[Blazor] JS initializers declared in RCLs run twice

[MackinnonBuck]

Summary

JS initializers declared in a Razor Class Libraries have each of their callbacks executed twice.

Steps to reproduce

1. Install versions 8.0.303 and 9.0.100-preview.6.24328.19 of the .NET SDK
2. Run dotnet new blazor -int None -o ./BlazorApp -f net8.0
3. Run dotnet new razorclasslib -o ./RazorClassLibrary -f net8.0
4. Run dotnet add ./BlazorApp/BlazorApp.csproj reference ./RazorClassLibrary/RazorClassLibrary.csproj
5. Create the file ./RazorClassLibrary/wwwroot/RazorClassLibrary.lib.module.js and add the following content:

   export function afterWebStarted() {
       console.log('Hello, world!');
   }

6. Run dotnet run --project .\BlazorApp\BlazorApp.csproj
7. ❌ Observe that the browser console window logged "Hello, world!" twice
8. Run dotnet new globaljson --sdk-version 8.0.303
9. Run dotnet run --project .\BlazorApp\BlazorApp.csproj
10. 🟢 Observe that the browser console window now only logs "Hello, world!" once

Other notes

1. This issue also occurs when creating projects with a net9.0 TFM
2. The .NET 8 SDK is not required to reproduce the bug - it was included in the repro steps only to demonstrate that the issue is unique to the .NET 9 SDK.

[javiercn]

@MackinnonBuck is this an 8.0 app compiled with the 9.0 SDK?

[MackinnonBuck]

@javiercn yes, but it also reproduces for a 9.0 app as well.

[javiercn]

@MackinnonBuck but it does not reproduce with a net 8.0 SDK, isn't it? (It's surprising that our tests didn't catch this)

[MackinnonBuck]

@javiercn yes, that's correct

[MackinnonBuck]

No longer reproduces in the latest SDK build.

It looks like dotnet/sdk#41995 was the culprit, and this is now fixed.