nvim/lua/conf/plugins/cmp.lua

local function has_words_before()
  unpack = unpack or table.unpack
  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

return { 'hrsh7th/nvim-cmp',
  requires = {
    'danymat/neogen',
    'nvim-treesitter/nvim-treesitter',
    'lukas-reineke/cmp-under-comparator' -- better results
  },

  -- suppliers for completions (they require nvim-cmp to be loaded before they are)
  deps = {
    'hrsh7th/cmp-buffer', -- buffers
    'FelipeLema/cmp-async-path', -- path
    'hrsh7th/cmp-nvim-lsp', -- lsp
    'hrsh7th/cmp-nvim-lsp-signature-help', -- completion information
    { 'L3MON4D3/cmp-luasnip-choice', -- luasnip
      requires = 'L3MON4D3/LuaSnip'
    }
  },

  function()
    local cmp = require('cmp')
    local luasnip = require('luasnip')
    local neogen = require('neogen')

    cmp.setup {
      -- disable when in comments
      enabled = function()
        local context = require('cmp.config.context')
        if vim.api.nvim_get_mode().mode == 'c' then
          return true
        else
          return not context.in_treesitter_capture("comment")
            and not context.in_syntax_group("Comment")
        end
      end,

      -- completion sources
      sources = cmp.config.sources {
        { name = 'nvim_lsp', priority = 999 },
        { name = 'luasnip_choice', priority = 750 },
        { name = 'buffer', max_item_count = 3 },
        { name = 'async_path', max_item_count = 5 },
        { name = 'neorg' },
        { name = 'nvim_lsp_signature_help' }
      },

      -- how to sort results
      sorting = {
        comparators = {
          cmp.config.compare.offset,
          cmp.config.compare.exact,
          cmp.config.compare.score,
          require('cmp-under-comparator').under,
          cmp.config.compare.kind,
          cmp.config.compare.sort_text,
          cmp.config.compare.length,
          cmp.config.compare.order,
        }
      },

      -- appearance of window
      window = {
        completion = {
          scrollbar = false,
          border = 'solid',
          winhighlight = "Normal:WinBarNC,FloatBorder:WinBarNC,Search:WinBarNC",
        },
        documentation = {
          border = 'solid',
          winhighlight = "Normal:WinBarNC,FloatBorder:WinBarNC,Search:WinBarNC",
        }
      },

      -- position of window
      view = {
        entries = {
          name = 'custom',
          selection_order = 'near_cursor'
        }
      },

      -- formatting of content
      formatting = {
        fields = { 'menu', 'abbr', 'kind' },
        format = function(entry, item)
          local menu_icon = {
            nvim_lsp = 'λ',
            nvim_lua = 'v',
            calc = '+',
            luasnip = '%',
            buffer = '@',
            path = '#'
          }

          item.menu = menu_icon[entry.source.name]
          return item
        end
      },

      experimental = {
        ghost_text = true
      },

      -- snippet integration
      snippet = {
        expand = function(args)
          luasnip.lsp_expand(args.body)
        end
      },

      -- mappings
      mapping = cmp.mapping.preset.insert {
        ["<Tab>"] = cmp.mapping(function(fallback)
          if #cmp.get_entries() == 1 then
            cmp.confirm({ select = true })
          elseif cmp.visible() then
            cmp.select_next_item()
          elseif luasnip.expand_or_locally_jumpable() then
            luasnip.expand_or_jump()
          elseif has_words_before() then
            cmp.complete()
            if #cmp.get_entries() == 1 then
              cmp.confirm({ select = true })
            end
          elseif neogen.jumpable() then
            neogen.jump_next()
          else
            fallback()
          end
        end, { "i", "s" }),

        ["<S-Tab>"] = cmp.mapping(function(fallback)
          if cmp.visible() then
            cmp.select_prev_item()
          elseif luasnip.jumpable(-1) then
            luasnip.jump(-1)
          elseif neogen.jumpable(-1) then
            neogen.jump_prev()
          else
            fallback()
          end
        end, { "i", "s" }),

        ['<CR>'] = cmp.mapping {
          i = function(fallback)
            if cmp.visible() and cmp.get_active_entry() then
              cmp.confirm({ behavior = cmp.ConfirmBehavior.Replace, select = false })
            else
              fallback()
            end
          end,
          s = cmp.mapping.confirm({ select = true }),
          c = cmp.mapping.confirm({ behavior = cmp.ConfirmBehavior.Replace,
            select = true }),
        },

        ["<C-u>"] = cmp.mapping.scroll_docs(-4),
        ["<C-d>"] = cmp.mapping.scroll_docs(4),
        ['<ESC>'] = cmp.mapping.close(),
        ["<C-e>"] = cmp.mapping.abort()
      }
    }
  end
}