GNU ELPA - corfu

• 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.
• Candidate sorting by prefix, string length and alphabetically.
• The selected candidate is previewed (configurable via corfu-preview-current).
• The selected candidate is automatically committed on further input by default. (configurable via corfu-preview-current).
• Supports the Orderless completion style. The filter string can contain arbitrary characters, after inserting a space via M-SPC (configurable via corfu-quit-at-boundary and corfu-separator).
• Lazy completion candidate highlighting for performance.
• Support for candidate annotations (annotation-function, affixation-function).
• Deprecated candidates are displayed as crossed out.
• Icons can be provided by an external package via margin formatter functions.
• Rich set of extensions: Quick keys, Index keys, Sorting by history, Candidate documentation in echo area, popup or separate buffer.

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 global-corfu-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, such that you can adapt it precisely to your requirements. However in order to quickly try out the Corfu completion package, it should be sufficient to activate global-corfu-mode. You can experiment with manual completion for example in an Elisp buffer or in an Eshell or Shell buffer. For auto completion, set corfu-auto to t before turning on global-corfu-mode.

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-separator ?\s)          ;; Orderless field separator
  ;; (corfu-quit-at-boundary nil)   ;; Never quit at completion boundary
  ;; (corfu-quit-no-match nil)      ;; Never quit, even if there is no match
  ;; (corfu-preview-current nil)    ;; Disable current candidate preview
  ;; (corfu-preselect 'prompt)      ;; Preselect the prompt
  ;; (corfu-on-exact-match nil)     ;; Configure handling of exact matches
  ;; (corfu-scroll-margin 5)        ;; Use scroll margin

  ;; 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-/).  See also the customization variable
  ;; `global-corfu-modes' to exclude certain modes.
  :init
  (global-corfu-mode))

;; 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))

Dabbrev completion is based on completion-in-region and can be used with Corfu. You may want to swap the dabbrev-completion with the dabbrev-expand key for easier access, if you prefer completion. Also take a look at the cape-dabbrev completion at point function provided by my Cape package.

;; Use Dabbrev with Corfu!
(use-package dabbrev
  ;; Swap M-/ and C-M-/
  :bind (("M-/" . dabbrev-completion)
	 ("C-M-/" . dabbrev-expand))
  ;; Other useful Dabbrev configurations.
  :custom
  (dabbrev-ignored-buffer-regexps '("\\.\\(?:pdf\\|jpe?g\\|png\\)\\'")))

If you start to configure the package more deeply, I recommend to give the Orderless completion style a try for filtering. Orderless completion 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.

;; Optionally use the `orderless' completion style.
(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 basic)
	completion-category-defaults nil
	completion-category-overrides '((file (styles partial-completion)))))

The basic completion style is specified as fallback in addition to orderless in order to ensure that completion commands which rely on dynamic completion tables, e.g., completion-table-dynamic or completion-table-in-turn, work correctly. See +orderless-dispatch in the Consult wiki for an advanced Orderless style dispatcher. Additionally enable partial-completion for file path expansion. partial-completion is important for file wildcard support. Multiple files can be opened at once with find-file if you enter a wildcard. You may also give the initials completion style a try.

See also the Corfu Wiki and the Cape manual for additional Capf configuration tips. For more general documentation read the chapter about completion in the Emacs manual. If you want to create your own Capfs, you can find documentation about completion in the Elisp manual.

