GADT syntax converter throws out all datatype comments

[uhbif19]

Your environment

haskell-language-server version: 1.8.0.0 (GHC: 8.10.7)

VS Code

Steps to reproduce

Run rewrite to GADT action on:

data AuctionTerms = AuctionTerms
  { -- | What is being sold at the auction?
    auctionLot :: !AssetClass
  }

Expected behaviour

Got:

data AuctionTerms where
  AuctionTerms :: {
     -- | What is being sold at the auction?
     auctionLot :: !AssetClass
  } -> AuctionTerms

Actual behaviour

Got:

data AuctionTerms where
  AuctionTerms :: {auctionLot :: !AssetClass} -> AuctionTerms

[July541]

It's a known limitation because dealing with comment much harder for me.

Any improvements are welcomed!

[uhbif19]

@July541 Could you point to any relevant parts of code or issues? Like are there any parts of HLS which do handle comments?

[July541]

Sure. @uhbif19

#2899 (comment) and #2899 (comment) and #2899 (comment) are some discussion described the pain while dealing with comment.

For code details, https://github.com/haskell/haskell-language-server/blob/master/plugins/hls-gadt-plugin/src/Ide/Plugin/GHC.hs#L88 used to convert data declarations to GADT syntax, all comments are dropped here.

While stepping in these codes, you may find the differences between different versions of ghc-exactprint, and another problem is how to identify the comments, comments can be attached to several elements.

Like are there any parts of HLS which do handle comments?

• ghcide has a simple handwritten parser to parse comments for top level definition, this is not what we want.
• hls-tactics-plugin has some module to work with ghc-exactprint, not sure if there is something about comments, but it doesn't work with ghc9.2+.
• hls-haddock-comment-plugin attach comments to function, but it is used to add comments instead of reading comments.

[uhbif19]

Thanks for references!

I also have comment duplicating bug with "Add import" refactoring, so that is probably related to ghcides "simple handwritten parser" too.

[July541]

I also have comment duplicating bug with "Add import" refactoring

Do we have a related issue?

[uhbif19]

@July541 I could not find anything matching it. I can create new.