I primarily program in four languages these days -

• Clojure
• C++
• Python
• Java

And most of the time, my Emacs configuration has handled each one differently. Cider for Clojure, Irony for C++, Elpy and Jedi for Python and Java I could never figure out. This is of course on top of tools that work across languages like company for completions, or flycheck for general language syntax checking.

A while ago I heard about lsp-mode - Language Server Protocol mode. Basically, you set up the mode and it connects to back end language servers. The idea is to keep configuration down and provide a consistent interface across langauges while leveraging the types of support these back ends can provide. I wrote a bit about lsp-mode and made a video and you can find it here.

When I first tried LSP it just didn't work. I tried it again later and it basically worked but was finicky. Configuration took more work than I wanted, particularly for customizing per language and even when working it didn't work as expected.

This past summer, I had to teach using Java so I tried lsp-mode again. Setup wasn't too bad and most of the issues were more related to Java than to lsp-mode but I didn't like the results. While it might be great for the professional developer there were too many popups and made the screen way too busy for teaching.

Still, the idea of a single simple configuration was enticing.

So, when I decided to get my configuration together for the Fall semester I decided to try yet again and discovered eglot for Emacs. Eglot turned out to be easier to install and gave me more of the experience I was looking for.

To start, I set it up for C++ using

(use-package eglot :ensure t)
(add-to-list 'eglot-server-programs '((c++-mode c-mode) "clangd-10"))
(add-hook 'c-mode-hook 'eglot-ensure)
(add-hook 'c++-mode-hook 'eglot-ensure)

Eglot defaults to ccls as a C++ language server. I didn't want to have to build it but was able to apt-get install clangd-10 and use that instead by adding clangd-10 to the eglot-server-programs in the second configuration line.

For python I had to install pyls, the Python Language Server but that was easy to do and then I just had to add (add-hook 'python-mode-hook 'eglot-ensure) to my config.

Finally, Java was more of an issue I had to get eclipse.jdt.ls on my system. It turns out that lsp-mode installed it for me already so I just had to point to it:

(defconst my-eclipse-jdt-home "/home/zamansky/.emacs.d/.cache/lsp/eclipse.jdt.ls/plugins/org.eclipse.equinox.launcher_1.5.800.v20200727-1323.jar")
(defun my-eglot-eclipse-jdt-contact (interactive)
  "Contact with the jdt server input INTERACTIVE."
  (let ((cp (getenv "CLASSPATH")))
    (setenv "CLASSPATH" (concat cp ":" my-eclipse-jdt-home))
    (unwind-protect (eglot--eclipse-jdt-contact nil)
      (setenv "CLASSPATH" cp))))
(setcdr (assq 'java-mode eglot-server-programs) #'my-eglot-eclipse-jdt-contact)
(add-hook 'java-mode-hook 'eglot-ensure)

So far, I'm liking eglot very much. I'll probably check lsp-mode out again somewhere down the line but as of now it's Cider for Clojure and Eglot for everything else.

The video has a run through and demo. Check it out.