neovim config for elixir development

init.lua

local execute = vim.api.nvim_command
local fn = vim.fn
local fmt = string.format

local pack_path = fn.stdpath("data") .. "/site/pack"

-- ensure a given plugin from github.com/<user>/<repo> is cloned in the pack/packer/start directory
local function ensure (user, repo)
  local install_path = fmt("%s/packer/start/%s", pack_path, repo)
  if fn.empty(fn.glob(install_path)) > 0 then
    execute(fmt("!git clone https://github.com/%s/%s %s", user, repo, install_path))
    execute(fmt("packadd %s", repo))
  end
end

-- ensure the plugin manager is installed
ensure("wbthomason", "packer.nvim")

require('packer').startup(function(use)
  -- install all the plugins you need here

  -- the plugin manager can manage itself
  use {'wbthomason/packer.nvim'}

  -- lsp config for elixir-ls support
  use {'neovim/nvim-lspconfig'}

  -- cmp framework for auto-completion support
  use {'hrsh7th/nvim-cmp'}

  -- install different completion source
  use {'hrsh7th/cmp-nvim-lsp'}
  use {'hrsh7th/cmp-buffer'}
  use {'hrsh7th/cmp-path'}
  use {'hrsh7th/cmp-cmdline'}

  -- you need a snippet engine for snippet support
  -- here I'm using vsnip which can load snippets in vscode format
  use {'hrsh7th/vim-vsnip'}
  use {'hrsh7th/cmp-vsnip'}

  -- treesitter for syntax highlighting and more
  use {'nvim-treesitter/nvim-treesitter'}
end)

-- `on_attach` callback will be called after a language server
-- instance has been attached to an open buffer with matching filetype
-- here we're setting key mappings for hover documentation, goto definitions, goto references, etc
-- you may set those key mappings based on your own preference
local on_attach = function(client, bufnr)
  local opts = { noremap=true, silent=true }

  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gd', '<cmd>lua vim.lsp.buf.definition()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gr', '<cmd>lua vim.lsp.buf.references()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gD', '<cmd>lua vim.lsp.buf.declaration()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'gi', '<cmd>lua vim.lsp.buf.implementation()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', 'K', '<cmd>lua vim.lsp.buf.hover()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<C-k>', '<cmd>lua vim.lsp.buf.signature_help()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<leader>cr', '<cmd>lua vim.lsp.buf.rename()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<leader>ca', '<cmd>lua vim.lsp.buf.code_action()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<leader>cf', '<cmd>lua vim.lsp.buf.formatting()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '<leader>cd', '<cmd>lua vim.diagnostic.open_float()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', '[d', '<cmd>lua vim.diagnostic.goto_prev()<CR>', opts)
  vim.api.nvim_buf_set_keymap(bufnr, 'n', ']d', '<cmd>lua vim.diagnostic.goto_next()<CR>', opts)
end

local capabilities = require('cmp_nvim_lsp').update_capabilities(vim.lsp.protocol.make_client_capabilities())

-- setting up the elixir language server
-- you have to manually specify the entrypoint cmd for elixir-ls
require('lspconfig').elixirls.setup {
  cmd = { "elixir-ls" },
  on_attach = on_attach,
  capabilities = capabilities
}

local cmp = require'cmp'

-- helper functions
local has_words_before = function()
  local line, col = unpack(vim.api.nvim_win_get_cursor(0))
  return col ~= 0 and vim.api.nvim_buf_get_lines(0, line - 1, line, true)[1]:sub(col, col):match("%s") == nil
end

local feedkey = function(key, mode)
  vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes(key, true, true, true), mode, true)
end

cmp.setup({
  snippet = {
    expand = function(args)
      -- setting up snippet engine
      -- this is for vsnip, if you're using other
      -- snippet engine, please refer to the `nvim-cmp` guide
      vim.fn["vsnip#anonymous"](args.body)
    end,
  },
  mapping = {
    ['<CR>'] = cmp.mapping.confirm({ select = true }),
    ["<Tab>"] = cmp.mapping(function(fallback)
      if cmp.visible() then
	cmp.select_next_item()
      elseif vim.fn["vsnip#available"](1) == 1 then
	feedkey("<Plug>(vsnip-expand-or-jump)", "")
      elseif has_words_before() then
	cmp.complete()
      else
	fallback()
      end
    end, { "i", "s" }),

    ["<S-Tab>"] = cmp.mapping(function()
      if cmp.visible() then
	cmp.select_prev_item()
      elseif vim.fn["vsnip#jumpable"](-1) == 1 then
	feedkey("<Plug>(vsnip-jump-prev)", "")
      end
    end, { "i", "s" }),
  },
  sources = cmp.config.sources({
    { name = 'nvim_lsp' },
    { name = 'vsnip' }, -- For vsnip users.
    { name = 'buffer' }
  })
})

require'nvim-treesitter.configs'.setup {
  ensure_installed = {"elixir", "heex", "eex"},
  sync_install = false,
  ignore_install = { },
  highlight = {
    enable = true,
    disable = { },
  },
}