Byte[] ilDeta) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture) --- End of stack trace from previous location --- at Microsoft.JSInterop.Infrastructure.DotNetDispatcher.InvokeSynchronously(JSRuntime jsRuntime, DotNetInvocationInfo& callInfo, IDotNetObjectReference objectReference, String argsJson) at Microsoft.JSInterop.Infrastructure.DotNetDispatcher.Invoke(JSRuntime jsRuntime, DotNetInvocationInfo& invocationInfo, String argsJson) at Microsoft.AspNetCore.Components.WebAssembly.Services.DefaultWebAssemblyJSRuntime.InvokeDotNet(String assemblyName, String methodIdentifier, String dotNetObjectId, String argsJson)

Also _framework/blazor-hotreload.js is not loaded and is not fetched (not causing 404 errors).

Related: #35194 #37462

Expected Behavior

Hot reload feature should not depend on the environment’s name? If it definitely should then please make it bolded in the documentation. Developers are often customizing these names, e.g. Local for the local development machine which breaks the functionality.

Steps To Reproduce

Change ASPNETCORE_ENVIRONMENT in the project’s launchSettings.json from Development to anything else.

Exceptions (if any)

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

.NET Version

6.0.100

Anything else?

.NET SDK (reflecting any global.json): Version: 6.0.100 Commit: 9e8b04bbff

Runtime Environment: OS Name: Windows OS Version: 10.0.19044 OS Platform: Windows RID: win10-x64 Base Path: C:\Program Files\dotnet\sdk\6.0.100\

Host (useful for support): Version: 6.0.1 Commit: 3a25a7f1cc

.NET SDKs installed: 3.1.416 [C:\Program Files\dotnet\sdk] 6.0.100 [C:\Program Files\dotnet\sdk]

.NET runtimes installed: Microsoft.AspNetCore.App 3.1.21 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 5.0.12 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 5.0.13 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 6.0.0 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.AspNetCore.App 6.0.1 [C:\Program Files\dotnet\shared\Microsoft.AspNetCore.App] Microsoft.NETCore.App 3.1.21 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 5.0.12 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 5.0.13 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 6.0.0 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.NETCore.App 6.0.1 [C:\Program Files\dotnet\shared\Microsoft.NETCore.App] Microsoft.WindowsDesktop.App 3.1.21 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 3.1.22 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 5.0.12 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 5.0.13 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App] Microsoft.WindowsDesktop.App 6.0.0 [C:\Program Files\dotnet\shared\Microsoft.WindowsDesktop.App]

[andylegear]

Confirming same issue here, when ASPNETCORE_ENVIRONMENT is Local. VS 17.1.0. Changing ASPNETCORE_ENVIRONMENT to Development “fixes” the issue, but would prefer not to have to make that switch.

I experienced this exact issue. Confirming that the switch of the ASPNETCORE_ENVIRONMENT back to Development in my profile fixed the problem

[lonix1]

I think I read somewhere that hot reload doesn’t work when any non-default environment variables or switches are used. Which is confirmed by basic testing - when you change any option it stops working, when you add switches it stops working. But if you keep the defaults (which includes the development environment) then it works.

Also debugging + hot reload don’t work at the same time.

I hoped it would be fixed in the latest v6.0.300 (from a few days ago), but unfortunately I still get the issue.