haskell/haskell-ide-engine

Hlint parser error on `pattern`

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#1,374 opened on Aug 28, 2019

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component: hlintgardening 🌱good first issue

Description

Given a module:

module Lib where

foo pattern = pattern

This error message is shown:

/tmp/ghc-mod4106/Lib4105-43.hs:3:5: error:
    parse error on input `pattern'
  module Lib where
  
> foo pattern = pattern

This is documented in https://github.com/ndmitchell/hlint/issues/607. Minimal project to reproduce: https://github.com/fendor/hlint-minimal-pattern

This happens because hlint assumes some default extensions. This makes sense, since hlint is normally not aware of a .cabal or package.yaml file, where extensions may be listed. However, HIE is aware of language extensions and could invoke hlint always with the right extensions.

Contributor guide

Tech stack
None
Domain
developer experiencetooling
Issue type
bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
stale
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic Haskell knowledgeFamiliarity with HIE internals
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
55
Research direction
Investigate how HIE invokes hlint. Look at the linked hlint issue #607 and the minimal reproduction repository. Identify where HIE passes or fails to pass language extensions to hlint. Modify the code to detect extensions from project files (e.g., .cabal or stack.yaml) and pass them to hlint. Test with the provided module to ensure no parse error.