Show type signature for selected Haskell expression

[Martinsos]

Is your feature request related to a problem? Please describe.

Often, I might want to learn the type of an expression in Haskell. So far I haven't figure out how to do that with hls and while looking through its features I also haven't found this listed as capability. On the other hand, if I remember correctly, Dante (or was it Intero?) has this functionality.

Describe the solution you'd like

If I select a piece of code in my editor (I am in Spacemacs but it shouldn't matter I assume), I would expect lsp to show information (type signature) for that piece of code, if it is a valid Haskell expression. If it is an invalid Haskell expression, it shouldn't show anything.

So for example, if we have myFunc = Just [3] <> Nothing, then currently we have:

• cursor on Just -> [Int] -> Maybe [Int]
• cursor on [ -> [Int]
• cursor on 3 -> Int

If I select Just [3], I would expect to see Maybe [Int]. However, right now lsp doesn't care about the selection, only about the position of the cursor itself, so if cursor is e.g. at the end of that selection, I will get just Int.

I don't know if cause of this is this feature not being implemented in HLS, or Spacemacs not passing the selection/region information to the HLS.

Describe alternatives you've considered

I remember this working either in Dante or Intero, can't remember exactly.

[kokobd]

Is this a duplicate of #709?

[Martinsos]

Ah yes it is, sorry haven't seen it! I was searching for region but should have searched for portion. Closing.