nvim/lua/lsp/cmp.lua

local cmp = require "cmp"
local luasnip = require "luasnip"
local cmp_autopairs = require "nvim-autopairs.completion.cmp"

cmp.setup {
    snippet = {
        expand = function(args)
            luasnip.lsp_expand(args.body) -- For `luasnip` users.
        end,
    },
    mapping = cmp.mapping.preset.insert {
        ["<C-u>"] = cmp.mapping.scroll_docs(-4), -- Up
        ["<C-d>"] = cmp.mapping.scroll_docs(4), -- Down
        ["<C-Space>"] = cmp.mapping.complete(),
        ["<CR>"] = cmp.mapping.confirm {
            behavior = cmp.ConfirmBehavior.Replace,
            select = true,
        },
        ["<Tab>"] = cmp.mapping(function(fallback)
            if cmp.visible() then
                cmp.select_next_item()
            elseif luasnip.expand_or_jumpable() then
                luasnip.expand_or_jump()
            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)
            else
                fallback()
            end
        end, { "i", "s" }),
    },
    sources = {
        { name = "nvim_lsp" },
        { name = "luasnip" },
    },
}

-- Set configuration for specific filetype.
-- cmp.setup.filetype("python", { sources = { { name = "nvim_lsp" } } })
-- cmp.setup.filetype("nix", { sources = { { name = "nvim_lsp" } } })
cmp.setup.cmdline("/", { mapping = cmp.mapping.preset.cmdline(), sources = { { name = "buffer" } } })
cmp.setup.cmdline(":", {
    mapping = cmp.mapping.preset.cmdline(),
    sources = { { name = "cmdline" }, { name = "path" } },
})

cmp.event:on("confirm_done", cmp_autopairs.on_confirm_done())