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+;;; corfu-history.el --- Sorting by history for Corfu -*- lexical-binding: t -*-
+
+;; Copyright (C) 2022-2026 Free Software Foundation, Inc.
+
+;; Author: Daniel Mendler <mail@daniel-mendler.de>
+;; Maintainer: Daniel Mendler <mail@daniel-mendler.de>
+;; Created: 2022
+;; Version: 2.10
+;; Package-Requires: ((emacs "29.1") (compat "31") (corfu "2.10"))
+;; URL: https://github.com/minad/corfu
+
+;; This file is part of GNU Emacs.
+
+;; This program is free software: you can redistribute it and/or modify
+;; it under the terms of the GNU General Public License as published by
+;; the Free Software Foundation, either version 3 of the License, or
+;; (at your option) any later version.
+
+;; This program is distributed in the hope that it will be useful,
+;; but WITHOUT ANY WARRANTY; without even the implied warranty of
+;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+;; GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public License
+;; along with this program.  If not, see <https://www.gnu.org/licenses/>.
+
+;;; Commentary:
+
+;; Enable `corfu-history-mode' to sort candidates by their history position.
+;; The recently selected candidates are stored in the `corfu-history' variable.
+;; If `history-delete-duplicates' is nil, duplicate elements are ranked higher
+;; with exponential decay.  In order to save the history across Emacs sessions,
+;; enable `savehist-mode'.
+;;
+;; (corfu-history-mode)
+;; (savehist-mode)
+
+;;; Code:
+
+(require 'corfu)
+(eval-when-compile
+  (require 'cl-lib))
+
+(defvar corfu-history nil
+  "History of Corfu candidates.
+The maximum length is determined by the variable `history-length'
+or the property `history-length' of `corfu-history'.")
+
+(defvar corfu-history--hash nil
+  "Hash table of Corfu candidates.")
+
+(defcustom corfu-history-duplicate 10
+  "History position shift for duplicate history elements.
+The more often a duplicate element occurs in the history, the earlier it
+appears in the completion list.  The shift decays exponentially with
+`corfu-history-decay'.  Note that duplicates occur only if
+`history-delete-duplicates' is disabled."
+  :type 'number
+  :group 'corfu)
+
+(defcustom corfu-history-decay 10
+  "Exponential decay for the position shift of duplicate elements.
+The shift will decay away after `corfu-history-duplicate' times
+`corfu-history-decay' history elements."
+  :type 'number
+  :group 'corfu)
+
+(defun corfu-history--sort-predicate (x y)
+  "Sorting predicate which compares X and Y."
+  (or (< (cdr x) (cdr y))
+      (and (= (cdr x) (cdr y))
+           (corfu--length-string< (car x) (car y)))))
+
+(defun corfu-history--sort (cands)
+  "Sort CANDS by history."
+  (unless corfu-history--hash
+    (let ((ht (make-hash-table :test #'equal :size (length corfu-history)))
+          (decay (/ -1.0 (* corfu-history-duplicate corfu-history-decay))))
+      (cl-loop for elem in corfu-history for idx from 0
+               for r = (if-let* ((r (gethash elem ht)))
+                           ;; Reduce duplicate rank with exponential decay.
+                           (- r (round (* corfu-history-duplicate (exp (* decay idx)))))
+                         ;; Never outrank the most recent element.
+                         (if (= idx 0) (/ most-negative-fixnum 2) idx))
+               do (puthash elem r ht))
+      (setq corfu-history--hash ht)))
+  (cl-loop for ht = corfu-history--hash for max = most-positive-fixnum
+           for cand on cands do
+           (setcar cand (cons (car cand) (gethash (car cand) ht max))))
+  (setq cands (sort cands #'corfu-history--sort-predicate))
+  (cl-loop for cand on cands do (setcar cand (caar cand)))
+  cands)
+
+;;;###autoload
+(define-minor-mode corfu-history-mode
+  "Update Corfu history and sort completions by history."
+  :global t :group 'corfu
+  (if corfu-history-mode
+      (add-function :override corfu-sort-function #'corfu-history--sort)
+    (remove-function corfu-sort-function #'corfu-history--sort)))
+
+(cl-defmethod corfu--insert :before (_status &context (corfu-history-mode (eql t)))
+  (when (>= corfu--index 0)
+    (unless (or (not (bound-and-true-p savehist-mode))
+                (memq 'corfu-history (bound-and-true-p savehist-ignored-variables)))
+      (defvar savehist-minibuffer-history-variables)
+      (add-to-list 'savehist-minibuffer-history-variables 'corfu-history))
+    (add-to-history 'corfu-history
+                    (substring-no-properties
+                     (nth corfu--index corfu--candidates)))
+    (setq corfu-history--hash nil)))
+
+(provide 'corfu-history)
+;;; corfu-history.el ends here