Running emacs/ELP with multiple kerl versions causes code to be compiled with the wrong version of OTP

[baronbosse]

Describe the bug

I need to edit 2 different project, and project A needs otp 25, and project B needs otp 27. In order for project B to compile correctly emacs is started in a terminal with kerl switched to otp-27.

But as soon as a file in project A is opened ELP seems to compile them again and overwrite the beam files with OTP-27 compiled versions of the same beam file. And it is very confusing to why all of a sudden tests start failing and so forth.

To Reproduce**

1. Create a project that depends on for instance jsonformat
2. Compile and run some tests for this project with otp-25.
3. In a separate terminal, activate otp 27 with . ~/.kerl/27.1.2/activate
4. In this other terminal open emacs with ELP as an IDE, now running otp 27.
5. Open one of the test suites in emacs.

Expected behavior

Running rebar3 ct should work as before opening emacs.

Actual behavior

Errors like these start popping up.

$ rebar3 ct 
===> Verifying dependencies...
=ERROR REPORT==== 9-Dec-2024::13:34:42.439545 ===
Loading of /home/user/project_/_build/default/lib/jsonformat/ebin/jsonformat.beam failed: {features_not_allowed,
                                                                                                      [maybe_expr]}

Context

• ELP Version (output of elp version): elp 1.1.0+build-2024-11-07
• Editor used: GNU Emacs 29.3

[alanz]

Have you tried using direnv to configure the otp in the project? emacs will honour that.

[baronbosse]

I have not. As stated above I'm using kerl for setting otp version per terminal. I would have to switch to asdf if I want to try direnv.

But what was the scary part was the surprise of projects seemingly randomly stopping to work. You run rebar3 ct and all is fine. You edit a file and add some logging and all of a sudden tests fail and rebar3 core dumps. It was very very hard to debug.

[alanz]

Maybe try something like this https://blog.differentpla.net/blog/2019/01/30/integrating-kerl-direnv/

I am suggesting this because emacs can be direnv-aware, so should pick up the path, regardless of when/where you start emacs. I use

(use-package direnv
 :config
 (direnv-mode))

in my init.el, and it works that way for me, for various .envrc files