init.lua/after/plugin/lsp.lua

-- note: diagnostics are not exclusive to lsp servers
-- so these can be global keybindings
vim.keymap.set('n', 'gl', '<cmd>lua vim.diagnostic.open_float()<cr>')
vim.keymap.set('n', '[d', '<cmd>lua vim.diagnostic.goto_prev()<cr>')
vim.keymap.set('n', ']d', '<cmd>lua vim.diagnostic.goto_next()<cr>') 

vim.api.nvim_create_autocmd('LspAttach', {
  desc = 'LSP actions',
  callback = function(event)
    local opts = {buffer = event.buf}

    -- these will be buffer-local keybindings
    -- because they only work if you have an active language server

    vim.keymap.set('n', '<leader>mh', '<cmd>lua vim.lsp.buf.hover()<cr>', opts)
    vim.keymap.set('n', '<leader>mgd', '<cmd>lua vim.lsp.buf.definition()<cr>', opts)
    vim.keymap.set('n', '<leader>mgD', '<cmd>lua vim.lsp.buf.declaration()<cr>', opts)
    vim.keymap.set('n', '<leader>mgi', '<cmd>lua vim.lsp.buf.implementation()<cr>', opts)
    vim.keymap.set('n', '<leader>mgo', '<cmd>lua vim.lsp.buf.type_definition()<cr>', opts)
    vim.keymap.set('n', '<leader>mgr', '<cmd>lua vim.lsp.buf.references()<cr>', opts)
    vim.keymap.set('n', '<leader>mgs', '<cmd>lua vim.lsp.buf.signature_help()<cr>', opts)
    vim.keymap.set('n', '<leader>mr', '<cmd>lua vim.lsp.buf.rename()<cr>', opts)
    vim.keymap.set({'n', 'x'}, '<leader>mf', '<cmd>lua vim.lsp.buf.format({async = true})<cr>', opts)
    vim.keymap.set('n', '<leader>ma', '<cmd>lua vim.lsp.buf.code_action()<cr>', opts)
  end
})

local lsp_capabilities = require('cmp_nvim_lsp').default_capabilities()

local default_setup = function(server)
  require('lspconfig')[server].setup({
    capabilities = lsp_capabilities,
  })
end

require('mason').setup({})
require('mason-lspconfig').setup({
  ensure_installed = {},
  handlers = {
    default_setup,
  },
})

local cmp = require('cmp')

cmp.setup({
  sources = {
    {name = 'nvim_lsp'},
  },
  mapping = cmp.mapping.preset.insert({
    -- Enter key confirms completion item
    ['<CR>'] = cmp.mapping.confirm({select = false}),

    -- Ctrl + space triggers completion menu
    ['<C-Space>'] = cmp.mapping.complete(),
  }),
  snippet = {
    expand = function(args)
      require('luasnip').lsp_expand(args.body)
    end,
  },
})