gleam-lang/gleam

Typescript declarations are not emitted with existing build directory

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#4,520 opened on Apr 29, 2025

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Description

Given a gleam application with target = "javascript" will build the application just fine. However when I enable typescript_declarations = true in the gleam.toml config and build the project again, the .d.ts are not emitted until I rm -rf the build directory that was emitted without the declarations turned on.

gleam v1.10.0 runtime: javascript

Contributor guide

Tech stack
typescriptjavascript
Domain
build systemcli
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.
1-3 hours
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
RustGleam compiler source
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate the build process in the Gleam compiler, likely in the `src/build/` or `src/compile/` modules. The issue suggests that the emission of TypeScript declarations is skipped when the build directory already exists from a previous build without declarations. Look for how the build system decides whether to regenerate output files, possibly checking file timestamps or comparing configurations. The fix might involve ensuring that when `typescript declarations` is enabled, the declaration files are emitted regardless of existing build artifacts.
Typescript declarations are not emitted with existing build directory · gleam-lang/gleam#4520 | Good First Issue