Monday, October 25, 2021

Lua backed completion engine for nvim

nvim-cmp

A completion engine plugin for neovim written in Lua. Completion sources are installed from external repositories and "sourced".

Kapture.2021-10-11.at.12.12.19.mp4

Readme!

  1. nvim-cmp's breaking changes are here.
  2. This is my hobby project. You can support me via GitHub sponsors.
  3. The bug reports are welcome, but I might not fix if you don't provide a minimal reproduction configuration and steps.

Concept

  • No flicker
  • Works properly
  • Fully customizable via Lua functions
  • Fully supported LSP's Completion capabilities
    • Snippets
    • CommitCharacters
    • TriggerCharacters
    • TextEdit and InsertReplaceTextEdit
    • AdditionalTextEdits
    • Markdown documentation
    • Execute commands (Some LSP server needs it to auto-importing. e.g. sumneko_lua or purescript-language-server)
    • Preselect
    • CompletionItemTags
  • Support pairs-wise plugin automatically

Setup

Recommended Configuration

This example configuration is using vim-plug.

call plug#begin(s:plug_dir)
Plug 'neovim/nvim-lspconfig'
Plug 'hrsh7th/cmp-nvim-lsp'
Plug 'hrsh7th/cmp-buffer'
Plug 'hrsh7th/nvim-cmp'

" For vsnip users.
Plug 'hrsh7th/cmp-vsnip'
Plug 'hrsh7th/vim-vsnip'

" For luasnip users.
" Plug 'L3MON4D3/LuaSnip'
" Plug 'saadparwaiz1/cmp_luasnip'

" For ultisnips users.
" Plug 'SirVer/ultisnips'
" Plug 'quangnguyen30192/cmp-nvim-ultisnips'

" For snippy users.
" Plug 'dcampos/nvim-snippy'
" Plug 'dcampos/cmp-snippy'

call plug#end()

set completeopt=menu,menuone,noselect

lua <<EOF
  -- Setup nvim-cmp.
  local cmp = require'cmp'

  cmp.setup({
    snippet = {
      expand = function(args)
        vim.fn["vsnip#anonymous"](args.body) -- For `vsnip` users.
        -- require('luasnip').lsp_expand(args.body) -- For `luasnip` users.
        -- vim.fn["UltiSnips#Anon"](args.body) -- For `ultisnips` users.
        -- require'snippy'.expand_snippet(args.body) -- For `snippy` users.
      end,
    },
    mapping = {
      ['<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({ select = true }),
    },
    sources = cmp.config.sources({
      { name = 'nvim_lsp' },
      { name = 'vsnip' }, -- For vsnip users.
      -- { name = 'luasnip' }, -- For luasnip users.
      -- { name = 'ultisnips' }, -- For ultisnips users.
      -- { name = 'snippy' }, -- For snippy users.
    }, {
      { name = 'buffer' },
    })
  })

  -- Setup lspconfig.
  local capabilities = require('cmp_nvim_lsp').update_capabilities(vim.lsp.protocol.make_client_capabilities())
  require('lspconfig')[%YOUR_LSP_SERVER%].setup {
    capabilities = capabilities
  }
EOF

I want to see more sources!

You can see the all of nvim-cmp sources here.

Configuration options

You can specify the following configuration options via cmp.setup { ... }.

The configuration options will be merged with the default config.

If you want to remove an option, you can set it to false instead.

mapping (type: table<string, fun(fallback: function)>)

Built in helper cmd.mappings are:

  • cmp.mapping.select_prev_item({ cmp.SelectBehavior.{Insert,Select} } })
  • cmp.mapping.select_next_item({ cmp.SelectBehavior.{Insert,Select} })
  • cmp.mapping.scroll_docs(number)
  • cmp.mapping.complete()
  • cmp.mapping.close()
  • cmp.mapping.abort()
  • cmp.mapping.confirm({ select = bool, behavior = cmp.ConfirmBehavior.{Insert,Replace} })

You can configure nvim-cmp to use these cmd.mappings like this:

mapping = {
  ['<C-n>'] = cmp.mapping.select_next_item({ behavior = cmp.SelectBehavior.Insert }),
  ['<C-p>'] = cmp.mapping.select_prev_item({ behavior = cmp.SelectBehavior.Insert }),
  ['<Down>'] = cmp.mapping.select_next_item({ behavior = cmp.SelectBehavior.Select }),
  ['<Up>'] = cmp.mapping.select_prev_item({ behavior = cmp.SelectBehavior.Select }),
  ['<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,
  })
}

