ndmitchell/hlint

Make it possible to forbid "`fromIntegral` without visible type arguments"

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#1,637 opened on Feb 17, 2025

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good first issue

Description

fromIntegral @Int16 @Int32 is refactor safe but fromIntegral is not. I want to allow the former but forbid the latter.

See https://github.com/haskell/core-libraries-committee/issues/314 for context and in particular Ad-hoc polymorphism erodes type-safety.

Contributor guide

Tech stack
None
Domain
tooling
Issue type
feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
4
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Basic Haskell knowledgeFamiliarity with hlint rules
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
25
Research direction
Study the existing hlint rule implementations, particularly those that inspect function applications and type arguments. The rule should detect calls to `fromIntegral` without visible type applications. Refer to the linked CLC issue for design rationale. Look at the file `hint/FromIntegral.hs` or similar in the hlint source.