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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="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.
*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/main/screenshot.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 automatically committed on any further input by default.
This behavior can be configured by adjusting ~corfu-commit-predicate~.
- Filter string can contain arbitrary characters and spaces, if
~corfu-quit-at-boundary~ is nil. This is needed when filtering with the
[[https://github.com/oantolin/orderless][Orderless]] completion style.
- Deferred completion style highlighting for performance.
- Jumping to location/documentation of current candidate.
- Show candidate documentation/signature string in the echo area.
- Support for ~annotation-function~ and ~affixation-function~.
* 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 local minor mode can be enabled with
=M-x corfu-mode=. In order to configure Corfu and other packages in your
init.el, you may want to use ~use-package~. I recommend to give Orderless
completion a try, which is different from the familiar prefix TAB completion.
However Corfu works well with the default completion styles, the use of
Orderless is not a necessity. 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-echo-documentation nil) ;; Do not show documentation in the echo area
;; Optionally 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))
;; 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))))))
;; Dabbrev works 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 work in 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
* 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=, =ESC ESC ESC= -> ~corfu-quit~
* 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~).
You may also want to look into my [[https://github.com/minad/vertico][Vertico]] package. Vertico is the minibuffer
counterpart of Corfu.
* Caveats
Corfu works well in most scenarios. However there are a few known technical
caveats.
- Corfu falls back to the default Completion buffer on non-graphical displays,
since Corfu requires child frames.
- The abort handling could be improved, for example the input could be undone.
- Some Company metadata extensions are not supported (~company-deprecated~, ~company-kind~, ~company-match~).
- No sorting by history, since ~completion-at-point~ does not
maintain a history (See branch =history= for a possible solution).
* 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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