Error message parsing issue

[walseb]

I'm using Emacs with LSP mode and static-ls.

If I create a file where I export the operator (||) twice:

{-# LANGUAGE NoImplicitPrelude #-}
module Main
  ( module Main
  , module X) where

import Prelude as X ((||)) 

(||) = undefined 

main = undefined

I get the following error in GHCIWatch:

Main.hs:4:5: error: [GHC-69158]
    Conflicting exports for ‘||’:
       ‘module X’ exports ‘X.||’
         imported from ‘Prelude’ at Main.hs:6:22-25
         (and originally defined in ‘ghc-prim-0.11.0:GHC.Classes’)
       ‘module Main’ exports ‘Main.||’
         defined at src/Main.hs:8:1
  |
4 |   , module X) where
  |     ^^^^^^^^

Which is correct.

However, in my editor, static-ls only sends the following cryptic error:

imported from ‘Prelude’ at Main.hs:6:22-25
(and originally defined in ‘ghc-prim-0.11.0:GHC.Classes’)
defined at Main.hs:8:1

It seems like static-ls has removed all lines with the characters || in them.

Can anyone reproduce this? I have edited what's above slightly to simplify file-names and such. I suspect it's an error in static-ls, but perhaps there could be some strange issue with my setup.

The conflicting exports error displays correctly with any other operator. I believe this to be an issue with parsing the characters ||.

Thoughts?

[walseb]

This regexp seems to be the cause of the issue.

static-ls/src/StaticLS/IDE/Diagnostics/ParseGHC.hs

Line 180 in 406a515

r2 = mkRegex [r|(\d+)?\s*\||]

It's checking each line with the regexp (\d+)?\s*\|, and dropping any that match.

This part of the regexp: (\d+)? can be discarded, as the ? means zero or one time.

That leaves us with \s*\|, which due to the *, meaning zero or unlimited times, can be simplified to \|, which means we are simply matching the character |, and dropping any lines containing it.

I think the intent of this check is to simply remove the preview lines that GHC generates:

src/Foo.hs:98:17: error: [GHC-87110]
    Could not find module ‘MV’.
    Use :set -v to see a list of the files searched for.
   |
98 |     , inpRef :: MV.MVar inp
   |                 ^^^^^^^

I think the best solution would be to use a proper parser to check whether we have reached that part of the error message where a preview is shown.

But that's given that GHC never starts printing any useful text after the preview, which I suspect to be the case, but I don't know.

Here's my proposed quick solution:

(\d+)?\s+\|[\s$]+

I believe the bars in the preview must have space to the left and right of them (or EOL, if to the right of it).

My regexp uses + to check for one or more spaces to the left of the bar, and a + to check for one or more spaces (or EOL) to the right of the bar \s+\|[\s$]+.

Thoughts on this solution?