gleam-lang/gleam

LSP fails to suggest completion for locally defined `use`d argument

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#5258 opened on Jan 3, 2026

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

Description

LSP fails to suggest completion for locally defined used argument. For example, if I use Lustre and want to create a custom effect I may write something like this:

fn load_data(msg: fn(String) -> msg) -> Effect(msg) {
  use dispatch <- effect.from
  let data = "Example data"
  dispatch(msg(data))
}

If I partially type disp in the last line expecting a suggestion — I wouldn't get it:

Note: suggestion works fine if I convert use to the callback-style call.

Versions:

  • Gleam: 1.14.0
  • VSCodium: 1.107.18627
  • Lustre: 5.4.0
  • macOS: 15.7.3

Contributor guide

Tech stack
rust
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.
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
Familiarity with Gleam languageKnowledge of LSP completion logicRust programming
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
40
Research direction
Investigate the LSP completion handler for `use` expressions in the Gleam compiler. Look at the file `compiler core/src/language server/completions.rs` (or similar) to understand how variables introduced by `use` are tracked. The issue indicates that when using the `use dispatch < effect.from` pattern, the `dispatch` variable is not suggested. Compare with the equivalent callback style call to identify where the symbol registration differs. Check for any recent changes that might have affected this behavior.