Record fields with underscores give TH machinery trouble

[ozataman]

The below yields a large error complaining about:

    Illegal data constructor"
<- " name: `_pgHostField'
    When splicing a TH declaration:
      instance Database.Groundhog.Core.PersistEntity Compute.Backends.PGCommon.PGConfig
    where data Database.Groundhog.Core.Key Compute.Backends.PGCommon.PGConfig

Example code:

data PGConfig = PGConfig
    { _pgHost     :: Text
    , _pgPort     :: Int
    , _pgUser     :: Text
    , _pgPass     :: Text
    , _pgDatabase :: Text
    , _pgSchema   :: Text
    , _pgSSL      :: SSLMode
    } deriving (Eq,Show,Generic)

- entity: PGConfig
  dbName: xxxxx
  constructors:
    - name: PGConfig

[lykahb]

The naming schema tried to create a field (GADT constructor) pgHostField which is an invalid constructor name. I would suggest modifying the naming schema. There are many ways to make the name valid (strip , add prefix) but putting these heuristics into the default schemas I think would make the library more "magical"

[ozataman]

Understood. However, we may want to expose some functionality that provides this prefix stripping, especially as lens becomes more and more prevalent and field names starting with are the norm there.

[lykahb]

Good point. My comment was about names normalization in general. If this is a common case, a NamingStyle adjustment function would be handy. Do you think that stripping underscores is the best option here?

[ozataman]

I guess so. It is not at all idiomatic to use underscores in general, so perhaps we can assume they are safe to strip. If someone has a special use case, they can always implement their own naming schema, right?

[lykahb]

That's right. I am not sure though if this case is popular enough to be included into the TH module. Otherwise you could use this schema modification just for your own project.

[yaitskov]

Workaround:

mkPersist
  (defaultCodegenConfig
   {  namingStyle = lowerCaseSuffixNamingStyle {
                      mkExprSelectorName =
                        \a b c d -> "Z" ++ (mkExprSelectorName lowerCaseSuffixNamingStyle) a b c d
                      }
   })
   [groundhog|
   ...