Scoped CSS is active in netcoreapp3.1 apps

[stefanloerwald]

Describe the bug

Even though scoped CSS is supposed to be a net5.0+ only feature, it is clearly (at least partially) active in projects targetting netcoreapp3.1.

To Reproduce

1. dotnet new blazorserver -f netcoreapp3.1
2. echo "" > foo.razor.css
3. dotnet build

We would expect a build success without scoped CSS, as a file called foo.razor.css should have absolutely no effect.

However, we get the scoped-CSS-related error

error BLAZOR102: The scoped css file 'foo.razor.css' was defined but no associated razor component was found for it.

@javiercn identified the issue here in a GH discussion as originating from https://github.com/dotnet/aspnetcore/blob/master/src/Razor/Microsoft.NET.Sdk.Razor/src/build/netstandard2.0/Sdk.Razor.CurrentVersion.targets#L76

Workaround until fix is available

As @javiercn mentioned, scoped CSS can simply be deactivated in affected projects by adding <ScopedCssEnabled>false</ScopedCssEnabled> to the csproj.

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[SteveSandersonMS]

We don't think this is likely to cause problems since people would not have .razor.css files if targeting older frameworks, hence closing.

[stefanloerwald]

Not quite true, because there have been solutions similar to scoped CSS before net5.0, which involved .razor.css files, but since it only concerns practically obsolete old frameworks, I'm not going to disagree with just ignoring this ;-)