gleam-lang/gleam

Elixir external functions don't work when no Elixir modules are present

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#1,986 opened on Feb 3, 2023

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

Description

When generating a new Gleam project:

gleam new exffi

And adding an FFI function to Elixir:

import gleam/io

pub fn main() {
  io.println("Hello from " <> cwd())
}

external fn cwd() -> String = 
  "Elixir.File" "cwd!"

Calling the function results in:

exffi:main().
% ** exception error: undefined function 'Elixir.File':'cwd!'/0
%      in function  exffi:main/0 (build/dev/erlang/exffi/_gleam_artefacts/exffi.erl, line 8)

Elixir files are not being generated in the build directory until there's an elixir dependency:

Screenshot 2023-02-02 at 21 00 51

Adding a .ex file to the project generates the files and solves this issue.

Contributor guide

Tech stack
elixirrust
Domain
backend
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.
active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Familiarity with GleamBasic Elixir knowledgeUnderstanding of FFI mechanisms
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
45
Research direction
Investigate how the Gleam compiler generates Elixir files during build. Look at the build system code that decides whether to emit Elixir modules. Check if there is a condition that skips Elixir generation when no .ex files are present. Reference the issue description and consider adding a check or always generating Elixir stubs if external functions are declared.