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#+title: corfu.el - Completion Overlay Region FUnction
#+author: Daniel Mendler
#+language: en
#+export_file_name: corfu.texi
#+texinfo_dir_category: Emacs
#+texinfo_dir_title: Corfu: (corfu).
#+texinfo_dir_desc: Completion Overlay Region FUnction
#+html: <a href="https://www.gnu.org/software/emacs/"><img alt="GNU Emacs" src="https://github.com/minad/corfu/blob/screenshots/emacs.svg?raw=true"/></a>
#+html: <a href="http://elpa.gnu.org/packages/corfu.html"><img alt="GNU ELPA" src="https://elpa.gnu.org/packages/corfu.svg"/></a>
#+html: <a href="http://elpa.gnu.org/devel/corfu.html"><img alt="GNU-devel ELPA" src="https://elpa.gnu.org/devel/corfu.svg"/></a>
* 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 [[https://github.com/minad/vertico][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, [[https://github.com/joaotavora/eglot][Eglot]] and [[https://github.com/emacs-lsp/lsp-mode][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 [[https://github.com/minad/cape][Cape]] package.
*NOTE*: Corfu uses child frames to show the popup; on non-graphical displays it
will fall back to the default setting of the ~completion-in-region-function~.
[[https://github.com/minad/corfu/blob/screenshots/light.png?raw=true]]
[[https://github.com/minad/corfu/blob/screenshots/dark.png?raw=true]]
* 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 [[https://github.com/oantolin/orderless][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 [[http://elpa.gnu.org/packages/corfu.html][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 [[https://github.com/minad/corfu/wiki][Corfu Wiki]] for additional configuration tips.
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-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))
#+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.
#+begin_src emacs-lisp
(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))
#+end_src
* 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 [[https://github.com/oantolin/orderless][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 [[https://github.com/minad/cape][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
[[https://github.com/jdtsmith/kind-icon][kind-icon]] package provides beautifully styled SVG icons based on monochromatic
icon sets like material design.
You may also want to look into my [[https://github.com/minad/vertico][Vertico]] package. Vertico is the minibuffer
counterpart of Corfu.
* Caveats
Corfu is robust in most scenarios. There are a few known technical caveats.
- Corfu falls back to the default Completion buffer on non-graphical displays,
since Corfu requires child frames.
- 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. This feature is implemented by the experimental function
~cape-super-capf~ of the [[https://github.com/minad/cape][Cape]] package.
* Contributions
Since this package is part of [[http://elpa.gnu.org/packages/corfu.html][GNU ELPA]] contributions require a copyright
assignment to the FSF.
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