Use Swagger schema format to distinguish wrapper types from primitives

[evanrelf]

Notes:

• These format values are non-standard / incorrect Swagger, so they're hidden behind a flag (off by default).
• Replacing the original instance ToSchema (OverrideToSchema ByteString) is okay because we don't have optional anymore, therefore Maybe ByteString now unambiguously refers to BytesValue.

cc @natefaubion

Commits are atomic.

[Gabriella439]

Instead of using CPP, a cleaner approach is to move all of the code into a separate module, which is conditionally included in the .cabal file. In other words:

if flag(swagger-wrapper-format)
  hs-source-dirs: swagger

The other benefit of doing it this way is that it also lets you conditionally depend on any necessary modules (not that we need that in this particular case)

[evanrelf]

Yeah you're right, in this case it would be a lot cleaner that way.

[evanrelf]

Hmm actually, I'm not so sure. I think I still need -XCPP for the conditional import. I'm inclined to stick with just -XCPP, and not -XCPP + a new module. As much as I hate -XCPP, in this case I think it's already as simple as it's going to get.

[evanrelf]

I think this is something better addressed in a future, more broad refactoring.

[Gabriella439]

You don't need a conditional import if you do it like this:

• Decide on the name for the separate module (e.g. Proto3.Suite.DotProto.Generate.Instances)
• Create two source directories: instances and no-instances
• Under no-instances, place a blank module of the desired name
• Under instances, place the module with the instances
• Use an if expression in the .cabal file to determine which source directory to import based on the configure flag
• Proto3.Suite.DotProto.Generate.Swagger unconditionally imports the desired module

[evanrelf]

Ah good point. I like that idea. Would you mind if I tackled that in a follow-up PR, so I can apply that technique to all our flags?

[Gabriella439]

Alright, that's fine