Corfu provides a completion overlay for the default completion in region function. The current candidates are shown in a popup overlay below or above the point. Corfu can be considered the minimalistic completion-in-region counterpart of Vertico.

Icomplete provides both completion-in-region and minibuffer completion in a single package. While Corfu and Vertico are technically similar to Icomplete, Corfu and Vertico are two separate packages in order to optimize the UI for the two distinct use cases, also leading to code bases which are easier to understand.

Corfu is a minimal package of less than 500 lines of code (my arbitrary limit for small components providing a single specific feature). In contrast to the featureful and complex Company package, Corfu only provides the completion UI. No custom backends are provided. The completions are provided by the completion-at-point-functions. However many code completion backends provide completion-at-point-functions, such that relying only on the default completion may often be sufficient.

• Popup display with scrollbar indicator and arrow key navigation
• The popup must be summoned explicitly by 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 (needed when filtering with the 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

Notable non-feature: Timer-based automatic completions are not supported.

Corfu is available from 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. Here is an example configuration:

;; Configure corfu
(use-package corfu
  ;; Optionally use TAB for cycling, default is `corfu-complete'.
  ;; :bind (:map corfu-map
  ;;        ("TAB" . corfu-next)
  ;;        ("S-TAB" . corfu-previous))

  ;; Enable the overlay only for certain modes.
  ;; For example it is not a useful UI for completions at point in the
  ;; minibuffer.
  :hook ((prog-mode . corfu-mode)
         (eshell-mode . corfu-mode))

  :config

  ;; Optionally enable cycling for `corfu-next' and `corfu-previous'.
  ;; (setq corfu-cycle t)
)

;; 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))))))

;; A few more useful configurations...
(use-package emacs
  :init
  ;; TAB cycle if there are only few candidates
  (setq completion-cycle-threshold 3)

  ;; Enable indentation+completion using the TAB key.
  ;; Completion is often bound to M-TAB.
  (setq tab-always-indent 'complete))

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 Orderless completion style, where the filtering expressions are separated by spaces.

You may also want to look into my Vertico package, which provides a vertical minibuffer completion system. Vertico is the minibuffer counterpart of Corfu.

This package is experimental and new. I am not yet claiming that this package works correctly. There are a few known caveats.

• No caching, the completion table is called directly.
• The :exit-function handling is probably insufficient.
• The overlay popup is brittle (Alternatives: Posframe, Postip?)
• The thin popup borders are only drawn if line-spacing=nil.
• The abort handling could be improved. Undo the completion input?
• The completion-in-region-mode-predicate is deliberatly ignored in order to give the completion style full control. This predicate checks if the start position of the completion changed by calling the backend.
• Completion is terminated if there are no matches. Add optional confirmation?
• Company kind icons are not supported (company-kind)
• Company metadata is not shown (company-docsig)

Since this package is part of GNU ELPA, contributions require copyright assignment to the FSF.