Compiler or analyzer should warn for lower-cased type names

[jcouv]

During LDM discussion on records, there was interest to have an analyzer warn on lower-cased type names. The motivation is that knowing that we discourage lower-cased type names would allow us to introduce new keywords (like record) with less concern about the breaking change.

I'm not sure whether this should be done by the compiler, a roslyn analyzer or some BCL analyzer.

Design:

• We use char.IsLower(...) for lower-case check.
• @ prefix avoids warning.
• All named types, included delegate types, are checked.
• Type and namespace aliases are checked too.

FYI @mikadumont @jmarolf

[CyrusNajmabadi]

If this is about the language and our ability to add such types in a more confident manner, then i think this should be part of the compiler proper. That way every gets it, and everyone sees that this is the official guidance from the team on what you should/shouldn't do.

[jcouv]

Just realized, one issue we'll have to figure out is how we define "lower-case".

[CyrusNajmabadi]

All(char.IsLower)?

[jmarolf]

Agree with @CyrusNajmabadi that the ideal here is for the compiler to emit a new warning as part of warning wave 7. If that cannot happen then we can consider shipping it as an analyzer. Considering that this is a fundamental part of C# it would seem to be appropriate for the dotnet/roslyn repo since dotnet/roslyn-analyzers is for warnings about .NET libraries instead of core language concepts.

[jcouv]

@jaredpar Should we contemplate doing this as part of warning wave 6 (ie. in .NET 6)?

[Youssef1313]

Will prefixing with @ remove the warning?

Otherwise, I can't think of a good workaround, for example, for Xamarin's System.nuint:

[jcouv]

From discussion with Jared, it's too late for .NET 6. We could make this any early preview for release after that (such as 17.1).

@Youssef1313 That's an excellent suggestion. It would make sense given that the @ prefix allows you to use other keywords as identifiers.

[JoeRobich]

Design Meeting Notes:

• Can this be covered by the NamingStyleAnalyzer?
  • By default these diagnostics are suggestions and compiler would prefer warnings.
  • Naming styles are configurable which is at odds with what the compiler is asking for.

Proposal: Keep IDE analyzers as they are. The compiler will add a diagnostic behind a warning wave for VS 17.1 Preview 1.