In addition, the mapping mode can be specified. The default is insert mode (i).

mapping = {
  ...
  ['<Tab>'] = cmp.mapping(cmp.mapping.select_next_item(), { 'i', 's' })
  ...
}

You can specify your own custom mapping function.

mapping = {
  ['<Tab>'] = function(fallback)
    if ...some_condition... then
      vim.api.nvim_feedkeys(vim.api.nvim_replace_termcodes('...', true, true, true), 'n', true)
    else
      fallback() -- The fallback function is treated as original mapped key. In this case, it might be `<Tab>`.
    end
  end,
}

enabled (type: fun(): boolean|boolean)

The function or boolean value to specify all cmp's features enabled or not.

Default:

function()
  return vim.api.nvim_buf_get_option(0, 'buftype') ~= 'prompt'
end

sources (type: table<cmp.SourceConfig>)

Global source lists are listed in the source table. These are applied to all buffers. The order of the sources list helps define the source priority, see the sorting.priority_weight options below.

It is possible to setup different source lists for different filetypes, this is an example using the FileType autocommand to setup different sources for the lua filetype. This will overwrite your global sources for the buffer.

" Setup buffer configuration (nvim-lua source only enables in Lua filetype).
autocmd FileType lua lua require'cmp'.setup.buffer {
\   sources = {
\     { name = 'nvim_lua' },
\     { name = 'buffer' },
\   },
\ }

Note that the source name isn't necessarily the source repository name. Source names are defined in the source repository README files. For example look at the hrsh7th/cmp-buffer source README which defines the source name as buffer.

sources[number].name (type: string)

The source name.

sources[number].opts (type: table)

The source customization options. It is defined by each source.

sources[number].priority (type: number|nil)

The manually specified source priority. If you don't specify it, the source priority will be determined by the default algorithm (see sorting.priority_weight).

sources[number].keyword_pattern (type: string)

The source specific keyword_pattern for override.

sources[number].keyword_length (type: number)

The source specific keyword_length for override.

sources[number].max_item_count (type: number)

The source specific maximum item count.

sources[number].group_index (type: number)

The source group index.

You can call built-in utility like cmp.config.sources({ { name = 'a' } }, { { name = 'b' } }).

preselect (type: cmp.PreselectMode)

Specify preselect mode. The following modes are available.

  • cmp.PreselectMode.Item
    • If the item has preselect = true, nvim-cmp will preselect it.
  • cmp.PreselectMode.None
    • Disable preselect feature.

Default: cmp.PreselectMode.Item

completion.autocomplete (type: cmp.TriggerEvent[])

Which events should trigger autocompletion.

If you set this to false, nvim-cmp will not perform completion automatically. You can still use manual completion though (like omni-completion via the cmp.mapping.complete function).

Default: { types.cmp.TriggerEvent.TextChanged }

completion.keyword_pattern (type: string)

The default keyword pattern. This value will be used if a source does not set a source specific pattern.

Default: [[\%(-\?\d\+\%(\.\d\+\)\?\|\h\w*\%(-\w*\)*\)]]

completion.keyword_length (type: number)

The minimum length of a word to complete on; e.g., do not try to complete when the length of the word to the left of the cursor is less than keyword_length.

Default: 1

completion.get_trigger_characters (type: fun(trigger_characters: string[]): string[])

The function to resolve trigger_characters.

Default: function(trigger_characters) return trigger_characters end

completion.completeopt (type: string)

vim's completeopt setting. Warning: Be careful when changing this value.

Default: menu,menuone,noselect

confirmation.default_behavior (type: cmp.ConfirmBehavior)

A default cmp.ConfirmBehavior value when to use confirmed by commitCharacters

Default: cmp.ConfirmBehavior.Insert

confirmation.get_commit_characters (type: fun(commit_characters: string[]): string[])

The function to resolve commit_characters.

sorting.priority_weight (type: number)

When sorting completion items before displaying them, boost each item's score based on the originating source. Each source gets a base priority of #sources - (source_index - 1), and we then multiply this by priority_weight:

score = score + ((#sources - (source_index - 1)) * sorting.priority_weight)

Default: 2

sorting.comparators (type: function[])

When sorting completion items, the sort logic tries each function in sorting.comparators consecutively when comparing two items. The first function to return something other than nil takes precedence.

