gleam-lang/gleam

LSP code action to discard unused variable

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#4950 opened on Sep 9, 2025

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 (9 comments) (0 reactions) (0 assignees)Rust (21,417 stars) (960 forks)batch import
help wanted

Description

Hi 👋 I'm not sure if I'm using the right term but I think it could be useful to add a code action that appends _ to a label in a pattern match to ignore it. There's already a hint for this case but it would be neat to quickly fix the issue via a code action. I added a screenshot to illustrate what I mean.

Contributor guide

Tech stack
rust
Domain
tooling
Issue type
feature
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.
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
RustLSP protocol basicsGleam pattern matching
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate how Gleam's LSP implements code actions, likely in `compiler core/src/lsp.rs` or related files. Look at existing code actions (e.g., adding missing patterns) to understand the pattern. Examine the AST structure for pattern matches to detect unused variables and generate the fix. Add tests in the LSP test suite.