Import list whitespace is inconsistent

[JakobBruenker]

Your environment

Output of `haskell-language-server --probe-tools``:

haskell-language-server version: 1.5.0.0 (GHC: 9.0.1) (PATH: C:\Users\user\AppData\Roaming\C
ode\User\globalStorage\haskell.haskell\haskell-language-server-1.5.0-win32-9.0.1.exe) (GIT h
ash: 311107eabbf0537e0c192b2c377d282505b4eff1)
Tool versions found on the $PATH
cabal:          3.4.0.0
stack:          Not found
ghc:            9.0.1

Which OS do you use: Windows
Which lsp-client do you use: VS Code

Steps to reproduce

Open a new Haskell file. Write

import Control.Monad

f = guard catMaybes

where auto-completion should be used to complete catMaybes.

HLS will insert a import statement at the top saying import Data.Maybe (catMaybes).

In VS Code, you can click above import Control.Monad to add an import list. This will result in import Control.Monad ( guard ).

Expected behaviour

The spaces inside the parentheses in the import lists should be consistent.

Actual behaviour

The two methods to automatically obtain an import list differ in whether or not there are spaces inside the parentheses.

[jneira]

Thanks for reporting the issue. I hope fix that will not be too much difficult. I would change the explicit import plugin to not add the extra spaces. The code to create the code edit is here:

haskell-language-server/plugins/hls-explicit-imports-plugin/src/Ide/Plugin/ExplicitImports.hs

Lines 243 to 256 in 4b7d139

	mkExplicitEdit :: (ModuleName -> Bool) -> PositionMapping -> LImportDecl pass -> T.Text -> Maybe TextEdit
	mkExplicitEdit pred posMapping (L src imp) explicit
	-- Explicit import list case
	| ImportDecl {ideclHiding = Just (False, _)} <- imp =
	Nothing
	| not (isQualifiedImport imp),
	RealSrcSpan l _ <- src,
	L _ mn <- ideclName imp,
	-- (almost) no one wants to see an explicit import list for Prelude
	pred mn,
	Just rng <- toCurrentRange posMapping $ realSrcSpanToRange l =
	Just $ TextEdit rng explicit
	| otherwise =
	Nothing

What is the behaviour if the import list has more than one definition? does it also add extra parenthesis?

[JakobBruenker]

The extra space is added for multiple definitions as well, e.g.

import Control.Monad ( guard, forM_, forM )

This is also the case if there are too many definitions for one line:

import Control.Monad
    ( guard,
      Monad(return),
      Functor(fmap),
      sequence,
      sequence_,
      forM_,
      void,
      forM )

[pepeiborra]

This is one of many whitespace inconsistencies amongst the many plugins that we use. Trying to address them all is an enormous task.

I suspect it would be more productive for you to enable "Format on save" and rely on the automated formatter to sort out whitespace for you.

[jneira]

This is one of many whitespace inconsistencies amongst the many plugins that we use. Trying to address them all is an enormous task.

still i think fixing inconsistences one by one could be a way to get started in the codebase

[cardenaso11]

Hi! Newcomer to the hls codebase, and I thought this'd be a good place to get started, mind if I take on this ticket?

[jneira]

sure and welcome, feel free to open a draft pr at any time or to ask here or in any of the chat rooms

[pepeiborra]

As a heads up, the import lists generated by the Imports plugin (which I maintain) are pretty-printed by GHC, and I'm afraid it will be very hard for me to accept any changes that replace the GHC pretty-printer with a custom printer.

[JakobBruenker]

Making both ways to add an import list use the GHC pretty-printer seems like it could be a good way to resolve the issue