Each function must return boolean|nil.

You can use the preset functions from cmp.config.compare.*.

Default:

{
  cmp.config.compare.offset,
  cmp.config.compare.exact,
  cmp.config.compare.score,
  cmp.config.compare.kind,
  cmp.config.compare.sort_text,
  cmp.config.compare.length,
  cmp.config.compare.order,
}

documentation (type: false | cmp.DocumentationConfig)

A documentation configuration or false to disable feature.

documentation.border (type: string[])

Border characters used for documentation window.

documentation.winhighlight (type: string)

A neovim's winhighlight option for documentation window.

documentation.maxwidth (type: number)

The documentation window's max width.

documentation.maxheight (type: number)

The documentation window's max height.

documentation.zindex (type: number)

The documentation window's zindex.

formatting.fields (type: cmp.ItemField[])

The order of item's fields for completion menu.

formatting.format (type: fun(entry: cmp.Entry, vim_item: vim.CompletedItem): vim.CompletedItem)

A function to customize completion menu.

The return value is defined by vim. See :help complete-items.

You can display the fancy icons to completion-menu with lspkind-nvim.

Please see FAQ if you would like to show symbol-text (e.g. function) and source (e.g. LSP) like compe.

local lspkind = require('lspkind')
cmp.setup {
  formatting = {
    format = lspkind.cmp_format(),
  },
}

event.on_confirm_done (type: fun(entry: cmp.Entry))

A callback function called when the item is confirmed.

experimental.native_menu (type: boolean)

Use vim's native completion menu instead of custom floating menu.

Default: false

experimental.ghost_text (type: cmp.GhostTextConfig | false)

Specify whether to display ghost text.

Default: false

Commands

CmpStatus

Show the source statuses

Autocmds

cmp#ready

Invoke after nvim-cmp setup.

Highlights

CmpItemAbbr

The abbr field.

CmpItemAbbrDeprecated

The deprecated item's abbr field.

CmpItemAbbrMatch

The matched characters highlight.

CmpItemAbbrMatchFuzzy

The fuzzy matched characters highlight.

CmpItemKind

The kind field.

CmpItemMenu

The menu field.

Programatic API

You can use the following APIs.

cmp.visible()

Return the completion menu is visible or not.

NOTE: This method returns true if the native popup menu is visible. For convenience to define mappings.

cmp.get_selected_entry()

Return the selected entry.

cmp.get_active_entry()

Return the active entry.

NOTE: The preselected entry does not returned from this method.

cmp.confirm({ select = boolean, behavior = cmp.ConfirmBehavior.{Insert,Replace} }, callback)

Confirm current selected item if possible.

cmp.complete()

Invoke manual completion.

cmp.close()

Close current completion menu.

cmp.abort()

Close current completion menu and restore current line (similar to native <C-e> behavior).

cmp.select_next_item({ cmp.SelectBehavior.{Insert,Select} })

Select next completion item if possible.

cmp.select_prev_item({ cmp.SelectBehavior.{Insert,Select} })

Select previous completion item if possible.

cmp.scroll_docs(delta)

Scroll documentation window if possible.

FAQ

I can't get the specific source working.

You should check :CmpStatus command's output. Probably, your specified source name is wrong.

NOTE: nvim_lsp will be sourced on InsertEnter event. It will show as unknown source but it isn't problem.

What is the pairs-wise plugin automatically supported?

Some pairs-wise plugin set up the mapping automatically. For example, vim-endwise will map <CR> even if you don't do any mapping instructions for the plugin.

But I think the user want to override <CR> mapping only when the mapping item is selected.

The nvim-cmp does it automatically.

The following configuration will be working as

  1. If the completion-item is selected, will be working as cmp.mapping.confirm.
  2. If the completion-item isn't selected, will be working as vim-endwise feature.
mapping = {
  ['<CR>'] = cmp.mapping.confirm()
}

How to set up like nvim-compe's preselect = 'always'?

