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:desert_island: corfu.el - COmpletion in Region FUnction
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readme

+title: corfu.el - COmpletion in Region FUnction

+author: Daniel Mendler

+language: en

+export_file_name: corfu.texi

+texinfo_dir_category: Emacs misc features

+texinfo_dir_title: Corfu: (corfu).

+texinfo_dir_desc: COmpletion in Region FUnction

+html: GNU Emacs

+html: GNU ELPA

+html: GNU-devel ELPA

+html: MELPA

+html: MELPA Stable

Corfu enhances in-buffer completion with a small completion popup. The current candidates are shown in a popup below or above the point, and can be selected by moving up and down. Corfu is the minimalistic in-buffer completion counterpart of the [[https://github.com/minad/vertico][Vertico]] minibuffer UI.

Corfu is a small package, which relies on the Emacs completion facilities and concentrates on providing a polished completion UI. In-buffer completion UIs in Emacs can hook into ~completion-in-region~, which implements the interaction with the user. Completions at point are either provided by commands like ~dabbrev-completion~ or by pluggable backends (~completion-at-point-functions~, Capfs) and are then passed to ~completion-in-region~. Many programming, text and shell major modes implement a Capf. Corfu does not include its own completion backends. The Emacs built-in Capfs and the Capfs provided by third-party programming language packages are often sufficient. Additional Capfs and completion utilities are provided by the separate [[https://github.com/minad/cape][Cape]] package.

NOTE: Corfu relies on child frames to show the popup, such that mixed fonts and font sizes won't interfere with the rendering. On non-graphical displays, Corfu falls back to the default setting of the ~completion-in-region-function~. There exists a feature branch with [[https://lists.gnu.org/archive/html/emacs-devel/2024-10/msg00491.html][child frame support for terminal Emacs]], which will hopefully land in Emacs 31. Until then you can use the [[https://codeberg.org/akib/emacs-corfu-terminal][corfu-terminal]] package as a stop-gap solution, which provides an alternative display based on overlays.

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+toc: headlines 8

Corfu is available from [[https://elpa.gnu.org/packages/corfu.html][GNU ELPA]]. You can install it directly via =M-x package-install RET corfu RET=. After installation, activate the global minor mode with =M-x global-corfu-mode RET=. For completion press =M-TAB= (or =TAB=) within a buffer. Auto completion is disabled by default for safety and unobtrusiveness.

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

| Binding/Remapping | Corfu command | |--------------------------+--------------------------| | ~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~ | | =M-TAB= | ~corfu-expand~ | | =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~ |

In order to configure Corfu and other packages in your init.el, you may want to use ~use-package~. Corfu is flexibly 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.

Auto completion is disabled by default in Corfu. Note that completion can be vulnerable to arbitrary code execution in untrusted files. In particular the ~elisp-completion-at-point~ completion function performs macro expansion and code evaluation. Auto completion can be enabled by setting ~corfu-auto~ to t locally or globally before enabling the local ~corfu-mode~ or the ~global-corfu-mode~.

Here is an example configuration:

+begin_src emacs-lisp

(use-package corfu ;; Optional customizations ;; :custom ;; (corfu-cycle t) ;; Enable cycling for `corfu-next/previous' ;; (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

;; Enable Corfu only for certain modes. See also `global-corfu-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 :custom ;; TAB cycle if there are only few candidates ;; (completion-cycle-threshold 3)

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

;; Emacs 30 and newer: Disable Ispell completion function. ;; Try `cape-dict' as an alternative. (text-mode-ispell-word-completion nil)

;; Hide commands in M-x which do not apply to the current mode. Corfu ;; commands are hidden, since they are not used via M-x. This setting is ;; useful beyond Corfu. (read-extended-command-predicate #'command-completion-default-include-p))

+end_src

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 [[https://github.com/minad/cape][Cape]] package.

+begin_src emacs-lisp

;; Use Dabbrev with Corfu! (use-package dabbrev ;; Swap M-/ and C-M-/ :bind (("M-/" . dabbrev-completion) ("C-M-/" . dabbrev-expand)) :config (add-to-list 'dabbrev-ignored-buffer-regexps "\") ;; Since 29.1, usedabbrev-ignored-buffer-regexps' on older. (add-to-list 'dabbrev-ignored-buffer-modes 'doc-view-mode) (add-to-list 'dabbrev-ignored-buffer-modes 'pdf-view-mode) (add-to-list 'dabbrev-ignored-buffer-modes 'tags-table-mode))

+end_src

If you start to configure Corfu more thoroughly, I recommend to give the Orderless completion style a try for filtering. Orderless completion offers more flexible filtering than the default completion styles. Note that Orderless is not a necessity; Corfu can be used just as well with the default completion styles.

