LSP Mode Demo

Context

RSEs often need to work with multiple programming languages. The Language Server Protocol (originally from Visual Studio Code) was designed to allow multiple language backends to provide a consistent interface to code completion, refactoring, jumping to symbol definitions, syntax highlighting, error messages etc. The lsp-mode package bring the power of LSP to the emacs world.

Meetup Notes

• Talk website: https://cc-a.github.io/lsp-mode-demo
• Defines an open standard for communication between an IDE/editor and an external service implementing programming assistance
  • Multiple languages can have a relatively consistent interface (e.g. keybindings)
  • Developed by MS as part of VSCode but an open standard and widely adopted
  • Reduces implementation effort from n×m to n+m (n language servers, m editors)
  • It’s been very successful, supports a large number of languages, and in some cases multiple server implementations for the same language. Tables: languages, editors
• Aside: if you use spacemacs, add the lsp layer plus whichever language layers you need (spacemacs develop branch only). Likewise Doom emacs has an lsp layer, and a +lap option for the debugger layer.

Demonstration

Config file

Start the demo emacs config by using the config file provided here.

• The config file shows some use-package commands in comments to install dependencies
• use-package has been configured with hooks for python-mode and f90-mode
• Config file configures
  • Company
  • flycheck
  • lsp-mode and lsp-ui (for pop-ups, hovers, minibuffer)

Python demonsration

• Open demo.py from the repository
• Errors and warnings are shown inline the extreme right hand side of the buffer, in what is know as the sideline
• If you have installed an lsp server for the language, you’ll see a message about the server starting when you open a buffer
• lsp-mode is used for completion (try typing datetime. followed by TAB)
• Completions are documented in a hover
• Opening the brackets creates a minibuffer with the function documentation
• you can format the code using lsp-formatter
• you can jump to definition ctrl . (right?)
• Chris demonstrated a more advance, opinionated config shown at the bottom of the config file. This some options for:
  • Smaller documentation popups
  • Hover text in sideline
  • Disabling auto-display of documentation

Fortran demonsration

• Open demo.f90 from the repository
• Similar features to Python are available
• Fortran features are a subset of what is available with Python
• Fortran has a language server written in Python

Other questions / discussion

• lsp runs locally, it doesn’t need of the internet! It typically uses the introspection in each language.
• lsp needs of an external server installed for each language. You can install the ones you like.
• there are ways to have it for different environments, but normally you need the python language server in that env. Some possibilities are:
  • dir-locals (a quick guide)
  • pyenv
  • No emacs: direnv; emacs-direnv
• eglot is a lightweight alternative to lsp-mode
• The debugger server looks cool (dap-mode)!

Resources

• All the material for this meetup has been shared on the lsp-mode demo github repository
• Language server
• emacs lsp documentation

Ideas for future sessions

• use-package
• Emacs “distributions” e.g. Spacemacs, Doom Emacs
• TRAMP