neovim/lua/lsp/go.lua

require("go").setup({
    lsp_cfg = false,
})

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

local cmp = require("cmp")

cmp.setup({
    snippet = {
        expand = function(args)
            vim.fn["vsnip#anonymous"](args.body) -- For `vsnip` users.
        end,
    },
    mapping = {
        ["<CR>"] = cmp.mapping.confirm({ select = true }), -- Accept currently selected item. Set `select` to `false` to only confirm explicitly selected items.
        ["<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() -- The fallback function sends a already mapped key. In this case, it's probably `<Tab>`.
            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" },
    }),
})

local cfg = require("go.lsp").config() -- config() return the go.nvim gopls setup
require("lspconfig").gopls.setup(cfg)