nvim-cmp and Completion

nvim-cmp is the most widely used Neovim completion engine. It aggregates completion sources (LSP, buffer words, file paths, snippets) and displays them in a popup menu.

Core Idea

nvim-cmp is a framework — it shows completions from multiple sources. Each source (LSP, buffer, path, luasnip) is a separate plugin registered with nvim-cmp.

Required Plugins

lua/plugins/completion.lua

return {
  {
    "hrsh7th/nvim-cmp",
    event = "InsertEnter",
    dependencies = {
      -- Sources
      "hrsh7th/cmp-nvim-lsp",      -- LSP completions
      "hrsh7th/cmp-buffer",         -- Buffer words
      "hrsh7th/cmp-path",           -- File paths
      "hrsh7th/cmp-cmdline",        -- Command-line completion
      "saadparwaiz1/cmp_luasnip",   -- Snippet completions

      -- Snippets engine
      {
        "L3MON4D3/LuaSnip",
        version = "v2.*",
        build = "make install_jsregexp",
        dependencies = {
          "rafamadriz/friendly-snippets", -- pre-made snippets
        },
        config = function()
          require("luasnip.loaders.from_vscode").lazy_load()
        end,
      },

      -- Icons in completion menu
      "onsails/lspkind.nvim",
    },
    config = function()
      local cmp = require("cmp")
      local luasnip = require("luasnip")
      local lspkind = require("lspkind")

      cmp.setup({
        snippet = {
          expand = function(args)
            luasnip.lsp_expand(args.body)
          end,
        },

        -- Key mappings
        mapping = cmp.mapping.preset.insert({
          ["<C-b>"] = cmp.mapping.scroll_docs(-4),
          ["<C-f>"] = cmp.mapping.scroll_docs(4),
          ["<C-Space>"] = cmp.mapping.complete(),
          ["<C-e>"] = cmp.mapping.abort(),
          ["<CR>"] = cmp.mapping.confirm({ select = false }),
          ["<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 (in priority order)
        sources = cmp.config.sources({
          { name = "nvim_lsp", priority = 1000 },
          { name = "luasnip", priority = 750 },
          { name = "path", priority = 500 },
        }, {
          { name = "buffer", priority = 250, keyword_length = 3 },
        }),

        -- Appearance
        formatting = {
          format = lspkind.cmp_format({
            mode = "symbol_text",
            maxwidth = 50,
            ellipsis_char = "...",
            symbol_map = {
              Text = "󰉿",
              Method = "󰆧",
              Function = "󰊕",
              Constructor = "",
              Variable = "󰀫",
              Class = "󰠱",
              Interface = "",
              Module = "",
              Property = "󰜢",
              Snippet = "",
              Color = "󰏘",
              File = "󰈙",
              Folder = "󰉋",
            },
          }),
        },

        -- Window
        window = {
          completion = cmp.config.window.bordered(),
          documentation = cmp.config.window.bordered(),
        },

        experimental = {
          ghost_text = true,   -- show preview inline
        },
      })

      -- Cmdline completions
      cmp.setup.cmdline({ "/", "?" }, {
        mapping = cmp.mapping.preset.cmdline(),
        sources = { { name = "buffer" } },
      })

      cmp.setup.cmdline(":", {
        mapping = cmp.mapping.preset.cmdline(),
        sources = cmp.config.sources({
          { name = "path" },
          { name = "cmdline" },
        }),
      })
    end,
  },
}

Completion Key Bindings

Key	Action
<C-Space>	Force open completion menu
<Tab>	Next item / expand snippet
<S-Tab>	Previous item / jump back in snippet
<CR>	Confirm selection
<C-e>	Abort / close menu
<C-b> / <C-f>	Scroll docs up/down

Completion Sources Reference

Source Plugin	Name	Provides
cmp-nvim-lsp	nvim_lsp	Language server completions
cmp-buffer	buffer	Words in open buffers
cmp-path	path	File system paths
cmp-cmdline	cmdline	Cmdline completion
cmp_luasnip	luasnip	Snippet completions
cmp-nvim-lua	nvim_lua	Neovim Lua API
cmp-calc	calc	Math expressions

Writing Custom Snippets with LuaSnip

local ls = require("luasnip")
local s = ls.snippet
local t = ls.text_node
local i = ls.insert_node
local f = ls.function_node

-- Define a custom PHP snippet
ls.add_snippets("php", {
  s("func", {
    t("function "),
    i(1, "functionName"),
    t("("),
    i(2, "$param"),
    t({ ") {", "\t" }),
    i(0),
    t({ "", "}" }),
  }),
})

What's Next

• Diagnostics and Linting
• Treesitter