You can use the following configuration.

cmp.setup {
  completion = {
    completeopt = 'menu,menuone,noinsert',
  }
}

I dislike auto-completion

You can use nvim-cmp without auto-completion like this.

cmp.setup {
  completion = {
    autocomplete = false
  }
}

How to disable nvim-cmp on the specific buffer?

You can specify enabled = false like this.

autocmd FileType TelescopePrompt lua require('cmp').setup.buffer { enabled = false }

nvim-cmp is slow.

I've optimized nvim-cmp as much as possible, but there are currently some known / unfixable issues.

cmp-buffer source and too large buffer

The cmp-buffer source makes an index of the current buffer so if the current buffer is too large, it will slowdown the main UI thread.

vim.lsp.set_log_level

This setting will cause the filesystem operation for each LSP payload. This will greatly slow down nvim-cmp (and other LSP related features).

How to show name of item kind and source (like compe)?

formatting = {
  format = require("lspkind").cmp_format({with_text = true, menu = ({
      buffer = "[Buffer]",
      nvim_lsp = "[LSP]",
      luasnip = "[LuaSnip]",
      nvim_lua = "[Lua]",
      latex_symbols = "[Latex]",
    })}),
},

How to setup mapping?

You can find all the mapping solutions in Example mappings.

Source creation

Warning: If the LSP spec is changed, nvim-cmp will keep up to it without an announcement.

If you publish nvim-cmp source to GitHub, please add nvim-cmp topic for the repo.

You should read cmp types and LSP spec to create sources.

  • The complete function is required but others can be omitted.
  • The callback argument must always be called.
  • The custom source only can use require('cmp').
  • The custom source can specify word property to CompletionItem. (It isn't an LSP specification but supported as a special case.)
local source = {}

---Source constructor.
source.new = function()
  local self = setmetatable({}, { __index = source })
  self.your_awesome_variable = 1
  return self
end

---Return the source is available or not.
---@return boolean
function source:is_available()
  return true
end

---Return the source name for some information.
function source:get_debug_name()
  return 'example'
end

---Return keyword pattern which will be used...
---  1. Trigger keyword completion
---  2. Detect menu start offset
---  3. Reset completion state
---@param params cmp.SourceBaseApiParams
---@return string
function source:get_keyword_pattern(params)
  return '???'
end

---Return trigger characters.
---@param params cmp.SourceBaseApiParams
---@return string[]
function source:get_trigger_characters(params)
  return { ??? }
end

---Invoke completion (required).
---  If you want to abort completion, just call the callback without arguments.
---@param params cmp.SourceCompletionApiParams
---@param callback fun(response: lsp.CompletionResponse|nil)
function source:complete(params, callback)
  callback({
    { label = 'January' },
    { label = 'February' },
    { label = 'March' },
    { label = 'April' },
    { label = 'May' },
    { label = 'June' },
    { label = 'July' },
    { label = 'August' },
    { label = 'September' },
    { label = 'October' },
    { label = 'November' },
    { label = 'December' },
  })
end

---Resolve completion item that will be called when the item selected or before the item confirmation.
---@param completion_item lsp.CompletionItem
---@param callback fun(completion_item: lsp.CompletionItem|nil)
function source:resolve(completion_item, callback)
  callback(completion_item)
end

---Execute command that will be called when after the item confirmation.
---@param completion_item lsp.CompletionItem
---@param callback fun(completion_item: lsp.CompletionItem|nil)
function source:execute(completion_item, callback)
  callback(completion_item)
end

require('cmp').register_source(source.new())

You can also create source by Vim script like this (This is useful to support callback style plugins).

  • If you want to return boolean, you must return v:true/v:false. It doesn't 0/1.
let s:source = {}

function! s:source.new() abort
  return extend(deepcopy(s:source))
endfunction

" The other APIs are also available.

function! s:source.complete(params, callback) abort
  call a:callback({
  \   { 'label': 'January' },
  \   { 'label': 'February' },
  \   { 'label': 'March' },
  \   { 'label': 'April' },
  \   { 'label': 'May' },
  \   { 'label': 'June' },
  \   { 'label': 'July' },
  \   { 'label': 'August' },
  \   { 'label': 'September' },
  \   { 'label': 'October' },
  \   { 'label': 'November' },
  \   { 'label': 'December' },
  \ })
endfunction

call cmp#register_source('month', s:source.new())


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