Initial commit of Corfu candidate overlay
The minor mode uses underlying corfu completion data to show the first candidate inline while typing.master
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;;; corfu-candidate-overlay.el --- Show first candidate in an overlay while typing -*- lexical-binding: t -*-
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;; Copyright (C) 2021-2023 Free Software Foundation, Inc.
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;; Author: Adam Kruszewski <adam@kruszewski.name>
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;; Maintainer: Adam Kruszewski <adam@kruszewski.name>
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;; Created: 2023
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;; Version: 0.1
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;; Package-Requires: ((emacs "27.1") (corfu "0.36"))
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;; Homepage: https://code.bsdgeek.org/adam/corfu-candidate-overlay/
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;; This file is part of GNU Emacs.
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;; This program is free software: you can redistribute it and/or modify
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;; it under the terms of the GNU General Public License as published by
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;; the Free Software Foundation, either version 3 of the License, or
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;; (at your option) any later version.
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;; This program is distributed in the hope that it will be useful,
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;; but WITHOUT ANY WARRANTY; without even the implied warranty of
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;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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;; GNU General Public License for more details.
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;; You should have received a copy of the GNU General Public License
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;; along with this program. If not, see <https://www.gnu.org/licenses/>.
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;;; Commentary:
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;; Show first candidate in an inline overlay while typing.
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;; When there is only one candidate the overlay text will
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;; be underlined.
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;;
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;; It is ment to be used with `corfu-auto' set to `nil', and
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;; executing the corfu completion popup with a keybind.
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;;
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;; Enable by executing `corfu-candidate-overlay-mode'.
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;;; Code:
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(require 'corfu)
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(defvar-local corfu--candidate-overlay nil
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"Overlay for Corfu candidates display when typing.")
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(defvar-local corfu--candidate-last-point nil
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"Last point location when the overlay was calculated for.")
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(defvar corfu--candidate-overlay-map nil
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"Keymap to dismiss the Corfu candidate overlay.")
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(defcustom corfu-overlay-auto-commands
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'("delete-backward-char\\'")
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"Additional commands apart from corfu-auto-commands which initiate
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completion candidate overlay."
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:type '(repeat (choice regexp symbol))
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:group 'corfu)
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(defface corfu--candidate-overlay-face
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'((((background light))
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:foreground "MistyRose4")
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(((background dark))
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:foreground "wheat"))
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"Face used for the overlay with the first candidate.")
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(defface corfu--candidate-overlay-face-exact-match
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'((t (:inherit 'corfu--candidate-overlay-face :underline t)))
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"Face used for the overlay when there is only one candidate.")
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(defun corfu--candiate-overlay-prepare (beg end)
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"Sets the default properties of the candidates overlay.
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The overlay can be dismissed with a mouse click."
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(when (not corfu--candidate-overlay-map)
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(setq corfu--candidate-overlay-map (make-sparse-keymap))
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(define-key corfu--candidate-overlay-map (kbd "<mouse-1>")
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(lambda ()
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(interactive)
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(delete-overlay corfu--candidate-overlay))))
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(if corfu--candidate-overlay
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(move-overlay corfu--candidate-overlay end end)
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(progn
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(setq corfu--candidate-overlay (make-overlay end end nil))
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;; priority of 1k is the value used by Corfu.
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(overlay-put corfu--candidate-overlay 'priority 1000))))
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(defun corfu--candidate-overlay-update (beg end prefix candidate how-many-candidates)
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"Updates the candidate overlay with the first candidate found by Corfu."
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(corfu--candiate-overlay-prepare beg end)
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(unless (string-empty-p candidate)
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(add-text-properties 0 1 '(cursor 1) candidate))
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(overlay-put corfu--candidate-overlay 'window (selected-window))
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(overlay-put corfu--candidate-overlay 'after-string
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(propertize
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candidate
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'face (if (= how-many-candidates 1)
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'corfu--candidate-overlay-face-exact-match
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'corfu--candidate-overlay-face)
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'keymap corfu--candidate-overlay-map)))
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(defun corfu-hide-candidate-overlay ()
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"Hide the candidate overlay."
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(when (and
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corfu--candidate-overlay
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(overlayp corfu--candidate-overlay))
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;; 'invisible property doesn't work really; deleting the overlay
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;; would need to recreate the object on basically each keystroke
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;; and I don't like the perspective of it, would also flicker
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;; for sure - so we keep the one overlay and we clear the contents.
