Language Server Protocol

June 04, 2018

Language Server Protocol

What is it?

• Started by Microsoft in 2015 (took me 3 years to hear about it).
• De-couple language support from IDE by splitting into IDE-agnostic language server and language-agnostic IDE client.
• Language developers write server to handle language related functionality of find definition, find references, code completion …
• IDE developers write client to handle IDE related functionality such as display definition on hovering, providing completion menu, display diagnostics in some pop-up menu …

Why?

• Implements modularity and microservices (to some extent)
• Increased code reusability.
• Converts m*n problem into m+n problems (just like compilers and architectures and intermediate representation).
• Can use your favorite editor(Vi/Emacs) for all languages. I’ve faced this problem when I’ve been forced to use IntelliJ/Eclipse for Java and even with a Vim plugin, it is not Vim, it is just a shadow. So now, hopefully, if I figure out how to use Vim + Java LS, I can get an amazing setup for using Java in Vim.

Why not?

• Increased communication could cause some latency issues (noticed when trying Eclipse + Cquery).
• It is only as good as the server (so cannot really replace IntelliJ with Emacs + Java Language Server, for example, since IntelliJ’s intellisense has not been reproduced yet).
• Bounded by the protocol => cannot get some language specific features like auto including dependencies etc.

Thank you LSP!

I was recently working on something related to language servers. To test stuff out and to get some idea of the working of language servers (Cquery), I decided to try it out with Emacs since:

• It was easily available on Windows.
• There were some nice tools like emacs-lsp and emacs-cquery which make using cquery with emacs just 2 package installs away.
• The result was spectacular. It is just beautiful.
• The list of packages that need to be installed for support are company-lsp, lsp-ui, lsp-mode
• Here is what needs to be added to your .emacs file to get nice lsp support:

;; In general wrt to lsp, autocompletion and snippets
(require 'lsp-mode)

(require 'lsp-ui)
(add-hook 'lsp-mode-hook 'lsp-ui-mode)

(require 'company-lsp)
(push 'company-lsp company-backends)
(setq company-transformers nil company-lsp-async t company-lsp-cache-candidates 'auto company-lsp-enable-snippet t)

(require 'yasnippet)
(yas-global-mode 1)

;; Specific to cquery
(require 'cquery)
(setq cquery-executable "/path/to/cquery/build/release/bin/cquery")
(setq cquery-sem-highlight-method 'font-lock)
(setq cquery-extra-init-params '(:index (:comments 2) :cacheFormat "msgpack"))
(cquery-use-default-rainbow-sem-highlight)

• To enable it, use:

M-x lsp-cquery-enable
M-x company-mode

Guess that needs to be automated.