+begin_src emacs-lisp

;; Optionally use the `orderless' completion style. (use-package orderless :custom ;; (orderless-style-dispatchers '(orderless-affix-dispatch)) ;; (orderless-component-separator #'orderless-escapable-split-on-space) (completion-styles '(orderless basic)) (completion-category-defaults nil) (completion-category-overrides '((file (styles partial-completion)))))

+end_src

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. 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 [[https://github.com/minad/corfu/wiki][Corfu Wiki]] and the [[https://github.com/minad/cape][Cape manual]] for additional Capf configuration tips. For more general documentation read the chapter about completion in the [[https://www.gnu.org/software/emacs/manual/html_node/emacs/Completion.html][Emacs manual]]. If you want to create your own Capfs, you can find documentation about completion in the [[https://www.gnu.org/software/emacs/manual/html_node/elisp/Completion.html][Elisp manual]].

** Auto completion

Auto completion is disabled by default for safety and unobtrusiveness. Note that completion can be vulnerable to arbitrary code execution. Auto completion can be enabled by setting ~corfu-auto~ to t. Only enable auto completion locally in trusted buffers or globally if you edit trusted files only.

You may want to configure Corfu to quit completion eagerly, such that the completion popup stays out of your way when it appeared unexpectedly.

+begin_src emacs-lisp

;; Enable auto completion and configure quitting (setq corfu-auto t corfu-quit-no-match 'separator) ;; or t

+end_src

I suggest to experiment with the various settings and key bindings to find a configuration which works for you. There is no one perfect configuration which fits all. Some people like auto completion, some like manual completion, some want to cycle with TAB and some with the arrow keys.

In case you like auto completion settings, where the completion popup appears immediately, better use a cheap completion style like =basic=, which performs prefix filtering. See the next section about setting Corfu-only completion styles. In this case Corfu completion should still be fast in buffers with efficient completion backends. You can try the following settings in an Elisp buffer or the Emacs scratch buffer. Note that such settings can slow down Emacs due to the high load on the Lisp runtime and garbage collector.

+begin_src emacs-lisp

(setq corfu-auto t corfu-auto-delay 0 ;; TOO SMALL - NOT RECOMMENDED! corfu-auto-prefix 0) ;; TOO SMALL - NOT RECOMMENDED!

(add-hook 'corfu-mode-hook (lambda () ;; Settings only for Corfu (setq-local completion-styles '(basic) completion-category-overrides nil completion-category-defaults nil)))

+end_src

** Buffer-local/Corfu-only completion styles

Sometimes it makes sense to use separate completion style settings for minibuffer completion and in-buffer Corfu completion. For example inside the minibuffer you may prefer advanced Orderless completion, while for Corfu, faster prefix completion is needed or literal-only completion is sufficient.

This matters in particular if you use aggressive auto completion settings, where the completion popup appears immediately. Then a cheap completion style like =basic= should be used, which performs prefix filtering only.

Such Corfu-only configurations are possible by setting the ~completion-styles~ variables buffer-locally, as follows:

+begin_src emacs-lisp

(orderless-define-completion-style orderless-literal-only (orderless-style-dispatchers nil) (orderless-matching-styles '(orderless-literal)))

(add-hook 'corfu-mode-hook (lambda () (setq-local completion-styles '(orderless-literal-only basic) completion-category-overrides nil completion-category-defaults nil)))

+end_src

If you want to combine fast prefix filtering and Orderless filtering you can still do that by defining a custom Orderless completion style via =orderless-define-completion-style=. We use a custom style dispatcher, which enables efficient prefix filtering for input shorter than 4 characters.

+begin_src emacs-lisp

(defun orderless-fast-dispatch (word index total) (and (= index 0) (= total 1) (length< word 4) (cons 'orderless-literal-prefix word)))

(orderless-define-completion-style orderless-fast (orderless-style-dispatchers '(orderless-fast-dispatch)) (orderless-matching-styles '(orderless-literal orderless-regexp)))

(setq corfu-auto t corfu-auto-delay 0 ;; TOO SMALL - NOT RECOMMENDED corfu-auto-prefix 0) ;; TOO SMALL - NOT RECOMMENDED

(add-hook 'corfu-mode-hook (lambda () (setq-local completion-styles '(orderless-fast basic) completion-category-overrides nil completion-category-defaults nil)))

+end_src

** Completing in the minibuffer

Corfu can be used for completion in the minibuffer, since it relies on child frames to display the candidates. The Corfu popup floats on top of the Emacs frame and can be shown even if it doesn't fit inside the minibuffer.

