Corfu candidate overlay

• Corfu candidate overlay package
  • Picture is worth a thousand words
  • Motivation
  • Prior art
  • Performance considerations
• Installation instructions
  • Requirements
  • Using straight.el
  • Customization
• How to contribute
• Footnotes

Corfu candidate overlay package

Simple corfu as-you-type auto-suggestion candidate overlay with a visual indication of whether there are many or exactly one candidate available.

Picture is worth a thousand words

Overlay during typing showing first auto-completion candidate when there are more than one (horizontal bar is the cursor):

Overlay showing auto-completion candidate when there is only one available (so invoking completion-at-point will complete without showing the completion menu):

It show the first auto-suggestion from corfu and when there is only one it will show it underlined (face attributes can be configured). In case of many suggestions available, invoking completion-at-point will open the corfu popup menu to choose from, in case of single completion available (i.e. underlined) it will get auto-completed seeing the menu when invoked completion-at-point.

Package exposes also one interactive function corfu-candidate-overlay-complete-at-point which you can bind to a key combination. Invoking the function will complete the exact candidate overlay is currently showing¹ (i.e. it will not show corfu's popup even if there are more candidates present, just complete what you see).

Motivation

Similarly to Michell Hashimoto² of HashiCorp fame, I like my editor to do less than more. I'm not as ascetic though ;-) From time to time I do use the auto-suggestion menu of corfu, especially when I forget the exact wording of a function. I do however trigger the auto-suggestion popup manually.

My need was to see some kind of indication, that there are suggestion ready for what I type and also to discern there is exactly one, usually long, name that I could auto-complete quickly (i.e. without seeing the distracting popup menu). That's how this rather simple³ package was born.

Prior art

As far as I'm aware company-mode provides similar, if not exactly the same, functionality out-of-the-box (company-mode is an alternative to corfu that preceded it).

Emacs Mono-Complete is basically built around the overlay and shows only one completion. It provides number of backends and can be used, or jugding from the installation instructions, should be used independently (i.e. not with corfu). Judging from the cursory look at the source code on top of those it provides multi-file deabbrev like functionality using Python background process for extra performace and can complete whole lines.

Performance considerations

When using slow or cpu-heavy corfu backends (e.g. cape's dict backend with a larger dictionary file⁴) you may experience lagging when writing fast contrary to normal experience with standard corfu with auto-suggestions popup enabled. This is caused by querying completion candidates for each character insert or deletion contrary to a timer-based approach of corfu. Querying of the backends is done in an interruptible manner (this part is based on corfu's internals) but heavy operations while searching for suggestion candidates can cause micro-stutters still.

Installation instructions

Requirements

Corfu is required with the corfu-auto set to nil (i.e. auto popup of auto-suggestions disabled). It is recommended to bing completion-at-point to combination of keys that are easily reachable to you. I use super + tab (i.e. „windows key” and tab) but I do use a custom ergonomic keyboard, where those keys are not too far from the home row. You may want to bind it to ctrl + tab, for example:

  (global-set-key (kbd "C-<tab>") 'completion-at-point)

Using straight.el

  (use-package corfu-candidate-overlay
    :straight (:type git
               :repo "https://code.bsdgeek.org/adam/corfu-candidate-overlay"
               :files (:defaults "*.el"))
    :after corfu
    :config
    ;; enable corfu-candidate-overlay mode globally
    ;; this relies on having corfu-auto set to nil
    (corfu-candidate-overlay-mode +1)
    ;; bind Ctrl + TAB to trigger the completion popup of corfu
    (global-set-key (kbd "C-<tab>") 'completion-at-point)
    ;; bind Ctrl + Shift + Tab to trigger completion of the first candidate
    ;; (keybing <iso-lefttab> may not work for your keyboard model)
    (global-set-key (kbd "C-<iso-lefttab>") 'corfu-candidate-overlay-complete-at-point))

Customization

Faces available for customization:

• corfu-candidate-overlay-face Defines the overlay text colour when there are more than one auto-suggestions available. Defaults to „MistyRose4” for light themes and „wheat” for dark themes.
• corfu-candidate-overlay-face-exact-match Defines the overlay's text colour when there is only one auto-suggestion present. By default inherits the corfu-candidate-overlay-face but adds :underline t.

Custom variables available:

• corfu-candidate-overlay-auto-commands Additional commands apart from corfu's built-in corfu-auto-commands which initiate completion candidate overlay. Default value: ("delete-backward-char\\'" "backward-delete-char-untabify") Which tracks also character deletions and allows to see the overlay when you delete previously typed characters (i.e. when you made a typo and just need to track back, but still would like to see the completions overlay).

How to contribute

The latest source code is available at https://code.bsdgeek.org/adam/corfu-candidate-overlay

Issue reports, questions, comments and code patches are welcome – you can send them to me over e-mail at adam at kruszewski dot name (please be patient as I'm not checking this account on a daily basis).

If you haven't sent code patches via e-mail yet and would like to learn how to work with an e-mail based workflow, you can read more at git format-patch man page or at git-send-email.io.

Footnotes

---

¹

Thanks to Terje Larsen for suggestion!

²

See video cast: Worst Practices in Software Development: Mitchell Hashimoto uses a simple code editor.

³

As of version 1.0 there are ~200 lines of code with additional ~100 lines of comments.

⁴

Cape's dict backend calls „grep” executable on the dictionary file when looking for completion candidates (it does cache the results, but still that's far from being free).