Langium LSP Java Conflict

[kapishsingla]

Hi,

I am currently facing an issue while initializing the workspace on browser. We are using theia plugin of java mentioned below

I'm using Langium for defining the backend grammar and providing the LSP server for my custom language. However, I'm running into a recurring issue when the Java plugin is also enabled in Theia.

Whenever .java files and a pom.xml are present in the workspace, the Java plugin starts resolving the Java files during workspace initialization. This appears to block or delay the Langium LSP server from initializing properly, and often leads to the Langium server crashing repeatedly.

To verify the issue, I tested by removing all .java files and the pom.xml from the workspace. With only my Langium language files present, the workspace initializes quickly, and the Langium LSP server works reliably without crashing.

This makes me suspect that the Java plugin is interfering with Langium's LSP server initialization—possibly due to resource contention or conflicting workspace handling.

Are there recommended ways to defer or disable Java file resolution, or otherwise isolate the Langium LSP server during initialization?

[msujew]

Hey @kapishsingla,

Are you running Theia on a heavily resource constrained machine? Both the Java ls and the Langium ls run in separate processes, so they shouldn't block each other in any way. However, on resource constrained machines (i.e. few CPU cores or little RAM), having both of them start up at the same time can probably lead to the issues you're experiencing.

As for deferring the Java initialization: In theory you can modify the package.json of your Java extension (see the activationEvents) to prevent it from starting up instantly. That way, it will only start the extension/language server if the user actively opens a .java file. I've used that trick a few times in the past for overly eager extensions that always wanted to start on startup of the plugin host.