my-nvim-setup/lua/plugins/configs/cmp.lua

vim.opt.completeopt = "menuone,noselect"

local cmp = require "cmp"

-- nvim-cmp setup
cmp.setup {
   snippet = {
      expand = function(args)
         require("luasnip").lsp_expand(args.body)
      end,
   },
   formatting = {
      format = function(entry, vim_item)
         -- load lspkind icons
         vim_item.kind = string.format(
            "%s %s",
            require("plugins.configs.lspkind_icons").icons[vim_item.kind],
            vim_item.kind
         )

         vim_item.menu = ({
            nvim_lsp = "[LSP]",
            nvim_lua = "[Lua]",
            buffer = "[BUF]",
         })[entry.source.name]

         return vim_item
      end,
   },
   mapping = {
      ["<C-p>"] = cmp.mapping.select_prev_item(),
      ["<C-n>"] = cmp.mapping.select_next_item(),
      ["<C-d>"] = cmp.mapping.scroll_docs(-4),
      ["<C-f>"] = cmp.mapping.scroll_docs(4),
      ["<C-Space>"] = cmp.mapping.complete(),
      ["<C-e>"] = cmp.mapping.close(),
      ["<CR>"] = cmp.mapping.confirm {
         behavior = cmp.ConfirmBehavior.Replace,
         select = true,
      },
      ["<Tab>"] = function(fallback)
         if vim.fn.pumvisible() == 1 then
            vim.fn.feedkeys(vim.api.nvim_replace_termcodes("<C-n>", true, true, true), "n")
         elseif require("luasnip").expand_or_jumpable() then
            vim.fn.feedkeys(vim.api.nvim_replace_termcodes("<Plug>luasnip-expand-or-jump", true, true, true), "")
         else
            fallback()
         end
      end,
      ["<S-Tab>"] = function(fallback)
         if vim.fn.pumvisible() == 1 then
            vim.fn.feedkeys(vim.api.nvim_replace_termcodes("<C-p>", true, true, true), "n")
         elseif require("luasnip").jumpable(-1) then
            vim.fn.feedkeys(vim.api.nvim_replace_termcodes("<Plug>luasnip-jump-prev", true, true, true), "")
         else
            fallback()
         end
      end,
   },
   sources = {
      { name = "nvim_lsp" },
      { name = "luasnip" },
      { name = "buffer" },
      { name = "nvim_lua" },
   },
}