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(overlay-put corfu--candidate-overlay 'after-string "")))
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(defun corfu-show-candidate-overlay ()
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"Computes completion candidates just like Corfu and updats the candidate
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overlay to reflect the first one. Uses different face when there is only
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one candidate available (defaults to underline)."
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(let ((value (while-no-input ;; Interruptible capf query
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(run-hook-wrapped 'completion-at-point-functions #'corfu--capf-wrapper))))
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(if (not value)
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(corfu-hide-candidate-overlay) ;; when empty, we hide the overlay.
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(pcase value ;; when not, we check the completion data.
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(`(,fun ,beg ,end ,table . ,plist)
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(let ((completion-in-region-mode-predicate
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(lambda ()
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(when-let (newbeg (car-safe (funcall fun)))
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(= newbeg beg))))
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(completion-extra-properties plist))
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(setq completion-in-region--data
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(list (if (markerp beg) beg (copy-marker beg))
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(copy-marker end t)
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table
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(plist-get plist :predicate)))
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(when (>= (- end beg) corfu-auto-prefix) ;; adhere to auto prefix length settings.
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(corfu--update)
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(let* ((candidate (car corfu--candidates))
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(how-many-candidates (length corfu--candidates))
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(len (- end beg))
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(prefix (buffer-substring-no-properties beg end))
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(suffix (substring candidate len)))
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(if (and
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;; need candidate
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candidate
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;; the prefix can't be empty (in case of corfu-auto-prefix equal 0)
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(not (string-empty-p prefix))
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;; prefix need to match the candidate as there are „fuzzy”
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;; found candidates, esp. when using templates and the user
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;; could see strage results at the first character.
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(string-prefix-p prefix candidate))
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(corfu--candidate-overlay-update
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beg
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end
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prefix
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suffix
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how-many-candidates)
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;; otherwise we hide the overlay.
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(corfu-hide-candidate-overlay))))))))))
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(defun corfu--candidate-overlay-post-command ()
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"Post command hook updating the candidate overlay when user inserts character
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and the cursor is at the end of word."
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(let* ((is-insert-command
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(corfu--match-symbol-p corfu-auto-commands this-command))
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(is-delete-command
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(corfu--match-symbol-p corfu-overlay-auto-commands this-command)))
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(if (and
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;; we are not in minibuffer, as it looks awkward.
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(not (minibuffer-window-active-p (selected-window)))
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(not (and ;; do not update it the point have not moved.
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corfu--candidate-last-point
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(= corfu--candidate-last-point (point))))
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(or ;; do not update if it is not one of the insert or delete commands.
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is-insert-command
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is-delete-command))
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(let ((next-char (char-after)))
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(when (or ;; do not update if we are not at the end of the word.
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(not next-char) ;; end of file
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;; one of whitespace, quoting character, punctuation,
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;; closing bracket, etc is next.
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;; When those characters follow next completion won't trigger
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;; eitherway: ' = * - + / ~ _ (have not investigated further)
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(memq next-char '(?\s ?\t ?\r ?\n
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?\" ?\` ?\) ?\] ?\>
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?\. ?\, ?\: ?\;)))
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;; When the completion backend is SLOW, i.e. like every LSP client,
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;; then the overlay will not update and will interfere with the typing.
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;; That's why we move preemptively when inserting and deleting the first
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;; character (look awkward when typing a different word than the completion
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;; but still looks better than flickering).
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;; When deleting -- we just move the overlay so it will show
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;; the „lagging” candidate.
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(when (and is-insert-command corfu--candidate-overlay)
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(let ((previous-text (overlay-get corfu--candidate-overlay 'after-string)))
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(when (not (string-empty-p previous-text))
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(overlay-put corfu--candidate-overlay 'after-string
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(substring previous-text 1)))
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(move-overlay corfu--candidate-overlay (point) (point))))
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;; preserve the current position, show and update the overlay.
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(setq corfu--candidate-last-point (point))
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(corfu-show-candidate-overlay)))
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;; or hide the overlay if the conditions where not met.
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(corfu-hide-candidate-overlay))))
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;;;###autoload
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(define-minor-mode corfu-candidate-overlay-mode
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"Show first candidate in an overlay while typing."
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:global t
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:group 'corfu
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(if corfu-candidate-overlay-mode
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(progn
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(add-hook 'post-command-hook #'corfu--candidate-overlay-post-command)
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(message "Enabled `corfu-candidate-overlay-mode'."))
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(progn
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(remove-hook 'post-command-hook #'corfu--candidate-overlay-post-command)
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(message "Disabled `corfu-candidate-overlay-mode'."))))
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;;; corfu-candidate-overlay.el ends here
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