~global-corfu-mode~ activates ~corfu-mode~ in the minibuffer if the variable ~global-corfu-minibuffer~ is non-nil. In order to avoid interference with specialised minibuffer completion UIs like Vertico or Mct, Corfu is only enabled if the minibuffer sets the variable ~completion-at-point-functions~ locally. This way minibuffers with completion can be detected, such that minibuffer commands like ~M-:~ (~eval-expression~) or ~M-!~ (~shell-command~) are enhanced with Corfu completion.

If needed, one can also enable Corfu more generally in all minibuffers, as long as no completion UI is active. In the following example we set ~global-corfu-minibuffer~ to a predicate function, which checks for Mct and Vertico. Furthermore we ensure that Corfu is not enabled if a password is read from the minibuffer.

+begin_src emacs-lisp

(setq global-corfu-minibuffer (lambda () (not (or (bound-and-true-p mct--active) (bound-and-true-p vertico--input) (eq (current-local-map) read-passwd-map)))))

+end_src

** Completing in the Eshell or Shell

When completing in the Eshell I recommend conservative local settings without auto completion, such that the completion behavior is similar to widely used shells like Bash, Zsh or Fish.

+begin_src emacs-lisp

(add-hook 'eshell-mode-hook (lambda () (setq-local corfu-auto nil) (corfu-mode)))

+end_src

When pressing =RET= while the Corfu popup is visible, the ~corfu-insert~ command will be invoked. This command does inserts the currently selected candidate, but it does not send the prompt input to Eshell or the Comint process. Therefore you often have to press =RET= twice which feels like an unnecessary double confirmation. Fortunately it is easy to improve this by using the command ~corfu-send~ instead.

+begin_src emacs-lisp

(keymap-set corfu-map "RET" #'corfu-send)

+end_src

Shell completion uses the flexible Pcomplete mechanism internally, which allows you to program the completions per shell command. If you want to know more, look into this [[https://www.masteringemacs.org/article/pcomplete-context-sensitive-completion-emacs][blog post]], which shows how to configure Pcomplete for git commands. Since Emacs 29, Pcomplete offers the =pcomplete-from-help= function which parses the ~--help~ output of a command and produces completions for command line options.

Pcomplete has a few bugs on Emacs 28 and older. We can work around the issues with the [[https://github.com/minad/cape][Cape]] library (Completion at point extensions). Cape provides wrappers which sanitize the Pcomplete function. On Emacs 29 the advices should not be necessary anymore, since most relevant bugs have been fixed. In case you discover any remaining Pcomplete issues, please report them upstream.

+begin_src emacs-lisp

;; Sanitize the `pcomplete-completions-at-point' Capf. The Capf has undesired ;; side effects on Emacs 28 and earlier. These advices are not needed on Emacs ;; 29 and newer. (when (< emacs-major-version 29) (advice-add 'pcomplete-completions-at-point :around #'cape-wrap-silent) (advice-add 'pcomplete-completions-at-point :around #'cape-wrap-purify))

+end_src

** Orderless completion

[[https://github.com/oantolin/orderless][Orderless]] is an advanced completion style that supports multi-component search filters separated by a configurable character (space, by default). Normally, entering characters like space which lie outside the completion region boundaries (words, typically) causes Corfu to quit. This behavior is helpful with auto-completion, which may pop-up when not desired, e.g. on entering a new variable name. Just keep typing and Corfu will get out of the way.

But orderless search terms can contain arbitrary characters; they are also interpreted as regular expressions. To use orderless, set ~corfu-separator~ (a space, by default) to the primary character of your orderless component separator.

Then, when a new orderless component is desired, use =M-SPC= (~corfu-insert-separator~) to enter the first component separator in the input, and arbitrary orderless search terms and new separators can be entered thereafter.

To treat the entire input as Orderless input, you can set the customization option ~corfu-quit-at-boundary~ to nil. This disables the predicate which checks if the current completion boundary has been left. In contrast, if you always want to quit at the boundary, set ~corfu-quit-at-boundary~ to t. By default ~corfu-quit-at-boundary~ is set to ~separator~ which quits at completion boundaries as long as no separator has been inserted with ~corfu-insert-separator~.

