gleam-lang/gleam

Runtime crash on erlang when constructing bit arrays

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#4,271 opened on Feb 20, 2025

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

Description

Currently, if you run the following code:

pub fn main() {
  let size = 2
  <<2.3:float-size(size)>>
}

The compiler will allow it, but when run, it produces an erlang Badarg error. This is probably not desired behaviour. I'm not sure if we consider this a breaking change, but since it never worked in the first place, I would lean no.

Contributor guide

Tech stack
rust
Domain
tooling
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.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
basic knowledge of Gleamunderstanding of bit arrays
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
60
Research direction
Investigate the code generation for bit array construction in the Gleam compiler, particularly the handling of float types with dynamic size. Look at the generated Erlang code to understand why it causes a Badarg error. Check the type checker to see if it should reject such expressions at compile time.