NullReferenceException in ApplyManagedCodeUpdates when running dotnet or aspire watch against Aspire AppHost

[danroot]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I get the error below when attempting to dotnet watch or aspire run --watch --debug an AppHost with a Blazor WASM project. While it may seem like a minor issue, this really could force a large project that I really want to use Blazor+Aspire for onto Angular. I have tried:

• Adding <script src="/_framework/aspnetcore-browser-refresh.js"></script>. this just results in it being loaded twice
• dotnet dev-certs https --trust This was already done but I did again, and confirmed the cert was trusted.
• Disabling auto-save in VSCode
• Updating to dotnet SDK latest (9.0.304) and aspire latest (9.4)
• Both Mac and Windows have same behavior
• both dotnet watch and aspire run --watch --debug show same stack trace
• Running dotnet watch on the individual projects (ASP.NET API and ASP.NET Blazor WASM) does not exhibit this behavior.

I can run on the individual projects, but then lose the benefits of Aspire! This aspnetcore ticket seems related, but since this is only happening when aspire is involved, I'm opening ticket here.

Expected Behavior

No error. Changing files in either API or Blazor project results in HMR and blazor app refreshes.

Steps To Reproduce

https://github.com/danroot/Spike.AspireWatchIssue I wrote a minimal repro here, but am getting a different error and behavior. There, dotnet watch won't start at all. That said, I have to think the errors are related

Exceptions (if any)

dotnet watch ⌚ File updated: /Users/MyName/Code/MyCompany.RetailPortal/MyCompany.RetailPortal.WebUI/Pages/Customers/CustomersList.razor dotnet watch 🔥 [MyCompany.RetailPortal.Api (net9.0)] Hot reload succeeded. dotnet watch 🔥 [MyCompany.RetailPortal.WebUI (net9.0)] Hot reload succeeded. info: Microsoft.Hosting.Lifetime[0] Application is shutting down... dotnet watch ⌚ [MyCompany.RetailPortal.WebUI (net9.0)] Exited info: Microsoft.Hosting.Lifetime[0] Application is shutting down... dotnet watch ⌚ [MyCompany.RetailPortal.Api (net9.0)] Exited dotnet watch ⌚ [MyCompany.RetailPortal.AppHost (net9.0)] Exited dotnet watch ❌ System.NullReferenceException: Object reference not set to an instance of an object. at Microsoft.DotNet.Watch.BlazorWebAssemblyDeltaApplier.ApplyManagedCodeUpdates(ImmutableArray1 updates, CancellationToken cancellationToken)
at Microsoft.DotNet.Watch.BlazorWebAssemblyHostedDeltaApplier.ApplyManagedCodeUpdates(ImmutableArray1 updates, CancellationToken cancellationToken) at Microsoft.DotNet.Watch.CompilationHandler.<>c__DisplayClass19_0.<<HandleManagedCodeChangesAsync>b__2>d.MoveNext() --- End of stack trace from previous location --- at Microsoft.DotNet.Watch.CompilationHandler.HandleManagedCodeChangesAsync(Func3 restartPrompt, CancellationToken cancellationToken)
at Microsoft.DotNet.Watch.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
at Microsoft.DotNet.Watch.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
at Microsoft.DotNet.Watch.HotReloadDotNetWatcher.WatchAsync(CancellationToken shutdownCancellationToken)
at Microsoft.DotNet.Watch.Program.RunAsync()
dotnet watch ❌ An unexpected error occurred`

.NET Version info

danielroot@MacBookPro Spike.AspireWatchIssue % dotnet --info
.NET SDK:
Version: 9.0.304
Commit: f12f5f6
Workload version: 9.0.300-manifests.407ced12
MSBuild version: 17.14.16+5d8159c5f

Runtime Environment:
OS Name: Mac OS X
OS Version: 15.3
OS Platform: Darwin
RID: osx-arm64
Base Path: /usr/local/share/dotnet/sdk/9.0.304/

.NET workloads installed:
[wasm-tools]
Installation Source: SDK 9.0.300
Manifest Version: 9.0.8/9.0.100
Manifest Path: /usr/local/share/dotnet/sdk-manifests/9.0.100/microsoft.net.workload.mono.toolchain.current/9.0.8/WorkloadManifest.json
Install Type: FileBased

[maui]
Installation Source: SDK 9.0.300
Manifest Version: 9.0.82/9.0.100
Manifest Path: /usr/local/share/dotnet/sdk-manifests/9.0.100/microsoft.net.sdk.maui/9.0.82/WorkloadManifest.json
Install Type: FileBased

Configured to use loose manifests when installing new manifests.

Host:
Version: 9.0.8
Architecture: arm64
Commit: aae90fa090

.NET SDKs installed:
6.0.301 [/usr/local/share/dotnet/sdk]
7.0.100 [/usr/local/share/dotnet/sdk]
7.0.401 [/usr/local/share/dotnet/sdk]
8.0.100 [/usr/local/share/dotnet/sdk]
8.0.203 [/usr/local/share/dotnet/sdk]
8.0.407 [/usr/local/share/dotnet/sdk]
9.0.100 [/usr/local/share/dotnet/sdk]
9.0.202 [/usr/local/share/dotnet/sdk]
9.0.300 [/usr/local/share/dotnet/sdk]
9.0.304 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
Microsoft.AspNetCore.App 6.0.6 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 7.0.11 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 8.0.14 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.3 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.5 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.AspNetCore.App 9.0.8 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
Microsoft.NETCore.App 6.0.6 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 7.0.11 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 8.0.14 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.3 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.5 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
Microsoft.NETCore.App 9.0.8 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

Other architectures found:
x64 [/usr/local/share/dotnet/x64]

Environment variables:
Not set

global.json file:
Not found

Learn more:
https://aka.ms/dotnet/info

Download .NET:
https://aka.ms/dotnet/download

Anything else?

No response

[davidfowl]

Looks like a bug in dotnet watch.

[danroot]

#48909 looks similar, but is closed and merged. Maybe a regression?