GNU bug report logs - #47294
27.1; completing-read: History handling and sorting

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From: Clemens <clemera <at> posteo.net>
To: 47294 <at> debbugs.gnu.org
Subject: bug#47294: 27.1; completing-read: History handling and sorting
Date: Sun, 21 Mar 2021 15:29:49 +0100

One can pass `t` to ignore history to `read-from-minibuffer`. I
assumed this is also true for `completing-read` and discovered this
would throw an error (for example when using icomplete
`completion-all-sorted-completions` is called which doesn't handle the
`t` value). Can we change things to allow this API also for
`completing-read`?

Another observation is that the implementation of
`completion-all-sorted-completions` could be made faster by using a
hash table as Daniel Mendler implemented it for Selectrum:

```elisp
(let* ((list (and (not (eq minibuffer-history-variable t))
                  (symbol-value minibuffer-history-variable)))
       (hist (make-hash-table :test #'equal
                              :size (length list))))
  ;; Store the history position first in a hashtable in order to
  ;; keep the sorting fast and the complexity at O(n*log(n)).
  (seq-do-indexed (lambda (elem idx)
                    (unless (gethash elem hist)
                      (puthash elem idx hist)))
                  list)
  (sort candidates
        (lambda (c1 c2)
          (let ((h1 (gethash c1 hist most-positive-fixnum))
                (h2 (gethash c2 hist most-positive-fixnum))
                (l1 (length c1))
                (l2 (length c2)))
            (or (< h1 h2)
                (and (= h1 h2)
                     (or (< l1 l2)
                         (and (= l1 l2) (string< c1 c2)))))))))
```

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