Empty project does not run in NET 9 WebAssembly on browser

[fraluderin]

Describe the bug

An empty project created with VS 2022 fails to load in browser WebAssembly if targeting NET 9.

To Reproduce

1. Create a new VS 2022 solution using template "Avalonia Cross Platform Application"

2. Select NET 9 as target framework.

3. Build the solution and try to run Browser application. The app loads but remains stuck in splashscreen.

4. Inspecting with dev tools reveals some errors.

Expected behavior

The app should load as expected; the same project starts to work if target framework is changed to NET 8 on all projects.

Avalonia version

11.2.1

OS

Windows

Additional context

These are the SDKs I have:

NET 8 and NET 9 WebAssembly build tools are installed:

[timunie]

Have you tried dotnet workload restore?

[fraluderin]

@timunie Just tried that, unfortunately it did not work. I ran it both in project (VS Dev PowerShell) and in Windows cmd prompt.

[stevemonaco]

Hmm, Browser worked fine for me a week or two ago for me when I tried it from a fresh install with a fresh project. I did create with 11.2.3 (you can type this into the template wizard) and only have 9.0.101 SDK.

My dotnet workload list shows:

Installed Workload Id      Manifest Version       Installation Source
---------------------------------------------------------------------------------
android                    35.0.24/9.0.100        SDK 9.0.100, VS 17.12.35527.113
aspire                     8.2.2/8.0.100          SDK 9.0.100, VS 17.12.35527.113
ios                        18.2.9170/9.0.100      SDK 9.0.100, VS 17.12.35527.113
maccatalyst                18.2.9170/9.0.100      VS 17.12.35527.113
maui-windows               9.0.0/9.0.100          VS 17.12.35527.113
wasm-tools                 9.0.0/9.0.100          SDK 9.0.100

IIRC, I installed via CLI instead of VS: dotnet workload install wasm-tools

[fraluderin]

Just tried again, specifying Avalonia version 11.2.3 in the wizard. The situation remains the same.
I also tried to run dotnet workload restore and dotnet workload update. Everything works fine if I'm on NET 8, but stops working on NET 9.

[timunie]

@fraluderin the wasm tools need to be in the exact correct version matching .NET version. Microsoft is currently breaking it frequently, which can be seen as a good sign imo since it means they are working hard to improve it in general.

Also clear the browser cache from time to time.