https://github.com/minad/corfu

:desert_island: corfu.el - COmpletion in Region FUnction
https://github.com/minad/corfu

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:desert_island: corfu.el - COmpletion in Region FUnction

• Host: GitHub
• URL: https://github.com/minad/corfu
• Owner: minad
• License: gpl-3.0
• Created: 2021-02-02T22:07:21.000Z (almost 4 years ago)
• Default Branch: main
• Last Pushed: 2024-05-23T07:53:11.000Z (6 months ago)
• Last Synced: 2024-05-23T08:56:34.036Z (6 months ago)
• Language: Emacs Lisp
• Homepage:
• Size: 2.48 MB
• Stars: 1,037
• Watchers: 20
• Forks: 41
• Open Issues: 1
• Metadata Files:
  • Readme: README.org
  • Changelog: CHANGELOG.org
  • License: LICENSE

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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: 

#+html: 

#+html: 

#+html: 

#+html: 

Corfu enhances in-buffer completion with a small completion popup. The current

candidates are shown in a popup below or above the point. The candidates 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 [[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 is

an effort towards [[https://lists.gnu.org/archive/html/emacs-devel/2024-10/msg00003.html][child frame support for terminal Emacs]], which will hopefully

arrive in Emacs 31 or 32. 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

* 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=.

- 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 [[https://github.com/oantolin/orderless][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.

* Installation

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=.

Set the variable ~corfu-auto~ to t in order to enable auto completion. For manual

completion press =M-TAB= (or =TAB=) within a buffer.

* Key bindings

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~              |

* Configuration

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. For auto completion,

set ~corfu-auto~ to t before turning on ~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-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. 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. As an alternative,

  ;; try `cape-dict'.

  (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, use `dabbrev-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 deeply, 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, but can be enabled by setting ~corfu-auto~

to t. Furthermore 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. 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-local corfu-auto        t

            corfu-auto-delay  0 ;; TOO SMALL - NOT RECOMMENDED

            corfu-auto-prefix 1 ;; TOO SMALL - NOT RECOMMENDED

            completion-styles '(basic))

#+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. Note

that such a setup is advanced. Please refer to the Orderless documentation and

source code for further details.

#+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-local corfu-auto        t

            corfu-auto-delay  0 ;; TOO SMALL - NOT RECOMMENDED

            corfu-auto-prefix 1 ;; TOO SMALL - NOT RECOMMENDED

            completion-styles '(orderless-fast basic))

#+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 can be shown even if it

doesn't fully 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

* Extensions

:properties:

:custom_id: extensions

:end:

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:

- [[https://github.com/minad/corfu/blob/main/extensions/corfu-echo.el][corfu-echo]]: =corfu-echo-mode= displays a brief candidate documentation in the

  echo area.

- [[https://github.com/minad/corfu/blob/main/extensions/corfu-history.el][corfu-history]]: =corfu-history-mode= remembers selected candidates and sorts the

  candidates by their history position.

- [[https://github.com/minad/corfu/blob/main/extensions/corfu-indexed.el][corfu-indexed]]: =corfu-indexed-mode= allows you to select indexed candidates with

  prefix arguments.

- [[https://github.com/minad/corfu/blob/main/extensions/corfu-info.el][corfu-info]]: Actions to access the candidate location and documentation.

- [[https://github.com/minad/corfu/blob/main/extensions/corfu-popupinfo.el][corfu-popupinfo]]: Display candidate documentation or source in a popup next to

  the candidate menu.

- [[https://github.com/minad/corfu/blob/main/extensions/corfu-quick.el][corfu-quick]]: Commands to select using Avy-style quick keys.

See the Commentary of those files for configuration details.

* Complementary packages

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.

- [[https://codeberg.org/akib/emacs-corfu-terminal][corfu-terminal]]: The corfu-terminal package provides an overlay-based display

  for Corfu. This is needed until child frame support for terminal Emacs

  arrives.

- [[https://code.bsdgeek.org/adam/corfu-candidate-overlay][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).

- [[https://github.com/oantolin/orderless][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~).

- [[https://github.com/minad/cape][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.

- [[https://github.com/LuigiPiucco/nerd-icons-corfu][nerd-icons-corfu]], [[https://github.com/jdtsmith/kind-icon][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.

- [[https://github.com/minad/tempel][Tempel]]: Tiny template/snippet package with templates in Lisp syntax, which

  can be used in conjunction with Corfu.

- [[https://github.com/minad/vertico][Vertico]]: You may also want to look into my Vertico package. Vertico is the

  minibuffer completion counterpart of Corfu.

* Alternatives

- [[https://github.com/company-mode/company-mode][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.

- [[https://github.com/minad/consult][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 [[https://github.com/minad/vertico][Vertico]] takes over. If you prefer to perform all

  your completions in the minibuffer ~consult-completion-in-region~ is your best

  option.

* Debugging Corfu

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

* Contributions

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

assignment to the FSF.