In this post I want to show you how to setup your favourite text editor, Emacs, as a super powerful and capable Scala IDE (integrated development environment) with the latest and most performant approach.
You might think I am crazy and I make my life more difficult than it needs to be. Let me tell you this already, my development experience in Emacs with Scala is 5 star ⭐. I use this setup at work extensively and cannot think of a better way to be productive.
I see VSCode and IntelliJ colleagues (peasants), prisoners of proprietary tech, stuck to mouse usage, having to click around and hide the countless panes and useless tooltips their IDEs throw at them, and they are unable to customize things to what they need, nor do they have an understanding of the inner workings of their IDE, which IMHO puts them at a disadvantage.
Just learn Emacs already!
Needless to say, the best way to get Scala working with "language-server" compatible integrations is to use Metals LSP. You can read more about it on their website and how it integrates with several editors. I usually install it with coursier doing something along the lines of:
coursier bootstrap --java-opt -XX:+UseG1GC --java-opt -XX:+UseStringDeduplication --java-opt -Xss4m --java-opt -Xms100m --java-opt -Dmetals.client=emacs org.scalameta:metals_2.13:0.11.12 -o $HOME/.local/bin/metals-emacs -f
Note: ensure that $HOME/.local/bin is in your path and
Emacs will automagically pick it up.
I am enjoying using Elpaca everyday. It's the most advanced, reliable
and performant package manager ever made for Emacs. It integrates also
seamlessly with use-package and pushes you into doing
things in a maintainable way. Read more about it here. You
can still learn from my config even if you don't use it, but I do
whole-heartedly recommend it.
I whole-heartedly recommend eglot. Eglot, a.k.a. Emacs
Polyglot is the Emacs LSP client that stays out of your way. You can
read more about it here.
Eglot is to be integrated into Emacs core, and is more performant and minimalistic than lsp-mode. I like to immediately start eglot when opening a Scala file.
(use-package eglot
:hook (
(scala-mode . eglot-ensure)
;; other modes go here
;; e.g.
;; (haskell-mode . eglot-ensure)
))
Once you install it (or load it, since in new Emacs versions it should be built-in), you will need to configure certain things to ensure it can work together with Scala Metals, the Scala language server.
Here we add a wonderful functionality of optimizing imports and formatting code on save.
(defun my-eglot-organize-imports () (interactive)
(eglot-code-actions nil nil "source.organizeImports" t))
(add-hook 'before-save-hook 'my-eglot-organize-imports nil t)
(add-hook 'before-save-hook 'eglot-format-buffer)
For all my syntax highlighting and syntax tree needs I use
tree-sitter, which soon will also be built into Emacs.
(use-package tree-sitter
:config
(global-tree-sitter-mode))
(use-package tree-sitter-langs
:after tree-sitter)
Enable scala-mode for indentation and certain language rules, with Treesitter highlighting.
(use-package scala-mode
:interpreter ("scala" . scala-mode)
:hook (scala-mode . tree-sitter-hl-mode)
)
Flycheck is an enhancement over flymake and helps better
visualize and interact with errors and warnings in your Emacs
buffers.
(use-package flycheck :config (global-flycheck-mode))
For integrating Flycheck and Eglot, check out the cool flycheck-eglot package.
For all my auto-complete needs I use company which works
wonderfully and is highly customizable.
(use-package company
:custom
(company-minimum-prefix-length 1)
(company-idle-delay 0.5)
(company-tooltip-align-annotations t)
(company-tooltip-margin 2)
:config
(global-company-mode))
The company-quickhelp package will help to visualize
available documentation right in the auto-completion tooltip, a feature
present in many modern IDEs.
(use-package company-quickhelp
:after (company)
:config
(company-quickhelp-mode))
With all of this setup you will be able to have a productive
experience, that surpasses the performance and joy of use of other IDEs.
You may want to, on a per project basis, run
sbt bloopInstall to get the full experience of Metals LSP.
This requires the plugin:
addSbtPlugin("ch.epfl.scala" % "sbt-bloop" % "1.5.6").
You may have more success with running the bloopInstall
as
sbt -Dbloop.export-jar-classifiers=sources bloopInstall.
Also, remember that running M-x eglot* will show all
eglot commands available, and teach you some of the shortcuts too.
Feel free to check my dotfiles on SourceHut which might help you get your Emacs setup just right 👌.
Have a nice development day today!