erlang-lsp.el

;; -*- lisp -*-

;; Define a utility function which either installs a package (if it is
;; missing) or requires it (if it already installed).
(defun package-require (pkg &optional require-name)
  "Install a package only if it's not already installed."
  (when (not (package-installed-p pkg))
    (package-install pkg))
  (if require-name
      (require require-name)
    (require pkg)))

;; Install the official Erlang mode
(package-require 'erlang)

;; Include the Language Server Protocol Clients
(package-require 'lsp-mode)

;; Customize prefix for key-bindings
(setq lsp-keymap-prefix "C-l")

;; Enable LSP for Erlang files
(add-hook 'erlang-mode-hook #'lsp)

;; Require and enable the Yasnippet templating system
(package-require 'yasnippet)
(yas-global-mode t)

;; Enable logging for lsp-mode
(setq lsp-log-io t)

;; Show line and column numbers
(add-hook 'erlang-mode-hook 'linum-mode)
(add-hook 'erlang-mode-hook 'column-number-mode)

;; Enable and configure the LSP UI Package
(package-require 'lsp-ui)
(setq lsp-ui-sideline-enable t)
(setq lsp-ui-doc-enable t)
(setq lsp-ui-doc-position 'bottom)

;; Enable LSP Origami Mode (for folding ranges)
(package-require 'lsp-origami)
(add-hook 'origami-mode-hook #'lsp-origami-mode)
(add-hook 'erlang-mode-hook #'origami-mode)

;; Provide commands to list workspace symbols:
;; - helm-lsp-workspace-symbol
;; - helm-lsp-global-workspace-symbol
(package-install 'helm-lsp)

;; Which-key integration
(package-require 'which-key)
(add-hook 'erlang-mode-hook 'which-key-mode)
(with-eval-after-load 'lsp-mode
  (add-hook 'lsp-mode-hook #'lsp-enable-which-key-integration))

;; Always show diagnostics at the bottom, using 1/3 of the available space
(add-to-list 'display-buffer-alist
             `(,(rx bos "*Flycheck errors*" eos)
              (display-buffer-reuse-window
               display-buffer-in-side-window)
              (side            . bottom)
              (reusable-frames . visible)
              (window-height   . 0.33)))