Finally, there exists the user option ~corfu-quit-no-match~ which is set to =separator= by default. With this setting Corfu stays alive as soon as you start advanced filtering with a ~corfu-separator~ even if there are no matches, for example due to a typo. As long as no separator character has been inserted with ~corfu-insert-separator~, Corfu will still quit if there are no matches. This ensures that the Corfu popup goes away quickly if completion is not possible.

In the following we show two configurations, one which works best with auto completion and one which may work better with manual completion if you prefer to always use =SPC= to separate the Orderless components.

+begin_src emacs-lisp

;; Auto completion example (use-package corfu :custom (corfu-auto t) ;; Enable auto completion ;; (corfu-separator ?_) ;; Set to orderless separator, if not using space :bind ;; Another key binding can be used, such as S-SPC. ;; (:map corfu-map ("M-SPC" . corfu-insert-separator)) :init (global-corfu-mode))

;; Manual completion example (use-package corfu :custom ;; (corfu-separator ?_) ;; Set to orderless separator, if not using space :bind ;; Configure SPC for separator insertion (:map corfu-map ("SPC" . corfu-insert-separator)) :init (global-corfu-mode))

+end_src

** TAB-only completion

By default, Corfu steals both the ~RET~ and ~TAB~ keys, when the Corfu popup is open. This can feel intrusive, in particular in combination with auto completion. ~RET~ may accidentally commit an automatically selected candidate, while you actually wanted to start a new line. As an alternative we can unbind the ~RET~ key completely from ~corfu-map~ or reserve the ~RET~ key only in shell modes using a menu-item filter.

+begin_src emacs-lisp

;; TAB-only configuration (use-package corfu :custom (corfu-auto t) ;; Enable auto completion (corfu-preselect 'directory) ;; Select the first candidate, except for directories

:init (global-corfu-mode)

:config ;; Free the RET key for less intrusive behavior. ;; Option 1: Unbind RET completely ;; (keymap-unset corfu-map "RET") ;; Option 2: Use RET only in shell modes (keymap-set corfu-map "RET" `( menu-item "" nil :filter ,(lambda (&optional _) (and (derived-mode-p 'eshell-mode 'comint-mode)

'corfu-send)))))

+end_src

** 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. Note that further input will not expand snippets or templates, which may not be desired but which leads overall to a more predictable behavior. In order to force snippet expansion, confirm a candidate explicitly with ~RET~.

+begin_src emacs-lisp

(use-package corfu ;; TAB-and-Go customizations :custom (corfu-cycle t) ;; Enable cycling for `corfu-next/previous' (corfu-preselect 'prompt) ;; Always preselect the prompt

;; 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 (global-corfu-mode))

+end_src

** Transfer completion to the minibuffer

Sometimes it is useful to transfer the Corfu completion session to the minibuffer, since the minibuffer offers richer interaction features. In particular, [[https://github.com/oantolin/embark][Embark]] is available in the minibuffer, such that you can act on the candidates or export/collect the candidates to a separate buffer. We could add Corfu support to Embark in the future, such that export or collect is possible directly from Corfu. Nevertheless, the ability to transfer the Corfu completion to the minibuffer is even more powerful, since further completion is possible.

The command ~corfu-move-to-minibuffer~ is defined here in terms of ~consult-completion-in-region~, which uses the minibuffer completion UI via ~completing-read~.

+begin_src emacs-lisp

(defun corfu-move-to-minibuffer () (interactive) (pcase completion-in-region--data (`(,beg ,end ,table ,pred ,extras) (let ((completion-extra-properties extras) completion-cycle-threshold completion-cycling) (consult-completion-in-region beg end table pred))))) (keymap-set corfu-map "M-m" #'corfu-move-to-minibuffer) (add-to-list 'corfu-continue-commands #'corfu-move-to-minibuffer)

+end_src

We maintain small extension packages to Corfu in this repository in the subdirectory [[https://github.com/minad/corfu/tree/main/extensions][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:

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.

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.

+begin_src emacs-lisp

(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)

+end_src

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.

+begin_src emacs-lisp

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

+end_src

Note that you will sometimes find crashes inside Capfs. Such issues are bugs in the Capfs must be fixed there. They cannot be worked around in Corfu.

Since this package is part of [[https://elpa.gnu.org/packages/corfu.html][GNU ELPA]] contributions require a copyright assignment to the FSF.