ndmitchell/hlint

Incorrect redundant bracket warning with OverloadedRecordDot

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#1,458 opened on Feb 13, 2023

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 (2 comments) (0 reactions) (0 assignees)Haskell (1,594 stars) (208 forks)batch import
buggood first issue

Description

given

newtype T = T { f :: B }

g :: A -> T
a :: A

The code

(g a).f

uses the record dot operator. HLint recognizes this as the compose operator and incorrectly warns of a redundant bracket. Removing the bracket breaks the code, of course.

Contributor guide

Tech stack
None
Domain
tooling
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
Haskell programmingfamiliarity with HLint internalsunderstanding of OverloadedRecordDot
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
35
Research direction
Examine the HLint source code to find the rule that flags redundant brackets, likely in a file like 'Hint/Bracket.hs' or similar. Understand how the rule currently handles the composition operator (.) and check if it incorrectly triggers when the dot is used for record field access (OverloadedRecordDot). The issue's comments may provide additional context on the expected behavior. A fix would involve adjusting the pattern matching to distinguish between the composition operator and the record dot operator.