Does Fleet not use LSP?

Considering how non-mature this LSP server is, probably not, Fleet probably uses whatever internal protocols JetBrains use inside their IDEs

> Backend – a headless service that does the heavy lifting: indexing, static analysis, advanced search, navigation, and the like. Every such operation is initiated by a request from the workspace, which then processes the response and dispatches the data to the components that require it.

> As a backend, you can use a headless IntelliJ IDEA or a language server.

https://www.jetbrains.com/help/fleet/architecture-overview.h...

Last time I checked it was only for Rust, specifically you couldn't use the LSP feature for arbitrary languages that aren't supported by Fleet yet.

Java and Kotlin are definitely not using the LSP but their proprietary backend.

>I know it's a difficult spot because such effort will also indirectly compete with their main product which is an IDE, so I'm not very optimistic it'll last.

I would say this if this step was taking early while Kotlin is still a new language in the market, but I think their late decision to develop an official LSP for Kotlin is because of reasons you just mentioned, but maybe they changed their minds because they saw other benifits including a wide adoption of Kotlin.

It also helped that whenever JB posted a Kotlin questionnaire there would be dozens of people asking “LSP?”.