Support auto-start repl

[ericdallo]

Most of the time I don't have a REPL running unless I'm creating tests or need to eval something to test, LSP provides all other things that I need, so when LLM tries to use brepl it doesn't find a repl running and fails, would be nice to have a flag to auto start the repl once if not running or even one time repl starts where when brepl runs, it starts the repl if not there, eval and then closes it.

[Ramblurr]

I've also thought that this would be handy. However the way the repl is launched should be configurable, I have a specific -M... incantation I like to use to bring in a standardized set of deps and functionality.

[ericdallo]

yeah, maybe a global ~/.config/brepl/config.edn which would specify whether to start or not and with what flags would be a start

[teehemkay]

Also Babashka (bb nrepl-server) does NOT write a .nrepl-port file contrary to what seems implied in the doc.

The babashka nREPL server currently does not write an .nrepl-port.

A bb task is proposed at the above URL to start a nREPL server that writes such a .nrepl-port at startup.

May I kindly suggest maybe incorporating nREPL port (and type) auto-discovery as in https://github.com/bhauman/clojure-mcp-light?

[licht1stein]

@teehemkay i added the stateless auto-discovery. It's quick enough to not have to store anything for evals.

@ericdallo I like the idea, let me think about it a bit.

[licht1stein]

Here's what I came up with, please let me know what you think @Ramblurr @ericdallo

Config: A new :repl-start key in .brepl/hooks.edn (that is already used to easily add brepl hooks):

{:repl-start {:command "bb nrepl-server" :timeout 30}}

Triggers when resolve-port returns nil (no REPL found) — in all contexts (CLI brepl '(inc 1)', hooks, ECA). It's a fallback at the end of the port resolution chain, not a new hook event.

Lock file coordination (.brepl/repl.lock) which prevents duplicate starts when multiple brepl invocations happen concurrently. It should have states like "starting", "ready ", "failed".

brepl will not control the lifecylce of the repl, which is thus started, so it's up to the user to kill it. There are some allowances in brepl to clean up at session end, so it's an option, to actually kill the repl after the session.