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

• move-beginning-of-line -> corfu-prompt-beginning
• move-end-of-line -> corfu-prompt-end
• 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-info-location
• M-h -> corfu-info-documentation
• M-SPC -> corfu-insert-separator
• C-g -> corfu-quit
• keyboard-escape-quit -> corfu-reset

We maintain small extension packages to Corfu in this repository in the subdirectory extensions/. The extensions are installed together with Corfu if you pull the package from ELPA. The extensions are inactive by default and can be enabled manually if desired. Furthermore it is possible to install all of the files separately, both corfu.el and the corfu-*.el extensions. Currently the following extensions come with the Corfu ELPA package:

• corfu-echo: corfu-echo-mode displays a brief candidate documentation in the echo area.
• corfu-history: corfu-history-mode remembers selected candidates and sorts the candidates by their history position.
• corfu-indexed: corfu-indexed-mode allows you to select indexed candidates with prefix arguments.
• corfu-info: Actions to access the candidate location and documentation.
• corfu-popupinfo: Display candidate documentation or source in a popup next to the candidate menu.
• corfu-quick: Commands to select using Avy-style quick keys.

See the Commentary of those files for configuration details.

Corfu works well together with all packages providing code completion via the completion-at-point-functions. Many modes and packages already provide a Capf out of the box. Nevertheless you may want to look into complementary packages to enhance your setup.

• corfu-terminal: The corfu-terminal package provides an overlay-based display for Corfu, such that you can use Corfu in terminal Emacs.
• corfu-candidate-overlay: Shows as-you-type auto-suggestion candidate overlay with a visual indication of whether there are many or exactly one candidate available (works only with corfu-auto disabled).
• Orderless: Corfu supports completion styles, including the advanced orderless completion style, where the filter expressions are separated by spaces or another character (see corfu-separator).
• Cape: Provides additional Capf backends and completion-in-region commands. Among others, the package supplies the file completion backend cape-file and the Dabbrev backend cape-dabbrev. Cape provides the cape-company-to-capf adapter to reuse Company backends in Corfu.
• nerd-icons-corfu, kind-icon: Icons are supported by Corfu via external packages. The nerd-icons-corfu package relies on the Nerd icon font, which is even supported on terminal, while kind-icon uses SVGs from monochromatic icon sets.
• pcmpl-args: Extend the Eshell/Shell Pcomplete mechanism with support for many commands. Similar to the Fish shell, pcmpl-args uses man page parsing to dynamically retrieve the completions and helpful annotations.
• Tempel: Tiny template/snippet package with templates in Lisp syntax, which can be used in conjunction with Corfu.
• Vertico: You may also want to look into my Vertico package. Vertico is the minibuffer completion counterpart of Corfu.

• Company: Company is a widely used and mature completion package, which implements a similar UI as Corfu. While Corfu relies exclusively on the standard Emacs completion API (Capfs), Company defines its own API for the backends. Company includes its own completion backends, following its own API, which are incompatible with the Emacs completion infrastructure. Company provides an adapter company-capf to handle Capfs as a Company backend. As a result of this design, Company is a more complex package than Corfu. Company by default uses overlays for the popup in contrast to the child frames used by Corfu. Overall both packages work well, but Company integrates less tightly with Emacs. The completion-styles support is more limited and the completion-at-point command and the completion-in-region function do not invoke Company.
• consult-completion-in-region: The Consult package provides the function consult-completion-in-region which can be set as completion-in-region-function such that it handles completion-at-point. The function works by transferring the in-buffer completion to the minibuffer. In the minibuffer, the minibuffer completion UI, for example Vertico takes over. If you prefer to perform all your completions in the minibuffer consult-completion-in-region is your best option.

When you observe an error in the corfu--post-command post command hook, you should install an advice to enforce debugging. This allows you to obtain a stack trace in order to narrow down the location of the error. The reason is that post command hooks are automatically disabled (and not debugged) by Emacs. Otherwise Emacs would become unusable, given that the hooks are executed after every command.

(setq debug-on-error t)

(defun force-debug (func &rest args)
  (condition-case e
      (apply func args)
    ((debug error) (signal (car e) (cdr e)))))

(advice-add #'corfu--post-command :around #'force-debug)

When Capfs do not yield the expected result you can use cape-capf-debug to add debug messages to a Capf. The Capf will then produce a completion log in the messages buffer.

(setq completion-at-point-functions (list (cape-capf-debug #'cape-dict)))

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