#+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 can be considered 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). Many 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 must be summoned explicitly by pressing =TAB=
  - The current candidate is inserted with =TAB= and selected with =RET=
  - Candidates sorting by prefix, string length and alphabetically
  - Completion is automatically terminated after candidate selection
  - 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 (Company extension)
  - 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-quit-at-boundary t) ;; Automatically quit at word boundary
      ;; (corfu-quit-no-match t)    ;; Automatically quit if there is no match

      ;; 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.
    ;; Enable `partial-completion' for files to allow path expansion.
    ;; You may prefer to use `initials' instead of `partial-completion'.
    (use-package orderless
      :init
      (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 various 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 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.
  - Company kind icons, docsig and match data are not supported
    (~company-kind~, ~company-docsig~, ~company-match~).
  - No support for multi-backends like Company. A possible multi-capf backend
    could be implemented.
  - 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.