Improve haddock comments

[kokobd]

Changes

• Try my best to preserve the original indentation of record fields
• Add haddock comments to data constructors
• Add me as a code owner to this plugin. I'll keep this plugin updated.

Limitations

• This PR doesn't include support for ghc-9.2. It will be added in a later one.

Motivation

Previously, when you execute the "Generate fields comments" action on the following record:

data Record = Record
  { a :: Int
  , b :: String
  }

You will get:

data Record = Record
  {
                -- | 
                a :: Int
  ,
                -- | 
                b :: String
  }

I think this is not satisfactory, and we should preserve the original indentation as much as we can.

[pepeiborra]

This looks great, the new code is very nicely commented and structured. Thanks!

[michaelpj]

Looks good and sensible. It seems like we go to some lengths to recognize Haddock - is this something we could ask upstream to tell us? i.e. identify comments as haddock comments when they are?

[michaelpj]

Should this just return False in the Nothing case? Or is it useful to be able to distinguish "don't know"?

[kokobd]

I think it's better to leave the caller to decide what to do when the given Located a is missing in the Anns. For example, the caller use False as the condition to enable the action for adding new haddock comments, but if it's Nothing, we should disable this action.

[kokobd]

Looks good and sensible. It seems like we go to some lengths to recognize Haddock - is this something we could ask upstream to tell us? i.e. identify comments as haddock comments when they are?

@michaelpj Oh, I actually didn't expect this to be merged so quickly ;) I'll check that in another PR, when handling ghc 9.2 support. ghc-exactprint surely doesn't take care of this for us, but maybe haddock has some related library functions