corfu.el - Completion Overlay Region FUnction

Introduction

Corfu enhances the default completion in region function with a completion overlay. The current candidates are shown in a popup below or above the point. Corfu is the minimalistic completion-in-region counterpart of the Vertico minibuffer UI.

Corfu is a minimal package, which relies on the Emacs completion facilities and concentrates on providing a polished completion UI. Completions are either provided by commands like dabbrev-completion or by pluggable backends (completion-at-point-functions, Capfs). Most programming language major modes implement a Capf. Furthermore the language server packages, Eglot and Lsp-mode, both use Capfs which talk to the LSP server to retrieve the completions.

Corfu does not include custom completion backends. In contrast, the complex Company package includes custom completion backends, which deviate from the Emacs completion infrastructure. The Emacs built-in Capfs are mostly sufficient, but a few additional Capfs and completion functions are provided by the Cape package.

NOTE: Corfu uses child frames to show the popup. For now Corfu falls back to the default setting of the completion-in-region-function on non-graphical displays. You may want to use consult-completion-in-region.

Features

Timer-based auto-completions (off by default, set corfu-auto).
Popup display with scrollbar indicator and arrow key navigation.
The popup can be summoned explicitly by pressing TAB at any time.
The current candidate is inserted with TAB and selected with RET.
Candidates sorting by prefix, string length and alphabetically.
The selected candidate is previewed (configuable via corfu-preview-current).
The selected candidate automatically committed on further input by default (configurable via corfu-commit-predicate).
The Orderless completion style is supported. The filter string can contain arbitrary characters, including spaces, if corfu-quit-at-boundary is nil.
Deferred completion style highlighting for performance.
Jumping to location/documentation of current candidate.
Show candidate documentation/signature string in the echo area.
Deprecated candidates are crossed out in the display.
Support for annotations (annotation-function, affixation-function).
Icons can be provided by an external package via margin formatter functions.

Installation and Configuration

Corfu is available from GNU ELPA, such that it can be installed directly via package-install. After installation, the global minor mode can be enabled with M-x corfu-global-mode. In order to configure Corfu and other packages in your init.el, you may want to use use-package.

Corfu is highly flexible and customizable via corfu-* customization variables. For filtering I recommend to give Orderless completion a try, which is different from the familiar prefix TAB completion. Corfu can be used with the default completion styles, the use of Orderless is not a necessity. See also the Corfu Wiki for additional configuration tips. In particular the Lsp-mode configuration is documented in the Wiki.

Here is an example configuration:

(use-package corfu
  ;; Optional customizations
  ;; :custom
  ;; (corfu-cycle t)                ;; Enable cycling for `corfu-next/previous'
  ;; (corfu-auto t)                 ;; Enable auto completion
  ;; (corfu-commit-predicate nil)   ;; Do not commit selected candidates on next input
  ;; (corfu-quit-at-boundary t)     ;; Automatically quit at word boundary
  ;; (corfu-quit-no-match t)        ;; Automatically quit if there is no match
  ;; (corfu-preview-current nil)    ;; Disable current candidate preview
  ;; (corfu-preselect-first nil)    ;; Disable candidate preselection
  ;; (corfu-echo-documentation nil) ;; Disable documentation in the echo area
  ;; (corfu-scroll-margin 5)        ;; Use scroll margin

  ;; You may want to enable Corfu only for certain modes.
  ;; :hook ((prog-mode . corfu-mode)
  ;;        (shell-mode . corfu-mode)
  ;;        (eshell-mode . corfu-mode))

  ;; Recommended: Enable Corfu globally.
  ;; This is recommended since dabbrev can be used globally (M-/).
  :init
  (corfu-global-mode))

;; Optionally use the `orderless' completion style. See `+orderless-dispatch'
;; in the Consult wiki for an advanced Orderless style dispatcher.
;; Enable `partial-completion' for files to allow path expansion.
;; You may prefer to use `initials' instead of `partial-completion'.
(use-package orderless
  :init
  ;; Configure a custom style dispatcher (see the Consult wiki)
  ;; (setq orderless-style-dispatchers '(+orderless-dispatch)
  ;;       orderless-component-separator #'orderless-escapable-split-on-space)
  (setq completion-styles '(orderless)
        completion-category-defaults nil
        completion-category-overrides '((file (styles . (partial-completion))))))

;; Use dabbrev with Corfu!
(use-package dabbrev
  ;; Swap M-/ and C-M-/
  :bind (("M-/" . dabbrev-completion)
         ("C-M-/" . dabbrev-expand)))

;; A few more useful configurations...
(use-package emacs
  :init
  ;; TAB cycle if there are only few candidates
  (setq completion-cycle-threshold 3)

  ;; Emacs 28: Hide commands in M-x which do not apply to the current mode.
  ;; Corfu commands are hidden, since they are not supposed to be used via M-x.
  ;; (setq read-extended-command-predicate
  ;;       #'command-completion-default-include-p)

  ;; Enable indentation+completion using the TAB key.
  ;; `completion-at-point' is often bound to M-TAB.
  (setq tab-always-indent 'complete))

TAB-and-Go completion

You may be interested in configuring Corfu in TAB-and-Go style. Pressing TAB moves to the next candidate and further input will then commit the selection.

(use-package corfu
  ;; TAB-and-Go customizations
  :custom
  (corfu-cycle t)             ;; Enable cycling for `corfu-next/previous'
  (corfu-preselect-first nil) ;; Disable candidate preselection

  ;; Use TAB for cycling, default is `corfu-complete'.
  :bind
  (:map corfu-map
        ("TAB" . corfu-next)
        ([tab] . corfu-next)
        ("S-TAB" . corfu-previous)
        ([backtab] . corfu-previous))

  :init
  (corfu-global-mode))

Key bindings

Corfu uses a transient keymap corfu-map which is active while the popup is shown. The keymap defines the following remappings and bindings:

beginning-of-buffer -> corfu-first
end-of-buffer -> corfu-last
scroll-down-command -> corfu-scroll-down
scroll-up-command -> corfu-scroll-up
next-line, down, M-n -> corfu-next
previous-line, up, M-p -> corfu-previous
completion-at-point, TAB -> corfu-complete
RET -> corfu-insert
M-g -> corfu-show-location
M-h -> corfu-show-documentation
C-g -> corfu-quit
keyboard-escape-quit -> corfu-reset

Complementary packages

Corfu works well together with all packages providing code completion via the completion-at-point-functions. Furthermore it supports completion styles, including the advanced Orderless completion style, where the filtering expressions are separated by spaces (see corfu-quit-at-boundary).

I collect additional Capf backends and completion-in-region commands in my small Cape package. For example the package provides a file name and a dabbrev completion backend.

Icons are supported by Corfu via an external package. For example the kind-icon package provides beautifully styled SVG icons based on monochromatic icon sets like material design.

You may also want to look into my Vertico package. Vertico is the minibuffer counterpart of Corfu.

Caveats

Corfu is robust in most scenarios. There are a few known technical caveats.

Corfu uses child frames to show the popup. For now Corfu falls back to the default setting of the completion-in-region-function on non-graphical displays. You may want to use consult-completion-in-region.
No sorting by history, since completion-at-point does not maintain a history (See branch history for a possible solution).
There is currently no equivalent for company-quickhelp. Documentation and source can be opened manually in a separate buffer.
Company has the ability to merge/group the candidates of multiple backends in some scenarios. Merging multiple backends is not directly supported by the completion-at-point-functions. The Cape package provides the function cape-super-capf which can merge multiple Capfs.

Contributions

Since this package is part of GNU ELPA contributions require a copyright assignment to the FSF.

akagr / corfu