[api evolution] Make all public enums into structs with static properties

[ktoso]

We need to do the usual trick of

public struct Thing { 
  let underlying: _Thing

  internal enum _Thing { 
  case example
  }

  public static example = .init(.example)
 
  internal init(_ underlying: _Thing) { 
    self.underlying = underlying
  }
}

to ensure future API compatibility -- for example for all settings, like singleton allocation strategy etc.

[ktoso]

This is required for 1.0

[ktoso]

For errors the dance is even more involved:

public struct SomeError: Error, Sendable { 
  let underlying: _Storage

  internal class _Storage { 
    let error: _SomeError
    let file: String
    let line: UInt
  }

  internal enum _SomeError { 
  case something(...)
  }

  internal init(error: _SomeError, file: String = #fileID (or path? I forgot?), line: UInt = #line) { 
    self.underlying = .init(error: error, file: file, line: line)
  }

  var description: String { 
    "(Self.self)(\(error: \(underlying.error), at: \(underlying.file):\(underlying.line))
}

or something like that...

Did I get that right @fabianfett @glbrntt ?

[fabianfett]

@ktoso That looks right. Don't forget the CustomStringConvertible conformance so that description is actually hit. #fileID is the correct one.

[ktoso]

Thanks for double checking :)