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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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

Research direction
Examine the bit array construction validation in the Gleam compiler's type checker or code generation phase to ensure floating point sizes are validated at compile time, preventing runtime crashes.
Tech stack
rust
Domain
compilers
Issue type
Bug
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
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
RustGit
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
75