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mono was the bottleneck restricting our ability to use a newer C# version. mono 6.12 is currently available. Although poorly documented on their website, this supports C# 9. https://www.mono-project.com/docs/about-mono/versioning/#mono-source-versioning indicates mono 6.12 uses Roslyn 3.9.0. https://github.com/dotnet/roslyn/blob/main/docs/wiki/NuGet-packages.md#versioning indicates Roslyn 3.9.0 supports C# 9. This unlocks C# 8 and C# 9 features previously unavailable to us. - https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-version-history#c-version-80 - https://learn.microsoft.com/en-us/dotnet/csharp/whats-new/csharp-version-history#c-version-9 A newer version of StyleCop is required to avoid rules tripping up on the new syntax. Currently only prerelease versions are available but their use is encouraged https://github.com/DotNetAnalyzers/StyleCopAnalyzers/issues/3420#issuecomment-994899135 Fix style rule violations on existing rules where the newer language version makes some existing casts redundant or allows use of the null coalescing assignment operator.