.NET SDK 6 Preview 7 generated file `ImplicitNamespaceImports.cs` contains error CS8773

[andyleejordan]

Good morning,

I just tracked down a CI failure to a .NET SDK update. With dotnet v6.0.100-preview.7.21379.14 our whole build is failing with the repeated error:

...obj\Debug\net6.0\PowerShellEditorServices.Test.ImplicitNamespaceImports.cs(2,1):
error CS8773: Feature 'global using directive' is not available in C# 9.0. Please use language version 10.0 or greater.

This error did not show up last night, with the same build on the same code, but using dotnet v6.0.100-preview.6.21355.2. The big difference seeming to be Preview 6 to Preview 7.

I looked at #19446, but we do not (as far as I can find) use any <Import Include=...> statements in any of our .csproj files.

We are explicitly using language version 9.0, so I will update us to 10.0 to work around this, but it seems like there may be an underlying and unintended change between the two previews?

[KalleOlaviNiemitalo]

#19599 already changed the feature to opt-in so the file will not be generated unless you set the ImplicitUsings property or define Using items. But this was merged after 6.0 preview 7. If you do not intend to use implicit usings in PowerShell, I suggest disabling them with DisableImplicitNamespaceImports until you can update to a version where they are disabled by default.

[andyleejordan]

Is the issue that Preview 7 opted everyone in, and the opt-out by default wasn't merged in time to fix that for Preview 7?

[davidfowl]

It’s changed in rc1 not preview 7

[AArnott]

I just hit this when upgrading a project from the 5.0 SDK to 6.0.100-preview.7.21379.14.
My project explicitly sets LangVersion to 9. IMO the SDK shouldn't generate files that require C# 10 without confirming that the LangVersion is at least set to that level.

[andyleejordan]

Yup, and I'm already looking to revert my language version back to 9.0 because I didn't realize that 10.0 would force all devs to update the SDK on their box to Preview 7 :/

[davidfowl]

It'll be fixed in rc1 builds. For now you can disable the feature.

[andyleejordan]

Oh, here's the information I needed, for those that come looking:

• https://docs.microsoft.com/en-us/dotnet/core/compatibility/sdk/6.0/implicit-namespaces
• https://docs.microsoft.com/en-us/dotnet/core/project-sdk/msbuild-props#disableimplicitnamespaceimports

[davidfowl]

More information on the latest changes #19521