dotnet watch not loading ASPNETCORE_HOSTINGSTARTUPASSEMBLIES

[kallebysantos]

Is there an existing issue for this?

• I have searched the existing issues

Describe the bug

I'm the author of tailwind-dotnet library that easily adds tailwindcss support for .net apps.

The lib its based in two packages:

1. Msbuild - To compile on build/publish ✅
2. Hosting startup - To launch tailwindcss cli process in watch mode. ❌

When I do dotnet run its successfully starts the tailwindcss Hosting assembly and I can see the css building logs correctly.

run logs

❯ dotnet run
Using launch settings from /Users/kallebysantos/projects/personal/tailwind-dotnet/examples/BlazorNet10/Properties/launchSettings.json...
Building...
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: http://localhost:5293
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
info: Microsoft.Hosting.Lifetime[0]
      Content root path: /Users/kallebysantos/projects/personal/tailwind-dotnet/examples/BlazorNet10
≈ tailwindcss v4.1.17

Done in 28ms
Done in 2ms
Done in 3ms

But when I do dotnet watch or dotnet watch run console only shows the default .net messages and editing a file doesn't trigger css building. Only works when Ctrl-R that forces rebuilding and triggers the MSBuild part.

I did also tried manually specif the --launch-profile but the problem persists.

watch logs

❯ dotnet watch run
dotnet watch 🔥 Hot reload enabled. For a list of supported edits, see https://aka.ms/dotnet/hot-reload.
dotnet watch 💡 Press Ctrl+R to restart.
dotnet watch 🔨 Building /Users/kallebysantos/projects/personal/tailwind-dotnet/examples/BlazorNet10/BlazorNet10.csproj ...
dotnet watch 🔨 Build succeeded: /Users/kallebysantos/projects/personal/tailwind-dotnet/examples/BlazorNet10/BlazorNet10.csproj
Using launch settings from /Users/kallebysantos/projects/personal/tailwind-dotnet/examples/BlazorNet10/Properties/launchSettings.json...
info: Microsoft.Hosting.Lifetime[14]
      Now listening on: http://localhost:5293
info: Microsoft.Hosting.Lifetime[0]
      Application started. Press Ctrl+C to shut down.
info: Microsoft.Hosting.Lifetime[0]
      Hosting environment: Development
info: Microsoft.Hosting.Lifetime[0]
      Content root path: /Users/kallebysantos/projects/personal/tailwind-dotnet/examples/BlazorNet10
warn: Microsoft.AspNetCore.HttpsPolicy.HttpsRedirectionMiddleware[3]
      Failed to determine the https port for redirect.
dotnet watch ⌚ Files updated: ./Components/Pages/4913, ./Components/Pages/Home.razor
dotnet watch ⌚ File deleted: ./Components/Pages/Home.razor~
dotnet watch 🔥 [BlazorNet10 (net10.0)] Hot reload succeeded.
dotnet watch ⌚ Files updated: ./Components/Pages/4913, ./Components/Pages/Home.razor
dotnet watch ⌚ No C# changes to apply.
dotnet watch ⌚ Files updated: ./Components/Pages/4913, ./Components/Pages/Home.razor
dotnet watch ⌚ File deleted: ./Components/Pages/Home.razor~
dotnet watch ⌚ No C# changes to apply.

Expected Behavior

.net watch command to also start the ASPNETCORE_HOSTINGSTARTUPASSEMBLIES

Steps To Reproduce

Follow tailwind-dotnet Getting Started

Exceptions (if any)

No response

.NET Version

10.0.100

Anything else?

dotnet info

10.0.100
❯ dotnet --info
.NET SDK:
 Version:           10.0.100
 Commit:            b0f34d51fc
 Workload version:  10.0.100-manifests.4c0ca8ba
 MSBuild version:   18.0.2+b0f34d51f

Runtime Environment:
 OS Name:     Mac OS X
 OS Version:  26.1
 OS Platform: Darwin
 RID:         osx-arm64
 Base Path:   /usr/local/share/dotnet/sdk/10.0.100/

.NET workloads installed:
There are no installed workloads to display.
Configured to use workload sets when installing new manifests.
No workload sets are installed. Run "dotnet workload restore" to install a workload set.

Host:
  Version:      10.0.0
  Architecture: arm64
  Commit:       b0f34d51fc

.NET SDKs installed:
  8.0.412 [/usr/local/share/dotnet/sdk]
  8.0.415 [/usr/local/share/dotnet/sdk]
  9.0.306 [/usr/local/share/dotnet/sdk]
  10.0.100-preview.4.25258.110 [/usr/local/share/dotnet/sdk]
  10.0.100 [/usr/local/share/dotnet/sdk]

.NET runtimes installed:
  Microsoft.AspNetCore.App 8.0.18 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 8.0.21 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 9.0.10 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 10.0.0-preview.4.25258.110 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.AspNetCore.App 10.0.0 [/usr/local/share/dotnet/shared/Microsoft.AspNetCore.App]
  Microsoft.NETCore.App 8.0.15 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.18 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.20 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 8.0.21 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 9.0.10 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 10.0.0-preview.4.25258.110 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]
  Microsoft.NETCore.App 10.0.0 [/usr/local/share/dotnet/shared/Microsoft.NETCore.App]

[kallebysantos]

I believe that it could be caused when Microsoft.AspNetCore.Watch.BrowserRefresh is injected as Startup assembly.
Seems its overrides the current ASPNETCORE_HOSTINGSTARTUPASSEMBLIES value instead of append to it 😕

Probably happen here

[kallebysantos]

Hey @javiercn & @MackinnonBuck, maybe not related with your work area,
but I believe that this one could be the root cause of this #63130
— I'm pretty sure that I did already use Hosting assemblies in a dotnet watch in the blazor app. And now its affecting the non-wasm apps too