gleam-lang/gleam

Emphasize mismatching part of complex type mismatches

Open

#4,578 opened on May 9, 2025

View on GitHubContributor guide
 (2 comments) (0 reactions) (0 assignees)Rust (960 forks)batch import
discussionhelp wanted

Repository metrics

Stars
 (21,417 stars)
PR merge metrics
 (PR metrics pending)

Description

When a type mismatch is complex, and some types are unbound (is this the correct term?), it can be hard to see where the error actually is. Here is a concrete example I actually wasted quite a bit of time on:

Expected type:

    drift.Step(List(String), Input, Output, Nil)

Found type:

    drift.Step(List(string), Input, a, b)

It could be made clearer by emphasizing where the type mismatch was exactly:

Expected type:

    drift.Step(List(String), Input, Output, Nil)
                    ^^^^^^

Found type:

    drift.Step(List(string), Input, a, b)
                    ^^^^^^

Contributor guide

Research direction
Investigate the compiler's type error reporting module and implement a method to highlight mismatching types.
Tech stack
rust
Domain
developer experiencecompilers
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
Half day
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Clear
Prerequisites
Rust
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
50