Missing ability to configure metals JVM options

[jypma]

Metals (at least on arch linux) defaults to a heap size of -XX:MaxRAMPercentage=25.0, which can be quite significant. This can be customized by setting the METALS_JAVA_OPTS environment variable when launching metals.

lsp-metals could provide a defcustom where such JVM options can be configured.

As for implementation, that might not be obvious, since lsp-stdio-connection expects a single command with arguments. env or bash could be used here, but that would be linux-specific. Not sure how to do that platform-independently.

[kurnevsky]

You can do it in a bit hacky way replacing metals command with env, see https://github.com/kurnevsky/nixfiles/blob/b153ac54f0a3491e4802d13627f1a8e36564a36a/modules/emacs/init.el#L1509 for the example.

[jypma]

Ah, creative, thanks for the tip. I ended up writing a small script wrapping metals myself.

Should we keep the topic open? It's still something that could be more user-friendly, especially since the requirement to add environment variables to an lsp server might be needing a small patch in lsp-mode itself.

[vikas-saxena02]

I am going to leave this over here in case somebody comes across this issue later. JVM options can be passed through setting this env variable JAVA_TOOL_OPTIONS . See scalameta/metals#7699 (reply in thread) for details. You will need to ensure its set up and available to non-interactive shells as well. For me because I work in a containerised env, it was easier to setup using ENV in my docker file