Expert breaks on a brand new Phoenix project

[JasterV]

When trying to run Expert on a brand new Phoenix project I get the following logs:

2025-12-12T10:32:13.812 helix_lsp::transport [ERROR] expert err <- "warning: the :backends key for the :logger application is deprecated.\n"
2025-12-12T10:32:13.812 helix_lsp::transport [ERROR] expert err <- "Here is how to proceed:\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "1. If you want to set it to [:console], simply remove the option.\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "2. If you want to disable logging, remove :backends and instead set:\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "    config :logger, :default_handler, false\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "3. If you want to configure any other backend, then it is recommended\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "   to add `{:logger_backends, \"~> 1.0\"}` as a dependency and call\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "   `LoggerBackends.add(CustomBackend)` in your application start callback\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "  (logger 1.19.4) lib/logger/app.ex:20: Logger.App.start/2\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "  (kernel 10.2.7.3) application_master.erl:295: :application_master.start_it_old/4\n"
2025-12-12T10:32:13.813 helix_lsp::transport [ERROR] expert err <- "\n"
2025-12-12T10:32:14.401 helix_lsp::transport [ERROR] expert err <- "(eval):1: can't change option: zle\n"

Elixir version:

Erlang/OTP 27 [erts-15.2.7.4] [source] [64-bit] [smp:20:20] [ds:20:20:10] [async-threads:1] [jit:ns]

Elixir 1.19.4 (compiled with Erlang/OTP 27)

[mhanberg]

Can you explain more?

What is in the .expert/expert.log

[JeremyAube]

I had the same issue and this was caused by fzf initialization in .zshrc. I am using fzf version 0.65.2 (brew) and I have the following line in my .zshrc:

source <(fzf --zsh)

The simple fix for me was to wrap the fzf initialization in a -o interactive:

if [[ -o interactive ]]; then
  source <(fzf --zsh)
fi

My best guess is that this is coming from here where we start an interactive shell. This will run the .zshrc file which will run the fzf initialization script which does contain calls to zle.

If I have time this week I'll try to debug this more in depth

[mhanberg]

Those zle errors are all written to stderr, so they don't cause any issues.

We'll need to see what's in the log file.

[JeremyAube]

For me, the zle error was the only thing in the log file unfortunately.

[JeremyAube]

Well, I have absolutely no idea what changed but it now works even after reverting the changes to my .zshrc

I was trying to see where the error was. Moving the mise initialization before fzf fixed the issue, then I reverted back to my old .zshrc and it still worked. I cannot reproduce anymore.

[badosu]

Do you have a file at project_root/.expert/expert.log? If so, could you share it?

[JasterV]

@badosu I am on Christmas holidays now and didn't bring a computer, I will do it once I'm back