gleam-lang/gleam

have `gleam check`, `gleam build` validate the gleam.toml schema

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#5301 opened on Jan 19, 2026

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

Description

Currently the inclusion of a spurious field in gleam.toml goes silently unremarked upon.

This caused me some grief just now as I didn't spot that a local dependency list should appear under [dependencies] not above it.

The proposal would be for gleam build to report the presence of unrecognized/unsupported fields in gleam.toml before it tries to build anything, i.e., for gleam build to validate the gleam.toml schema. (As versioned by the Gleam version.)

Contributor guide

Tech stack
rust
Domain
build systemdeveloper experience
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.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Rust programmingGleam language basicsTOML format
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
65
Research direction
Explore the gleam.toml parsing logic in the Gleam compiler codebase, likely in the `src/` directory. Identify where configuration fields are read and where validation for unknown keys can be added. Consider referencing the TOML library used and how to emit warnings or errors. Engage with the existing issue comments for any additional constraints.